HP SCR-1P Series Operating And Service Manual page 20

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4-43 Protection, Diodes CR5Cl and CRSl prevent
anode Induced reverse gate currents from being
f«d back to the control circuit, Resistors R54 and
~55 limit current In the SCR gates. '
4..:44 BIAS AND REFERENCE CIRCUIT
4-45 The bias and reference circuit supplies four
voltages (+33, +o. 7,' -10 and -30V) for Internal
power supply operation, and maintains the pro-
gramming currents constant, The -28 and -l0V
outputs are regulated,
4;.45 The output of secondary winding 5-6 of
transformer T2 ls full-wave rectified by CR30 and
CR31. Capacitors C20.and C,21 each charge to
the' peak rectlfled voltage (voltage doubling), The:
0. 7Vdc (with respect to -S) ls maintained by diode
CR14. The +33Vdc ls the voltage across C21. The
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-33V across C20. provides the unregulated Input to
the regulator, ',,,'
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4-47, For the -30Vdc:, Jranslstor Ql0 ls the erro'r
detector/amplifier, Zener diode V~l and diode :
CR6 provide ll''ref
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rence' voltage,at the emitter of
010. Voltage dlv,der R35-R36 supplies an error
voltage to the base of Ql0 which amplifies and
applies lt'to the base of series regulator Qll, The,,,
base drive of Qll'adJ.ists the voltage a,cro,s Qll
as required to compensate for the error In' the -30V.
Resistor R37., sets the optimum current through tem-
peraturo'-compersated zener diode VRl, Resistor
R33 reduces power dissipation In .Qll and capacitor
C22 stabilizes the loop. T.he -30V,ls divided down
to -l0V by stage Q5. Th~ conduction of Q5 Is
h'eld constant by VRl on the base Gnd R39 Is oe-,
lecte.d to provide exactly,-l0V output,
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