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`QSC Audio Products Exhibit 1003 Page 1
`
`

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`QSC Audio Products Exhibit 1003 Page 2
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`Win
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`Vlllfllls X “nuns
`
`A power supply does not appear as a resistive load to
`the line. Therefore current flows that does not transmit
`
`power. This current is composed of two elements, line
`frequency current that is out ofphase with the line
`voltage, and hamionic currents. The out of phase
`component dominates for large reactive loads such as
`motors. Harmonic currents dominate in power sup-
`plies.
`
`lnrush current: the maximum possible input current when
`input voltage is first applied to the supply. This worst
`case for this is when the supply is turned on near the
`peak of the AC input voltage. At this point there is no
`charge on the storage capacitors, the line sees a virtual
`short circuit, and only parasitic elements in the supply
`limit the current unless there are specific measures
`taken to reduce this current. This current can be 4 - 8
`times the nomial input current, and stresses the affected
`components of the supply. Example; 70A.
`1.2 Electro-magnetic Compatibility (EMC)
`Conducted emissions: the noise that appears on the AC line
`due to the operation of the power supply. This is typi-
`cally described by referencing the appropriate
`specification that the supply complies with. These
`specs are generated by standards bodies such as the
`FCC and the Gemtan VDE. They specify the allow-
`able level of emissions versus frequency. They also
`describe the technique used to measure the emissions.
`The range of frequencies limited is from l50kHz to
`30Mhz. with some specs reaching down to l0kHz. A
`detailed discussion can be found in [1]. Example;
`Conducted EMI confonns to FCC Class B.
`
`Radiated emissions: the noise that is propagated into the space
`surrounding the supply, similar to a radio transmitter.
`Similar to above. Example; Radiated EMI confonns to
`FCC Class A.
`
`Conducted susceptibility: the ability of the power supply to
`function correctly despite the presence of noise on the
`input lilies.
`In this case military standards are used to
`
`(cid:52)(cid:54)(cid:38)(cid:3)(cid:36)(cid:88)(cid:71)(cid:76)(cid:82)(cid:3)(cid:51)(cid:85)(cid:82)(cid:71)(cid:88)(cid:70)(cid:87)(cid:86)(cid:3)(cid:40)(cid:91)(cid:75)(cid:76)(cid:69)(cid:76)(cid:87)(cid:3)(cid:20)(cid:19)(cid:19)(cid:22)(cid:3)(cid:3)(cid:51)(cid:68)(cid:74)(cid:72)(cid:3)(cid:22)
`QSC Audio Products Exhibit 1003 Page 3
`
`

`
`describe the performance of the supply, such as MIL-
`STD-46 l C, CS03.
`It is usually not specified for
`non-military equipment.
`Radiated susceptibility: the ability of the supply to function
`correctly despite the presence of radiated noise
`impinging on the chassis. Similar to above. This is a
`very real world problem with audio equipment being
`operated in the vicinity of a radio transmitter, as anyone
`who has heard Barry Manilow through their mixing
`board will attest. Example: MIL-STD-461C, RS02.
`1.3 DC Output
`Output voltage: the nominal voltage that the supply is intended
`to deliver. Example; 70VDC.
`Maximum current: the maximum continuous current that the
`
`supply can deliver at its rated outputi-voltage. Different
`values can be specified for different ambient tempera-
`tures, as most supplies can deliver more current safely
`at lower temperatures. Example; 7.5A @ 40°C, 6.0A
`@ 50°C, 5.0A @ 60°C, 3.0A @ 71°C.
`Line regulation: the variation in DC output voltage that occurs
`while the input voltage is varied over its specified
`range. Stated as percentage of the nominal output
`voltage. Example; 0.1%.
`Load regulation: the variation in DC output voltage that occurs
`while the load current is varied over a specified range
`referenced to the rated maximum output current.
`Example; 0.1% from full load to 10% load.
`Ripple: the RMS level of AC present on the output of the
`supply. Example; l0mV RMS.
`Noise: the peak to peak level of AC present on the output of
`the supply. The measurement method must be defined
`as different methods result in large changes in this
`reading. Typically a scope probe is connected directly
`to the output with the shortest leads possible from the
`ground ring and the tip. A bandwidth can also be
`specified. Example; 50inV pk-pk, 20MHz bandwidth.
`Overload protection: the characteristics of the output voltage
`versus output current are described for loads greater
`than specified. The protection method is given.
`Example; Output current is limited to a maximum of
`l 15% of the rated value. Unit will return to nomial
`
`operation automatically upon removal ofthe overload.
`
`(cid:52)(cid:54)(cid:38)(cid:3)(cid:36)(cid:88)(cid:71)(cid:76)(cid:82)(cid:3)(cid:51)(cid:85)(cid:82)(cid:71)(cid:88)(cid:70)(cid:87)(cid:86)(cid:3)(cid:40)(cid:91)(cid:75)(cid:76)(cid:69)(cid:76)(cid:87)(cid:3)(cid:20)(cid:19)(cid:19)(cid:22)(cid:3)(cid:3)(cid:51)(cid:68)(cid:74)(cid:72)(cid:3)(cid:23)
`QSC Audio Products Exhibit 1003 Page 4
`
`

