Reference Design Based on TWH8778 Electronic Switch IC - Switching DC Power Supply

Probe domestic switch needle KG-300K needle head diameter is 3.0mm normally open switch needle

One-piece inductor

This circuit realizes the role of DC stabilized power supply by applying TWH8778 type electronic switch integrated circuit.

First, the working principle of the circuit

The circuit diagram of the switching DC stabilized power supply is shown in Figure 45.

When the switch S is closed, the 220V AC voltage is rectified by VD1~VD4, and the capacitor C1 is filtered, and then output in two ways. One is applied to pin 1 of the IC integrated circuit, and the other is applied to the emitter terminal of the transistor VT through the resistors R1 and R3, so that the transistor VT is in a saturated conduction state. At this time, the collector voltage (1.6V or more) is output to the 5th pin of the IC integrated circuit, so that the internal electronic switch of the IC is turned on, and the voltages of the 2 and 3 pins are output, so that the current in the inductor increases and is supplied to the load. When the output voltage reaches 6V, the Zener diode VS breaks down, and the current on the resistor R3 increases, causing the voltage on R3 to increase. When the output voltage reaches 12V, the transistor VT changes from saturation to amplification. When the output voltage exceeds 12V, the emitter junction voltage of the triode VT decreases, causing the collector output voltage to drop. When the voltage drops to 1.6V (ie, the potential of the 5th pin of the IC integrated circuit drops to 1.6V), the IC switch IC is disconnected. The current of the inductor L drops, and the output voltage also decreases. When it drops to 12V, the collector potential of the transistor VT rises to 1.6V or more, and the IC integrated circuit is turned on again, so that the output voltage is always stable at 12V.

Second, the choice of components

IC selects TWH8778 type electronic switch integrated circuit; R1~R5 selects RTX-1/4W type carbon film resistor; C1 selects aluminum electrolytic capacitor with voltage resistance of 25V, C2, C4 selects CD11-16V electrolytic capacitor, C4 selects CT1 type high Frequency ceramic capacitor; VD1~VD5 selects IN4004 silicon type rectifier diode, VD6 selects IN4148 silicon type switching diode; VS selects IN4106 or 2CW60 silicon steady voltage diode; RP can use WSW type organic solid fine adjustment variable resistor; the rest of the device can refer to the figure Marked on.

Third, production and debugging methods

The structure of the circuit is simple, as long as the welding according to the circuit diagram, the selected components are correct, and the debugging can work normally. The regulated power supply has an output voltage of 12V and a current of 1A.