AN4129 datasheet(13/39 Pages) STMICROELECTRONICS

Part #	AN4129

Description	STEVAL-ILL044V1: 9 W Triac dimmable, high power factor

PDF	39 Pages

Scroll/Zoom	100%

Manufacturer	STMICROELECTRONICS [STMicroelectronics]

Direct Link	http://www.st.com

Logo

13 / 39 page

AN4129

Power converter performance

Doc ID 023314 Rev 1

13/39

3.4

Addition of diode clamp to limit input current

Since the peak FET current is directly controlled by the voltage on the ILED pin, a diode

clamp can be added to limit the voltage increase to reasonable levels. The graph below

shows the results for two diode types, a fast P-N diode having about 0.6 V forward drop, and

a Schottky diode having about 0.3 V forward drop, placed across the DC filter capacitor.

Figure 15.

Power loss vs. sinusoidal input voltage

The input current increase can now be limited to a reasonable value. There are two

consequences of this addition:

●

Line regulation is lost at low input voltages (the ILED pin cannot rise to regulate

current).

Figure 16.

Output current vs. input voltage

●

And THD is significantly improved at low input voltage:

Figure 17.

THD vs. input voltage

AN4129 Datasheet(PDF) 13 Page - STMicroelectronics