Protection device and principle of DC stabilized power supply

Probe current voltage pin 420*4450 head diameter 5.0 over current current and voltage pin

SR05 SOT143 package 5V ESD electrostatic protection

As shown in the figure, the DC stabilized power supply protection circuit. The device is composed of a buck rectifier power supply, a monostable delay circuit, a relay control circuit, and an audio feedback oscillation circuit. The buck rectification power supply provides a DC voltage VDD for the entire circuit, and VDD = + (5-12) V, the specific VDD value depends on the voltage regulator block IC1.
The monostable delay circuit consists of IC2 (555), R3, C4, and so on. Normally, the normally closed contact J1-1 is closed, and the IC24 pin potential is high (1V or more) when the load is normal. When the load is short-circuited, 555 is forced by the 4-pin potential to be low (<0.6V). Reset, the low level of the 3-pin output causes the relay J to pull in, the contact J1-1 is turned off, and the short-circuit load is cut off. At the same time, the contacts J2-2 and J3-3 are respectively turned on, so that the audio feedback oscillator composed of BG1, BG2, C6, C7 and R6 oscillates due to the voltage applied, and emits an acoustic signal of about 1 kHz to remind the use. Note. After contact J3-3 is turned on, C4 is charged by R3, causing the potential of IC2 to drop. When the potential of pin 2 falls below 1/3VDD, 555 is set. The high level of the 3-pin output causes J to be released and the contact J1-1 is turned on. If it is still short-circuited at this time, then protect it. The charging time of the corresponding C4 is the delay protection time of 555 td=1.1R3C4. The length of the protection time can be adjusted by changing the time constant R3C4.
This protection circuit protects the DC voltage source from short-circuiting, so it can be used as an accessory to the regulator source or integrated during power supply design. The voltage source in the range of DC output 1.5~50V switches the load at a speed of 0.1 second in the event of a short circuit, and the circuit also has a delay automatic recovery function.