I. Overview of H-Bridge Motor Controller:
The H-Bridge is basically a motor reversing circuit that is able to be switched very rapidly. The ability
for the circuit to be switched on and off very rapidly allows the use of a pulse width modulation, or
PWM signal to control the circuit. As the PWM signal is applied to various transistors within the HBridge, the result is an average voltage applied to the motor, or load varies with the duty cycle of the
PWM signal. At 100% duty cycle, the load will have 100% of the source voltage applied across it. At
50% duty cycle, the load will experience an average voltage of ½ that of the source voltage. Varying
the average voltage applied to a motor will ultimately affect its speed of rotation, and torque output.
Being able to control the angular velocity of the motor will allow the platform to move at various
speeds. In addition to controlling speed of the motor, the H-Bridge also allows for motor reversing.
Applying the same PWM signal to the opposite pair of transistors will have the same affect as before,
except this time the polarity of applied voltage across the DC motor changes, resulting in rotation of
the armature in the opposite direction.
II. Proposed Concepts
A. H-Bridge from P07021
The first candidate for the H-Bridge system is the one which was designed by a previous RIT
Senior Design Team.
1. Pros:
a) Already designed
b) Simple design
2. Cons:
a) Low power output
b) Thermal problems
B. H-Bridge Driver IC and a custom designed NMOS Bridge
Figure 5.2.1: Schematic of HIP4081A H-Bridge Driver and NMOS Bridge
The figure above shows how the Harris Semiconductor HIP4081A NMOS H-Bridge driver IC
would be implemented with a NMOS Bridge. The HIP4081A allows the upper NMOS to be
turned fully on as the IC has a pump circuit which allows the gate of the NMOS to be driven
higher than the supply voltage, thus achieving a VGS which is much greater than the threshold
voltage. For this reason, the H-Bridge can be constructed of all NMOS transistors, which have
a much lower RON than their PMOS compliments.
1. Pros:
a) Low resistance through bridge
b) High power efficiency
c) NMOS Bridge can be customized for application
2. Cons:
a) Not completely open source
b) Higher complexity
C. Custom Complimentary MOSFET H-Bridge Design with built in Driver
Figure 5.2.2: Schematic CMOS H-Bridge Logic Circuitry
Figure 5.2.3: Schematic of CMOS H-Bridge
The figures above show the Complementary MOSFET H-Bridge design. The way this design
functions is that there is a direction and PWM signal from the main controller. The direction bit
is used to turn on (continuously) one of the upper PMOS transistors. The NMOS transistor
connected to the other side of the load is pulsed on and off by means of the PWM signal. This
allows for just 1 transistor to be switched resulting in less dynamic power consumption.
However, compared to other NMOS bridges, the on resistance will be slightly higher due to the
use of PMOS transistors. As a benefit, there is no need for a pump circuit or driver, resulting in
lower cost and reduced complexity.
Figure 5.2.4 shows simulation results of the proposed circuit. In particular it shows the voltage
applied to the load, PWM input, as well as current through the load.
Figure 5.2.4: Simulation of CMOS H-Bridge
1. Pros:
a)
b)
c)
d)
e)
High power efficiency
Has integrated E-Stop and brake
Does not require NMOS driver pump circuit
Inexpensive
Open Source
2. Cons:
a) Requires PCB layout and assembly
b) Slightly higher RON due to PMOS
D. Off Shelf H-Bridges
Figure 5.2.5: Tecel Microcontrollers D200 Model H-Bridge
Figure 5.2.6: Robot Power Simple-H
Figures 5.2.4 and 5.2.5 are two examples of off the shelf, assembled H-Bride solutions. These
are similar to the circuits mentions previously, except here all the design, building and testing
have already been performed. In addition to these perks, some of the available off the shelf
board have additional functionality than the circuits previously mentioned. Some are available
in multiple channel models and may come with LED indicators or cooling fans. Some also
incorporate dynamic motor braking depending upon certain inputs to the module. Data for
these particular boards can be seen in table 5.2.1.
1. Pros:
a) High power efficiency
b) May have braking functions
c) Ready to use
2. Cons:
a) Expensive
b) Not open source
c) May not be optimized for application
III. Selection Criteria
Model
P07201
Imax
Icont
5A
Vpower
24V
Vlogic
5V
Input Form
PWM
Frequency
RON
Static Power Loss
2A Draw
10A Draw
Price w/o E-Stop
HIP4081A
CMOS
D200
Simple-H
75A
30A
15 to 30V
5V
PWM
0 to 10kHz
0.008 Ω
50A
36A
5 to 40V
3 to 5V
PWM
0 to 10Khz
0.018 Ω
45A
10A
55V
5V
PWM
-
45A
20A to 25A
24V
3 to 5V
PWM
0 to 20kHz
0.016 Ω
60 mW
1.6 W
140 mW
3.6 W
~$24 + PCB
~$15 + PCB
130 mW
3.2 W
$35.00
$79.99
Table 5.2.1: Option Specifications
H-Bridge
Manufacturability
Cost
Efficiency
Modularity
Open Source
Robust
Size
Durability
Total
P07021
0
0
0
0
0
0
0
0
0
MOSFET Design
+
0
+
+
+
+
+
3
Table 5.2.1: Pugh's Matrix for Motor Driver Systems
Off Shelf
0
0
+
0
+
0
+
2
H-Bridge
Manufacturability
Cost
Efficiency
Modularity
Open Source
Robust
Size
Durability
Total
Weight
20.0%
20.0%
12.5%
12.5%
10.0%
10.0%
10.0%
5.0%
100%
Rating
5
2
3
3
2
2
4
2
23
P07021
Weighted Score
1
0.4
0.375
0.375
0.2
0.2
0.4
0.1
3.05
MOSFET Design
Rating
Weighted Score
2
0.4
5
1
4
0.5
5
0.625
5
0.5
3
0.3
3
0.3
4
0.2
31
3.825
Rating
3
1
4
3
1
4
1
4
21
Off Shelf
Weighted Score
0.6
0.2
0.5
0.375
0.1
0.4
0.1
0.2
2.475
Table 5.2.3: Weighted Pugh's Matrix for Motor Driver Systems
Both the weighted and non weighted Pugh’s matrixes in Table 3.1.2 and Table 3.1.3 show that
the Custom MOSFET design has the highest ratings. The team decided that ease in
manufacturing, cost, modularity and power efficiency were among the most important aspects
to rate the different designs.
IV.
Conclusion
The in-house CMOS design was chosen by the platform team as the best overall design for
this project. Being completely designed and built in house, the design is completely open
source. It also allows the team to design the unit to custom fit the rest of the system both
electronically as well as mechanically. These custom boards can be designed to be stackable
so that they can easily be added or removed as needed, making for a very modular system.