AN437

How to design snubber circuit for turn-off improvement

7/18

2

How to design snubber circuit for turn-off

improvement

2.1

Step response of an RLC series circuit

on Figure 7). At turn-off, the snubber circuit limits the slope of the reapplied voltage

off to respect both the reapplied voltage slope ((dV/dt)c) and the maximum peak off-state

The electrical circuit analyzed in this paragraph is given by Figure 7.

Figure 7.

Application circuit and its equivalent diagram at turn-off

For a second order linear differential equation with a step function input, the voltage

Equation 1

Equation 2

With damping factor:

Equation 3

Undamped natural resonance:

Equation 4

V

T

I

G

G

I

T

V

Mains

Load

LR

I

T

V

T

E

Load

LR

R

S

C

S

R

S

C

S

Application circuit

Equivalent diagram at turn-off

VV

Cs

Cs

≈

E

)

t

(

V

dt

)

t

(

dV

2

dt

)

t

(

V

d

1

Cs

Cs

0

2

Cs

2

2

0

=

+

+·

.

·

ω

ξ

ω

)

t

(

V

dt

)

t

(

dV

C

R

)

t

(

V

Cs

Cs

S

S

T

+

·

·

=

)

H

(

)

F

(

S

)

(

S

L

C

2

)

R

R

(

·

Ω

+

=

ξ

)

F

(

S

)

H

(

)

s

/

rad

(

0

C

L

1

·

=

ω