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Knowledge summary of LED power supply

Ether Photoelectric Ltd | Updated: Oct 31, 2017

What is an LED power source

LED drive power supply the power supply is converted into a certain voltage current to drive the LED voltage converter, normally: LED drive power supply input, including high voltage ac power frequency (mains), low-voltage dc, high-voltage direct current, low voltage high frequency ac (such as the output of electronic transformer). The output of LED power supply is the constant current source that can change the voltage with the change of the positive pressure drop of the LED. The core components of the LED power supply include switch controllers, inductors, switch components (MOSfet), feedback resistance, input filter parts, output filters, etc. According to the requirements on different occasions, the circuit of over-voltage protection circuit, input voltage protection circuit, LED open circuit protection and overcurrent protection circuit are required.

2. Characteristics of LED power supply

(1) high reliability

Especially like LED street lamp drive power supply, installed in high altitude, maintenance is not convenient, the cost of maintenance is also big.

(2) high efficiency

LED is an energy-saving product, which drives the efficiency of power supply. It is very important for power supply to be installed in the lamp. The efficiency of power supply is high, its loss power is small, heat in lamps and lanterns is small, also reduce the temperature rise of lamps and lanterns. It is advantageous to delay the light of LED.

(3) high power factor

Power factor is the requirement of power grid for load. General 70 watt below use electric appliance, do not have mandatory index. Although the low power factor of a single electric appliance with low power has little impact on the power grid, the use of lighting in the evening is large and the same kind of load is too concentrated, which can cause serious pollution to the power grid. For 30-watt-40 watts LED power supply, it is said that there may be some indicators of power factors in the near future.

(4) driving mode

There are two types of traffic: one is a constant pressure source for multiple constant current sources, and each constant current source is supplied to each LED. This way, the combination of flexible, LED failure, does not affect the work of other leds, but the cost will be slightly higher. The other is direct current constant current power supply, which is "zhongke huibao" to adopt the mode of drive, LED series or parallel operation. It has the advantage of low cost, poor flexibility, and the need to solve an LED failure without affecting other LED running problems. These two forms coexist for a period of time. Multi-channel constant current output power supply mode can be better in cost and performance. Maybe in the future.

(5) surge protection

The ability of LED surge resistance is poor, especially anti-reverse voltage. It is also important to strengthen the protection of this aspect. Some LED lights are installed outdoors, such as LED street lamps. Due to the load of the power grid and the lightning strike, the power grid system will invade all kinds of waves, and some surge can lead to the damage of the LED. Therefore the driving power of analysis "zhongke hui bao" in surge protection should have certain lack of, and as for the power supply and frequent replacement of lamps and lanterns, LED drive power to suppress surge intrusion, protect the LED is not damaged.

(6) protection function

In addition to the conventional protection function, it is better to increase the negative feedback of LED temperature in the constant current output to prevent LED temperature. Comply with safety and electromagnetic compatibility requirements.

3. Classification by driving mode

(1) constant flow

Constant current drive circuit of the output current is constant, and the output dc voltage is different as the size of the load resistance within a certain range, load resistance is small, the output voltage is low, the greater the load resistance, the higher the output voltage.

The constant current circuit is not afraid of load short circuit, but it is forbidden to load completely.

Constant current drive circuit driving LED is ideal, but relatively high price;

Note that the maximum load current and voltage value are used, which limits the number of leds used.

(2) stable pressure type

When the parameters in the stable circuit are determined, the output voltage is fixed and the output current varies with the load.

The stable circuit is not afraid of load opening, but it is strictly prohibited to short circuit.

To drive the LED with a stable driving circuit, each string needs to be added with the appropriate resistance to display the brightness average of each LED display.

The brightness will be affected by the voltage change in the rectifier.

4. The advantages and disadvantages of overall constant current and road - by-line constant flow

Compared with the overall constant current, the road flow constant flow has more disadvantages and higher costs. But it can really protect the LED and extend the life of the LED, so the future trend is the constant flow of the road.

5. Insufficient LED power supply

Reasons for the current shortage of LED power supply:

Production of LED lighting and related products of the company's technical staff understanding of switch power supply is not enough, the power supply can be normal work, but some critical evaluation and electromagnetic compatibility of consideration is not enough, still have some hidden trouble;

Most of the LED power supply enterprises have been transformed from the ordinary switching power supply to make LED power supply, and the characteristics and use of leds are not enough.

At present, there are almost no standard of LED, most of which are the reference switch power supply and electronic rectifier standard;

The majority of LED power supply is not unified now, so much of it is relatively small. The purchase quantity is small, the price is on the high side, and the component supplier is not too cooperative;

Stability of LED power supply: wide voltage input, high temperature and low temperature work, overtemperature, overpressure protection and other problems are not solved.

First, the overall life of the drive circuit, especially the key devices such as the life of the capacitor in the high temperature directly affect the life of the power supply;

Higher conversion efficiency is the LED driver should challenge, especially when driving high power leds even more so, because all not as light output power as heat dissipation, power conversion efficiency is low, influence the exertion of LED energy saving effect;

At present, in the application of small power (1-5w), the proportion of constant current driving power supply is close to 1/3, which is close to the cost of the light source, which has affected the market promotion to some extent.