H-Bridge and Direction Control

ECE 206: H-Bridge and Direction Control

Introduction
In previous labs, you have learned about
controlling and measuring the speed of a
(DC) motor. For this lab, we will introduce
the H-bridge circuit, which is made up of four
transistors (shaped as an H, as the name
would imply). For this lab, we will use two
pairs of complementary power MOSFETs,
but an H-bridge may also be built out of BJTs
or other transistors. What is important is to Figure 1: Experimental Setup
have a combination of both N and P type devices (hence, complementary pair). The N-type device (in
this case, N channel MOSFETs) will conduct when the gate voltage is ~1.5V (or more) higher than the
source voltage. The P-type device will conduct when the gate voltage is ~1.5V (or more) lower than
the source voltage. You should note that with the circuit in Figure 1, the two top transistors (P1 & P2)
are PMOS devices (arrow points into source), while the two bottom transistors (N1 & N2) are NMOS
devices (arrow points out of source). The small arrows also denote which direction the current should
flow in our circuit if that transistor is in the ON-state.
In the simple case where we are not concerned about speed control, the H-bridge is controlled by inputs A
and B, which will come from your Arduino. P1 and N1 share the same gate input A. P2 and N2 share the
same gate input B. As part of the prelab, you will fill in a truth table to understand how to control the
motor.

Prelab Deliverables:

Fill out the following truth table.
For each row:
1. The circuit state describes which state each of the 4 transistors are in.
2. You need to find the A and B inputs (HIGH/5V or LOW/0V) necessary to produce that desired
state. Note: Not all the combinations of 4-states are possible given only 2 inputs A and B. With
only A and B, we can produce 4 different input combinations, but there are 16 different possible
circuit states. Our limiting factor will be how we connect the MOSFETS in the circuit.
3. Assume the motor will spin clockwise if the current is in the direction indicated by the blue
arrow and counterclockwise if the current is reverse of the blue arrow, and no spin if there is no
current.

Circuit State Inputs Needed to
Produce Circuit State Motor Result
P1 P2 N1 N2 Possibility A-Input B-Input
OFF OFF OFF OFF Not Possible N/A N/A N/A
Modified 11/2/2020
OFF OFF OFF ON
OFF OFF ON OFF
OFF OFF ON ON
OFF ON OFF OFF
OFF ON OFF ON
OFF ON ON OFF
OFF ON ON ON
ON OFF OFF OFF
ON OFF OFF ON
ON OFF ON OFF
ON OFF ON ON
ON ON OFF OFF Possible 0V 0V Motor does not spin
ON ON OFF ON
ON ON ON OFF
ON ON ON ON

1. To have the motor spinning clockwise
a. A-input has to be HIGH/5V LOW/0V (Circle One)
b. B-input has to be HIGH/5V LOW/0V (Circle One)
2. To have the motor spinning counterclockwise
a. A-input has to be HIGH/5V LOW/0V (Circle One)
b. B-input has to be HIGH/5V LOW/0V (Circle One)


References:
• H-bridge https://en.wikipedia.org/wiki/H_bridge
• Also see references (linked on website) for 2SJ652 P-MOS and 2SK3703 N-MOS
Challenges:
• Build a circuit which can control the motor direction. Motor should be able to change speeds
according to user input (using either serial terminal, potentiometer, and/or the encoder knob) and
directions depending on which way the potentiometer/encoder knob is turned.


Procedure:
• Set up the circuit as shown in Figure 1. For each of the 4 transistors, make sure you connect the 3
legs properly. If you mix up matching the 3 legs to Gate/Drain/Source, you could create a short and
damage the circuit components. The DC power supply should not be giving more than 100mA.
• Demonstrate to your TA a working H-Bridge.

Report Deliverables:
• Provide descriptions with accompanying diagrams of your circuit and experimental setup. Include
annotated photographs of your experimental setups if you wish, but you must have circuit schematics
made from Fritzing. Circuit schematics are preferred over breadboard schematics, as breadboard
schematics tend to be less clear. Points will be taken off for incorrect/misleading/unclear schematics.
• Have your TA check verify your H-bridge. The motor should be able to spin in both directions, and
the speed of the motor should change depending on user input.
Report Element Value
Documentation of Lab Completion 40
Circuit Diagrams 30
Report Quality and all other elements 30
Total Possible Score 100/100