M51995AFP datasheet(33/43 Pages) RENESAS

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M51995AP/AFP

REJ03D0835-0300 Rev.3.00 Jun 06, 2008

Page 31 of 40

2. Application circuit to make the OVP-reset time fast

The reset time may becomes problem when the discharge time constant of CFIN • (R1 + R2) is long. Under such the

circuit condition, it is recommended to discharge the CVCC forcedly and to make the VCC low value. This makes the

OVP-reset time fast.

To main

transformer

VCC

GND

CVCC

CFIN

The time constant of

this part should be short

M51995A

Figure 27 Example Circuit Diagram to Make the OVP-Reset-Time Fast

3. OVP setting method using the induced third winding voltage on fly back system

For the over voltage protection (OVP), the induced fly back type third winding voltage can be utilized, as the

induced third winding voltage depends on the output voltage. Figure 28 shows one of the example circuit diagram.

Main

transformer

third winding

VCC

OVP

GND

CVCC

470

Ω

M51995A

Figure 28 OVP Setting Method Using the Induced Third Winding Voltage on Fly Back System

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