AN2711 datasheet(22/36 Pages) STMICROELECTRONICS

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Performance

AN2711

22/36

Doc ID 14425 Rev 3

Figure 16.

Stress on FET and diode

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Yellow = Q2 drain voltage, 100 V/div

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Blue = Q2 current (actually the voltage across R25 and 26)

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Magenta = voltage on D9 (bootstrap), rated for 100 V, 20 V/div

Figure 16 above was taken with 132 VAC input, near the peak of the input sine wave. The

transition-mode operation is clearly visible - the drain voltage (yellow trace) begins to fall as

the output diode stops conducting, at 6.2 divisions. Gate drive (not shown) comes on at 6.7

divisions, and the drain voltage falls to zero. Drain current (blue trace) then begins to rise,

with only a minimal current spike as stray capacitance is discharged. The gate is turned off

at 8.6 divisions, and the drain voltage rises abruptly due to flux stored in the transformer air

gap. The drain voltage overshoot is due to leakage inductance in the transformer - the drain

current is caught by D8, and the leakage energy is dumped into C4.

6.1.3

Setup for maximum power

16 W out, 10 series LEDs, jumpers at W2-W3, W6-W8, 0.5A:

Trace colors:

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Yellow = line voltage, 100 V/div

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Magenta = line current, 200 mA/div

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Green = LED current, 100 mA/div

AN2711 Datasheet(PDF) 22 Page - STMicroelectronics