Power Main Board - HP 8133A Service Manual

Power Input

Power Main Board

+
15 V Regulation
The AC line voltage is applied to the power input module F1 which
consists o f
A line filter for filtering RFI from the AC line voltage
A line fuse F1
A line voltage selector for 100/120/220/240 VAC operation.
The main ordoff switch S1, isolates the input power from the voltage
selector. Depending on the voltage selector setting, the primary
windings of the transformer
four modes:
1. 1OOV the two 120V windings are connected in parallel, but power
is supplied to the lOOV tapping (A) - orange wire.
2. 120V the two 120V windings are connected in parallel and power
is supplied to them (C), (D) - black, black-green wires.
3. 220V thle two 120V windings are connected in series, but power is
supplied to the lOOV tapping (A) - orange wire.
4. 240V the two 12OV windings are connected in series and power
supplied to (C)- black wire.
It is important to set the voltage selector according to the nominal Iine
voltage supply. This is to prevent:
Malfunction the supply voltage
if
High power losses or blowing of fuse
high.
The transformer secondary windings are center tapped, and provide
an additional highAow tapping for each of the four output voltage
levels. They are all connected to the power main board.
Regulation circuits are basically the same for all six output voltages,
+
so only the 15 supply is described here.
There are two complete regulation paths. They are applied together
to:
Have a common output at
Have a common control by feedback signals generated at R113
Supply the power control board with:
A voltage sensing signal
A current sensing signal R + 1 5 fed to 53(15)-X3(15)
The high tapping path
is
The Red 3 and Blue 3 wires of
Schottky power diodes, CRlOl and CR102, for full wave
rectification
Filtering capacitor ClOl
Series voltage regulation via the power MOSFET QlOl
of
The gate QlOl, is controlled by the voltage drop across R101, which
is produced by controlling the current signal G + 15H, from the power
control boiud. QlOl is turned
are
connected in one of the following
is too low
if the supply voltage is too
+
15 V fed to 53(14)-X3(14)
formed by:
off
when there is:
Theory of Operation
is
7-25