HP BENCH Series User Manual

shunting the programming resistors, increases the
high frequency gain of the input amplifier.
4-17 DRIVER AND ERROR AMPLIFIER (Refer to over
all schematic at rear of manual)
4-18 The error and driver amplifiers amplify the
error signal from the constant voltage input circuit
to a level sufficient to drive the series regulator
transistor. Driver Q5 also receives a current
limiting input if GR4, the current limiting diode,
becomes forward biased.
4-19 Stage Q4 contains a feedback equalizer net
work, C3 and R17, which provides for high fre
quency roll off in the loop gain in order to stabi
lize the feedback loop.
4-20 CURRENT LIMITING CIRCUIT
4-21 Current limiting occurs when transistor Q3
conducts. This is determined by the voltage drop
across current sampling resistor R33 and the adjust
ment of current limit potentiometer R50. When the
output current reaches the limit value, the positive
voltage (with respect to+S) on the wiper arm of R50
causes Q3 to conduct. Diode CR4 becomes forward
biased clamping the base of C5 to a potential which
decreases the conduction of the series regulator,
thus limiting the output current. Potentiometer R50
permits the base potential of C3 to be varied and
thus changes the current limiting threshold.
4-22 REFERENCE CIRCUIT (Refer to schematic at
rear of manual)
4-23 The reference circuit is a separate power
supply similar to the main supply. It provides
stable reference voltages which are used through
out the unit. The reference voltages are all de
rived from smoothed dc obtained from the full wave
rectifier (CRIO and CRll) and filter capacitor C5.
The -6. 2V reference voltage is derived from VRl
which is a second dc source regulating at 6. 2vdc.
Current for VRl is supplied by the (-) side of C5
and flows through VRl, the base-emitter junction
of Q7, R20, and back to the positive side of C5.
4-24 The base-emitter junction of Qll is held
constant by 6. 2V zener diode VR7 which regulates
line voltage changes that alter the voltage across
C5. Thus Qll is a constant current source feeding
12. 4V zener diode VR4 and 6. 2V temperature-com
pensated zener diode VR6.
4-25 Resistors R27 and R30 form a voltage divider
across the stable 6. 2 volts developed by VRl. The
base-emitter junction of Q9 is therefore held con
stant by the voltage developed across R27. Thus
Q9 provides a constant current to zener diode VR3,
which regulates the -6. 2V source.
4-26 METER CIRCUIT
4-27 This circuit provides indications of output
voltage or output current. With METER SELECTION
switch 82 set to VOLTS position the meter, in
series with R38, is connected directly across the
output of the supply. With S2 set to the MA posi
tion the meter, in series with R37 and R47, is
connected across the current sampling resistor
R33. Potentiometer R47 adjusts the electrical
meter zero in the MA position.
4-3

HP BENCH Series Specifications

General

Brand	HP
Model	BENCH Series
Category	Power Supply
Language	English