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`6/1986
`5/1996
`2/1998
`3/1999
`10/1999
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`9/2000 Brockmannetal.
`6,118,249 A
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`12/2000 Hayesetal.
`6,160,374 A
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`6,490,176 B2 * 12/2002 Holzer et al. oe. 363/20
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`2002/0141208 Al * 10/2002 Nanbuet al... 363/37
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`FOREIGN PATENT DOCUMENTS
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`DE
`3544955
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`DE
`4438387
`DE
`19633171
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`Loeteea
`DE
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`11283854
`JP
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`* cited by examiner
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`;
`Primary Examiner—ShawnRiley
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`(74) Attorney, Agent, or Firm—Michael Best & Friedrich
`(21) Appl. No.: 10/306,666
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`LLP
`Nov. 28, 2002
`(22)
`Filed:
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`ABSTRACT
`(57)
`Prior Publication Data
`(65)
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`The present invention relates to an inductive contactless
`US 2003/0151930 Al Aug. 14, 2003
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`. power transmitter having a primary side includingafirstan .
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`Foreign Application Priority Data
`inductor (Lp) on the primary side and an oscillator for
`(30)
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`Nov. 30, 2001
`(DE)
`cessssssssssscsssesseseeseesssssssessest 10158794
`producing an alternating signal which is supplied to the
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`;
`inductor (L,) on the primary side, and having a secondary
`,
`(51)
`See e eee cece eee eee ee ee eee eee eee eee eee ee eee eens. H02M 3/335
`side which includes an inductor on the secondary side that
`Int. Cl.
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`(52)
`UWS. Ch. once cc eeecerseececererecenens 363/21.03
`can be coupled to the inductor (L,) on the primary side, a
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`(58) Field of Search... ee 363/16, 131, 178,
`load (R,) which is variable in time, and a detection means
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`363/21.03; 307/150
`(42) for determining a power demand of the load on the
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`secondaryside,the first oscillator being a voltage-controlled
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`References Cited
`oscillator having a frequency that is adjustable in response
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`US. PATENT DOCUMENTS
`(42). power demand determined by the detection means
`
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`5,959,433 A
`9/1999 Rohde
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`6,018,467 A
`1/2000 Majid et al.
`14 Claims, 4 Drawing Sheets
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`
`a2, United States Patent
`US 6,912,137 B2
`(10) Patent No.:
`
`
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`
`
` Berghegger (45) Date of Patent: Jun. 28, 2005
`
`
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`US006912137B2
`
`(54)
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`INDUCTIVE CONTACTLESS POWER
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`TRANSMITTER
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`(75)
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`(*) Notice:
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`Inventor: Schroder Ralf gen Berghegger,
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`Glandorf (DE)
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`(73) Assignee: Friwo Geraetebau GmbH, Ostbevern
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`(DE)
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`Subject to any disclaimer, the term ofthis
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`patent is extended or adjusted under 35
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`US.C. 154(b) by 110 days.
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`(56)
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`{\01
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`C3
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`—— C1
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`NI
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`G2o—/
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`S2.
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`/\D2
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`C4
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`0 Vc
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`N2
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`C2
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`Page 1 of 13
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`Volkswagen Exhibit 1007
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`Page 1 of 13
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`Volkswagen Exhibit 1007
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`U.S. Patent
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`Jun. 28, 2005
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`Sheet 1 of 4
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`US 6,912,137 B2
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`Uge
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`Z
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`Gio/ —5(1st /\0I C3
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`Nt
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`lp
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`Cp
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`6ze—/
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`C4
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`0 Ve
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`Fig.1a
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`Us 0V
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`Fig.1b
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`Jun. 28, 2005
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`Sheet 2 of 4
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`US 6,912,137 B2
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`Uy
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`VCO
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`vcd
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`Fig.3
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`U.S. Patent
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`Sheet 3 of 4
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`US 6,912,137 B2
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`Cp
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`INDUCTIVE FEEDBACK
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`INTERMEDIATE CIRCUIT
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`U.S. Patent
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`Jun. 28, 2005
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`Sheet 4 of 4
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`US 6,912,137 B2
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`greFESSSEREERERDERORECRaETGENimenceened 0onenessesscoon
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`SWITCHING
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`RESONANT
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`POWER
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`CONVERTER
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`SUPPLY
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`Fig.6
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`(prior art)
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`Page 5 of 13
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`1
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`INDUCTIVE CONTACTLESS POWER
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`TRANSMITTER
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`US 6,912,137 B2
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`BACKGROUND OF THE INVENTION
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`The present invention relates to an inductive contactless
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`powertransmitter according to the preamble of patent claim
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`1. Such a powertransmitter is known from U.S. Pat. No.
