14 W high efficiency LED drive power source design

14 W high efficiency LED drive power source design

One, the design characteristics

1, high temperature environment (75 degrees)

2, energy efficiency

Three, all the EU CoC/CEC 2008 / energy star 2.0 requirements, with high efficiency in mode (up to 86%, 79.6% required for); In 265 VAC input of load when the input power < 250 mW, required for the 300 mW

4, sluggish overheating shut off the protection

5, load disconnect protection

6, foot EN55015B conduction EMI limit, EMI allowance > 8 dB microvolts

Second, working principle

Figure 1 shows is a typical 20 V, 14 W constant pressure (CV), constant current (CV) the output power supply circuit. LED the array of light output and the electricity flows through is proportional to the flow. Therefore, the LED drive should have constant current output, and not constant voltage output. In this design, DC and AC input output not isolation, thus LED array and the shell and users should be safely isolated.



AC input by BR1, C1 and C2 for rectification and filtering. Inductance L1 and C1 and C2 together make up a ¦Ð form filter, and provide EMI filter. The fuse F1 serious fault in providing protection. For the power load in work normally under and not damaged, use VR2 zener diodes are constant pressure adjusted and that the voltage keep in about 21 V.

Through testing the electric current detection resistance on the pressure drop R7 to realize constant flow characteristics. Parallel stabilizer IC U3 and R9, R8 and R8A together in operational amplifier U2 reverse input generation 0.07 V voltage reference for the accurate. Reach a set when the current, voltage R7 will be more than a reference voltage, this would make the operational amplifier output increased. At this time will be positive bias, the base of the 25 th D4 drive, and then from the U1 will current EN/UV pins pull out. R11 resistance and capacitance C7 provide compensation loop. Use the current limit of operational amplifier way to make current voltage minimize sampling, which reduces the loss, the efficiency is highest.

As long as EN/UV pins pull out of the current more than 115 ¦Ì A, U1 MOSFET will be with the one cycle of the way be banned (on/off control). Through the adjustment that can switch the proportion of the cycle is forbidden, feedback loop can adjust output voltage or current. On/off control mode and optimize the different load cases of converter efficiency, to comply with the energy efficiency standards.

Due to the environmental temperature is high, the U1 will reduce the current limit flow in point mode. This can improve the overall efficiency of the power supply and to improve its thermal performance. The primary ground-clamp (D1, VR1, C3 and R3) will be the biggest leak a peak voltage control in the internal

The MOSFET 700 V BVDSS under breakdown voltage. R23 reduce leakage resistance of high frequency vibration sense, and to reduce EMI. The output of the subprime side by diode D2 and D3 and C6 and filter for rectification.

Three, the key points of design

1, want to choose fast diode and can't choose the super fast diode, through the recovery part leakage are energy to improve efficiency.

2, let the C3 used to improve EMI performance.

3, choose resistance, used in the lowest R10 is 6 V output voltage to offer one of the mA U3 power supply current.

4, U1 optional current limit flow on the current limit flow allows point point and device optimized the size, in order to adapt to the environment temperature. For example, in order to reduce dissipation, can pass will C3 from 1 u F change for 0.1 u F to in the same design USES TNY280GN devices. Or, in the heat of the high performance environment, can pass will change from 1 C3 u F for 10 u F to use TNY278GN devices.

5, source in LED light string of voltage between 6 V to 20 V between all can work properly. But because the output current constant of the lower voltage, lamp, the lower the power output.

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