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Rowan Hall 238A
http://rowan.jkbeard.com
April 09, 2006
Sophomore Clinic ENGR 01-202 5, CRN 20686Integrating the PIC and the H-Bridge
James K. Beard, Ph.D.
Sophomore Clinic IIApril 09, 2006 Slide 2
Topics
Driving the MOSFETs from 5 Volts
The pin out of the H-bridge
Connecting the H-bridge and the PIC board
Sophomore Clinic IIApril 09, 2006 Slide 3
MOSFETs in Switching
Switching properties Off
When they’re off, they’re off Gate-source voltage must be below threshold voltage
On When they’re on, the drain-source resistance is very, very
low The achieved on resistance is a function of the drive voltage Drive must be much higher than the threshold voltage
5 Volts drive provides sufficient drive
Sophomore Clinic IIApril 09, 2006 Slide 4
On V-I Characteristics
N-Channel P-Channel
Sophomore Clinic IIApril 09, 2006 Slide 5
Conclusion
Typical characteristics from the IRC data sheets N-channel is IRFZ24N P-channel is IRF9Z24NPbF
Data sheet shows N-channel on resistance of 1/8 Ohm P-channel on resistance of 2/5 Ohm Both limit current to about 2.5 A
Good to go for Sophomore Clinic Project motor drives
A good choice for magnet drive – switch directly from the PIC
Sophomore Clinic IIApril 09, 2006 Slide 6
Pin-Out of the H-Bridge Board
Power connector+5 Volts, ground from the railsPower to the motors comes from here
Connectors for the motors Three redundant ground connections Eight lines to the PIC board
Sophomore Clinic IIApril 09, 2006 Slide 7
1 3 5 7 8 6 4 2
A B C DG 5
G2 G4 G1 G3 G6 G8 G5 G7
G2
G1G3
G4
VDD
H12 H34
H78 H56 H34 H12
Sophomore Clinic IIApril 09, 2006 Slide 8
The H-Bridge Drive
The MOSFETs are complementary – The P-channel is driven by the reverse polarity signal to the gate +5 Volts is OFF Ground is ON
We want to drive them form the PIC hardware, not the software
Solution We use the PWM output of the PIC We use the motor direction toggle from the PIC We drive the H-bridge with hardware using these
signals
Sophomore Clinic IIApril 09, 2006 Slide 9
Interface Circuitry
G2 G4 G1 G3 G6 G8 G5 G7
Toggle PWM
G4
G1
G2
G3
From PIC
To H-Bridge
Sophomore Clinic IIApril 09, 2006 Slide 10
The Chips
CMOS to provide full 5 Volt swing on logic one
4000 series to allow use in other circuits up to 15 Volts
Two-chip solution for both motorsCD4011 or MC14011 quad NANDCD4069 or MC14069 hex inverter
Sophomore Clinic IIApril 09, 2006 Slide 11
Chip Pin-Outs
Sophomore Clinic IIApril 09, 2006 Slide 12
Wiring the Interface Logic:
G2
G4
G1
G3
G6
G8
G5
G7
C0 C1 C2 C3 C4 ... ... ...
PIN 14: HOOK TO +5VDC
PIN 7: HOOK TO GND
TAKE YOUR TIME – TRIPLE CHECK EVERY CONNECTION!
Errors here can cause permanent damage to the uC board and/or H-Bridge!
CD40111 7
14
2 3 4 5 6
13 12 11 10 9 8
On both ICs:
CD40691 2 3 4 5 6 7
14 13 12 11 10 9 8
Sophomore Clinic IIApril 09, 2006 Slide 13
The Interface Logic Wired
Sophomore Clinic IIApril 09, 2006 Slide 14
Electromagnet Drive Circuit
D SG
Electromagnet
220 OutputFrom PIC
+5 VoltsFrom RailOr H-Bridge
IRFZ24NN-ChannelMOSFET (same one thatthe H-bridge uses)
GS
D
