HP 330 Service Information Manual page 84

Rectification and Switching Control Circuits
Functions of the Rectification and Switching Control circuits are:
• Full-Wave Bridge Rectifier.
• Switching Control Circuit.
• Power Transformer.
Full-Wave Bridge Rectifier
Part of the input ac voltage is applied across a full-wave bridge network that outputs a DC
voltage. Large storage capacitors charge up to this voltage and provide a constant energy
supply to the individual power supply circuits.
Switching Control Circuit
Voltage from the rectifier feeds a Switching Control Circuit that controls the amount of power
going to each of the output voltage regulators. +5 V dc feedback is applied to the Switching
Control Circuit to regulate the +5 V dc output. Overvoltage protection signals also input the
Switching Control Circuit that will cause the power supply to shut down if voltage in the output
supplies goes too high. A +5 V dc over-current sensor input is another input to the Switching
Control Circuit.
Power Transformer
Input ac voltage is also applied to the primary windings of a power transformer. Three sets
of secondary windings each feed a voltage regulator for the output voltages. A voltage select
switch is set to the line voltage range and causes the power transformer to have the same voltage
output for both line voltage ranges.
Power Supply Regulators
Functions of the Power Supply Regulators are:
• +5 Vdc Power Supply.
• +12 Vdc Power Supply.
• -12 V dc Power Supply.
+5 Vdc
Voltage from the power transformer feeds through a +5 V dc current sensor than goes to the
+5 V dc rectifier. Output from the +5 V dc rectifier is nominally 5.07 V dc ±0.18 V dc. The +5
V dc output is also fed to the +5 V dc Feedback Loop Circuit for regulation. It also is fed to the
Overvoltage Protection Circuit and Reset Circuit. If the +5 V dc fails, the Power-On LED on
the front panel will go out as the +5 V dc is part of the controlling voltage for the Switching
Control Circuit.
+12 Vdc
Voltage from the power transformer feeds through a rectifier then to a +12 Vdc Post Regulator.
The output from the Post Regulator is nominally + 12.29 V dc ±0.43 V dc. In addition to being
distributed in the computer (or expander), the +12 Vdc output is also fed to the Overvoltage
Protection Circuit and Reset Circuit. External to the power supply, the
+
12 V dc is connected
to one side of the Power-On LED on the front panel.
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Functional Description