Proceedings of the 12th WSEAS International Conference on AUTOMATIC CONTROL, MODELLING & SIMULATION
Research of Active Gate Drivers for MOSFET by Thermography
ANNA ANDONOVA, SVETOSLAV IVANOV, IVAN NEYCHEV, NADEZHDA KAFADAROVA
Department of Microelectronics
Technical University of Sofia
1797 Sofia, 8, Kl. Ohridski str.
BULGARIA
n_kafadarova@yahoo.com; ava@ecad.tu-sofia.bg
Abstract: - New drivers are proposed to reduce losses of power and energy during the transitional processes of
switching on and turning off of powerful transistor, which is associated to an increased energy efficiency of power
converters. Infrared thermography study and analysis of dynamic losses and heating temperature of MOSFET are
committed in managing transistor drivers by four different circuits.
Key-Words: - Infrared, Thermography, Driver, Energy Conversion efficiency, MOSFET
1 Introduction
In many of renewable energy sources (e.g. fuel cells and
photovoltaic systems) the constant voltage has to be
converted into alternative with exactly specified
parameters. For that purpose there are used electronic
transducers, which are a major source of harmonics [1].
An important point to improve the energy efficiency of
switching power converters is to reduce energy losses in
the key transistors. To lower the switching losses in the
management of key power transistors has been studied a
new method for active management of the driver – by a
feedback on dID/dt or dUD/dt. For a contactless testing of
dynamic thermal losses and the impact of the transitional
processes in the management of power MOSFET
transistors in key mode and the radiator there is used
infrared thermography [2]. The thermal control of the
devices for active management of power transistors
operating in key mode is directly related to improving
energy efficiency and increasing reliability during the
power transistors operation [3].
Fig.1. Schematic of the driver with a feedback on
dID/dt.
Transitional processes in the management of power
transistor with a new driver circuit are given fig.2a, b for switching on at Vd[20V/div], Id[4A/div], P[80W/div],
t[500ns/div] and for turning off
at Vd[50V/div],
Id[4A/div], P[200W/div], t[500ns/div] (the graphics 1:
drain - source voltage of transistor; the graphics 2: drain
current; the graphics 3: the power dissipated on the
transistor).
2 Active Gate Drivers for MOSFETS
An important issue in the research to improve the energy
efficiency of switching power converters is associated
with reduction of energy losses in the key transistors [4].
Using methods and devices for active management of
drivers’ circuits leads to lower switching losses in power
key transistors. To demonstrate the use of modern
infrared technology for improvement of the design
qualification process and for revealing the potential
problems at a very early stage in the product
development cycle there are compared four drivers. One
of them is a standard driver of the company
MICROCHIP-TC4421. The second driver is controlled
with a feedback on dID/dt, as ID is controlled
continuously throughout the whole switching intervals
regardless of the value of the dID/dt. Principle scheme of
the driver is shown in Figure 1.
ISSN: 1790-5117
a)
b)
Fig.2. Transient processes in power transistor
circuit with the driver from fig.1.
For comparison there are also given oscillograms
obtained during the control of MOSFET by a standard
driver of the company MICROCHIP (fig.3a,b) for
switching on at Vd[50V/div], Id[4A/div], P[200W/div],
t[500ns/div] and for turning off at Vd[200V/div],
Id[8A/div], P[1600W/div], t[500ns/div]). Studies are
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ISBN: 978-954-92600-1-4
Proceedings of the 12th WSEAS International Conference on AUTOMATIC CONTROL, MODELLING & SIMULATION
performed with MOSFET type IRF350 with value of
supply voltage for power circuit UPOWER=50V, activeinductive load with parameters Rt=8Ω и Lt=100mH. The
frequency of the input control pulses from the signal
generator is 10KHz and the duty cycle is 50%. The
time- diagrams are obtained using gate resistivity with
resistance value of 10 Ω.
The fourth driver is with a two-stage switching and with
a feedback on dUD/dt. The principal scheme of this
driver is given in fig.6.
