Pulse-Width Modulator, FETS, and Isolation Transformer
The
In this way current flows from the + dc rail through the primary of T201 to the - dc rail. When Q201 and Q204 are on, current flows through the primary of T201 in one direction. When Q202 and Q203 are on, current flows through the primary of T201 in the opposite direction. This generates the positive and negative pulses on the secondary winding of T201. The output of T201 is then rectified and filtered to produce the dc output.
T202, located in series with T201, is part of the peak current limit circuit, which limits the amount of current that can flow through the FETs. This protects the internal and external circuits from excessive currents that may result when the output of the module is shorted.
Downprogrammer Circuit
The downprogrammer circuit internally draws current through the output rectifier and filter to keep the FET circuits turned on when the module is programmed to a low or zero output. The maximum current that flows through the downprogrammer is 10% of the total output current .
The downprogrammer circuit monitors the current at the output of the module and turns off when the output current reaches 1/2 of its
Additionally, when voltage is programmed to a low value or programmed off, the downprogrammer helps to pull down the output of the supply to speed up downprogramming time.
Readback Multiplexer
The readback multiplexer and the readback A to D are used to read back information from the module during normal operation and during selftest. The microprocessor selects an input on the readback multiplexer and reads back data on that input. The following signals comprise the inputs to the multiplexer:
IMON
VMON
+12V reference
+5V reference temperature reference power
CC DAC output
The multiplexer inputs are between 2.5 volts and
64 Thoery Of Operation