High Efficiency Power Converters Using Gallium Nitride Transistors

Marl NakmaliMentors:

Dr. Leon TolbertYutian Cui

Room for Improvement

5-2

Material Properties and Limitations

5-3

Size Minimization

5-4

Data Sheet Comparison

5-5

  Gallium Nitride Silicon

VDS [V] 30 30

RDS(on) [Ω] 0.001 1.3

ID [A] 60 42

VGS [V] -4<VGS<6 -20<VGS<20

Size [mm2] 13.915 30

But what about the price?

5-6

How it works

5-7

The Buck Converter

5-8

The Buck Converter

5-9

The Buck Converter

5-10

Loss Analysis

5-11

These losses are:• Switching Loss• Conduction Loss

Results

5-12

Efficiency Graphs

5-13

11.995 23.977 36.0380

0.10.20.30.40.50.60.70.80.9

1

3V Input Performance

Output Power [W]

Effi

cie

ncy

GaN: Silicon:

200kHz600kHz1MHz

200kHz600kHz1MHz

Efficiency Graphs

5-14

11.996 23.992 35.9810

0.10.20.30.40.50.60.70.80.9

1

4V Input Performance

Output Power [W]

Effi

cie

ncy

GaN: Silicon:

200kHz600kHz1MHz

200kHz600kHz1MHz

Efficiency Graphs

5-15

11.991 24.006 35.9770

0.10.20.30.40.50.60.70.80.9

1

5V Input Performance

Output Power [W]

Effi

cie

ncy

GaN: Silicon:

200kHz600kHz1MHz

200kHz600kHz1MHz

Efficiency Graphs

5-16

11.996 23.994 35.9880

0.10.20.30.40.50.60.70.80.9

1

6V Input Performance

Output Power [W]

Effi

cie

ncy

GaN: Silicon:

200kHz600kHz1MHz

200kHz600kHz1MHz

Silicon Switching Period

5-17

GaN Switching Period

5-18

GaN Physical Switching Period

5-19

Conclusion

5-20

Gallium Nitride has:• Desirable material

properties in a transistor.• High frequency, allowing

smaller circuits.• Development into

becoming cheaper.

Applications:• Smaller, more efficient

power converters.• Faster, more reliable

data transfer.

Acknowledgements

This work was supported primarily by the ERC Program of the National Science Foundation and DOE under NSF Award Number EEC-1041877.

Other US government and industrial sponsors of CURENT research are also gratefully acknowledged.

21

Questions and Answers

22

5-23

Power Converters

A power converter converts electrical energy from:• AC to AC• AC to DC• DC to AC• DC to DC

Types of DC to DC converters:• Step Down (Buck) Converters• Step Up (Boost) Converters

Result Analysis

• Put in efficiency of simulation versus efficiency of measured values

• Compare these efficiencies with data from Silicon OptiMOS directFET

What is existing technology?

Silicon MOSFETs• Currently the industry is

mostly reliant on Silicon MOSFETs

• It has a cheap price• Its manufacturing processes

are matured• It is already in enhancement

mode, which is easier and safer

GaN MOSFETs• GaN MOSFETs are not as

cheap• Its manufacturing processes

are not yet mature• It is not inherently in

enhancement mode and steps must be taken for it to be in that mode

Switching Loss

5-27

• How do we make it smaller? We could make the die area small which will decrease the

capacitance which in turn decreases the tsw but this will raise the Rdson

Change the material and we can minimize both

Conduction Loss

5-28

• How do we make it smaller? We could increase its area to lower the resistance, but it will

increase the capacitance of the device, causing longer transient time, and larger passive components

We could change to a more conductive material

Gate Loss

5-29

• How do we make it smaller? By making a smaller die, the body capacitance is much smaller

so less charge is needed and smaller voltages can drive the gate

We can use a different material