final file EDC1

The Electronic Development Company Ltd.

Further valve tester desciption.

6.3vAC Heater PSU

The voltage is fixed at 6.3vAC but a 14pin micro (opto coupled to the main micro as it has to float) measures the heater voltage and current (full wave average rectifier).
This PSU is on the main micro’s pcb.

0 to –30vDC Grid PSU
This is supplied from an op-amp driven from one of the main micro’s PWM outputs.
This PSU is on the main micro’s pcb.

Main micro’s pcb and switches/display pcb
All the above PSUs are switched on and off via relays driven from the main micro.
The main (40pin) micro measures the chassis ground referenced voltages and currents and the power device temperatures (via ntc thermistors). When a power device gets hot a corresponding fan under the heatsink turns on and if the device gets dangerously hot the PSU in question shuts down.
The main micro communicates with the four floating 14pin micros via opto-isolators.
It also controls the 2 line * 20 character vacuum fluorescent display.
The VFD along with push switches and leds are mounted on a separate pcb.
To keep I/O requirements down to a reasonable level all the push switches are read via parallel to series shift registers and relay, fan, led and AWD outputs are driven via series to parallel shift registers, this also minimises interconnections between the main micro pcb and the switches/display pcb.
Up / down then enter push switches are used to set the required voltages.
Each PSU has two push switches associated with it, one to turn it on or off and the other to show its associated voltage and current on the VFD.
The VFD can also show power device temperatures if desired.
A line of leds indicates which supply is selected to have its voltage and current on the VFD and another line indicates whether a PSU is on or off.
There are also three leds to warn of high power device temperature(s).

Operating modes
The unit can be operated manually as described above or it can be programmed to perform a series of measurements at preset voltages on the different PSUs.

This mode of operation is to allow matching of valves to be done semi-automatically, the main micro calculating the valve parameters from the measurements it has just made.

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