Power Supply Circuit - HP 333A Operating And Service Manual

Model 333А/334А
becomes abnormally large during anoverload, A2CR8
breaks down and provides a lower resistance charg-
ing path for А2С15, which reduces the transient re-
covery time ofthe meter amplifier. Negative ac feed-
back is applied from the collector circuit of A2Q9 to
the emitter circuit of A2Q5. This feedback is used
to ensure flat frequency response, to improve linear-
ity, and to reduce the effect of variationoftransistor
parameters with environmental changes. In this
manner, the calibration of the instrument is made
dependent on high quality passive components.
4-47, METER RECTIFIER CIRCUIT.
4-48. The meter rectifier is connected in a bridge
type configuration with a diode in each upper branch
and a dc milliammeter connected across the midpoints
of the bridge. The simplified meter rectifier is illus-
trated in Figure 4-8, The generator represented by
A2Q5 through A2Q9 with the internal impedance Ro
provides the meter, M1, with current for full scale
deflection and develops a voltage across the calibra-
tion network, which closes the ac feedback loop.
Capacitors A2C27 and A2C28 are used as coupling
capacitors for the ac feedback loop, output signal to
the OUTPUT connector, and the bridge error signal
to the input of the automatic fine tuning loops. The
mechanical inertia of the meter and A2C26 prevents
the meter from responding to individual current
pulses, Therefore, the meter indication corresponds
to the average value of the current pulses rather than
the peak value. The meter is calibrated to indicate
the rms value of a sine wave. Resistor A2R45 im-
presses a fixed bias across diodes A2CR6 and A2CR7
(biasing them close to the barrier voltage) to make the
meter amplifier response linear to large variations
LonceoccuJ
A2R34
Figure 4-8.
Section IV
in signal amplitude. The linearity of this type of cir-
cuit is also increased by including the meter circuit
in the overall feedback loop.
4-49, POWER SUPPLY CIRCUIT.
(Refer to Figure 7-6)
4-50. The power supply circuit consists of a +25 volt
series regulated supply anda -25 volt series regulated
supply which is the reference supply for the +25 volt
supply.
4-51, The -25 volt regulated supply is ofthe conven-
tional seriesregulator type. The amplifier A1Q5 is
used to increase the loop gain of the circuit, thus im-
proving voltage regulation. The positive feedback
applied to the junction of A1R11 and A1R12 is used to
further improve the line frequency suppression of the
circuit,
4-52, The +25 volt regulated supply is of the conven-
tional series regulator type and operates the same as
the -25 volt regulated supply.
4-53. RF DETECTOR CIRCUIT. (334A only)
(Refer to Figure 7-2)
4-54, The RF detector circuit consists of a rectifier,
ААСВ1, and filter circuit. The RF signal is applied
to the circuit through the RF INPUT connector onthe
rear panel. The rectifier diode A4CR1 recovers the
modulating signal from the RF carrier and the fiiter
circuit removes any RF components before the signal
is applied to the impedance converter circuit through
the NORM-RF DET switch, 87.
3334/3344- AO
Simplified Metering Circuit
4-7