Circuit diagram of 5V electronic switch (1)
The following figure shows the circuit design of 50W off-line switching power supply. The circuit is powered by a MOSFET. BUZ80A / ixtp4n8220v AC voltage input and geirf823110v AC input voltage. The output will be 5VDC and current up to 10A.
The schematic shows the 50W power supply with 5-v10a output. This is indeed a continuous mode flyback converter inside. The circuit has the function of primary side and secondary side controllers will be all, for example, over-current protection fault factors. When the error condition has been eliminated, the power supply will run normally with recommendation before entering the soft start cycle.
Circuit diagram of 5V (electronic switch)
USB charger kit, also known as MP3 / MP4 charger, input ac160-240v, 50 / 60Hz, rated output: dc5v250ma (label sticker is 500mA, if you want to output more current for a long time, please replace Q1 to 13003). MP3 and MP4 are popular all over the country. However, as daily necessities, the charger has the characteristics of high failure rate and easy damage due to its direct connection with 220 V high voltage.
The following is the circuit schematic diagram drawn for the real object: (there are various installation methods of components on the circuit board, please refer to the schematic diagram and physical drawing for installation. Some component holes on PCB board are not to be installed, some components should be installed on other component holes, please note this point!) Note: in order to simplify the circuit and achieve the purpose of learning, the resistance F1 of 1 ohm is used as a fuse, and a diode D1 is used to complete the rectification. After the power supply is connected, C1 will have a DC voltage of about 300V, which will supply current to the base of Q1 through R2, and the emitter of Q1 has R1 current detection resistance R1. When Q1 base is powered on, collector current will be generated through T1 (3, 4), and induced voltage will be generated on (5, 6) (1, 2) of T1 at the same time. These two secondary insulation coils have the same number of coils, and T1 (1, 2) output is rectified by D7 After filtering by C5 and C5, the load is supplied with power through USB seat; T1 (5, 6) is rectified by D6 and filtered by C2 through IC1 (actually 4.3v voltage regulator) and Q2 to detect the output voltage; among them, T1 (5, 6), C3 and R4 also form a positive feedback circuit of Q1 triode, which makes Q1 work at high frequency oscillation and continuously supply power to T1 (3, 4) switch. When the load becomes lighter or the power supply voltage increases for any reason, the comparison of T1 (5, 6) and IC1 leads to Q2 conduction, Q1 base current decreases, collector current decreases, and load capacity decreases, resulting in the decrease of output voltage; when the output voltage decreases, Q2 sampling will be cut off again, and Q1’s load capacity will become stronger, and the output voltage will rise again To the role of automatic voltage regulator.
Although the circuit has few components, it also has the function of over-current, overload and short-circuit protection. When the load is overloaded or short circuited, the collector current of Q1 will increase greatly, and the emitter resistance R1 of Q1 will produce a high voltage drop. The high voltage generated by overload or short circuit will saturate Q2 through R3, so that Q1 can stop output and prevent overload damage. Therefore, the load capacity can be changed by changing the size of R1. If the output current is required to be small, for example, only 5v100ma is required, the resistance value of R1 can be increased. Of course, if you need to output 5V500mA, you need to reduce R1 appropriately. Note: the possibility of burning Q1 will be increased if R1 is reduced. If high current output is required, it is recommended to replace the medium and high power tubes 13003 and 13007.
What are the functions of C4, R5 and D5? T1 transformer is an inductive element. Q1 works in the switching state. When Q1 is cut off, a high voltage will be induced at the collector, which may be as high as 1000 V, which will damage Q1. Now with the high-speed switch D5, this voltage can charge C4, absorb the high voltage, and discharge through R5 immediately after C4 charging, so Q1 will not be broken down due to high voltage of collector It is damaged. Therefore, if the three components are switched or damaged, Q1 is very dangerous and may be damaged every minute.
Circuit diagram of 5V electronic switch (3)
Circuit diagram of 5V, 2A isolated switching power supply
Circuit diagram of 5V electronic switch (4)
The circuit of the light control switch is shown in the figure below. The main features are that there is light in the day, the bulb is not bright, and the night is dim. The circuit is automatically powered on and the bulb is on.
In the daytime, under strong light, the resistance value at both ends of the light guide 227a (a kind of photosensitive resistance) is very small, about 20 ~ 50K Ω. The transistor vt2 gets the base current and turns on, VT1 gets the positive bias voltage from R2, and the relay coil Ka is powered on, the normally closed contacts of relay ② and ③ are disconnected, and the two thyristors V1 and V2 are not connected without triggering signal, so the bulb el is not on.
When night falls, with the decrease of light intensity, the resistance value of 227a of optical tube increases continuously, and finally reaches about 1m Ω. VT1 is cut off because the base current is too small, and VT1 is also cut off accordingly. Relay KA loses power and releases, normally closed electric shock ② and ③ are closed. Thyristors V1 and V2 are in bidirectional conduction state because of the connection of their two controls. The power supply is connected and the lamp is on.
In the figure, the capacitor C3 is used to prevent the lamp from going out due to the interference of instantaneous strong light at night. When the light intensity changes slowly near the critical point, it is easy to cause the relay to vibrate and make the light flash. C2 can filter out the pulse current and avoid the lamp flashing.