| Build
a 5A H-Bridge motor driver!
Using cheap
TIP127 and TIP122 transistors
Small & high efficiency home-made solution!
By
Ibrahim Kamal
Last update:
5/6/08
 Overview
In this article, I am going to show you how to build a relatively
High power H-bridge motor controller (which is the most common
way to control DC motors) With cheap TIP transistors..
My goals were:
1-To build a small module, that can be added to any robot
or any system where motor control is required.
2- To build a high efficiency device with a relatively high
continuous current rating.
5 Amperes
of continuous current through an H-bridge module may not seen
"high power" to some
of you, depending on your field and experience,
That's why i used the word "relatively".
But in the field of hobby electronics and robotics,
yes a controller capable of controlling motors with currents
as high as 5A at 24V is considered a high power device.
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Key Features:
5A Continuous current, 8A peak
High performance cooling system
Protection Circuit included
Compact
Design
Unexpensive components |
This article will be splitted in two main parts The
Theory and the Hardware construction
The
H-Bridge & DC Motors..
 The
H-Bridge is principally a configuration of 4 switches, that are
switched in a specific manner to control the direction the
of the current through the motor. (For brushed DC motors,
the direction of rotation of the armature of the motor is changed
by changing the direction of the current flowing though it). While
we are talking about DC motors, here is a small useful note to bear
in mind: "Current flowing though a motor is proportional
to the output torque, while the angular velocity (rpm) of the the
output shaft is proportional to the the voltage across the motor
windings"
Below is a simplified diagram showing the operation of the H-Bridge
configuration.
(you
can notice the shape of the schematic, it looks like an
'H' letter.. this is how this famous circuit got this name!)
There are 2 possible paths for the current:
1- The red path,
where the the current is directed to the motor through the
switches S3 and S2, causing
the motor to turn clockwise
2- The green path,
where the current is directed to the motor through the switches
S1 and S4, causing the
motor to turn anti-clockwise.
The only difference between this simple H-Bridge and the
real H-bridge module explained on this page, is that the
switches are replaced by Transistors, in order to electronically
control the flow of current in the motor, Hence, allowing
us to |
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control the speed and direction of the motor from
a microcontroller, for example.
In case you are a beginner or just not familiar with transistors,
I am going to explain in the next section most of what you need
to know about transistors to understand and build an H-Bridge.
Introduction
to switching transistors:
One very simple way to use transistors is to use them as switches,
to electronically control the flow of current though other electrical
elements. The same transistor may be used as a signal amplifier,
but this is the messy part of the transistor studies, and we don't
need this for our H-bridge. Using transistors as a switch is also
called "using transistors in saturation and cut-off
mode".
This schematic below simply shows the meaning of using a transistor
as a switch. the only difference between a mechanical switch and
a transistor switch is that a normal switch is turned ON or OFF
mechanically while a transistor switch is turned ON and OFF using
small
electrical currents
applied on the Base,
usually smaller than 20 mA. For
an NPN transistor, when a small current flows into the Base
of the transistor, current will flow from the Collector
to the Emitter,
otherwise, no current will through the CE junction (Collector-Emitter
junction). On the other hand, for a PNP transistor,
when a small current is allowed out from the base of the transistor,
current will flow from the Emitter
to the collector.
In order to use the transistor as a switch, the base voltage
has to be
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Higher than the Collector voltage (in case of NPN
transistor), or Lower than the collector voltage (in case of PNP
transistor). Also, to ensure the transistor is saturated, you must
calculate the suitable value of Rb shown in the
schematic (this will be discussed in detail later).
You may wonder why are there two different implementations of the
Transistor switch, one with NPN transistor, the
other with a PNP one. the answer is very simple.
it is to ensure that the base voltage is at a suitable level to
ensure the transistor is saturated whether it is connected to ground
or to 12V. (in the H bridge, 2 transistors are connected to 12V,
while the 2 others are connected to Ground.)
Base
Resistor calculations for an NPN transistor:
Calculating the suitable Base resistance for an
NPN transistor is very easily done by following those steps:
1- Depending on the transistor you are using, gather
from the datasheet the following values. sometimes for beginners,
finding those values in the datasheet, or the nearest suitable values,
need some patience!
| VBE |
The voltage
drop between the Base and the Emitter |
| IBmax |
The maximum current that
can flow into the Base without damaging the
transistor (also called Ib Peak in some datasheets) |
| HFE |
The current gain of the
transistor |
2- chose a suitable value for Ibase
but without getting too close the the value of Ib max.
