Each SCR is encapsulated in a high thermal conductivity epoxy resin which eliminates problems associated with moisture. All SCR power supplies are designed to withstand extremes of shock, vibration, acceleration, and thermal shock in accordance with MIL-STD-810. The power supply is generally mounted to PC boards via five 0.045” diameter pins.
The SCR Series of high voltage power supplies are regulated by virtue of Pulse Width Modulation topology. The normal input voltage of 12 VDC is stepped up by resonant action to a high voltage output which is referenced to the input ground (Pin 4). The output voltage is adjusted by using a remotely located trim pot of 20kŮ connected between pins 2 and 3 or by means of an external voltage of up to 5V applied at pin 3 with respect to ground. Pin 2 provides a reference output voltage of 5 VDC. The output voltage of the SCR unit is NOT FLOATING. The output high voltage return and the input power return are internally connected together.
The output voltage may be controlled in two ways. In the voltage programming mode , a control voltage (Pin 3) between 0 VDC and 5 VDC will adjust the output between 0 and full output. In the resistance programming mode, a resistor placed between the control voltage pin and ground will set the output to a voltage which depends on the value of the resistance used. Typically a 10 k Ohm resistor will set the output voltage to 50%. Zero resistance yields zero output. The limiting output current is set for each unit to be 120% above the nominal value determined by the 5-W limit. The current limit circuitry internal to the SCR high voltage power supply has a reaction time constant of less than 0.1 second.
