Application
Note
from Europe
for the World
European PowerSemiconductor and
Electronics Company
Effect of Gate-Emitter Capacitor CGE
Attached you find some informations, which should give explanations about the advantages
of using an additional gate capacitor CG.
The main idea behind this is to control dIC/dt and dVCE/dt independently at turn-on. The
need for this is given by the wish for lowest IGBT turn-on losses and a not unlimited di/dtcapability of the free wheeling diode.
By just raising the RG (until the dIC/dtmax is ok) would increase the turn-on losses Eon. With the
additional component CG the dIC/dt can be controlled by the time constant given by RG and
CGE//CG. For the turn-on dVCE/dt only RG and CG//CGC (CGC: Miller-capacity) are effective. Because CGC >> CG, finally only RG (and not CG) is responsible for the resulting dVCE/dt value !
By this measure the RG and therefore the switching losses can remain on a low value.
210
180
180
160
150
140
120
120
100
90
80
60
60
40
30
20
0
0
1
range
1
2
3
4
2
3
determined by
VGE < VGEth
VGEth < VGE < VGEM
VGE = VGEM
VGE > VGEM
condition
Ciss = const.
Ciss= const.
VGE = const.
Ciss = const.
4
influenced by influence on
C‘GE
tdon
C‘GE
dIC / dt
RG, CGC
dVCE / dt
C‘GE // CGC
dVCEsat / dt
C’GE = CGE // CG
For further information contact:
eupec
Marketing Department
Max Planck Str. 5
D-59581 Warstein
Tel: +49 2902 764-0
Fax: +49 2902-764-256
Internet:: http://www.eupec.com
AN_CGE.doc
Application Note
page 2 of 4
Example : FZ1200R33KF1, turn-on without CG
VCE: 500V / div, IC: 600A / div
IGBT Turn-On
(dI/dt=10kA/us)
Rg:1,8Ω
150
180
120
90
120
60
60
30
0
0
t: 2µs/div
high dIC/dt due to low gate resistor RG
IGBT Turn-On
dI/dt=5kA/µs
Rg:8,2Ω
150
300
250
120
200
90
150
60
100
30
50
0
0
t: 2µs/div
low dVCE/dt and high turn-on losses due to high gate resistor RG
For further information contact:
eupec
Marketing Department
Tel: +49 2902 764-0
Max Planck Str. 5
Fax: +49 2902-764-256
D-59581 Warstein
Internet:: http://www.eupec.com
AN_CGE.doc
Application Note
page 3 of 4
Solution:
An additional Capacitance between Gate & Emitter allows
independent control of dIC/dt and dVCE/dt
CGC
R
CG
CGE
•
dVCE/dt is controlled via RG and CGC
•
dIc/dt is controlled via RG and CGE//CG
For further information contact:
eupec
Marketing Department
Tel: +49 2902 764-0
Max Planck Str. 5
Fax: +49 2902-764-256
D-59581 Warstein
Internet:: http://www.eupec.com
AN_CGE.doc
Application Note
page 4 of 4
Example:
FZ1200R33KF1
Variation of RG and CG
RG=8,2Ω, CG=0, IC/dt= 5kA/µs, dVCE/dt=0,6kV/µs, Eon=6,4J
RG=3,3Ω, CG=100nF, IC/dt= 4,5kA/µs, dVCE/dt=1kV/µs, Eon=4,1J
RG=1,0Ω, CG=330nF, IC/dt= 5,1kA/µs, dVCE/dt=2,8kV/µs, Eon=2,8J
For further information contact:
eupec
Marketing Department
Tel: +49 2902 764-0
Max Planck Str. 5
Fax: +49 2902-764-256
D-59581 Warstein
Internet:: http://www.eupec.com
AN_CGE.doc