Modes of operation

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Doc ID16539 Rev 1

A.2

Constant current operation

Figure 22 presents the principle used for controlling the average output current of the

flyback converter.

The output voltage of an auxiliary winding is used by a demagnetization block to generate

the control signal for the MOSFET switch Q1. A resistor (R) in series with it absorbs the

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

side (Figure 23).

and the system works in DCM (this is the case because the IC is in QR mode), it is possible

to obtain the equation:

Equation 5

Equation 5 shows that the average output current no longer depends on input or output

voltage, nor on the transformer inductance values. The parameters defining the output

Figure 22.

Current control principle

I

OUT

n

2

---

V

CREF

R

SENSE

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×

=