Dynamic power supply for power amplifier controlled by thyristor

As shown in the figure below, the AC power input is filtered by T1 and divided into two outputs. One path goes to the step-down transformer T3. A bidirectional thyristor KS is connected in series in the primary circuit of T3 to change the primary AC power of transformer T3. The other path is stepped down by capacitor C1 and rectified, and then stabilized by D1 to provide a DC working voltage to the trigger control circuit. R3, C3, Q3 and transformer T2 form a relaxation oscillation circuit. R2, R4, Q1 and Q2 form a current source to charge capacitor C3 with a constant current. When the voltage across C3 is charged to the breakdown voltage of Q3, C3 discharges through the emitter e of Q3, the base b1 and the primary coil of transformer T2, and the trigger pulse of thyristor KS is obtained at the secondary of transformer T2, which controls the conduction of thyristor KS and makes transformer T3 work. At the secondary of transformer T3, the positive and negative symmetrical DC voltage required by the power amplifier is obtained after rectification and filtering. When the voltage across capacitor C3 is discharged to the valley voltage of Q3, the emitter e and base b1 of Q3 are closed, and the next cycle of charging and discharging of capacitor C3 is ready.

R6~R9, Q4, D2 and W1 form a voltage comparison amplifier circuit. Adjusting W1 can change the output voltage, and control the current of Q1 and Q2 current sources through IC1 to change the charge and discharge time of C3, control the conduction angle of thyristor KS, thereby changing the primary AC power of transformer T3, and obtaining a constant output voltage at the secondary, ensuring the instantaneous power of the power amplifier.

Component selection and debugging: Transformer T2 is made of 5×5mm E-type iron core, the primary can be wound with ∮0.15mm enameled wire for 200 turns, and the secondary can be wound with 135 turns. Transformer T3 can be wound with 40mm×60mm iron core, the primary can be wound with ∮0.9mm enameled wire for 352 turns, the secondary can be wound with ∮1.26mm enameled wire for 176 turns, and the tap is at 88 turns.

The debugging is very simple. Don't connect the power amplifier first. After checking everything, you can turn on the power first. Use an oscilloscope to measure the two ends of the primary of transformer T2. There should be a sharp pulse waveform. Use a voltmeter to measure the output voltage. Adjust W1 so that the output voltage is positive and negative 45V. Then connect the power amplifier. At this time, you can see that the conduction angle of the thyristor moves back and forth, and the output voltage is stable at positive and negative 45V. The debugging is completed. The power consumption of this amplifier dynamic power supply is about 1W in static state, the output power is greater than 250W, and the voltage stability rate is less than 0.15%.