The power control circuit board controls the system sequencing for power up/down. The micro
program has been completed and fully tested and provides the functionality as described below:
The circuit board is based on a PIC16F84 microcontroller. The micro monitors the power on
signal (opto-coupled) and when asserted turns on the fan relay.
After a 5 second delay the filament relay is turned on and a 3 minute filament timer is
started. At the end of the filament delay the relay that controls the high voltage (either
directly or via a contactor) is turned on and then starts another timer for the high voltage
slow start delay. After 2 seconds the slow start relay operates and bypasses the current
limiting resistor (47 ohm 50 watt). After this, the power supply is ready for use.
An input (opto-coupled) monitors any alarm conditions from the amplifier and if asserted
immediately turns off the high voltage relay. To ensure that operation is immediate there
is both a hardware control that operates immediately and a software control that latches the
Another input (opto-coupled) is provided to reset the fault condition and re-apply high voltage.
A forth input (opto-coupled) is provided to turn off the power supply. The turn off sequence
is a reverse of the turn off procedure. The high voltage is turned off then the bypass relay
is turned off. After a short delay the filament relay is turned off. The fan continues to
operate for 30 seconds after the filaments are turned off. All times are adjustable in
software to accommodate different valve types and control requirements.