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`6,118,249.
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`SUMMARYOF THE INVENTION
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`US. Pat. No. 6,118,249 is concerned with the detection of
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`a mobile part on a secondary side by an inductive charging
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`station forming a primary side. On the secondaryside, the ac
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`voltage generated in the coil on the secondary side is
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`rectified and supplied via a field effect
`transistor to a
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`smoothing capacitor. The smoothing capacitor is discharged
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`by a load including batteries. The field effect transistor is
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`driven into the conductive state when the voltage at the
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`smoothing capacitor falls below a lower value andis driven
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`into the non-conductive state when said voltage exceeds an
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`upper threshold value, resulting in hysteresis. The change in
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`load effected by the switching on and off of a field effect
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`transistor on the secondary side modulates the frequency and
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`powerinput of the oscillator on the primary side. A feedback
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`is realized in this way. The coil on the primary side is fed by
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`a free-running oscillator. Due to the changes in load on the
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`secondary side,
`the frequency of the oscillator is also
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`changed. Said change in frequency can be determined by a
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`simple frequency discriminator, such as a PLL (phase-
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`locked loop), and a first control signal can be generated.
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`Moreover,the current input of the oscillator can be measured
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`as a voltage drop at an impedance. Said voltage drop is
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`filtered, a second control signal being produced therefrom.
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`In the presence of one of the two control signals,
`the
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`oscillator is supplied with power. A third control signal
`ensures that the oscillator is switched on from time to time
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`independently of the first two control signals.
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`German Offenlegungschrift DE 197 41 279 Al shows a
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`device for charging batteries,
`the device consisting of a
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`mobile electric device and a charging unit and inductively
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`transmitting electrical power by means of a magnetic alter-
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`nating field from a primary winding in the charging unit to
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`a secondary winding in the mobile device. If there is no
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`device in the charging unit or when a foreign body affects the
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`magnetic alternating field, the charging unit should pass into
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`a low-powerwaiting state. To this end, the magnetic alter-
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`nating field supplied by the charging unit is produced by the
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`primary windings of a free-running push-pull oscillator.
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`DE 196 33 171 Al describes the contactless charging of
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`batteries of a cordless hand-held apparatus via inductive
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`transmitters which are arranged in a sub-housing. The induc-
`tive transmitters have connected thereto a control device
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`whichis also arranged in the sub-housing for controlling the
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`charging operation and which also assumes a monitoring of
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`the charge state of the electric energy storage devices.
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`USS. Pat. No. 5,959,433 describes a universal inductive
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`battery charger which charges a battery pack when the pack
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`is placed on the charger. The battery pack comprises a
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`pick-up coil for this purpose.
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`USS. Pat. No. 6,160,374 describes an inductive charger as
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`can e.g. be used for charging batteries of an electric vehicle.
`A further embodiment of a known inductive contactless
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`power transmitter is shown in FIG. 6. Typically, an alter-
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`nating voltage V,,. is supplied to the power transmitter at a
`Page 6 of 13
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`frequency of 50 to 60 Hz. A switching power supply 61
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`converts the ac voltage V_,. into a de voltage V,. which is
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`supplied to a resonant converter 62. The resonant converter,
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`in turn, generates an ac voltage, typically in the range of
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`several 100 kHz. On the secondary side there is provided an
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`inductor L, which is magnetically coupled to the inductor L,
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`on the primary side. The circuit 63 on the secondary side
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`comprises a rectifier and supplies the rectified voltage to a
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`load R,. Typically, the load R, comprises batteries whose
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`power demand decreases with an increasing load.
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`Furthermore, the circuit 63 additionally includes a detection
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`means for determining the power required on the secondary
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`side. Said detection means measures either the voltage
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`generated by the inductor L, on the secondary side or the
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`voltage at the batteries and produces a signal therefrom that
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`is transmitted via the feedback 64 to the primary side and
`controls the resonant converter 62.