The value of Ib you choose must be enough to drive the transistor
and deliver the required Collector Current: [ Ib
= Ic / HFE ] (where
HFE is the current gain of the transistor).
You can always choose a value of Ib higher than
what you've calculated, it's even better, as long as it is lower
than the Maximum base current specified in the datasheer.
3-Calculate the volt across the resistance Rb.
Assuming you are controlling the device with a Standard CMOS or
TTL compatible device (5v and 0v outputs):
[ Vr = 5 - Vbe ]
4- Now that we know the voltage across the resistance
(Vr), and the current flowing into the Base through
that resistance, we can calculate its value:
[Rb = Vr/Ib]
Or,
[Rb = (5-Vbe)/Ib]
Another approach by John Hewes in this very interesting
article about switching
transistors is to use this formula:
RB = |
Vc × hFE |
where
Vc = the supply voltage of the device driving the base of
the transistor (5v in our TTL example)
(Ic is multiplied by 5 as a safety factor)
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5 × Ic |
Base
Resistor calculations for a PNP transistor:
Since NPN and PNP transistors react the same way
(except all polarities are inverted), You can choose the same base
resistor for both types. For the H-bridge circuit, you can calculate
the value of the Base Resistors for the NPN transistors and use
the same value for the PNP transistor.
The
applied circuit
This is the electronics circuit of the device you've
seen in the picture at the top the document.
It will be presented to you in 4 main sections, each one shaded
with a different color.
1- The Protection And Logic circuit, shaded in light yellow.
3- The H-Bridge, composed of the 2 TIP122 and 2 TIP127 Transistors,
shaded in light red.
4- The Fan connections and the 'Power on' LED.
Click on any shaded part to jump to the corresponding explanation
in the rest of the document.
Note:
Any
transistor that is not labled in the schematic, is a 2N2222
BJT
The
protection and Logic circuit:
This
section's job is to prevent the controller device from giving destructive
orders to the H-Bridge, like turning ON all 4 transistors at the
same time (this would cause a terrible short circuit, destructing
at least one or 2 of the transistors)
It also has the function of taking the input
from another control circuit (a microcontroller or any control
device that will control the H-Bridge) with a minimum number of
input wires, and, through this simple gate array, control the 4
transistors.
Each one of the 4 end transistor of this stage (Q1, Q2, Q3 and Q4)
have the function of inverting the signal and performing voltage
& current amplification. They provide Active turn OFF
output to control the power transistors of the H bridge.
Active Turn Off, means that when the transistor is OFF, it provides
output through a pull up or pull down resistor, but when turned
ON, they switch off what ever device attached to their output. Active
Turn OFF provide a smaller Turn-OFF time, increasing the H bridge
performance.
Note that NPN transistors like the TIP122 are switched OFF by applying
a 0V on its base, while a PNP transistors like the TIP127 are switched
OFF by applying a High (12v) on its base.
The 4 resistors R2, R4, R5 and R10
must be at least 1/2 W rating in order to sustain high currents
passing through it, especially if you intend to use this H bridge
with a 24V power supply.
In the truth table below, the 3 inputs to the gates (P1,P2
and P3) and their relation with the outputs of 4 end transistors
in the yellow area (Q1,Q2,Q3 and Q4).
Inputs |
Outputs |
Result
on the H-bridge
|
P3 |
P1 |
P2 |
Q1 |
Q2 |
Q3 |
Q4 |
0 |
X |
X |
1 |
1 |
0 |
0 |
Motor
is Freewheeling |
1 |
0 |
0 |
1 |
1 |
1 |
1 |
breaking the motor (0v
at both leads) |
1 |
0 |
1 |
1 |
1 |
0 |
0 |
Turn
the motor clockwise |
1 |
1 |
0 |
0 |
0 |
1 |
1 |
Turn
the motor anti-clockwise |
1 |
1 |
1 |
0 |
0 |
0 |
0 |
breaking the motor (12v
at both leads) |
*(X mean Don't care), 1 = High level Voltage, 0
= Low level voltage.
