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5.2 THEORY OF OPERATION
The 2070-4A Power Supply module consists of several sub-systems that perform different functions in
order to meet the requirements listed on TEES 2009.
This section provides a little insight of the sub-systems’ functionality.
AC Input, Fuse and Switch
The AC line is fed to the Power Supply from the AC cord to the AC INPUT header providing the Hot,
Neutral and Earth lines to the input protection circuitry. The Hot line is routed from the AC INPUT header
to the 2A fuse and then to the switch, the next stages are the input protection and the EMI filter.
Input protection
The input protection consists of the next:
Two 1.5Ohms 15W resistors, one placed on the AC+ line and the other one on the AC- line.
Three surge arrestors placed between AC+ and AC-, AC+ and EG, AC- and EG.
One .68uF capacitor located between AC+ and AC-, between the resistors and surge arresters.
EMI Filter
The EMI filter is contained into a discrete device. It receives the AC input signal and delivers the power
already filtered to the circuitry in the Power Supply module.
Power Supply Modules
The Power Supply filters the 120 VAC line and then feeds three power modules. These power modules
generate the required voltage outputs:
+5VDC module, is used for providing +5VDC.
+12VDC module, is used for providing +12VDC and -12VDC (the -12VDC are obtained through a
switching regulator on control board).
+12VDCISO module, is used for providing +12VDCISO.
The Power Supply modules are connected to the Control board via a set of harnesses.
Zero-Crossing Detector circuit
This circuit is based on the MC33161P which is a universal voltage monitor with two comparator channels
with hysteresis, a Mode Select Input, a pinned out 2.54V reference and two open collector outputs.
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