HP 85662A, Руководство по устранению неисправностей и ремонту

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R126, and form an input filter. The values of and ensure that the
current in is continuous; therefore, the 30 component is minimal in the load current
presented to the V unregulated supply. R126 is used to lower the Q of and Cl00 to
less than one. This ensures that there will be no ringing at their resonant frequency. is a
toroidal inductor to minimize radiated magnetic field.
The synchronous pumping circuit consists of
UlOlA, and and associated
passive components. is a pulse width modulated switching regulator IC. It has a ramp
generator and several comparators that can terminate the output pulse that starts at the
beginning of the ramp.
and determine the slope of the ramp.
is a comparator that observes the ac voltage of the tank circuit formed by and
the high voltage transformer primary. When the voltage passes through zero volts from high
to low, the output of goes high. This signal is connected to the EXT SYNC input of
and causes the ramp to reset and start. Resistors and are not the value,
ensuring that the comparator will trigger a ramp at start up (when there is no ac signal in the
tank circuit).
The output pulse,
OUT COLLECTOR, starts at the beginning of the ramp and is terminated
by one of several events. The output is an open collector that is pulled to V by
This signal is inverted and buffered by UlOlA. UlOlA is able to provide large peak currents to
drive the gate capacitance (approximately 1200 maximum) of
R122 limits the peak
current at the gate and slows the switching time slightly. This protects UlOlA and helps to
reduce
When
is turned on, current begins to flow in is a toroidal inductor to
minimize radiated magnetic field. This current builds up during the duration of the output
pulse from
When the output from is turned off, is turned off also. Then the
current in continues to flow, forward biasing CR103. The current begins to flow into
Cl22 and through R120 and back into R120 dissipates most of the stored energy from
Cl22 slows the rise time of the voltage into R120 and helps reduce some radiated
The turn off time of also slows the rise of the voltage into CR103, minimizing
This shows the ability to sense the downward zero crossing of the sine wave voltage of the
tank circuit and pull it down in phase so that energy may be added to the tank. has
the ability to control the maximum possible output pulse length. This is done by and
and is set so that the pulse is always less than one quarter of the resonant period. This
is essential to prevent a gain reversal where longer pulses would begin to subtract energy from
the tank once the voltage began to go positive.
The current in is sensed by R124 and is fed back to the
CURRENT LIMITING
input of
If the average current rises too high, the output pulse will be cut off. This should only
happen in a fault situation and is used primarily for damage control. R124 also provides a
test point to observe the currents in
The cathode voltage output from the high voltage power module is sampled by and
is fed to this board as the
HV FEEDBACK
signal. The cathode voltage is approximately
-2400 V dc and is 30 HV FEEDBACK comes into a pot R103 and then to
a resistor, R102 to V dc. CR100 and CR102 protect the input of in case of
arcing in the high voltage section that might cause any excessive voltage on the HV
FEEDBACK input. El is a spark gap that is designed in as part of the PC board traces. It
should break down at about 1500 V in dry air (less in humidity). Normally, there is only a
few volts at El and no leakage should occur.
4 Al A7