Discussion on the Design of Switching Stabilized Voltage Power Supply
The function of this part is to provide the driving voltage of the chip used in the main power supply part and use it as a reference voltage.
The power supply provides a stable DC power +5V, itsThe main function is to provide comparator, decoder and encoderThe drive voltage is +5V. Figure 1.
The power supply provides a stable DC power supply +12V, and its main function is to provide the driving voltage +12V for 2803 and provide the reference voltage of the comparator. Figure 2.
The power supply is mainly composed of three parts: rectification, filtering and voltage stabilization, and some functions are as follows:
Bridge rectifier circuit:
In the positive half cycle of U2, the potential of point a is higher than that of point b, D1 and D3 are turned on, D2 and D4 are cut off, and the current returns from terminal a to terminal b of the power supply through D1, RL and D3; in the negative half cycle of U2 , the potential at point b is higher than the potential at point a, D2 and D3 are turned on, D1 and D3 are cut off, and the current returns from end b to end a of the power supply through D2, RL and D4. Compared with the half-wave rectifier circuit, under the same conditions of U2 and RL, the output current and voltage are doubled; the current ripple degree is reduced; the transformer
There are symmetrical currents flowing in the positive and negative half cycles, which are fully utilized and there is no problem of single magnetization, but four rectifying diodes are required, and the circuit is slightly complicated. Compared with full-wave rectification, although 2 more rectifier diodes are used, the reverse withstand voltage is doubled, the secondary of the transformer is one turn less, and the overall cost is lower than that of a full-wave rectifier circuit.
The power supply provides a stable DC power supply +12V, and its main function is to provide the driving voltage +12V for 2803 and provide the reference voltage of the comparator. Figure 2.
The power supply is mainly composed of three parts: rectification, filtering and voltage stabilization, and some functions are as follows:
Bridge rectifier circuit:
In the positive half cycle of U2, the potential of point a is higher than that of point b, D1 and D3 are turned on, D2 and D4 are cut off, and the current returns from terminal a to terminal b of the power supply through D1, RL and D3; in the negative half cycle of U2 , the potential at point b is higher than the potential at point a, D2 and D3 are turned on, D1 and D3 are cut off, and the current returns from end b to end a of the power supply through D2, RL and D4. Compared with the half-wave rectifier circuit, under the same conditions of U2 and RL, the output current and voltage are doubled; the current ripple degree is reduced; the transformer
There are symmetrical currents flowing in the positive and negative half cycles, which are fully utilized and there is no problem of single magnetization, but four rectifying diodes are required, and the circuit is slightly complicated. Compared with full-wave rectification, although 2 more rectifier diodes are used, the reverse withstand voltage is doubled, the secondary of the transformer is one turn less, and the overall cost is lower than that of a full-wave rectifier circuit.
2 Design of the main power supply
This part adjusts the voltage through the three-terminal adjustable integrated voltage regulator. When the potentiometer R2 is adjusted, the voltage will change with the resistance value of the resistor.
3 Design of protection circuit part The protection circuit adopts the function of field effect tube, and its working
The operation principle is as follows: when the power supply output is short-circuited, the gate-source of the field effect transistor VT2 becomes equal potential and conducts, and its drain-source will share the base current of the adjustment transistor VT1 to reduce the conduction current of the adjustment transistor. Function, R2 is the protection resistor of the gate of the field effect transistor. When selecting a field effect tube, the conduction voltage drop (the voltage between the drain and the source) should be smaller than the conduction voltage drop of the emitter junction of the adjustment tube.
4 Design of relay drive part
The design of this part mainly utilizes the special function of the relay: when there is voltage at both ends of the relay, the relay is turned on, otherwise the relay is turned off. The relay is driven by a 2803 chip, as shown in Figure 3, it can be seen that both ends of A and B are connected to the rectifier part, and the input terminal of 2803 is connected to the decoding part. When the decoding signal is transmitted to 2803, it will judge that the output of that end is high level, and the relay connected to this end is turned on, that is, it is connected to the first gear of the transformer to play the role of shifting.
