AN4376 datasheet(8/37 Pages) STMICROELECTRONICS

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EVLHVLED815W10A - main characteristics and circuit description

AN4376

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EVLHVLED815W10A - main characteristics and

circuit description

The main characteristics of this single-stage LED driver demonstration board are:



Line voltage range: 85 to 265 VAC



Line frequency (fL): 47-63 Hz



LED string voltage drop: 70 V nominal



LED nominal current: 140 mA ± 3%



LED current ripple: 100 mA



Rated output power: 10 W



Power factor > 0.9



Efficiency: 86 - 88% at full load



Maximum ambient temperature: 50 °C



Conducted EMI: in accordance with EN55022 Class-B



Protections against overvoltage, load disconnection and short-circuit

The LED driver provides a constant nominal current of 140 mA to an LED string with

a nominal voltage drop of 70 VDC in all the wide range input mains [85 - 265] VAC. Due to

the power factor correction, the input current of the driver is almost in phase with the mains

voltage and the power factor is close to the unity.

The power supply utilizes a typical non-isolated buck-boost converter topology with a simple

inductor to transfer energy to the LED load.

The inductor T1 (layer type, with standard ferrite size EF-20 and manufactured by

Magnetica) is charged by the internal Power MOSFET when it is turned on, and it

discharges into the three output parallel capacitors C11, C12, C16 (with 100 VDC rating -

see Figure 9 on page 12) and into the LED load when Power MOSFET turns off. In this

demonstration release the auxiliary winding is used to sense the inductor current

demagnetization, to sense the input line voltage for the voltage feed forward compensation,

to trigger the overvoltage protection and to self-supply the IC during normal operation. An

external high-voltage start-up circuitry is not needed because it is already embedded into

the IC. Also the buck-boost switch is embedded into the HVLED815PF in order to

maximizing the current sensing and the gate driving.

The board power cell has been designed using the procedure described in the AN1059

(See 2. in Section 8: Supporting material on page 36) used to design a standard high power

factor flyback; this document has been used as reference for calculating this demonstration

board, since the buck-boost topology can be considered as a simple flyback with a unity

transformer turn ratio and with the output voltage corresponding with the reflected voltage of

the flyback. Additional information has been reported in Section 2.1.

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