The Input P3 is the 'Enable' input. Any professional
H-Bridge, have an enable input to turn On or Off the whole motor
controller, and when turned off, the motor should act as if it wasn't
connected to anything (High Impedance). and this exactly what the
pin P3 does in this circuit. This functionality
is mostly used to control the speed of motors using PWM (pulse width
modulation). I am not going to explain what is PWM in this tutorial,
but briefly PWM is a way to control the speed of a DC motor by turning
it ON and OFF very fast, varying the ON time and the OFF time will
affect the speed of the motor.
All the values of the resistors are calculated using the formulas
at the top the document, to ensure all transistor are in saturation
mode, especially the 4 TIP transistors.
The
H-Bridge, composed of the 4 TIP Transistors:
TIP122/TIP127 are power transistors, each one composed
of 2 transistors in series in one integrated package, with a current
gain of 1000 (which is very high for transistors, causing it to
saturate very easily) which makes this transistor very suitable
to be used as a switch or in an H-Bridge configuration.
The Diodes D2 to D5 are very important to protect the Transistors
from the Back E.M.F. voltages produced by any inductive loads when
switched ON or OFF. (DC motors are inductive loads that can cause
important back E.M.F. currents)
Note that the TIP122/127 have integrated protection diodes,
but we added more diodes as a factor of safety.
| J5 is the jack to connect the motor. |
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The
Fan connections and the 'Power on' LED:
Nothing critical about this part, just a connection
to power the FAN to cool the transistors, and a red LED as a status
to show whether the module is powered or not.
PART
2: Hardware construction |
Now let's see how to construct this H-bridge module.
Note that I'm am not going to show you how to make PCBs, you can
learn this anywhere on the net.
An
overview on The PCBs
As you can see there are 2 boards. One of them is
the PCB which will hold the control circuit with the 4 TIP transistors.
The
other is a heat sink board. actually its a PCB on which i've
printed 2 regions, all in copper. (those copper surfaces will
act a good heat sink when firmly attached to the transistor)
Why Divide the heat sink in 2 regions? simply because the
the back of the transistor that dissipates heat is internally
connected to the collector of the transistor, thus each group
of 2 transistors (TIP122 & TIP127) have to be electrically
isolated from the other 2 transistors.
Below is a view of the TIP122 and TIP127 mounted
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on the heat
sink board. notice there are still 4 unused holes. those
will be connected to the Fan and to the main board. |
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Main PCB |
The
assembly
After
the PCB is ready and all components are soldered, plug the
FAN+Heat sink+Transistors in the main board.
If your drilling is accurate, the assembly process should
be very easy.
Notice How the 6 pins connector is firmly soldered to the
wires by the mean of a piece of PCB. This will make a very
rigid connector.
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Now you're done with the construction of the H-bridge
module, start testing your H-bridge with constant currents up to
5A, and peak currents of 8A or even more.. i didn't try beyond this
limit!
Download
the zip file for this project
containing the full schematic, PCB designs and datasheets
to all used transistors.
[note: i use ExpressPCB(FREEWARE)
to design the schematics and the PCB]
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Preview of the last 15
messages discussing this page. Messages are sorted from the newest to
the oldest. |
Posted
by:
ikalogic
on:
04 Sep 2008 |
Re: I want to have my DIY CNC controller |
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| Quoting williamkmcn: I want to build a CNC mill, as I found in the internet, most of them were not "DIY kit" but commercial fully installed set only. Could you give me a good suggestion in motor controlling? |
Yes, i can, but what type of motor are you using? What is the power rating? What voltage? What current rating? 
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Posted
by:
williamkmcn
on:
10 Aug 2008 |
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I want to have my DIY CNC controller |
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I want to build a CNC mill, as I found in the internet, most of them were not "DIY kit" but commercial fully installed set only. Could you give me a good suggestion in motor controlling?
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Posted
by:
kemo0o
on:
12 Jul 2008 |
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Posted
by:
ikalogic
on:
12 Jul 2008 |
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Re: 5A H-Bridge motor controllers |
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Quoting kemo0o:
Quoting ikalogic:
kemo did you make any of those H-B on your own? can you share some pics? |
Do You Mean That i make own design For H-Bridge
Or i make yours ??  |
I mean did you build this H-Bridge? for your own robot? if you did, then i would like to see some pics.