`
`Another example; Supply is protected by a normal
`blow 15A 3AG fuse. (Maximum output current not
`specified.)
`Holdup time: the length of time that a supply can continue to
`operate in the absence of line voltage. Of primary
`interest in data processing applications. Example;
`25mS.
`
`1.4 Safety
`I solation: the common-mode voltage that the unit can with-
`stand across its input, output, and chassis. Example;
`Input to Output: 3000V RMS, Input to Chassis:
`l50OV RMS, Output to Chassis: 500V RMS.
`Approvals: a listing of safety agency approvals that have been
`obtained for the supply in question. These are issued
`by organizations such as UL and CSA. They are
`approved to a particular specification number which
`covers the application and environment that the device
`is used in. Example; ULl950 approval has been
`obtained.
`
`1.5 Thermal
`
`Thermal protection: the method in which the supply protects
`itself from an overtemperature condition is described.
`Some supplies have none. Others shutdown, and may
`require a cycling of the input power to re-start.
`Operating temperature range: specifies the minimum and
`maximum temperatures at which the supply will meet
`all specs.
`It is related to the output current rating
`described above. Example; Operation from -20°C to
`+71°C with suitable derating above 40°C
`Storage temperature range: specifies the temperature range that
`the supply can handle on the shelf. Example; -40°C to
`+85°C.
`
`Cooling: states whether the supply uses convection or fan
`cooling.
`1.6 Mechanical
`
`Size and Weight: self explanatory.
`Shock: states the maximum acceleration that the supply can
`withstand in a single pulse in any axis. Usually speci-
`fied by stating the MIL-spec that the unit complies
`with. The MIL-spec describes the pulse shape.
`Vibration: states the maximum acceleration that the supply can
`withstand continuously in any axis. Similar to above.
`
`(cid:52)(cid:54)(cid:38)(cid:3)(cid:36)(cid:88)(cid:71)(cid:76)(cid:82)(cid:3)(cid:51)(cid:85)(cid:82)(cid:71)(cid:88)(cid:70)(cid:87)(cid:86)(cid:3)(cid:40)(cid:91)(cid:75)(cid:76)(cid:69)(cid:76)(cid:87)(cid:3)(cid:20)(cid:19)(cid:19)(cid:22)(cid:3)(cid:3)(cid:51)(cid:68)(cid:74)(cid:72)(cid:3)(cid:24)
`QSC Audio Products Exhibit 1003 Page 5
`
`