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`It is the object of the present invention to indicate an
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`energy-efficient, inductive contactless power transmitter.
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`Said object is achieved by an inductive contactless power
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`transmitter according to claim 1.
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`Preferred embodiments are the subject matter of the
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`dependent claims.
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`A disconnector for temporarily switching off the inductor
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`on the primary side offers the advantagethat in the switched-
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`off state of the inductor on the primary side the power
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`transmitter only consumes only a small amount of power.
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`The control of a pulse duty cycle control unit in response
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`to the power demand on the secondary side, as determined
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`by a detection means, offers the advantage that a sufficient
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`amount of electrical power is always available on the
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`secondary side andthat this permits an automatic transition
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`from a continuous to a pulsed operation.
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`The advantage of the combination of a continuous opera-
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`tion with a pulsed operation is an enlarged power range in
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`which the power input on the primary side is adapted to the
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`power demand on the secondary side without an unneces-
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`sarily large amount of energy being consumed on the
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`primaryside.
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`The separation of the continuous operation from the
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`pulsed operation by a threshold value offers the advantage
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`the more energy-efficient continuous operation is
`that
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`exploited in an optimum way.
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`The advantage of an optical transmission path is that
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`control signals need not be modulated on the secondary side
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`to the high currents and voltages used for power transmis-
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`sion and that said high voltages and currents need not be
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`filtered out therefrom on the primaryside. Rather, the optical
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`interface exclusively serves to transmit data from the sec-
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`ondary side to the primary side. An optical transmission path
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`further offers the advantage that
`it does not
`lead to an
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`electrical coupling between primary side and secondary
`side.
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`A modulation of the data transmitted from the secondary
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`side via the photodiode to the photodetector on the primary
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`side leads to reduced sensitivity to ambient light.
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`The supplementing of the inductor on the primary side by
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`a capacitor to obtain a serial resonant circuit has the advan-
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`tage that the powertransmission from the primaryside to the
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`secondary side is improved. Advantageously,
`the highest
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`frequency that can be produced by the voltage-controlled
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`oscillator is chosen to be equal to the resonant frequency of
`said serial resonantcircuit.
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`The use of a short-circuit switch or of a disconnector
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`switch is that an existing interface is used for the data
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`transmission from the secondary side to the primary side.
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`Page 6 of 13
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`US 6,912,137 B2
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`3
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`in
`The generation of pulses (whose duration is short
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`comparison with the period duration of the alternating signal
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`produced by the voltage-controlled oscillator) by a short-
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`circuit switch or a disconnector switch has the advantage
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`that the power transmission is only impaired for a short
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`period of time. Furthermore, such pulses clearly differ from
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`the alternating signal used for power transmission, so that
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`they can be filtered out from the alternating signal on the
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`primary side with relatively small efforts regarding the
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`circuitry.
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`The use of frequency modulation for transmitting the
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`power demand onthe secondary side, as determined by the
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`detection means, by meansof a pulse train to the primary
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`side, and of the frequency-to-voltage converter thus needed
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`on the primary side has the advantage that the frequency
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`modulation is interference insensitive relative to amplitude
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`variations resulting from the phase position changing in time
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`between the signals supplied by the two oscillators.
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`Moreover, a frequency-to-voltage converter can be realized
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`by a few components. To modulate the frequency of the
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`pulses, a second voltage-controlled oscillator is advanta-
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`geously used on the secondary side.
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`Advantageously,
`the frequency-to-voltage converter
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`evaluates the signal supplied by the pulse detector only if
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`poweris transmitted from the primary side to the secondary
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`side, i.e. an alternating signal is supplied to the inductor on
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`the primary side, because, otherwise, no pulses can be
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`transmitted and the pulse packet control would thus be
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`regulated in a faulty way.
`BRIEF DESCRIPTION OF THE DRAWINGS
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`Preferred embodiments will now be explained in the
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`following in more detail with reference to the enclosed
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`drawings, in which:
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`FIG. 1a showsa basic circuit for driving the inductor of
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`a resonant transmitter on the primary side,
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`FIG. 1b showsa simplified basic circuit according to 1a;
`FIG. 2 showsa drive circuit for the switches of the basic
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`circuit shown in FIG. 1;
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`FIG. 3 shows a diagram for explaining the influence of a
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`voltage-controlled oscillator and of a duty cycle control unit;
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`FIG. 4 shows a resonant
`transmitter with an optical
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`feedback path;
`FIG. 5 shows a resonant transmitter in which the two
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`magnetically coupled inductors are used for transmitting the
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`feedback signal; and
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`FIG. 6 showsa resonant transmitter according to the prior
`art.
