Regulated DC Power Supply Employs Digital Control for Firing its SCRs

Abstract

A regulated DC power supply using full-wave rectification by SCRs’, with digitally-variable firing angle, is described. The output voltage is sampled by a high-gain operational amplifier which controls the frequency of a voltage-controlled oscillator (VCO). The firing angle of the SCRs' is varied to stabilize the output voltage by counting a fixed number of variable-frequency pulses from the VCO, from each zero crossing of the mains sinusoidal voltage. The merit of the circuit is the inherent stability achieved through the digital negative feedback loop. The load regul-tion, line regulation, ripple factor and temperature stability of the circuit are measured. In particular, the circuit has an excellent temperature stability from 12°C to about 45°C.

Indexing Terms:

• Regulated Power Supply
• SCR
• Firing Angle Control
• VCO
• Digital Negative Feedback
• Stability