`
`The MIL-spec describes the spectrum of vibration
`applied, and whether it is sine or random excitation.
`
`2 TYPES OF POWER SUPPLIES
`
`2.1 Low Level Supplies
`The power supplies used in audio equipment can be broken down into
`two categories, hi-level and lo-level. Lo-level supplies are used in
`signal processing equipment such as mixers, pre-amps, limiters, and so
`forth. They have output voltages less than 18V and moderate current
`draw dependent on the complexity of the device. The critical specifi-
`cations are noise, ripple, and regulation. Efficiency, size and weight
`are less important. Conventional supplies (described below) with lin-
`ear regulators added to their outputs meet these requirements well.
`They are cost effective in this application. A drawback is the low
`power factor and attendant abundance of harmonics generated back
`into the AC line. Engineers have existed with this for a long time by
`paying careful attention to layout and grounding. However, the new
`generation of 20 bit recording is going to make this more difficult. A
`DC bus power distribution system would make life easier. Regulated
`voltages of +15, -15, +5, and +48 could be distributed around the stu-
`dio, eliminating numerous redundant power supplies, and a large
`source of hum. Any odd voltages required could be created with DC
`to DC converters operating from the +48V bus. Standardized connec-
`tors would make hook-up convenient.
`
`2.2 High Level Supplies
`Hi-level supplies are used in power amplifiers. They are required to
`supply high levels of voltage and current, proportional to the amplifier
`rating.
`[3] describes the low impedance (~ 1 ohm) presented by a
`loudspeaker when driven with non-sinusoidal waveshapes. The ability
`of the amplifier to supply this current is dependent on the current gain
`of the output stage and the equivalent series resistance (ESR) of the
`storage capacitors. Because the tiansfomier is off for a large portion of
`the AC cycle, it can not be relied upon to supply these transient cur-
`rents. Efficiency is very important, as only small losses add up to a lot
`of heat at the power levels required. Size and weight become a factor,
`and in fact the power supply dominates the construction of power
`amplifiers. Ripple and regulation are less important, as the feedback
`used in the amplifier compensates for slow voltage changes in the
`supply. Noise is generally not a problem due to the filtering action of
`the large storage capacitors used. Conventional supplies are used
`
`(cid:52)(cid:54)(cid:38)(cid:3)(cid:36)(cid:88)(cid:71)(cid:76)(cid:82)(cid:3)(cid:51)(cid:85)(cid:82)(cid:71)(cid:88)(cid:70)(cid:87)(cid:86)(cid:3)(cid:40)(cid:91)(cid:75)(cid:76)(cid:69)(cid:76)(cid:87)(cid:3)(cid:20)(cid:19)(cid:19)(cid:22)(cid:3)(cid:3)(cid:51)(cid:68)(cid:74)(cid:72)(cid:3)(cid:25)
`QSC Audio Products Exhibit 1003 Page 6
`
`

`
`almost exclusively in this application. This supply is described below.
`
`M
`2.21 Description
`It
`The basic schematic for a conventional supply is shown in Figure 2.
`consists of a line frequency transformer (T 1) followed by a bridge rec-
`tifier (D14) and a pair of storage capacitors (C1,2) to generate a
`bipolar output voltage. A small cap (C3) may be present on the input
`to filter out some noise. This supply is an unregulated supply because
`there are no active elements to control the output voltage.
`It is also
`called a peak-detecting supply because the output tends to approach the
`peak of the secondary voltage as the load is reduced. An amplifier
`incorporating this type of supply was subjected to a series of mea-
`surements that are documented in Figures 3 - 7. The test setup is
`documented in Figure 8. Referencing Figure 2, a brief description of
`the operation of the supply is described below.
`
`0° to 65°
`At the beginning of the AC cycle, 0°, the secondary output
`voltage, vm, is zero, the bridge rectifiers are biased off, and no
`secondary current, im, flows. The secondary voltage then
`increases in proportion to the line voltage until it equals the
`voltage on the storage capacitors, V9,‘, plus two diode drops, 2 x
`vd, at 80°. The storage capacitor voltage declines as it supplies
`current to the load.
`65° to 135°
`At 65° current starts to flow through the bridge when v”, > vgp
`+ 2vd. During this period,
`
`vm - (vcap + 2vd)
`
`lsec
`
`rail‘
`
`re“. is the combined resistance of the storage capacitor, trans-
`former secondary, and reflected resistance of the primary and
`input line impedance. Because r,” is quite low, ism has a high
`peak value, which can seen in Figure 5. Larger power supplies
`have even lower values of re” , and generate correspondingly
`higher peak currents. During this period, Vcap rises due to the
`large current flowing into it.
`135° to 180°
`At the beginning of this time period, vcap + Zvd has risen to V“
`, and iw goes to zero. veal, resumes its decline.
`
`(cid:52)(cid:54)(cid:38)(cid:3)(cid:36)(cid:88)(cid:71)(cid:76)(cid:82)(cid:3)(cid:51)(cid:85)(cid:82)(cid:71)(cid:88)(cid:70)(cid:87)(cid:86)(cid:3)(cid:40)(cid:91)(cid:75)(cid:76)(cid:69)(cid:76)(cid:87)(cid:3)(cid:20)(cid:19)(cid:19)(cid:22)(cid:3)(cid:3)(cid:51)(cid:68)(cid:74)(cid:72)(cid:3)(cid:26)
`QSC Audio Products Exhibit 1003 Page 7
`
`