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Posted
by:
kemo0o
on:
12 Jul 2008 |
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Re: 5A H-Bridge motor controllers |
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Quoting ikalogic:
kemo did you make any of those H-B on your own? can you share some pics? |
Do You Mean That i make own design For H-Bridge
Or i make yours ??
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Posted
by:
ikalogic
on:
11 Jul 2008 |
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Re: 5A H-Bridge motor controllers |
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Quoting kemo0o: it isn' the 5th TIP
It is Regulator ( LM 7805 ) 
About The components , It is shown in the schematic 
just count them |
kemo did you make any of those H-B on your own? can you share some pics?
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Posted
by:
kemo0o
on:
11 Jul 2008 |
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Posted
by:
irongoat
on:
11 Jul 2008 |
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5A H-Bridge motor controllers |
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Another question regarding this circuit :
What is U2? It looks to be a 5th TIP on
the picture, but the schematic does not
include a 5th tip.
PS. Can you post a parts list? It would
greatly simplify construction.
Thanks much,
Charles
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Posted
by:
hex0r
on:
06 Jul 2008 |
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5A H-Bridge motor controllers |
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Hello .
How can i connect R\C Reciver to this schimatic (a standard remote controller reciver)
and if its posiable to change the schimatic to work with a 7 kgm 900rpm 12v dc motor
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Posted
by:
ikalogic
on:
03 Jul 2008 |
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Re: 5A H-Bridge motor controllers |
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Quoting irongoat: Greetings,
Im in the midst of building this project, but I have a small concern.
Will the PCB traces withstand 5A if they are a bit "dotty"? I used
the toner transfer method in order to produce the PCB, and my best
print out of several trials resulted in small dots/holes in the copper.
They aren't too bad, but at a few points, it cracks up the trace. At
these points I have tried to solder-reinforce them.
Also, I am planning on connecting this to a car battery and a
motor which draws 4.5 amps. Is there any worry about arching
on the board? Should it be cooled as well as heat sinked?
Thank you much
Charles |
Hello,
As for the tracks, it's hard to say.. your best way to find out is to try.. however i don't think it'll be your major problem.
About the heat sinking, well i think that for as much as 4.5 Amps, heat sinking+fan colling is advisable... good luck
by the way, if you can take some pics of your finished product, could you post them here? it's nice to see how the work was applied elsewhere
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Posted
by:
irongoat
on:
03 Jul 2008 |
|
5A H-Bridge motor controllers |
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Greetings,
Im in the midst of building this project, but I have a small concern.
Will the PCB traces withstand 5A if they are a bit "dotty"? I used
the toner transfer method in order to produce the PCB, and my best
print out of several trials resulted in small dots/holes in the copper.
They aren't too bad, but at a few points, it cracks up the trace. At
these points I have tried to solder-reinforce them.
Also, I am planning on connecting this to a car battery and a
motor which draws 4.5 amps. Is there any worry about arching
on the board? Should it be cooled as well as heat sinked?
Thank you much
Charles
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Posted
by:
ikalogic
on:
13 Jun 2008 |
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Re: 5A H-Bridge motor controllers |
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| Quoting blrmkr: Thank you for the tuitorial!! I have a question about R1 and R9. They seem to be marked as 3k8. What is a 3k8 resistor? Or am I just reading the schematic wrong? Thank you very much for your help. |
3k8 means 3.8 KOhm
exactly like 3M8 would mean 3.8 mega ohms, or also 3800 Kohm or ahain 3 800 000 ohm!
you can see it this way: The prfix"k" or "M" is used also as a decimal point, to simplify the reading. This a convention that you'll find everywhere
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Posted
by:
blrmkr
on:
13 Jun 2008 |
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5A H-Bridge motor controllers |
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Thank you for the tuitorial!! I have a question about R1 and R9. They seem to be marked as 3k8. What is a 3k8 resistor? Or am I just reading the schematic wrong? Thank you very much for your help.
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Posted
by:
ikalogic
on:
10 May 2008 |
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Re: 5A H-Bridge motor controllers |
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Quoting HeX0R:
HI i dont remember the motor info, i need to talk with my friend.
But i know that eche motor need 65 Amper... |
well.. 65Amps >>>> 5 Amps!
This H-bridge is not for your application..
However.. 65Amps seems huuuuuuge...!!! are you sure about that?
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