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SS6578

VIN

1

DUTY

2

SHDN

3

FB

4

GND

5

DRI

6

CS-

7

CS+

8

U1 SS6578

R3

47K

R4

27K

C2

0.1uF

Rs

+

C4

470

µF

D1

SS32

+

C1

100

µF

L1

33

µH

R6

1M

Q1

SSM4435

R7

*

Q2

R1

3K3

C3

1

µF

D2

LL4148

R2

100K

<15V

***

*

***

R6 can adjust the duty cycle max. It can be 0

Ω

B. Short Circuit Protection Design

1.

As

we

know,

Short

Circuit

Protection

(abbreviated as SCP) does not always exist in

the DC-DC converter circuit. The fact is usually

the DC-DC converter provides the circuits

attached to VOUT with low power or low

voltage. Sometimes there is less concern about

safety, as the probability of short-circuit is

quite low. That gives users reasons to ignore

the use of an SCP circuit. However, we would still

like to point out the importance of the

protection. With SCP, the system will be well

protected in any situation. Two SCP circuits

are introduced as follows for your reference.

2.

Design1: shown as Fig. 12.

A fuse can be selected to pass

the start up current, but open quickly

with a large unexpected current. Of

course,

replacement

of

the

fuse

is needed after short circuit.

3.

Design 2: shown as Fig. 13.

Method: Add a SCP circuit

Note: 1. The time constant, which is

directly related to R1 and C1,

has a serious effect on the

circuit.

2. Circuit can be recovered by

removing the short circuit

event from the system.

3. The condition for applying

Rev.2.02 4/06/2004