1

EE462L, Spring 2014H-Bridge Inverter

(partially pre-fall 2009 version)

2

Fuseholders and 10A fuses for DC input not shown in this photo

10µF input ripple current capacitor across DC input

LC output filter (100µH, 10µF)

To minimize your time and produce an inverter that works properly, it is very important that you follow the procedure in the lab document

3

VGS of A+

VGS of A–

blanking time to eliminate overlap

actual MOSFET turn on

Save screen snapshot #1

Multimeter check of VGS for

A+ and A–. Expect about 4.0Vdc.

Simultaneously View VGS for A+ and A−

(use both scope ground leads)

Asymmetrical firing circuit produces slow turn on, fast turn off, to provide blanking

A− Off A+ On

You must avoid overlap in “on” times

!

4

Once the H-Bridge is wired, you cannot simultaneously view VDS

of A+ and A− (or B+ and B−) on the scope because their source nodes are not the same

But you can simultaneously

view

VDS on A+, and −VDS on A−,

and then

VDS on B+, and −VDS on B−,

to check for overlap

+

VDS of A+

–

–

VDS of A–

+

A+ off

A– on

A+ on

A– off

+

VDS of B+

–

–

VDS of B–

+

B+ off

B– on

B+ on

B– off

5

Loaded (with a resistor) and no output filter

Load Voltage – No Filter. ma 1.

!

6

With Filter

Load Voltage – With Filter. ma 1.

Very Effective!

!

7

The Filter Has a Cutoff Frequency of About 5kHz

+

Vac output

–

10µF, 50V, bipolar, high-frequency capacitor

100µH, 9A or 10A inductor

Point “a” in H-bridge

Point “b” in H-bridge

a b

+ Vac output −

symbolic

8

Transfer Function

+Vacoutput−

+Vac

input−

Inverter Filter Vout/Vin

0

0.5

1

1.5

2

2.5

3

3.5

4

1 10 100 1000 10000 100000

Hz

Vo

ut/

Vin 12ohm

8ohm

4ohm

L = 100µh

C = 10µF

R = 12, 8, or 4Ω

9

Your circuit

10

Effect of the carrier frequency

11

Effect of the carrier frequency