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220V to 5V power supply design
Release time:
2022-10-25 09:23
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DC. The filter circuit can remove the pulse, but the output DC voltage is unstable. The voltage regulator circuit greatly improves the stability of the voltage, and the whole process is shown in Figure 2.1. The main difference between the two schemes is the voltage stabilizing circuit, and the other circuit structures are basically the same. Then, let's understand the high voltage of 220V first, and the specific actual speed ratio of the transformer is determined by the lower circuit. The current after the transformation is still AC, through the rectifier circuit into a pulse DC. The filter circuit can remove pulses, but the output DC voltage is unstable. The voltage stabilizing circuit greatly improves the voltage stability. The main difference between the two schemes is the voltage stabilizing circuit. Other circuit structures are basically the same. Then, let's understand the design of 220V to 5V power supply together!
voltage regulator circuit
The voltage regulator circuit mainly through further processing of the rectified and smoothed current to make its voltage more stable, while the entire circuit has a certain load capacity, so that the output voltage does not change with the change of external load. The current amplification ratio can be greatly increased and the input resistance can be reduced. LED2 both power indicator and the role of the regulator tube. LED1 and R3 form a simple overload and short circuit protection circuit. R5 and R4 are divided, and the voltage on R4 is fed back to the amplifier circuit consisting of Q1 Q2 via Q3. The stability of the voltage can be further improved.
1) Input voltage determination
Part of the input voltage of the circuit is the output voltage of the rectifier filter circuit, which is the large output voltage of 5V. The voltage between the collector and emitter of transistor Q1. Generally, 3~8V transistors are selected to ensure the operation in the amplification area. I choose a transistor around 5V.
2) Determine the transistor
The value of the transistor is evaluated, and the transistor is selected according to the limit parameters of the transistor. If it is greater than the above calculated value, it can be Q1. In addition, in order to meet the previous input voltage conditions, I chose 2N5551. The current and voltage of Q2 and Q3 are not large, and the power consumption is also small, so there is no need to calculate its value. Generally, a small power tube can be selected. I chose 2N2222A.
3) Determination of reference voltage
where n is the sampling ratio of the sampling circuit. The working voltage of the LED is 1.66V, and the forward curve characteristic is steep, so the reference voltage can be provided instead of the regulator tube.
4) Calculation of current limiting resistance
Wherein, the operating current of LED 2 can be selected between 2 ~ 10mA. I chose 9mA. The emitter current of Q3 can be selected between 0.5 and 2mA. I chose 1mA.
5) parameter calculation of sampling circuit
First, the operating current of the sampling circuit is determined. This current is the current flowing through R5 and R4, and the base current of Q3 is negligible and small. If the acquisition is too much, the power consumption of the sampling circuit will also become large. If it is too small, the change of Q3 base current will cause the sampling ratio n to be unstable, and at the same time it will become unstable. In practical applications, it is generally used. I chose the 3.1.2 transformer rectifier filter circuit
1, 220V to 5V power supply to determine the number of transformer turns
Considering that the voltage between IO3 and IO4 has been determined to be 10V, the effective value of the voltage after passing through the rectifier filter becomes large, and the voltage on the secondary side of the transformer.
2. The determination of the rectifier diode, the rectifier diode only requires its high reverse working voltage to ensure that it will not break down in the reverse direction. I used 1N4001.
3, 220V to 5V power supply filter capacity determination
Among them, the capacitor should meet T = 20ms (the period of the input AC power). I use a 470F capacitor, and a larger capacitor can get a better filtering effect.
Test of the whole circuit of 220V to 5V power supply
The 220V to 5V power supply uses a Multisim AC source instead of the real mains, and its voltage effective value is set to 220V and the frequency is set to 50Hz. A sliding resistor is connected at the output to replace the real load. Change the resistance value of the sliding resistor to observe the DC voltage display value of the multimeter. It can be seen that the voltage changes less and has a certain load capacity.
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