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`FIG. 1a showsa basic circuit for driving an inductive
`resonant transmitter. The basic circuit includes a first and
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`second switch $1 and S2, a first and second diode D1 and
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`D2, two large capacitors Cl and C2, two small capacitors C3
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`and C4, a resonant capacitor C, as well as an inductor L, on
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`the primary side. Nodes N1 and N1are additionally plotted
`in FIG. 1.
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`The inductor L, on the primary side forms a resonant
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`circuit with the resonant capacitor Cp. The circuit operates
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`at an oscillator frequency f,, which is excited by switches
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`S1 and $2. Whenever following the switching off of one of
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`the switches the inductor L, on the primary side produces—
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`at node N1—a voltage which is by the conducting-state
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`voltage of the diode D1 above the operating voltage U,, said
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`voltage is short-circuited by the diode D1 towards the
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`operating voltage U,. Likewise, an under-voltage at node
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`N1 which is below massby the conducting-state voltage of
`Page 7 of 13
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`4
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`diode D2 is short-circuited against mass. The small capaci-
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`tors C3 and C4 serve interference suppression because they
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`short-circuit high-frequency signals that are created during
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`opening and closing of the switches or MOSFETs and when
`diodes D1 and D2 becomeconductive.
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`The large capacitors C1 and C2 are electrolyte capacitors
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`in one embodiment. They serve to stabilize the operating
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`voltage U, and form a virtual mass on node N2, so that
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`voltage U,/2 is here applied. That is why the capacitors C1
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`and C2 as well as the resonant capacitor C, must have a
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`dielectric strength of slightly more than U,/2.
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`An embodiment which is simplified in comparison with
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`the above description is shown in FIG. 1b. Switches $1 and
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`S2 are here replaced by MOSFETs (MOSFET:metal oxide
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`semiconductorfield effect transistor). The diodes D1 and D2
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`can be omitted; their functions are taken over by the inverse
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`diodes of the MOSFETs. Moreover, a capacitor C1 or C2 can
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`be replaced by a short-circuit link by connecting L, and C,
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`to the operating voltage. In this form the circuit operates in
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`an unchanged way, but a de voltage of Ub/2 is superposed
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`on Cp.In these embodiments the respectively other capaci-
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`tor and the resonant capacitor C, must have a dielectric
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`strength higher than the operating voltage U,.
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`In the charge mode the inductor L, on the primaryside is
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`magnetically coupled with an inductor L, on the secondary
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`side, as shown in FIGS. 4 and 5. Without a load on the
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`impedance L, on the secondaryside, the switches S1 and $2
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`are opened and closed at a higher frequency than the
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`resonant frequency of the resonant circuit which is formed
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`by the inductor L, on the primary side and the resonant
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`capacitor C,. A load on the coil on the secondaryside results
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`in a change in impedanceofthe coil L, on the secondaryside
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`and thus in an off-resonance setting of the resonant circuit
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`towards higher frequencies. As a consequence, at a constant
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`oscillator frequencyf,,the oscillation frequency approaches
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`the resonant frequency, whereby the transmitted power
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`increases. To avoid switching looses and high-frequency
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`disturbances, switching is carried out in the voltage-free
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`state. This is referred to as ZVS (zero voltage switching).
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`When switch S2 is switched off,
`the current
`is first
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`maintained by inductor L,. As a result, the voltage on node
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`N1rises, with the small capacitor C3 being discharged and
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`the small capacitor C4 charged. Finally, when the voltage on
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`node N1 exceeds the operating voltage U, by the diode
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`forward voltage of diode D1, diode D1 becomes conductive,
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`thereby defining the voltage on node N1. It is only now that
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`switch S1 is activated. After switch S1 has been deactivated,
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`switch $2 will only be activated when the voltage on node
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`N1 falls below OV by the forward voltage of diode D2.
