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AN628 APPLICATION NOTE

Table 5. Half power range at 110Vac

(*) Most significant losses balance at half power (110Vmains):

– Power-mos (Q1+Q2) dissipated power = 7.5W.

– Bridge (B1) dissipated power = 3.7W.

– Boost turbo-diode (D4) dissipated power = 1.1W.

– Boost inductor L1 = 1.3W

– Aux. Inductor L2 = 0.95W.

– NTC dissipated power = 0.7W.

– Snubber = 1W

Table 6. Half power range at 220Vac

(*) Most significant losses balance at half power (220Vmains):

– Power-mos (Q1+Q2) dissipated power = 5.64W.

– Bridge (B1) dissipated power = 1.9W.

– Boost turbo-diode (D4) dissipated power = 0.88W.

– Boost inductor L1 = .5W

– Aux. Inductor L2 = 0.6W.

– NTC dissipated power = 0.52W.

– Snubber = 0.7W

Significant waveforms

Since the described application is provided with a "magnetic snubber circuitry", it is of some interest to have a

look at some switching waveform.

In figure 28, it is depicted the power drain voltage and the current measured in L2 (aux. Inductor) .

To be observed the "delay effect" of the current and the control of its slope. In fact, this circuitry allows to hardly

reducing the Voltage-Current power crossing and the ramp rate of the drain current, reducing in this way the

power dissipated inside the switch and the high frequency contents of the switching.

In figure 29, it is shown both the switching edge and pointed the recovery charge due to the boost diode and the

effect of the Voltage Clamp (D7, C14, R18).

In figure 30, the switch-off edge is magnified and pointed out the effect of the RCD snubber to ground (Cs, Q4

R25) limiting the dV/dt and the above-mentioned Voltage Clamp.

Finally, in figure 31, it is shown and pointed, in the reverse recovery region, the demagnetization effect of the

D5+D6 and its control on the second slope of the recovery itself.

THD

PF

Eff.

88Vac

219W

420Vdc

239W

2.4%

0.999

.916

110Vac (*)

220W

421Vdc

238W

3.6%

0.999

.925

132Vac

222W

423Vdc

237W

2.7%

0.999

.937

THD

PF

Eff.

176Vac

223W

424Vdc

236W

8%

0.993

.945

220Vac (*)

223W

424Vdc

235W

10.5%

0.994

.949

264Vac

223W

424Vdc

235W

15%

0.978

.95