Stray Inductance

8/11/2019 Stray Inductance

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from Europefor the World

ApplicationNote

European Power-Semiconductor andElectronics Company

For further information contact:eupecMarketing Department Tel: +49 2902 764-0Max Planck Str. 5 Fax: +49 2902-764-1256D-59581 Warstein Internet:: http://www.eupec.com

AN_Stray_Inductance_Definition.doc

Definition of the module stray inductance LsFig.1 shows the principle circuit of a half-bridge and the resulting voltage and current wave-

forms when switching IGBT1. The circuit stray inductance L, shown as a concentrated ele-

ment, represents all distributed inductances (of capacitors, busbars and IGBT modules)

within the commutation loop (striped area).

D1

IGBT1 turn-on

MVcc

-15V

IGBT2

C

IGBT1

L

0

LD2

0

VIGBT2

D2I

IGBT1I

IGBT1 turn-off

0

VIGBT1

VGE

Fig.1: Half-bridge circuit with current and voltage waveforms when switching IGBT1

Due to the changing current a voltage drop of L* dioff/dt occurs across the stray inductance

L. It is overlayed to the DC link voltage VCCand seen as a voltage spike across the turning-

off IGBT1. Permissible limits for turn-off current di/dt and overvoltage can be deduced from

the RBSOA diagram of the IGBT. This curve (see Fig.2) is valid when the measurement is

done through the CE auxiliary terminals. Also a derated curve is given in the data-sheet for

measurements at the power terminals, taking into account the internal module stray induc-

tance between main and auxiliary terminals of the module. For dual modules, this diagrams

refers to the voltage across one of the both commutating IGBT switches.

For calculations the value for the internal module stray inductance L s is given in the data-

sheets. For single switch modules, this value is the before mentioned stray inductance be-

tween main and auxiliary terminal. For dual modules or modules containing several phase

legs, this value corresponds to the application relevant effective commutation loop between

upper and lower switch. Due to the construction this value is clearly lower than the sum of


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Application Note page 2 of 3



V

dIF/dtIF

V0

separately determined induc-

tances of upper plus lower arm.

In modules with more than one

phase leg always the worst

case commutation path from

plus supply voltage through the

phase leg back to minus supply

voltage is considered.

The measurement is performed, while the diode turns off. The voltage drop happens at a

point of time, where the di/dt is constant and the diode still

has no blocking capability. Therefore the voltage drop can

only be caused by the module stray inductance. No other

effects have to be considered. The module stray inductance

is calculated according to Ls= V / diF/dt.

Dependent on the type designation, the data sheet value for

the stray inductance has to be interpreted in the following way:

Sicherer Arbeitsbereich IGBT (RBSOA)

Reverse bias safe operating area IGBT (RBSOA)

0

600

1200

1800

2400

3000

0 500 1000 1500 2000 2500 3000 350

VCE

[V]

IC[A]

IC,Modul

IC,Chip

RG,off

= 1,2,Tvj= 125C

Fig.2: RBSOA diagram for FZ1200R33KF2

DUT:

half-bridge

-15 V

-15 V

LL

CVCC

V

DUT:

single sw itch

-15 VLL

CVCC

V

Fig.3: Measuring circuit


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Application Note page 3 of 3



Single modules type FZ... or ...GA... and Tripacks:

The module stray inductance is measured between the C and E main terminals.

Dual modules type FF... (with exception of FF200R33KF):

These modules contain two independent switches. Given is the

stray inductance between the C and E main terminals of one switch.

Half-Bridges type ...GB... and FF200R33KF (modules with three main terminals):

The given data sheet value covers the full

commutation loop between upper and lower

switch, including the inductance between

upper C1 and lower E2 terminals.

4-packs type F4-...:

These modules contain two independent phase-legs. The given data sheet

value covers thefull commutation loop between upper and lower switch

within one phase-leg, including the inductance between + and - terminals.

Six pack modules type FS...:

The given data sheet value covers thefull commutation loop between up-

per and lower switch within one phase-leg, including the inductance be-

tween + and - terminals.

3-Phase full bridges or PIM type ...GD... or ...GP...:

The given data sheet value covers the full commutation loop

between upper and lower switch at the worst position within

the module, containing the full inductance towards the P+

and N- terminals (terminals named 22 and 24 with PIM).

Stray Inductance

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