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`According to a preferred embodiment the control elec-
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`trodes G1 and G2 are controlled by the drive circuit 2 shown
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`in FIG. 2. The drive circuit 2 comprises a voltage-controlled
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`oscillator (VCO,),
`two delay elements 3 and 5, a delay
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`flip-flop D and gates 6, 7, 8, 9 as well as a duty cycle control
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`unit VCD. Both the voltage-controlled oscillator VCO, and
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`the duty cycle control unit VCD have a control signal U.
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`supplied thereto. The control signal U. depends on the
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`power demand of the secondary side. It will be explained
`further below with reference to FIGS. 4 and 5 how the
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`control signal is generated.
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`In one embodimentthe control signal is an analog voltage
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`which can vary between an upper and a lowerlimitvalue. In
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`one embodiment the control signal U. has its maximum
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`voltage at a maximum output load on the secondary side.
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`Under these circumstances the voltage-controlled oscillator
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`VCO, producesits minimum frequency. This correspondsto
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`Page 7 of 13
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`5
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`the resonant frequencyof the resonant circuit. Whenthe load
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`on the secondary side decreases, the voltage of the control
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`signal decreases as well. As a result, the voltage-controlled
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`oscillator VCO, produces an increasing frequency that
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`shifts the oscillator frequency f, relative to the resonant
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`frequency of the resonant circuit formed by L, and C,. At
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`this point the control signal U; reaches a threshold value.
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`A further reduction of the transmitted power is achieved
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`with the help of the voltage-controlled duty cycle control
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`unit VCD. The duty cycle control unit produces a frequency
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`that is small in comparison with the oscillator frequency
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`VCO,. Small in this context means smaller than half as
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`great. Depending on the control signal U,, the duty cycle
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`control unit changes the duty ratio of the output signal.
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`Whenthe control signal U, has a value above the threshold
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`value, the duty ratio is 100%, so that the duty cycle control
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`unit always outputs a logic one. This meansin the case of a
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`CMOSlogic (complementary metal oxide semiconductor)
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`that the duty cycle control unit outputs a voltage slightly
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`below the operating voltage U,. It is only when the control
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`signal falls below the threshold value that the duty cycle
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`control unit actually outputs an ac voltage. With a decreasing
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`control signal the duty ratio becomes smaller and smaller,
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`and even whenthe control signal U. assumesits minimum
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`value,
`the duty ratio remains still greater than zero. For
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`instance,
`the smallest adjustable duty ratio may be 1 or
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`0.1%. As will be explained further below,it can no longer be
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`detected at a duty cycle ratio of 0 whether a secondary side
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`is magnetically coupled with the primary side, i.e. whether
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`e.g. a mobile device is placed in the chargingtray.
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`The alternating signal of the voltage-controlled oscillator
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`VCO, on the primary side is supplied to the two delay
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`elements 3 and 5 and tothe delayflip-flop D. The output 0
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`of the delay flip-flop D and the output of the delay element
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`3 are supplied to the AND gate 6. The output Q of the delay
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`flip-flop D and the output of the delay element 5 are supplied
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`to the AND gate 7. At the outputs of the AND gates 6 and
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`two output signals that are phase-shifted by 180° are
`7,
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`thereby created at a duty ratio of slightly below 50% for
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`controlling switches S1 and S2. Thanks to the ANDingofthe
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`duty signal U; with the output signals of the AND gates 6
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`and 7 in the AND gates 8 and 9, ac voltage is supplied at
`timesto the control electrodes G1 and G2 in accordance with
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`the duty signal U; andis not supplied at times. This is shown
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`in FIG. 3. While the duty signal is at a high level, which
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`corresponds to a logic one, ac voltage is supplied to the
`control electrodes G1 and G2 andthusto the resonant circuit
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`consisting of L, and C,. The frequency of the ac voltage is
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`determined by the voltage-controlled oscillator VCO. While
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`the duty signal has a low level, no ac voltage is passed on
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`through the AND gates 8 and 9. In another embodiment, the
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`ANDgates 6 and 8 and the AND gates 7 and 9 may each be
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`realized by an AND gate with three inputs.
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`In another embodiment,
`the operating ranges of the
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`voltage-controlled oscillator VCO, and the duty cycle con-
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`trol unit VCD are overlapping, so that a central range exists
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`in which upon a change in the control signal both the duty
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`ratio of the duty signal U; and the frequency of the alter-
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`nating signal are changed. Apart from such a transitional
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`range, there may be an upper range in which a changein the
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`control signal U, just
`influences the frequency of the
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`voltage-controlled oscillator VCO, on the primary side and
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`a lower range in which a changein the control signal U, just
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`influences the duty cycle ratio of the duty signal U;.
