Technical Analysis of Design of Constant Current and Constant Voltage LED Street Light Driver Circuit of Nanke Company

1 Introduction

The luminous flux of white LEDs can now easily reach 80 lumens per watt, making the LED lighting industry, especially LED streetlights, more feasible.

However, in the application of LED street lamps, most of the current drive circuits of various manufacturers adopt switching power supply schemes. The voltage is generally between 24 and 48 volts. Because the power of street lamps is relatively large, generally more than 120W, it is necessary to use multiple sets of switches at the same time. The power supply is not only costly, but the average power consumption loss of the switching power supply itself is between 15% and 20%. This makes the LED street light that was originally energy-saving and wasteful, which wastes 15~20% of energy consumption, which is worthless. At the same time, due to the switching power supply used by each household, the voltages are not the same, which makes the use unit face different standards in the future, and the cost is too high. In addition, the switching power supply generally only provides constant voltage, but the LED is long-term at high temperature. After the work, the problem of the voltage drop and the current rise is faced, which causes problems in the stability and reliability of the LED street lamp. In view of this, how to develop a LED driver circuit with low power loss (should be within 5~10%), low cost, long service life, and constant voltage and constant current function is already in the LED application field. A major topic.

On November 29, 2008, the China Lighting Association Outdoor Lighting Professional Committee and the Transportation Lighting and Optical Signal Committee and China Lighting Network held a debate on the status quo of high-power LED street lamps in Guangzhou, where Guangzhou and Shanghai street lamps were held. It is recommended that the power supply circuit of the LED street lamp should be standardized to facilitate user maintenance, and the author will provide the reference for the LED street lamp solution developed by our company with Chinese intellectual property rights.

2, LED street light circuit design essentials

Because the current common metal sodium lamp power is about 250W each. If the LED street lamp is to become a competitive street lamp alternative, it should basically play an advantage in the power-saving function. Since the LED is unidirectional, in the case of the same light effect, the lamp has four-side illumination than the metal sodium. The lighting effect is much stronger, so as an alternative to the 250W metal sodium lamp, the power of the LED street light should be between 120~160W.

At present, the commonly used light sources on the market are generally 1W chips, that is, the general street lamps have 120~160 chips, and the on-voltage of each chip is between 3.3~3.6V. Even, the voltage across the chip will be close to 400V or more.

Since the power of each street lamp is above 120W, the power factor correction problem must be considered in the power supply design.

The ICs commonly used in the market with power factor correction function include L6561 of ST Company, R2A20116 of Japan Renesas Company and ML4812 of LINEAR Company. The typical circuit is shown in Figure 1. The AC power supply is bridge-rectified and then adjusted to a stable voltage of about 400V after the frequency modulation or pulse width adjustment of the power factor correction IC (Fig. 1). The circuit is simple, the cost is low, and the power factor can reach 98% or more at 220V normal voltage, but this circuit can only ensure that the output of constant voltage is still insufficient for the target of constant current output of LED street lamps.

3, Nanke company's LED street light drive circuit

At present, LED street lamp circuits on the market use low voltage (24~48V), high current (1A~3A) multi-channel power supply drive scheme. After nearly 3 years of research and development, Nanke has successfully developed high-voltage (400V), low-current (0.3~0.5A), LED street light source and power supply solution with constant voltage and constant current function, at normal voltage 220V. At the time of its power efficiency is greater than 94%, and has obtained a number of patents, the characteristics of which are described as follows:

(a) Nanke's original CCS-L high voltage constant current source device

After years of research and development, Nanke has successfully developed a semiconductor constant current source device capable of withstanding high voltage (greater than 50V). The constant current source device can maintain a constant current source state (current fluctuation is about 10%) at a voltage of about 4 to 40 volts. Although constant current cannot be maintained at low voltage (<4V), because the current is small, it will not cause damage to the chip, and only the brightness of the light source will be weakened. At present, Nanke's CCS-L series products can be divided into several types according to the requirements of current (Schedule 1), and the product specifications can be increased as the market demands changes in current requirements.

