DocID029000 Rev 2

19/30

HVLED001A

Application information

30

7.2

Control loop

The control loop is based on the current mode quasi resonant flyback control scheme and is

therefore performed by turning off the MOSFET when the peak of its source current reaches

the threshold set by the control loop, and by turning on the MOSFET in correspondence of

the resonant valley following the demagnetization of the transformer or inductor.

A detail of the block involved into this scheme is shown in Figure 8.

Figure 8. Control loop blocks

7.2.1

Current sense input

The peak of the primary current is read across a shunt resistor placed between the

MOSFET's source and compared with a threshold equal to:

Equation 1

and is used to compensate the dependency on the input voltage of the open loop gain

and CS threshold.

A leading edge blanking time (LEB) is applied after the MOSFET's turn-on.

limited to 55 mV.

A second level OCP threshold is present to temporarily stop the switching activity in case of

inductor saturation.