High power LED constant current source designed to drive in series

With the advent of high-power LED, general fluorescent or incandescent 5 to 7 times its luminous efficiency, energy-saving effect is very significant. Thus, the high-power LED has broad application prospects. Currently, a single high-power LED has 1W, 3W, 5W and 10W, has been heavily used 1W and 3W high power LEDs, multiple high-power LED series and parallel, the the combination output power reached 70W ~~ 100W.

High-power LED with high luminous efficiency and energy-saving advantages, but inconsistent pipe pressure drop is the need to overcome the shortcomings. Second, poor temperature characteristics of the high-power LED. Tube current and luminous efficiency varies greatly with the junction temperature and ambient temperature changes, which bring inconvenience to use.

High power LED above shortcomings, people use more than two drive options: 1. Constant voltage source driver. That is, using a plurality of LED in parallel with a constant voltage source driver. Thus, since the tube voltage drop of the LED is inconsistent, so that the diode current is inconsistent, so that the luminous efficiency is also quite different. This program is seldom used in high-power LED. 2 constant current source driver. Inconsistent pipe pressure drop of the high-power LED, LED by their junction temperature and ambient temperature influence, so the number of LED series and driven with a constant current source can effectively overcome these shortcomings.

The main features of the high-power LED

Operating wavelength
The operating wavelength of the high-power LED with its glowing colors. For example, cold white LED operating wavelength of 525 angstroms to 600 angstroms, while warm white LED operating wavelength between 525 angstroms to 675 angstroms.

Forward voltage drop
High power LED's forward voltage for each change of 0.1V, the current change of about 100mA.

The relationship of the working current and luminous intensity
The high power LED luminous intensity of its junction temperature and ambient temperature. This is mainly due to temperature increases, the operating current is also reduced correspondingly, Similarly, LED's luminous intensity and its current relationship is approximately linear, and its working current each reduction 100mA for 1W and 3W LED, the light emitting intensity is reduced about 15%.

High power LED series constant current

The principle of the source drive
Currently appearing on the market of high power LED series drive has its limitations, typically three to six LEDs in series, and the number to be sure, can not be any connection. In this paper, an arbitrary (1 to 20) LED constant current source driver program series, shown in Figure 1, the following works:

1W LED, for example, the rated current of 350mA. For some reason, the LED current is reduced, the constant current source circuit of the acquisition to the current value of the change (decrease) after having amplified by U1 transmission to the control circuit. Inversion processing in the control circuit of the sampling signal, the output pulse width is increased. Power tube D5 conversion stage of the driving power of the output pulse width increases, so that the secondary output voltage increases. In this way, the voltage across the LED in series also increases, therefore, the current flowing through the LED is also increased, which maintain a constant LED current. Similarly, if for some reason, so that the LED current is increased, contrary to the control process. Advantages that: The constant current source drives regardless of the LED voltage drop difference Junction ambient temperature changes cause changes in diode current much, can be accessed through the rapid adjustment of the high-speed constant-current source circuit to Maintain constant current LED.

High power LED constant current source
To pay attention to the design of the drive

The design of high-power LED constant current source drives should pay attention to the following points:
1. To select the control of the control chip of the circuit in accordance with the number of the LED series. Because of the number of LED chips required output power is different. Figure 1 ICE 2A165, also choose other similar switching power supply control chip.

2. Switching power supply transformer leakage induction is as small as possible, otherwise the drive will reduce the reliability. Because the leakage inductance of the transformer, switch off instantly produces very high reverse voltage spikes, severe cases may exceed the breakdown voltage of the control switch, leaving the LED chip breakdown, causing the reliability of the drive is greatly reduced. Switching power supply transformer T1 is the key parts of the product, it is necessary to the production of the professional manufacturers.

3. The operating speed of the constant-current source circuit to be fast, so that can make the LED safer. In this paper, series of LED drive any number (1 to 20) of the series, this would require the change of the output voltage of the switching power supply faster to adjust slowly, and may cause damage to the LED's.
Practice has proved that this paper, high-power LED constant current source drives the program is feasible, and compared with other drives, lower cost, which has broad application prospects.