APPLICATION NOTE
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Effect of Gate-Emitter
Voltage on Turn on Losses
and Short Circuit Capability
AND9072/D
Introduction

IGBT Turn-on Switching Loss Considerations

This application note describes some of the impacts of thegate-emitter voltage on the IGBT device performance.
Unlike the MOSFETs and BJTs, the magnitude of thegate-emitter supply voltage of an IGBT has a moresignificant impact on the performance of the device. Themagnitude of the gate-emitter voltage impacts the turn-on
loss and short circuit survival capability of the devices.

There are three major areas of consideration whenselecting the VGE value for an IGBT.
1. VCE variation – Unlike a MOSFET that gets fullyenhanced at relatively low gate voltage (in mostMOSFET output characteristics, there is minimal
gain once VGS crosses 10 V), the output/saturation
characteristics of the IGBTs show continuing
dependence on the VGE voltage. This is best
illustrated in the attached Figure 1 from an IGBT
datasheet. As shown in the curves, there isa significant gain to be had in the saturation
voltage (VCE), as the VGE value is increasedbeyond 11 V for same collector current value. Infact, higher current is not supportable until VGE is
increased above 13 V. Given high current
applications, even a 0.1 V improvement in VCE
translates into power savings of 1 W for every
10 A of collector current.

Background

While both MOSFETs and IGBTs have certain
similarities in terms of a gate terminal being used to switch
the device, there are operational differences that need to beconsidered when driving the IGBTs. A typical MOSFET’sswitching behaviour is minimally impacted by the gatevoltage levels beyond a certain level. As a result, it makes
sense to restrict the gate voltage in MOSFET drive circuit sothat the total gate charge (QG) value is minimized. However,in case of IGBTs, there are other considerations, so whentransitioning from MOSFETs to IGBTS, theseconsiderations may require a re-evaluation of optimum gate
voltage level.
50
TA = 25°C

15 V

VGE = 17 V

13 V

IC, Collector Current (A)

40

11 V

30

209V

107V

00123

4

5VCE, Collector-to-Emitter Voltage (V)Figure 1. Output Characteristics of a 15 A, 600 V IGBT

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September, 2022 − Rev. 2

1Publication Order Number:AND9072/D

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charge that has to be delivered every switchingcycle. If we partition the gate-voltage vs. Q chartin three regions as shown in the figure, the firstsection is the QGE – from origin to the point theplateau region is reached. The next one is the QGC– which represents the plateau region and finally,
the charge in the 3rd region is proportional to theactual value of VGE. In this instance, every 2 V
increase in VGE value beyond the plateau voltage,
leads to increase of about 10 nC in QG value. This
increase leads to higher dissipation in the device aswell as in the drive circuit due to the additional
gate charge, but will also result in a lower VCE. In
that sense, it is advisable to keep the VGE value
always above the plateau voltage, but not too
much higher than it.

2. Gate charge considerations – In order to fully
turn-on the device in high voltage application,
both MOSFET and the IGBT drivers must supply
voltage beyond the plateau voltage that is needed
to overcome the equivalent of the Miller effect inthe device (providing the QGD and QGC charge ata constant voltage to the MOSFET and IGBT,respectively). The plateau voltage is shown inFigure 2. As shown here, the typical IGBT hasa higher plateau voltage (near 10 V) than a typical
MOSFET (near 5 V). There is also a higher
variability in the IGBT plateau voltage asa function of collector current. As a result, it
makes sense to set the IGBT VGE value higher
than the typical FET VGS value. However, in bothcases, increasing the gate voltage beyond theplateau voltage increases the value of total gate
16ICE = 15 AVGE, Gate-emitter Voltage (V)

14VCES = 300 V

12Region 1Region 2Region 3

10VCES = 400 V

864200

10

20

30

40

50

60

70

80

90

QG, Gate Charge (nC)

Figure 2. Gate Voltage vs. Gate Charge Characteristics (15 A, 600 V IGBT)

hence increasing the VGE value may have less
impact in the applications where these drivers areused.

