The input capacitor then begins to discharge through the series regulator, and the voltage across the regulator decreases until Q20 turns off. The discharge time (typically ½ to 4 seconds) depends on the voltage and current ratings of the supply, the main filter capacitor, and the control settings. Once this recovery time has elapsed, the output current will return to the level set by the current controls, and the preregulator will return the voltage across the series regulator to the normal 3.5V level, thus limiting the power dissipated by the
s cries regulator.
4-31CONSTANT VOLTAGE COMPARATOR
4-32 This circuit consists of the programming resistors (A5R121 and A5R122) and a differential amplifier stage (Z1 and associated components). An integrated circuit is used for the differential amplifier to minimize differential voltages due to mismatched transistors and thermal differentials.
4-33 The constant voltage comparator continuously compares the voltage drop across the VOLTAGE controls with the output voltage and, if a difference exists, produces an error voltage whose amplitude is proportional to this difference. The error signal ultimately alters the conduction of the series regulator which, in turn, alters the output current so that the output voltage becomes equal to the voltage drop across the VOLTAGE controls. Hence, through feedback action, the difference between the two inputs to Z1 is held at zero volts.
4-34 One input of the differential amplifier (pin
10)is connected to the output voltage sensing ter- minal of the supply (+S) through impedance equaliz- ing resistor R23. Resistors R1 and optional resistor R110 are used to zero bias the input. If the supply is equipped with Option 020, resistor R114 and po- tentiometer R 113 provide a variable input bias that allows the output voltage to be adjusted to exactly zero volts when the supply is programmed for zero output. The other input of the differential amplifier (pin 1) is connected to a summing point (terminal
A2) at the junction of the programming resistors and the current pullout resistors R3, R4, end R5. In- stantaneous changes in the output voltage or changes in the voltage at the summing point due to manipulation of the VOLTAGE controls produce a dif- ference voltage between the two inputs of the dif- ferential amplifier. This difference voltage is am- plified and appears at the output of the differential amplifier (pin 12) as an error voltage which ulti- mately varies the conduction of the series regulator.
4-3 S Resistor R6, in series with the summing-point input to the differential amplifier, limits the current through the programming resistors during rapid voltage turn-down. Diode CR7 prevents excessive current drain from the +6.2 volt reference supply
TM 11-6625-2958-14&P
during rapid down-programming; diodes CR5 and CR6 prevent excessive voltage excursions from over-driving the differential amplifier. Capacitor C2 prevents the gain of the feedback loop from changing during manipulation of the VOLTAGE con- trols. Resistor R2 limits the discharge current through C2. Resistors Z2F, Z2M, and Z2N bias the differential amplifier; diode CR4 provides temperature compensation.
4-36 During constant voltage operation, the programming current flowing through the programming resistors (VOLTAGE controls) is held constant because the value of shunt resistor R3 is factory selected to allow all of the +6.2 volt reference to be dropped across R3, R4, and RS. Linear constant voltage programming is thus assured with a constant current flowing through A5R121 and A5R122. If the supply is equipped with Option 020, resistor R111 and potentiometer R 112 allow the programming current to be adjusted by varying the bias applied to the summing point.
4-37 Main output capacitor A3C3 stabilizes the series regulator feedback loop and helps supply high-current pulses of short duration during constant voltage pulse loading operation. An additional output capacitor (C 19), connected directly across the output bus bars, helps maintain a low ac output impedance by compensating for the inductive reactance of the main output capacitor at high frequencies. C19 also prevents any spikes in the output from reaching the load.
4-38CONSTANT CURRENT COMPARATOR
4-39 This circuit is similar in appearance and operation to the constant voltage comparator circuit. It consists of the coarse and fine current controls (A5R123 and A5R124) and a differential amplifier stage (Z 1 and associated components). As in the constant voltage comparator, an integrated circuit is used for the differential amplifier to minimize differential voltages due to mismatched transistors and thermal differentials.
4-40 The constant current comparator circuit continuously compares the voltage drop across the CURRENT controls with the voltage drop across the current sampling resistor, A4R123. If a difference exists, the differential amplifier produces an error signal which is proportional to this difference. The remaining components in the feedback loop (mixer amplifier, error amplifiers, and the series regulator) function to maintain the voltage drop across the current sampling resistors, and hence the output current, at a constant value.
4-41 One input of the differential amplifier (pin 7) is connected to the output bus through impedance equalizing resistor R20 and is zero-biased by R21