AN4130 datasheet(12/41 Pages) STMICROELECTRONICS

Part #	AN4130

Description	LED driver using the HVLED815PF

PDF	41 Pages

Scroll/Zoom	100%

Manufacturer	STMICROELECTRONICS [STMicroelectronics]

Direct Link	http://www.st.com

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12 / 41 page

Theory of operation

AN4130

12/41

Doc ID 023315 Rev 1

The scope shots below show the result on the input current waveform.

Where:

●

Yellow = line voltage

●

Magenta = line current, 50 mA/div ref -3div

●

Blue = Voltage at ILED pin, ref -3 div

●

Green = Voltage at bottom of 4.7 µF cap on ILED pin.

2.7

Diode clamp effects on dimming

The diode-improved waveform also helps when the circuit is dimmed with a Triac, especially

at low conduction angles. The ILED pin voltage is not allowed to rise. Note how high the

ILED pin voltage (green trace) has risen in the first image, compared to the second, as the

chip attempts to regulate the average output current. The voltage on that pin directly

controls the peak FET current.

Figure 13.

70 Vrms input, no diode

Figure 14.

BAT48, ~0.3 V drop

Figure 15.

40 Vrms dimmed input, no diode

Figure 16.

40 Vrms dimmed input, BAT48

diode

AN4130 Datasheet(PDF) 12 Page - STMicroelectronics