Power Supply - Keithley 2425 Service Manual

4-8 Troubleshooting
plexer directs the voltage feedback, current feedback, reference, or ground signal to the
A/D converter. An opto-isolated interface provides control signals for both DACs, analog
circuit control, and A/D converter communication to the digital section.

Power supply

Figure 4-3 shows a block diagram of the Model 2425 power delivery system.
The offline switching power supply provides all power for the instrument while providing
universal inputs and power factor correction for the 120/240V line. The digital board runs
off of 5V and 12V supplies derived from the switcher. The +12VD supply is set to pro-
gram the flash ROM. (See Digital circuitry below.)
A constant-frequency switching supply runs off the +24VD supplies and generates all the
floating and output supply voltages for the analog board: +5V and ±15V, ±42V and
±150V.
Figure 4-3
Power supply block diagram
Analog Board
+15V
Constant Frequency
Low Noise Floating
Switching Supply
Line
Neutral
PFC
+5V
F
F F
+24Vdc
D
DC/DC
Converter
Output Stage
-15V -150V -42V
F
+24dc
+12Vdc
DC
Regulators
+5Vdc
D
Model 2425 Service Manual
O +42V +150V
Digital
Circuits
D