FA13842, 13843, 13844, 13845

11

Fig. 12

Fig. 13

Fig. 14

Fig. 11

~+

~

DB

R1

D1

C2

+

MOSFET

Rs

6

1

7

FA13842

R4

R6

D5

R7

R8

PC1

Tr1

Tr2

R15

Tr5

R16

PC1

C6

R3

C1

T1

D6

R13

Tr4

+

C7

R14

AC INPUT

+

~+

~

R1

D1

C2

+

MOSFET

Rs

6

1

7

FA13842

R4

R6

D5

R7

R8

PC1

Tr1

Tr2

C6

R3

DB

ZD2

PC1

C1

T1

D6

+

C7

R9

AC INPUT

+

~+

~

6

1

7

FA13842

R4

R6

D5

Tr1

Tr2

ZD1

C6

R3

DB

R1

D1

C2

MOSFET

Rs

C1

T1

AC INPUT

+

+

~+

~

6

13

7

FA13842

R4

R6

D5

Tr1

Tr2

C6

R3

DB

R1

D1

C2

+

MOSFET

R12

Tr3

C8

R10

R11

Rs

C1

T1

AC INPUT

+

3-1 The method of detecting an overvoltage (detection

on primary side)

A typical latched shutdown circuit to protect against

overvoltages detected on the primary side is shown in Fig. 11.

When the secondary voltage increases in the flyback circuit,

the voltage of the bias winding also increases in proportion.

When this voltage increase is detected by zener diode ZD1, a

latched shutdown is accomplished. As the secondary voltage

is detected through a transformer, detection accuracy is low.

3-2 The method of detecting an overvoltage (detection

on secondary side)

A typical latched shutdown circuit to protect against

overvoltages detected on the secondary side is shown in

Fig. 12.

The detected voltage accuracy is high compared to

overvoltage detection on the primary side.

3-3 The method of detecting an overcurrent (detection

of primary current)

A typical primary overcurrent detection circuit is shown in

Fig. 13.

3-4 The method of detecting an overcurrent (detection

of secondary current)

A typical secondary overcurrent detection circuit is shown in

Fig. 14.