VIPER27

Operation descriptions

Doc ID 15133 Rev 5

15/31

7.3

Power-up and soft-start up

page 6) the power MOSFET starts switching and the HV current generator is turned OFF.

See

Figure 23 on page 16.

the self-supply circuit (typically an auxiliary winding of the transformer and a steering diode)

develops a voltage high enough to sustain the operation.

switching operation before the controller receives any energy from the auxiliary winding.

Equation 1

estimated by applicator according to the output stage configurations (transformer, output

capacitances, etc.).

During the converter start up time, the drain current limitation is progressively increased to

the maximum value. In this way the stress on the secondary diode is considerably reduced.

It also helps to prevent transformer saturation. The soft-start time lasts 8.5 ms and the

feature is implemented for every attempt of start up converter or after a fault.

Figure 22.

C

VDD

I

DDch

t

SSaux

×

V

DDon

V

DDoff

–

----------------------------------------

=

BURST MODE

NORMAL MODE

START- UP

NORMAL MODE

I

I

DD1

I

DD0

V

FBbm

V

FBbmhys

V

FBlin

V

FBolp

V

DDoff

V

DDon

t

t

t

t