M51996AP データシートの表示（PDF） - MITSUBISHI ELECTRIC

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M51996AP

SWITCHING REGULATOR CONTROL

MITSUBISHI ELECTRIC  

OVP circuit

(1)To avoid the miss operation of OVP

It is recommended to connect the capacitor between OVP

terminal and GND for avoiding the miss operation by the spike

noise.

The OVP terminal is connected with the sink current source

(~150µA) in IC when OVP does not operate,for absorbing the

leak current of the photo coupler in the application.

So the resistance between the OVP terminal and GND for leak-

cut is not necessary.

If the resistance is connected,the supply current at the OVP

reset supply voltage becomes large.

As the result,the OVP reset supply voltage may become higher

than the operation stop voltage.

In that case,the OVP action is reset when the OVP is triggered

at the supply voltage a little high than the operation stop

voltage.

So it should be avoided absolutely to connect the resistance

between the OVP terminal and GND.

To REG or Vcc

Vcc

5.6k

M51996A

OVP

GND

PHOTO COUPLER

Fig.21 Peripheral circuit of OVP terminal

(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.

(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.Fig.23 shows

one of the example circuit diagram.

MITSUBISHI (Dig./Ana. INTERFACE)

M51996AP/FP

SWITCHING REGULATOR CONTROL

TO MAIN

TRANSFORMER

R1

Vcc

~

CFIN R2 Cvcc M51996A

GND

THE TIME CONSTANT OF

THIS PART SHOULD BE SHORT

Fig.22 Example circuit diagram to make the

OVP-reset-time fast

Vcc

M51996A

OVP

470Ω

CVcc

GND

MAIN

TRANSFORMER

THIRD

WINDING

FIG.23 OVP setting method using the induced

third winding voltage on fly back system

(4)Method to control for ON/OFF using the OVP terminal

You can reset OVP to lower the OVP terminal voltage lower

than VTHOVPL.

So you can control for ON/OFF using this nature.

The application is shown in Fig.24.

The circuit turns off by SW OFF and turns on by SW ON in this

application.

Of course you can make use of the transistor or photo-transistor

instead of SW.

REG

5.1k

SW

M51996A

ON/OFF

FIG.24 Method to control for ON/OFF using the

OVP terminal

( 16 / 22 )

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