High Voltage Supply Control - Motorola R-2001A Service Manual

7-10. Short circuit protection is implemented by monitoring the current in the primary winding of theoutput
transformer. If a secondary output is shorted the primary current will increase significantly causing the
overcurrent detector to pull the control line low shutting down the supply. However, with the supply shut down
primary current will cease and the overcurrent detector will release the control line. With the control line
released the supply will come back on. If the short is still present the cycle will repeat itself. Delay is provided in
the overcurrent detector so that with a shorted output the supply cycles at about a 0.5 second rate.
7-11. Overtemperature protection is obtained by using a thermal switch mounted on the most heat critical
capacitor. If the capacitors temperature exceeds the temperature setting of the thermal switch, the switch
closes to ground shorting the control line and shutting down the supply. Normal operation of the supply will be
resumed when the temperature returns to a safe operating level.
7-12. Protection for high or low DC and AC line inputs is provided by monitoring the voltage on the DC Bus. If
the bus voltage exceeds 20 volts or if the voltage falls below 10 volts, the shutdown circuitry pulls the control
line to ground shutting down the supply. When the bus voltage returns to normal limits, supply operation
automatically resumes.
7-13. High Voltage Supply Control. A 12 volt regulator from the DC BUS provides the bias voltage for the
High Voltage Power Supply (AIO). The primary power for the High Voltage Supply comes from the high
voltage control circuitry. A control line from the high voltage supply regulates the input voltage to the high
voltage transformer. The current used in the high voltage supply is the bias current for the pulse width
modulator circuitry for improved power supply efficiency.
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