`
`2.22 Analysis
`Several observations can be made from the data depicted in Figures 3
`-7.
`
`Power output of the amplifier is strongly dependent on line
`-
`voltage, varying l.6dB from low to high line.
`-
`Power factor increases with load. This is due to the widening
`conduction angle as the output capacitor voltage decreases.
`-
`In Figure 4 the input current waveform does not resemble the
`input voltage waveform. This is reflected in the power factor of .78
`noted for full load, ll5Vin in Figure 3.
`~
`Figures 5 and 6 show the load regulation of the supply, taken
`from ground to Vcc. Note the drop in voltage and increase in ripple
`when the load is increased. The data in Figure 3 reflects the poor line
`and load regulation of the supply in the amplifier, reflecting its passive,
`unregulated nature. This helps explain why some amps have more
`‘punch’ than others. Music has power peaks that greatly exceed the
`average, such that to reproduce music with little overload, the amp
`must operate at around 15% of its rated power. The output voltage of
`the power supply in the amp rises at low load, and the amp can deliver
`power for transients greater than its steady-state rating. This is called
`dynamic headroom. The measured amp can deliver 225 watts into 8
`ohms for short periods, thus having 2dB dynamic headroom. Poor
`load regulation will increase dynamic headroom. The drawback is
`greater dissipation in the supply due to higher internal resistance.
`-
`Figure '7 is the ripple voltage on the output vs. the input cur-
`rent. 600 Hz ripple is overlaid on the 120 Hz ripple. The quick rise in
`voltage is correlated with the input current pulse. The amplifier is able
`to reject this noise due to its high open loop gain.
`An examination of most amplifier literature does not specify
`what line voltage the output power ratings were obtained at, or a range
`of acceptable input voltage. More optimistic ratings could be obtained
`at a voltage that most users will not see, and therefore not obtain the
`power rating that they paid for. The literature also does not specify the
`maximum allowable ambient temperature at which the amplifier can be
`operated at rated output.
`
`2.23 SPICE Simulation
`Figure 9 and 10 show a SPICE model of the conventional power sup-
`ply closely resembling the measured supply and its associated
`waveforms. Note the similarity to the waveforms present in the actual
`amplifier. Figure ll is an FFT analysis of the input current wavefomi
`
`(cid:52)(cid:54)(cid:38)(cid:3)(cid:36)(cid:88)(cid:71)(cid:76)(cid:82)(cid:3)(cid:51)(cid:85)(cid:82)(cid:71)(cid:88)(cid:70)(cid:87)(cid:86)(cid:3)(cid:40)(cid:91)(cid:75)(cid:76)(cid:69)(cid:76)(cid:87)(cid:3)(cid:20)(cid:19)(cid:19)(cid:22)(cid:3)(cid:3)(cid:51)(cid:68)(cid:74)(cid:72)(cid:3)(cid:27)
`QSC Audio Products Exhibit 1003 Page 8
`
`

