AN4376 datasheet(11/37 Pages) STMICROELECTRONICS

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AN4376

EVLHVLED815W10A - main characteristics and circuit description

Figure 8. ILED pin modulation with the input mains voltage

In Section 7.3: ILED pin modulation with the line voltage on page 25 is showed the behavior

of the ILED pin depending on the action of the switch represented by the BJT Q2 (SW in

Figure 8, Q2 in Figure 9). At the low line the switch is Off (BJT base is low) and the pin is

modulated by the divider composed by RAC_H and RAC_L1. When, at the high line, the

BJT is ON the pin ILED is modulated by a different ratio of the divider (RAC_H and the

parallel of RAC_L1 with RAC_L2) in order to keep the same dynamic on the ILED pin.

2.6

High-voltage start-up generator and VCC capacitor

At a startup, a 5.5 mA internal current source of the HVLED815PF device [1. in Section 8:

Supporting material on page 36] charges the VCC capacitor (C8), until the voltage on the

pin Vcc reaches the start-up threshold, and then it is shut down. With a 22

f of the VCC

capacitor, the device turns-on typically in:

Equation 5

The T1 auxiliary winding (pins 4 - 5) and a diode D2 and a limiting resistor R9 generate

a constant VCC voltage that powers externally the HVLED815PF device during normal TM

(transition mode) operation. See the real behavior in Section 7.4: Controller startup and

light-ON on page 26.

m s

m A

c h

O N

C C

V c c

u p

S t a r t













a r g



AN4376 bảng dữ liệu(PDF) 11 Page - STMicroelectronics