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The principle of capacitor voltage reduction in LED driver power supply

Article Source：Kinri Energy | Author：Kinri Energy | Issuing Time：2024.05.24
As for the current trend in LED driver power supply design in China, products that use the principle of capacitor voltage reduction to complete driver circuit design have gradually established a foothold in the market. LED power products designed in this way have good stability and low cost consumption. In today's article, we will briefly analyze and introduce the principle of capacitor voltage reduction in LED driver power supplies.


Capacitors in LED driver power supply

The block diagram of the voltage reduction principle in the LED driver power circuit made using the capacitor voltage reduction principle is shown in the following figure. When a sinusoidal AC power supply U (using the most common 220VAC, 50HZ as an example) is applied to a capacitor circuit, the charges on the two plates of the capacitor and the electric field between the plates are functions of time. That is to say, the effective value and amplitude of voltage and current on the capacitor also follow Ohm's law. When the voltage amplitude and frequency applied to the capacitor are constant, a stable sinusoidal AC current ic will flow. The smaller the capacitance, the greater the capacitance value, and the greater the current flowing through the capacitor. By connecting a suitable load in series on the capacitor, a reduced voltage source can be obtained, which can be rectified, filtered, and stabilized for output.

One issue to note here is that in this circuit system, capacitors only consume energy in the circuit, so the efficiency of capacitor buck circuits is very high.



In general, LED power supplies designed using the principle of capacitor voltage reduction will consist of main driving circuits such as voltage reduction capacitors, current limiting, rectification and filtering, and voltage regulation and shunt circuits. Among them, the step-down capacitor is equivalent to a step-down transformer in a regular voltage stabilizing circuit, which is directly connected to the AC power circuit and can withstand almost all of the AC power U, so non-polar metal film capacitors should be selected. At the moment when the power is turned on, there may be a peak to peak value of the positive or negative half cycle of U, and the instantaneous current will be very high. Therefore, a current limiting resistor needs to be connected in series in the circuit to ensure the safety of the circuit, which is the main reason why current limiting circuits are essential.

The design requirements for the rectification and filtering circuit are the same as those for ordinary DC stabilized power supply circuits. The reason why a voltage stabilizing and shunt circuit is needed is because in the voltage reducing circuit, the effective value I of the current is stable and not affected by changes in the magnitude of the load current. Therefore, in the voltage stabilizing circuit, there should be a shunt circuit to respond to changes in the magnitude of the load current.
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