Hitachi IGBT Module Application Manual

5.7.2 Calculating Delay Times of IGBTs

5.7.2.1

Turn-ON and Turn-OFF Switching Waveforms

Figure 43. Inductive Load Turn-ON and Turn-OFF Switching Waveforms

5.7.2.2

Calculating Switching Delay Times

Note:

V

GP

and V

GN

in the equations are positive values.

At turn-ON, driver output voltage v

g

( out ) changes from -V

GN

to V

GP

, the gate input capacitance

C

ies

is charged, the gate voltage ( V

GE

) exceeds the gate threshold voltage ( V

th

), and a collector current

( i

c

) starts flowing. Immediately after the collector current starts flowing, the gate voltage remains constant

at voltage V

th

( on ) determined by collector current I

C

for some time (several microseconds) due to effects

of reverse transfer capacitance ( C

res

), and discharges return capacitance due to the gate current I

G res

(on)

(see Equation 29).

Equation 29:

I

G res

(on) = (V

GP

- V

th

(on))/(R

c

+ Z

on

))

where Z

on

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

The time until a collector current starts flowing, that is, the turn-ON delay time t

d

(on) is given by

Equation 30:

t

d

(on) = -( R

G

+ Z

on

)

!

C

ies

[ln{( V

GP

- V

th

(on))/( V

GP

+ V

GN

) }]

Note:

Here, t

d

(on) is a delay time from the time when the gate voltage is

( -V

GN

). If the gate voltage becomes an intermediate voltage due

to a narrow control signal input, V

GN

should be replaced with the

intermediate voltage.

39