`An embodiment of the feedback of the load on the
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`secondary side to the primary side will be explained with
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`reference to FIG. 4. FIG. 4 shows a controller 40,
`the
`Page 8 of 13
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`6
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`resonant circuit formed by L, and C,,the inductor L, on the
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`secondaryside, a rectifier GL, a load R,, a detection means
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`42, a modulator 43, a photodiode 44, a photoelement 45, a
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`demodulator 41, and an analyzing means 46.
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`Circuit 40 substantially contains the drive circuit 2 shown
`in FIG. 2 and the basic circuit 1 shown in FIG. 1 and used
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`for driving the inductor L, and the resonant capacitor C, on
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`the primary side. The inductor L, on the secondary side is
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`magnetically coupled to the inductor L, on the primaryside.
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`The ac voltage supplied by the inductor on the secondary
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`sideis rectified in the rectifier GL and supplied to a load R;.
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`The load R, can also include batteries so that the power
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`required by the batteries decreases with an increasing load.
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`In this instance the power required by load R,is variable in
`time.
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`A detection means 42 determines the power demand on
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`the secondary side. The detection means 42 can e.g. measure
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`the voltage decreasing on the load, the voltage across the
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`batteries or also the load current. The output signal of the
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`detection means is preferably an analog voltage which is
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`supplied to the modulator 43. Said modulator modulates the
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`voltage supplied by the detection means 42 to a carrier signal
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`and controls the photodiode 44. Thelight of the photodiode
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`44 impinges on a photoelement which can e.g. be realized as
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`the phototransistor. The output signal supplied by the pho-
`toelement is demodulated in the demodulator 41 and ana-
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`lyzed in the analyzing means 46 and thus converted into the
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`control signal U.. The demodulation operation takes place
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`in the reverse order compared to the modulation operation.
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`Sensitivity to ambient light, which can also impinge on
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`the photoelement, can be reduced by modulating the output
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`signal supplied by the detection means. In particular, ambi-
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`light variations are most of the time slow and not
`ent
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`periodic, so that they clearly differ from a modulated signal.
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`Frequency modulation can advantageously be employed as
`a kind of modulation.
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`The primary side can e.g. be designed as a charging tray
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`while the secondary side may be a mobile or cordless
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`telephone or also an electric toothbrush. Charging tray and
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`secondary device are designed such that
`the secondary
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`device can easily be removed from the charging tray and that
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`upon insertion of the secondary device into the charging tray
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`the two inductors L, and Lg, are closely positioned side by
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`side, so that a magnetic coupling takes place. The photo-
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`diode 44 is also positioned near the photoelement when the
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`secondary device is inserted in the charging tray, so that a
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`sufficiently large amount of the light produced by the
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`photodiode 44 impinges on the photoelement.
`FIG. 5 shows an embodimentin whichin contrast to FIG.
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`4 a signal about the power demand onthe secondary side is
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`transmitted via the two inductors L, and L, to the primary
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`side. FIG. 5 showsa controller 40, a resonant circuit formed
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`by L, and C,, the inductor L, on the secondary side, a
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`short-circuit switch S, as well as a disconnector switch S,,
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`a short-circuit resistor R,, a rectifier GL, a load R,, a
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`detection means42, a voltage-controlled oscillator VCO, on
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`the secondary side, a pulse detector 51, as well as a
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`frequency-to-voltage converter f/v.
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`As described above, the detection means 42 determines
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`the power required on the secondary side. It outputs an
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`analog voltage. The voltage-controlled oscillator VCO, con-
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`trols either the short-circuit switch S,, the disconnector
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`switch S, or both types of switches S, and S, together. To
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`avoid undesired power loss, the short-circuit switch S, is
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`only closed for a very short period of time, i.e. considerably
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`shorter than the period duration of the alternating signal
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`US 6,912,137 B2
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`US 6,912,137 B2
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`8
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`converter f/v. The frequency-to-voltage converter f/v will
`supplied by the voltage-controlled oscillator VCO, on the
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`only changeits output voltage if poweris transmitted to the
`primary side. Moreover,
`the frequency of the voltage-
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