CIRCUIT DESCRIPTION
.
As shown in the block diagram and on the schematic diagram, Fig-
ures 8 and 9, the power transformer feeds D10 and C5 to provide -30 volts. The 30
volt supply provides current to the bases of the transistors in the series regulator,
to the preregulator control circuit, and to the -15 volt bias regulator. The -15 volt
bias regulator is comprised ofbR18, D9 (a 15 volt zener diode), C4 in an emitter
follower configuration, and R6, a bleed resistor. The 15 volt bias supply provides
current to the preregulator control circuit, to the overvoltage protection circuit (P5
etc) and to the -12 volt reference regulator. In the 12 volt reference circuit D14 is
used to provide a constant voltage on the emitter of 06. The output of the reference
supply is picked off by R20 and R21 and connected to the base of 06 via the tempera-
ture compensating network of Dll, D12, R25, and R26. Any change in the output
of the 12 volt reference supply voltage will cause a change in base current in QS,
and thus eventually a change in current in 03 tending to hold the voltage of the
reference supply constant. R16 is used to reduce the power dissipation in Q3. P2
and R19 is a circuit to provide a compensation for slight changes of the -15 volt
supply due to line voltage variations.
The output of the power supply is sensed by two transistors, Q1 and
02, in a differential amplifier configuration. The base of Q2 is connected to the
minus sensing lead via a 1.5K resistor which for sake of easy explanation tightly ties
the base to the minus sensing, Normally, the minus sensing is connected to the
minus output terminal of the supply. The base of Q1 is connected via a 2K resistor
to the Junction of R1 and P8. R1 is connected to the -12 volt reference supply and
P8 to the positive output terminal. Now if any potential difference occurs between
the base of Ql and 92, the signal is amplified and applied to the series regulator.
The signal is such that the voltage on the output of the supply is charged until there
no longer exists any potential difference between the bases of 01 and QZ. Thus,
the potential at the junction of R1 and P8, usually called the "summing point", will
remain at approximately zero with respect to the minus sensing lead. R4 is used to
protect P8 from damage under overload conditions. D1 and D2 protect 01 from over-
load. R10 and P1 form a positive feedback loop used to adjust the load regulation of
the supply. D20, D21, and D22 provide a positive 2.4 volt bias supply with respect
to the minus output bus. D3 and 07 comprise a 1.3 volt bias source for the emitters
of the differential amplifiers .
The output signal from the differential amplifier is coupled to the
predriver base via two diodes. In addition to the differential amplifier signals, the
base of QS, the predriver, also receives information if the current of the supply
exceeds a specific limit. The current is sensed by monitoring the voltage drop
across R27. P4 is the current overload adjustment. If the current output of the supply
exceeds a certain value, the diode D8 is forced into conduction and causes QS to
conduct heavily which will cause the series regulator to limit the current output of
the supply, C6, C8, and P3 connected as collector to base feedback in the collector |
ACEC