`
`generated by the SPICE model. The spectrum is that of the sound of
`hum in an audio installation where careful attention to grounding and
`layout is not made. Additional even harmonics can originate from the
`ripple on the output of the supply. This noise is a combination of the
`pulsating nature of the current into the storage capacitors and the
`reverse recovery spike of the bridge rectifier diodes. The reverse
`recovery spike is due to a non-ideal characteristic of rectifiers in that
`they do not turn off immediately upon the reversal of current. They
`allow a small amount of reverse current to flow before snapping off
`rapidly. The reverse recovery spike generates a rich spectrum of har-
`monics that can flow into the AC line. This turn off transient can be
`seen in Figure 10 at the end of the current pulse.
`
`2.24 Design Alternatives
`The transformer in a conventional supply needs to be designed to
`handle the highest expected line voltage, say 128VAC. This means
`that the transformer is larger than necessary for normal line voltages of
`around 115VAC. A triac or anti-parallel SCR's are placed in series
`with the primary of the power supply illustrated in Figure 2. They are
`then triggered to provide a constant voltage (say IOOVAC) across the
`primary of the transformer, indepedent of line voltage. One possible
`resulting voltage waveform is shown in Figure 12. The transfonner
`size can then be optimized for this voltage. This results in a smaller
`transformer. Control of the output voltage and a degree of short circuit
`protection are possible. This scheme will not eliminate the pulsating .
`input current similar to that in Figure 4, and can make it worse if the
`SCR's are turned on at 90°.
`It also adds complexity and cost.
`
`3 SWITCHING POWER SUPPLIES
`
`Another way to reduce the size of the power transformer is to use a
`switching power supply. This type of supply is widely used in the
`computer and telecommunication industries. Every PC contains one.
`They are called switching supplies because the transistor used to regu-
`late the output voltage is switched between the on and the off state, as
`opposed to a linear regulator where the transistor is operated in the
`linear region. One advantage of the switching power supply is that the
`transistor dissipates little power compared to the device in a linear
`regulator. There are two basic topologies used in switching power
`supplies, the buck and the boost.
`
`3.1 Theory of Operation
`
`(cid:52)(cid:54)(cid:38)(cid:3)(cid:36)(cid:88)(cid:71)(cid:76)(cid:82)(cid:3)(cid:51)(cid:85)(cid:82)(cid:71)(cid:88)(cid:70)(cid:87)(cid:86)(cid:3)(cid:40)(cid:91)(cid:75)(cid:76)(cid:69)(cid:76)(cid:87)(cid:3)(cid:20)(cid:19)(cid:19)(cid:22)(cid:3)(cid:3)(cid:51)(cid:68)(cid:74)(cid:72)(cid:3)(cid:28)
`QSC Audio Products Exhibit 1003 Page 9
`
`

`
`The buck regulator is shown in Figure 13, and associated waveforms in
`Figure 15. Operation is as follows:
`
`to - tl
`
`Switch S1 is turned on, such that Vin - Vout is applied across
`Ll. CR1 is biased off. The current through Ll increases by:
`
`AIL] = jVin-Vout) (tl - t0)
`L1
`
`tl - t2
`
`Switch S1 is turned off, and L1 forces CR1 to turn on and
`continues to supply current to C1. The voltage across L1 is equal to
`-Vout. The current through Ll decreases by:
`
`L
`
`The boost regulator is shown in Figure 14, and associated waveforms
`in Figire 15. Operation is as follows:
`
`t0 - tl
`
`Switch S2 is turned on, and Vin is applied across L2. The
`current through L2 increases by:
`
`tl - t2
`
`L2
`
`Switch S1 is turned off, and L1 forces CR1 to turn on and
`continues to supply current to C1. The voltage across L1 is equal to
`Vin-Vout. The current through.Ll decreases by:
`
`AIL, = (Vout - Vin1(t2 - tl)
`L1
`
`The ratio of the on time to off time of the switch is called the duty
`cycle, and is defined as:
`
`D = ton
`ton + toff
`
`(cid:52)(cid:54)(cid:38)(cid:3)(cid:36)(cid:88)(cid:71)(cid:76)(cid:82)(cid:3)(cid:51)(cid:85)(cid:82)(cid:71)(cid:88)(cid:70)(cid:87)(cid:86)(cid:3)(cid:40)(cid:91)(cid:75)(cid:76)(cid:69)(cid:76)(cid:87)(cid:3)(cid:20)(cid:19)(cid:19)(cid:22)(cid:3)(cid:3)(cid:51)(cid:68)(cid:74)(cid:72)(cid:3)(cid:20)(cid:19)
`QSC Audio Products Exhibit 1003 Page 10
`
`

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`QSC Audio Products Exhibit 1003 Page 11
`
`

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`QSC Audio Products Exhibit 1003 Page 12
`
`

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`QSC Audio Products Exhibit 1003 Page 13
`
`

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`QSC Audio Products Exhibit 1003 Page 14
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