Output Stage - Keithley SourceMeter 3A 2420 Service Manual

The offline switching power supply provides all power for the instrument while providing
universal inputs and power factor correction for the 110/120V line. The digital board runs off
of 5V and 12V supplies derived from the switcher. The +12VD supply is set to program the flash
ROM. (See Digital circuitry below.)
A constant-frequency switching supply runs off the +24VD supplies and generates all the float-
ing and output supply voltages for the analog board: +5V and ±15V, ±42V and ±85V.

Output stage

Figure 4-4 shows a simplified schematic of the output stage.
Figure 4-4
Output stage simplified
schematic
+15Vf
Maindrive
300K
O
F
-15Vf
+85V
Q500
HI Drive
Q504
Q514
Q516
Q518
+
-
Q521
F
Q523
Q525
Q507
Q503
HI Drive
Troubleshooting
+42V
F
-42V
-85V
4-7