Device description

HVLED807PF

20/36

Doc ID 023464 Rev 5

4.5

Constant current operation

Figure 16 presents the principle used for controlling the average output current of the

flyback converter.

The voltage of the auxiliary winding is used by the demagnetization block to generate the

control signal for the internal MOSFET switch Q. A resistor R in series with it absorbs a

capacitor.

The flip-flop's output is high as long as the transformer delivers current on secondary side.

This is shown in

Figure 17.

Figure 16.

Current control principle

Figure 17.

Constant current operation: switching cycle waveforms

AM13566v1

VILED

Icled

CC

S

R

Q

DMG

ILED

Q

R

.

Iref

CLED

DEMAG

LOGIC

Aux

Rf b

Rdmg

From CS pin

To PWM Logic

AM13567v1

t

IREF

Q

t

t

t

VILED/R

T