Parallel switch type voltage regulator circuit schematic diagram

Principle of parallel switch type voltage regulator circuit

In the circuit of Figure (1) below, L1 is the energy storage inductor, VT1 is the switch tube, VD1 is the pulse rectifier diode, C1 is the filter capacitor, and R1 is the load resistor of the voltage stabilization circuit. It can be seen from the circuit that the switch tube and the load resistor are connected in parallel to the Ui terminal of the DC input circuit.

During the period when the VT1 base switch pulse is at a high level: VT1 is turned on. At this time, the input voltage to the inductor L1 and the turned-on VT1 collector and emitter form a loop. At this time, the energy storage inductor L1 generates a self-inductance voltage with positive on the left and negative on the right, which hinders the increase of current. During the VT1 conduction period, since the collector of VT1 is at a low level, VD1 is cut off. After the cut-off, VD1 disconnects the filter capacitor C1 and the load circuit from the previous energy storage inductor and other circuits. During this period, the DC working voltage is provided to the load circuit in the form of discharging the electric energy stored in the capacitor C1 to the load circuit.

During the period when the VT1 base switch pulse is at a low level: the low level cuts off VT1, and the energy storage inductor L1 generates a reverse electromotive force to hinder the reduction of the current in the inductor. The direction of the electromotive force is negative on the left and positive on the right. This electromotive force turns on VD1, and the current I generated by the electromotive force flows through VD1, charges C1, replenishes the electrical energy in C1, and supplies power to the load circuit.

In the circuit above, changing the characteristics of the VT1 base pulse can change the size of the output voltage of the voltage regulator circuit, and can make the output voltage higher than the input voltage, so this is a circuit that can increase the DC output voltage without voltage transformation. Its boost principle is: when VT1 is cut off, the voltage added to capacitor C1 is the sum of the self-inductance voltage of L1 and the input voltage in series with the same polarity.

The circuit shown in the figure (2) below is a parallel switch type voltage regulator circuit. T1 is a pulse transformer, L1 is the primary winding of the pulse transformer and also acts as an energy storage inductor; L2 is the voltage obtained by the mutual inductance of the secondary winding of the pulse transformer T1, which is rectified by VD1 and filtered by C2 before being supplied to the rear load circuit; VT1 is a switch tube and R1 is a load resistor.

When the excitation pulse is at a high level, VT1 is saturated and turned on, and the input voltage is conducted to the ground through the L1 coil and VT1. A self-inductance electromotive force with a positive top and a negative bottom is generated at both ends of the energy storage L1 coil, which hinders the increase of the current passing through. At the same time, the mutual inductance of the secondary coil L2 of the transformer generates a negative voltage at both ends (the principle of the same-name terminals of the transformer). VD1 is cut off and does not work, and the voltage on the capacitor C is discharged to power the load circuit.

When the excitation pulse is at a low level, VT1 is cut off, and a self-inductance voltage with a negative top and a positive bottom is generated at both ends of the transformer L1 coil. The mutual inductance at both ends of the L2 coil obtains a positive top and a negative bottom voltage. In this way, the energy stored in transformer T1 is rectified by VD1 and filtered by C1 to power the load circuit.

In contrast to the series switching power supply, the parallel switching power supply is a flyback switching power supply, that is, when the switch tube VT1 is turned on, the rectifier tube VD1 is turned off; when the switch tube is turned off, the rectifier tube is turned on to provide energy to the load.

Parallel switch type voltage regulator circuit diagram (I)

When the transistor T is turned on, the diode D is reverse biased and cut off, and when the transistor T is cut off, the diode D is turned on.

Parallel switch type voltage regulator circuit diagram (II)

The following is a parallel pulse width modulation switching voltage regulator circuit. The main circuit of the parallel pulse width modulation switching voltage regulator circuit is shown in Figure 2-73 (a). In the figure, the switch adjustment tube VT, input voltage, and output voltage are connected in parallel, so it is called a parallel type.

When a positive pulse voltage is applied to the base of the switch adjustment tube VT, VT is turned on, the collector potential is approximately zero, and VD is reverse biased and cut off. The input voltage U passes through the current i. Energy is stored in the inductor L. At this time, the load current is supplied by the discharge current of the capacitor C that has been charged in the previous few cycles, and the current direction is shown in Figure 2-73 (b).

When there is no positive pulse voltage on the base of the switch adjustment tube VT or a negative pulse voltage is applied, VT is cut off. Since the current in the inductor cannot change suddenly, a self-inductance potential is generated at both ends of L and the capacitor C is charged through the freewheeling diode VD to replenish the electric energy consumed during discharge, and at the same time supply power to the load RL. The current direction is shown in Figure 2-73 (c). When the switch adjustment tube is applied with a positive pulse voltage again, the process of UI transferring energy to L will be repeated again, and the cycle will continue.

The above analysis can summarize the working principle of the switching regulated power supply: during the on-time of the switch regulating tube, the energy storage inductor stores energy, and the energy storage capacitor supplies power to the load; during the off-time of the switch regulating tube, the energy storage inductor releases energy to charge the energy storage capacitor and supplies power to the load. These two components also have filtering effects to make the output waveform smooth.