How to choose aluminum electrolytic capacitors correctly for long-life LED driver

Factors affecting the service life of LED energy-saving lamps:

In practical applications, the actual life of LED lights is not high, and even less than a year is damaged. According to the investigation, nearly 80% of the LED energy-saving lamps failed due to the driving power supply. Aside from the poor performance of the driver circuit design, another important reason is that the life of some electronic components used in the driver circuit is much lower than the life of the LED lamp bead . In the high-temperature LED cavity of the LED energy-saving lamp, if the device is selected Improper type, aluminum electrolytic capacitors may become the most vulnerable components on the LED driver!

LED drive circuit features

The LED driver circuit is actually a special case of the switching power supply. Because of its light, thin and small development trend, the requirements for the driver circuit are also getting higher and higher. In addition to the requirements of aluminum electrolytic capacitors for ordinary power products, LED drive power supplies have special requirements for high temperature resistance, miniaturization and long life of aluminum electrolytic capacitors.

The following is a typical typical LED driver circuit. There are three main aspects applied to the electrolytic capacitor, namely the pre-stage rectification filter, the post-stage output rectification filter and the decoupling capacitor used to control the IC power port.

Typical LED energy-saving lamp drive circuit

Selection of medium electrolytic capacitor models for LED drive circuits

Hunan Aihua Group, which has been focusing on the lighting market for a long time, launched the CD11GC series of electrolytic capacitors at 130 °C for 5,000 hours (105 °C 20,000 hours) in 2009, and put this series into the market in 2010. According to the calculation formula of electrolytic capacitor life (Arrhenius equation), the capacitor can be used for 40,000 hours at 95 °C ambient temperature, which can fully meet the energy-saving requirements of high-quality, long-life LED. The aluminum electrolytic capacitors produced by Hunan Aihua Group account for nearly half of the market share in the international lighting industry. The company has more than 3 billion aluminum electrolytic capacitors used in lighting every year.

The following is a further introduction to the selection of electrolytic capacitors from Hunan Aihua Group in LED lighting drive power supply. It is mainly explained from three aspects of the function of the electrolytic capacitor on the driving power supply. The place where the electrolytic capacitor is needed in the LED driving circuit is: 1. The input rectifying and filtering capacitor; 2. The output rectifying and filtering capacitor; 3. The decoupling capacitor of the control IC power terminal.

1. Input rectification filter capacitor

Function: â–º Smooth input rectification voltage;

â–º Absorb the low frequency ripple current generated by the rectifier circuit;

â–º Absorb the high frequency ripple current from the LED driver circuit.

Requirements: high temperature resistance, long life, resistance to large ripple current, high pressure resistance, and miniaturization.

Input rectification filter capacitor circuit diagram and its ripple current waveform

Figure: Input rectification filter capacitor circuit diagram and its ripple current waveform

About the choice of input rectification filter capacity

Because the LED energy-saving lamp driving power supply circuit topology is complex and diverse, it is applied to various power supply topologies and various life requirements, and the switching power supply IC manufacturers used in each driving circuit have different design schemes. Therefore, the capacitance of the electrolytic capacitor should be selected according to the specific circuit design requirements, the specific power supply topology, and the specific circuit design parameters. However, for electrolytic capacitors, the ripple current and peak voltage value in actual use should not exceed their rated ripple current value and rated voltage value, and it is preferable to leave a certain margin.

Here Iowa recommended capacitor series models: Recommended CD11GD, CD11GN, CD11GK, CD11GES, CD11GC series;

2, output rectification filter

Function: â–º Smooth output finishing voltage;

â–º Absorb the high frequency ripple current of the switching frequency;

Requirements: high temperature resistance, long life, miniaturization, resistance to large ripple current, high frequency and low resistance.

Figure: Output rectification filter capacitor circuit diagram and its ripple current waveform

It is required to have sufficient capacitance for the output rectifying and filtering capacitor. If the capacitance is too low, the converter will be unstable. It is obvious that the aluminum electrolytic capacitor with small volume and large capacity is the best choice;

Here Iowa recommends capacitor series models: RJ, RZ, RS, RF, RG, RM, NB and other low-voltage products;

3. Control IC chip power terminal coupling capacitor

Function: â–º Smooth IC input power voltage;

â–º Absorb the coupling interference from the line to make the regulated output more stable;

â–º Make the IC output control signal more accurate and reduce the burden of the output filter capacitor.

Requirements: high temperature resistance, miniaturization, high stability, low leakage.

The IC power supply decoupling capacitors in the control state also require tens of thousands of hours of life, in which the stability of the capacitance is critical, and it is related to whether the control voltage is smooth and whether the driving power supply can work stably. Although the electrolytic capacitor has a small capacity and a small volume, no large ripple current flows. However, it requires a long-term stable capacitance, especially a small volume is more detrimental to the ultra-long life characteristics. The electrolytic capacitor is often close to other heat-generating components, so the working environment temperature is high.

Recommended capacitor series models: RM, NB, RS, WH and other low-voltage products;

Figure: Control IC power supply coupling capacitor circuit diagram and its ripple current waveform