Power Supply - HP 340 Series Service Manual

Power Supply
A sealed assembly, the power supply has no replaceable parts except for the fuse. When any
part of the power supply fails (except for the fuse), replace the complete supply. Exchange
power supplies are not available.
The unit contains the AC line input, RFI filters, on/off switch, fan, power rectifier circuit and
dc output connector in a inclosed can.
Electrical dc output consist of three outputs with a common return and one output (9 V dc)
which has it's own return. The outputs are
• 5.1 V dc
~]
15 A.
• +12 V de
@
2.,3 A.
• -12 V de
@
250 MA.
• 9 V dc (g 250 rnA.
The 0.1 volts over the 5 V is for the electrical potential drop of the connector system. The + 12,
-12, and 9V de outputs are three terminal linear regulators and therefore have over current
and thenual protection. 5.1 V dc output is power limited by primary eurrent limit. The 5.1
V c de also has a shut down comparator at about 6 volts. The -12 V dc output is reverse bias
protected. The 9 v de is a floating output for the local area network.
AC line current inrush is limited by negative temperature coefficient resistors and therefore do
not limit the inrush of current if hot. The power supply also has a line select switch. The power
supply will be damaged if this switch is set to 115 and ac line potential of 230 V ac is applied.
Start up circuit is a line frequency transformer and therefore will not start on a dc line input.
Start up time is a function of the line potential and at low line (100 V ac) is about 1 second.
The self enclosed fan is powered by the + 12 V dc output and will not run if there is a + 12 V dc
short on the output. A thermal shut-down switch is attached to the +12 V dc/+5.1 V dc heat
sink. This will provide protection from cooling failure such as blocked air vents, fan failure, or
a short on the
+
12 V dc output.
Functional Description
45