Fig.6. Schematic of a driver with two-stage
switching and a feedback on dUD/dt.
a)
b)
Fig.3. Transient processes in the management of
the power transistor by driver scheme ofMICROCHIP.
The transitional processes in the management of
MOSFET by the driver are given fig.7a, b (1UDS[20V/div],
2-ID[4A/div],
3-PON[80W/div],
t[500nS/div]) - for switching on at (1-UDS[50V/div], 2ID[4A/div], 3-POFF[200W/div], t[500nS/div]) and for
turning off at (the graphics 1: drain - source voltage of
transistor; the graphics 2: drain current; the graphics 3:
the power dissipated on the transistor).
The proposed drivers for active management of powerful
transistors operating in key mode improve the power
efficiency by reducing the dynamic energy losses in the
management of key elements, restrict electromagnetic
fields, eliminate the need to use protective RC groups
and increase the reliability during the operation of power
In addition to the feedback on current the driver can be
implemented with a feedback on dUD/dt of the power
transistor. The third driver used in the research is of this
type, and its principal scheme is shown in fig. 4.
The transitional processes in the management of
MOSFET by the driver with a feedback on dUD/dt are
given fig.5a, b for switching on at Vd[20V/div],
Id[4A/div], P[80W/div], t[500ns/div] and for turning off
at Vd [50V/div], Id[4A/div], P[200W/div], t[500ns/div]
(the graphics 1: drain - source voltage of transistor; the
graphics 2: drain current; the graphics 3: the power
dissipated on the transistor).
transistors.
a)
b)
Fig.7. Transient processes during the control of the power
transistor by the drivers from fig.6
Fig.4. Schematic of a driver with a feedback on
dUD/dt.
The experimental results can again be compared with the
results obtained in the management of power transistor
by the conventional driver circuit of the firm
MICROCHIP -TC4421 (fig.2).
3 Thermography research of MOSFETS
Heating
One of the main limiting factors affecting the power
capability and reliability of any electronic power
converter system is the operating temperature of key
power stage components. Excessive component
temperature will reduce product operating lifetimes and
could result in early field returns. Traditionally,
thermocouples are used to measure the operating
temperature of components. Whilst thermocouples can
a)
b)
give very accurate temperature measurements, they do
Fig.5. Transient processes during the control of the power
have a few potential drawbacks:
transistor by the drivers from fig.4.
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Proceedings of the 12th WSEAS International Conference on AUTOMATIC CONTROL, MODELLING & SIMULATION
• Thermocouples can pick up noise if they are placed
near to power components with high dv/dt switching
waveforms present and this can give misleading
measurement results.
• Thermocouples will sink a small amount of heat away
from the device they are attached to. For physically
small components, this can lead to measurement
inaccuracy.
• Thermocouples are often only placed on components
which are expected to show a reasonable temperature
rise. Other components may not be monitored at all and
this could lead to problems if a design error leads to a
high operating temperature on a component which hasn’t
been monitored
IR thermography is a non-contact measurement
technique which uses a calibrated infrared camera to
form athermal image of the system under test. As the
measurement technique is noncontact, the noise
susceptibility and heatsinking effects sometimes
encounteredwith thermocouples are no longer an issue.
More importantly, an entire PCB can be imaged which
immediately shows up any hotspots or problem
components that may have otherwise been overlooked.
Infrared camera FLIR ThermaCAM P640 and
thermocouples are used to examine power transistors and
its radiators surface temperature distributions. Stored
images are processed by software ThermaCAM
Researcher Pro 2.9 (fig.8).
