Hitachi IGBT Module Application Manual

At turn-OFF, it moves to an OFF state due to the discharge of C

ies

. However, C

res

is discharged due to

the gate current I

Gres

(off) (see Equation 31) until it becomes constant at the voltage V

th

(off) where v

ge

depends only on I

C

and the collector voltage v

ce

becomes source voltage V

CE

. Collector current I

C

declines only when v

ce

= V

CE

.

Equation 31:

I

Gres

(off) = (V

GP

+ V

th

(off))/( R

G

+ Z

off

)

where Z

off

is the OFF-gate voltage output impedance of the driver.

The turn-ON delay time is a time t

d

(off) until C

res

is charged to V

CE

whose value can be determined

using Equation 32:

Equation 32:

t

d

(off)= -( R

G

+ Z

off

)

!

(C

ies

+ C

res

(0))

!

ln{(V

GN

+ V

th

(off))/

(V

GP

+ V

GN

)} + Q

GQ

/ I

Gres

(off)

= -(R

G

+ Z

off

)(3 C

ies

)

!

ln{(V

GN

+ V

th

(off))/(V

GP

+ V

GN

)} + Q

GQ

/ I

Gres

(off)

Definitions:

C

res

(0)

Q

GQ

Reverse transfer capacitance (set equal to 2 C

ies

here)

when V

CE

is approximately 0V

Total recharging charge (gate charge) of C

res

(see Figure 44).

Figure 44. Parasitic Capacitance

40