3. Transition time considerations – In addition to thefactors described above, the turn-on time of thedevice is also determined by the VGE value. Witha given VGE value, the available drive current isinversely proportional to the value of RG. Witha fixed RG, an increase in VGE results in a higher
current and reduces the QGE section of the charge.
This also results in shorter switching interval andsignificantly reduced turn-on energy – note thatturn-on and turn-off energies in hard-switching
applications are dominated by the collector currentand voltage transitions. Many of the IC drivers arespecified in terms of current drive capability, andAs shown in Figure 3, there is a dramatic drop in theturn-on energy, Eon, once the VGE value goes above 12 V.
However, there is not much difference in Eon for VGE values
between 15 V and 20 V. This applies for the full current
range. As depicted in Figure 4, the variations in RG also
resulted in a significant variations in the Eon value. Basedon these figures, it can be surmised that a high VGE value(between 15 V and 18 V) and a low RG value are the best
combination for driving IGBTs.

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2AND9072/D
6
RG = 22 W
12 V15 V
17 V
20 V

5Eon (mJ)

432
100

51015

2025Ipk (A)Figure 3. Turn-on Energy Characteristics (Fixed RG and varying VGE)

1.15

Eon (mJ)

0.9

0.65

0.4
1015

20

25

30

35

RG (W)

Figure 4. Turn-on Energy Characteristics (Fixed VGE and varying RG)
Short Circuit Fault Operation

Based on the above three considerations, following key
summaries can be drawn about the impact of VGE value on
IGBT switching performance:• It is better to use higher drive voltage, VGE, (around15 V) for IGBTs compared to the FET drive circuits• While higher voltage helps in many ways (saturation,transition time etc.), pushing it too high can increase thegate charge requirements.
• Some margin from absolute maximum values (±20 V,typically) must be maintained to prevent any transientson the drive voltage from damaging the IGBTs.

A major concern in inverter and motor drive applications
is the ability to survive a short circuit fault condition. During
the short circuit fault, the device is exposed to the supply
voltage across the device, while the gate potential is at fulloperating value (see Figure 5). Because of the high gain
characteristic of the IGBTs, the collector current will rise tosome undetermined value limited by the gate-emitter
voltage. During this time the device will have a large amountof energy across the device, and if the energy is beyond thecapability of the device it will be destroyed due to thermal
breakdown. For non-rugged devices, the large current cancause parasitic NPN bipolar transistor to turn on and cause
the device to latch, wherein the gate control will be lost.

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AND9072/D
Short Circuit Fault

VGG

VCC

Figure 5. Equivalent Short Circuit Condition

be to inherently build current sensing capability into thedevice – however, that is not an option in most cases.
Another method of increasing the short circuit survivability
is to decrease the gate voltage when the short circuit acrossthe device is observed. Figure 6 data shows the relationshipbetween the gate voltage, short circuit current, and the shortcircuit survival time period. As shown in Figure 6, it is clearthat the smaller gate voltage limits the current at lower value
and increases the short circuit time duration. Thus, if morerugged performance and longer short circuit survivability isneeded, it may make sense to trade-off some of the switchingloss gain and reduce the VGE voltage in the application.

Since an IGBT is less sensitive to second breakdown due
to hot spot formulation compared to a BJT, it can survivea short circuit condition if the energy delivered to the device
is maintained below some value that is tolerable to thedevice. An IGBT is typically specified with a guaranteedshort circuit withstand time under given conditions(a typical value is 10 ms). It is expected that this withstandtime allows an external circuitry to be activated andintervene to rectify the condition.
There are many different ways to protect the device fromthe short circuit condition for some duration. The mosteffective way to provide the short circuit survivability would
60.0

200
180

50.0

160

tSC (ms)

ISA

120
100

30.0

8020.0ISC (A)

140

40.0

60tSC

4010.02000.0101214161820

VGE (V)

Figure 6. Short Circuit Response of IGBT
Summaryof the device. But on the other hand, the designer needs tounderstand that the high gate-emitter voltage reduces theshort circuit survivability of the device. Using these two
relationships and taking into consideration specificapplication requirements, the designer can choose the bestvoltage value (and the best IGBT) which will meet thedesign requirements.

IGBTs are high current and high voltage devices that offer
certain benefits compared to the MOSFETs. Because of theiruse in high power applications, both lifetime considerations(ruggedness) and efficiency (low losses) are important. As
discussed in this section, the magnitude of the gate-emitter
voltage can be optimized in order to reduce the turn-on loss

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AND9072/D

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