EE462L, Spring 2014
H-Bridge Inverter
(partially pre-fall 2009 version)
1
To minimize your time and produce an inverter that works properly, it
is very important that you follow the procedure in the lab document
LC output filter
(100µH, 10µF)
Fuseholders and 10A fuses for
DC input not shown in this photo
10µF input ripple
current capacitor
across DC input
2
!
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
blanking time to
eliminate overlap
actual MOSFET
turn on
Multimeter check of VGS for
A+ and A–. Expect about
4.0Vdc.
VGS of A+
VGS of A–
Save screen
snapshot #1
A− Off
A+ On
You must avoid overlap in “on” times
3
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
A+ off
A+
on
A– on
A–
off
+
VDS of A +
–
–
VDS of A –
+
But you can simultaneously
view
VDS on A+, and −VDS on A−,
and then
VDS on B+, and −VDS on B−,
B+ off
B+
on
B– on
B–
off
+
VDS of B+
–
to check for overlap
–
VDS of B–
+
4
!
Loaded (with a resistor) and no output filter
Load Voltage – No Filter. ma  1.
5
!
With Filter
Load Voltage – With Filter. ma  1.
Very Effective!
6
The Filter Has a Cutoff Frequency of About 5kHz
a
100µH, 9A or 10A
inductor
b
+
Vac
output
−
symbolic
Point “a” in H-bridge
+
Vac output
10µF, 50V, bipolar,
high-frequency
capacitor
–
Point “b” in H-bridge
7
Transfer Function
+
Vac
input
−
L = 100µh
+
Vac
output
−
C = 10µF
R = 12, 8, or 4Ω
Inverter Filter Vout/Vin
4
3.5
Vout/Vin
3
2.5
12ohm
2
8ohm
1.5
4ohm
1
0.5
0
1
10
100
1000
10000
100000
Hz
8
Your circuit
9
Effect of the carrier frequency
10
Effect of the carrier frequency
11