An initial temperature of 24,8° on the MOSFET package
surface is red. The image on the fig.10 shows
temperature when the transistor is heated by di/dt active
gate control after 30 min of working and control
frequency of 10KHz. The temperature of the heated
transistor is 62,7°. The image on fig.11 shows the grade
of power transistor heating again after 30min of working
and control frequency of 10KHz, but using the standard
driver ТС4421. Before starting the experiment the
transistor has been cooled to initially measured
temperature of fig.9. At the end of the experiment a
temperature of 64,5° is received. On fig.12 is given a
thermogram of the transistor controlled with active
driver with feedback by di/dt after 30min of working at
control frequency of 40KHz. The measured temperature
of the MOSFET is 83,1°. The image on fig.4.13 shows
the grade of power transistor heating again after 30min
of working at frequency of 40KHz, in the case of
standard driver ТС4421 used. In the end of the
experiment a temperature of 89,2° is red. The tests from
fig.9-13 are done when the transistor is laid in a specially
prepared closed box with dimensions of 210mm x
160mm x 50mm.
Fig.11. 30 min, 10KHz ,
driver TC4421
The peak distributed power of the switched transistor
during turn-on and turn-off is given on the fig.14.
Experimental results for feedback gate controlled di/dt
and dv/dt are compared with those of the frequently used
driver MICROCHIP - TC4421. Using the standard
driver without gate current limitation, the peak
distributed power is vastly higher than this one for active
gate control realization of the other three drivers. The
dissipated power grows up vastly in the time of turn-off,
because of active-inductive load. The presence of activeinductive load leads to dangerously high over voltage on
power transistor during turn-off as a result of permissible
commutation (fig.15). From this figure it can be seen
that the voltage on the power switch IRF350 during turnoff reach 340V which is closed to the maximal
admissible for this transistor - 400V when is used the
traditional driver. This denote that the input voltage can
not been increased since the over voltages will exceed
the maximal permissible value.
Fig.8. IR image processing with
ThermaCAM Researcher
Thermography research results are illustrated with some
images of the both drivers – the driver with feedback by
di/dt and the MICROCHIP’s driver.
The thermogram on fig.9 shows the MOSFET
temperature during turn-off state.
Fig.9. turn-off state
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Fig.12. 30 min,40KHz,
gate controlled di/dt
Fig.10. 30 min, 10KHz,
gate controlled di/dt
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Proceedings of the 12th WSEAS International Conference on AUTOMATIC CONTROL, MODELLING & SIMULATION
[2] Minkina W., Dudzik S., Infrared Thermography,
Wiley, 2009.
[3] Ruedi H., Thalheim J., IGBT Drivers – Design for
Quality, PCIM Conference, Nuremmberg ,May,2004.
[4] Motto E., Gate Drive Techniques for Large IGBT
Modules, PCIM Magazine, 1996.
Fig.13. 30 min, 40KHz, Fig.14. Peak distributed
driver TC4421
power of switched transistor
Fig.15. Uds vs turn-off Fig.16. gate controlled dv/dt
for active-inductive load and two-stage commutation
The new driver with two-stage commutation is
combining the advantages of the standard driver in the
case of using small and big gate resistance namely: fast
transitional process, good stability and small over
voltage. Heating of the gate controlled power transistor
with gate resistors of 10Ω and 250Ω are given on fig.16
for the cases of standard driver TC4421 and two-stage
commutation driver. The investigations are done for
different control frequencies 10KHz, 20KHz, 30KHz
and 40KHz respectively at ambient temperature ta=21°С
30min after transistor turning-on.
The same
measurements have also been done with thermocouples.
4 Conclusion
Realization of driver circuits with negative feedback by
di/dt, dv/dt and two-stage commutation is explored.
Thermography approach is used for effectiveness
evaluation by measure MOSFET heating temperature.
The offered drivers can be realized as Integrated
Circuits. In that case the differentiated circuit elements
should be outside to be possible their values choice
according to power circuit parameters. Dynamical losses
and heating temperature of MOSFET transistor during
gate control by four different driver schemes are studied.
It is shown that the infrared thermography can be used
successful for evaluation of the energy control of switch
transistors in converters.
Acknowledgements
The authors would like to thank for the support of BME–
SIF under which contract 1-854/2007 the present work
was conducted
References:
[1] Stepherd W., Zhang L., Power Converter Circuits,
New Age Int., 2004.
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