AN4376 datasheet(10/37 Pages) STMICROELECTRONICS

10 / 37 page

EVLHVLED815W10A - main characteristics and circuit description

AN4376

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DocID025380 Rev 1

2.4

External compensation network of the voltage loop

The compensation network composed by C6, C7 and R7 is placed between this pin and

GND to achieve stability and good dynamic performance of the voltage control loop.

Normally it is not working and operates only during an OVP.

2.5

Power factor corrector function and ILED pin modulation

with the input mains voltage

Once the signal at the current sense pin has reached the level programmed by reference

signal on the pin ILED, the internal MOSFET turns off.

The network composed by R15, R17, R21, R20 and R4, R22 and modulated by Q2, works

as a divider and it provides to the ILED pin of the HVLED815PF the information of the

instantaneous input voltage which is used to modulate the current flowing into the inductor.

Through this network the controller works as a power factor corrector.

The converter is connected after the mains rectifier and the capacitor filter, which in this

case is quite small to avoid damage to the shape of the input current maximizing the power

factor performances.

Referring to Figure 8 on page 11, a voltage Vx proportional to the input rectified mains is

summed on the average voltage present on the ILED pin trough the CLED capacitor

generating a voltage reference proportional to the input voltage (AC coupling).

Equation 4

The ILED pin voltage is compared with the CS pin voltage, generating a primary current

proportional to the input voltage reaching the high power factor condition.

The average value of the ILED pin is not depending from the Vin input voltage (AC

coupling), as a consequence the desiderated output current can be programed trough the

current sense resistor Rsense according to Equation 1 (see the HVLED815PF device

datasheet for more details [1. in Section 8: Supporting material on page 36] ).

A C

p k

I N

p k

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