Nanke CCS-L constant current source device (Schedule 1)

(b) Full-tandem high-power LED light source or first-sequence and low-power LED light source

The LED street light source used by Nanke Company is composed of one or more sets of LED chips connected in series. The current of each series of chips in series is different with the size of the chip, generally between 20mA and 150mA, but each The voltage across the chip in series is set between 390 and 395V at rated current.

(c) LED drive scheme with constant current and constant voltage function and low power loss

Nanke's LED driving scheme is based on (as shown in Figure 1) power factor correction IC, one or more sets of LED light sources as described in (b) are connected in series at the output voltage end, and then one end is connected in series at each end. Nanke's CCS-L constant current source device. (Figure 2)

Since the power factor of the power factor correction IC can be as high as 98% above 220V, and the output voltage is basically constant voltage of about 400V (trimmable), and the voltage across the LED light source is between 390 and 395V, so the remaining 5 The voltage of ~10V is added to the CCS-L, and the constant current is ensured. Since each group of light sources has a CCS-L constant current source device, the current of each group can be stable for a long time, and has power saving. The function.

(d) Nanke's LED street light scheme is currently the highest effective power in the streetlight power supply, with the lowest power loss and the highest power factor.

Nanke's power supply scheme, the current power factor can reach more than 98%, because the output voltage of the voltage regulator circuit is 400V and the voltage drop on the CCS-L is only 5-10V, so the loss is about 1.25~2.5%. In addition, the loss of the voltage regulator circuit composed of the power factor correction IC is about 3 to 6%, so the overall loss is only between 6 and 8%, which is much smaller than the 15-20% loss of the conventional switching power supply. It is.

4 Conclusion

The LED street light circuit must have a constant current function to ensure long-term use of the LED street light. It is well known that the LED street light chip will have a lower turn-on voltage of the LED at a high temperature. If only a power supply circuit with a constant voltage function is used, the current of the LED street lamp will increase with time, thereby reducing the service life of the LED street lamp. If the LED street light circuit adopts a constant current circuit, since the current constant current switching power supply on the market is low voltage and large current, it is necessary to use multiple ways of parallel connection, that is, currently, there are 8, 12 or 14 LEDs on the market. The driving circuit composed of the parallel connection and the parallel connection scheme, because there are 8 or 12 or 14 in each group, the conduction voltage of each group is different, that is, the current distribution of each group after paralleling is uneven, after long-term use. A group of currents with a low voltage will be distributed more and burned in advance, causing each group to be burned one by one.

In this paper, Nanke's LED street light circuit scheme adopts high voltage (400V), low current (0.3~0.5A) multi-group full-series LED chip solutions (each group has 110~128) LED chips are connected in series. One end of each chip is connected to the output of the voltage regulator circuit composed of the power factor correction IC, and the other end is connected to the positive terminal of the high voltage constant current source device CCS-L developed by our company, and the negative of CCS-L. Extremely connected to the system ground. Since each group of chips connected in series has a constant current source of CCS-L, the LED street lamp circuit scheme of Nanke Company is not only simple and low in cost, but also has high power factor (>98%). High (>92%) excellent characteristics, the current high-voltage LED chip manufacturing method, high-voltage constant current source device (CCS-L) manufacturing method and constant voltage and constant current function, low-loss LED driving circuit All have obtained the patent authorization of China. Currently applying for patents in the United States, Japan, Europe and other countries, the entire program is the best solution with complete multiple intellectual property protection in China. It will greatly reduce the dependence of China's LED street lighting on key technologies such as foreign chips, and power supply.

Although Nanke's LED street light scheme has complete and multiple intellectual property protection, Nanke will not monopolize technology and make huge profits. On the contrary, Nanke Company will promote the development of energy saving and consumption reduction in China. It is 20~30% cheaper than the current street lamps, and we hope that the relevant departments in China can be certified and considered as industry and national standards.

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