Capacitor step-down power supply principle and precautions

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Capacitor step-down power supply principle and precautions [Copy link]

In common small low-voltage power supplies, in addition to switching power supply modules, there is also a power supply that uses capacitors to step down voltage (actually capacitor current limiting). Capacitor step-down power supplies have the characteristics of small size, economy, reliability, and high efficiency, but the disadvantage is that they are not as safe as power supplies that use transformers to transform voltage.

The capacitor step-down power supply introduces AC power into the load through a capacitor, and there is a 220V voltage to the ground, which can easily cause electric shock. If it is used in an internal circuit that does not require human contact, the disadvantage is not a disadvantage. Capacitor step-down power supplies are low-cost and non-isolated low-current power supplies, such as LED bulbs used in plastic shells. Their output voltage is usually from a few volts to tens of volts, and their output current is also around tens of milliamperes. The power supply of refrigerator electronic thermostat or remote control power switch is made of capacitor voltage reduction. The working principle of capacitor voltage reduction power supply is to use the capacitive reactance generated by capacitor under certain AC signal frequency to limit the maximum working current. Compared with resistor voltage reduction, for the lower frequency 50Hz AC, the heat energy loss generated on the capacitor is very small, and capacitor voltage reduction is better than resistor voltage reduction.

Precautions for using capacitor step-down circuit:

1. After the capacitor steps down, it needs to be sorted, filtered and stabilized by a voltage regulator to obtain a stable voltage power supply (the rectifier circuit can use half-wave rectification).

2. Select appropriate capacitance according to the load current and the operating frequency of the AC power. The capacitor's withstand voltage should be above 630V. Polarized capacitors cannot be used.

3. The current limiting capacitor must be connected to the live wire, and a surge protection resistor and a parallel discharge resistor must be added in series.

4. If a power switch is added, the load must be connected in parallel to prevent surge current.

5. Pay attention to the power consumption of the Zener diode. It is strictly forbidden to disconnect the Zener diode for operation.

6. Capacitor step-down circuit is not suitable for capacitive load, inductive load, dynamic load and high-power load. Generally, the current is small and unsafe.

7. It is not suitable for single-chip microcomputer. Generally, the interference is serious.

8. During the assembly and debugging process, the 1:1 isolation transformer must be connected to the AC220V circuit to prevent electric shock.

The output DC voltage of the capacitor step-down circuit is not isolated from the input AC power supply, and is often used in electronic devices that do not require isolation. For example, it is widely used in control, detection, and analysis electronic devices, in household appliances and other electronic devices, especially in the field of small household appliances.

qiushenghua

Series capacitor voltage division, can this also be considered a "capacitive step-down power supply"?

倾心思梦

Thanks for sharing!

宋元浩

Thanks for sharing!