This document discusses controlling high power devices using microcontrollers. It covers using transistors as switches to interface microcontroller outputs with higher voltage/current loads. Specific circuits are presented using Darlington transistors, optocouplers, and relays to control loads like motors and lamps. The document also describes an H-bridge circuit to control the direction of a DC motor using either relays or transistors. Integrated circuits like the L298N are introduced for easily implementing an H-bridge.

1. 1
02-Interfacing High
Power Devices
By : Mohamed Fawzy
Programming AVR Microcontrollers
© Mohamed F.A.B 2015

2. Lecture Notes:
2
o Set Your Phone To Vibration Mode.
o Ask any time.
o During labs, Feel Free To Check Any Materials or
Internet.
o Slides are self content.
o Feel Free To Share This Materials With Your Friends.
o Work Hard For Achieving Most Of This Course.
© Mohamed F.A.B 2015

3. 3
Don't Forget !!!!
© Mohamed F.A.B 2015
Any Expert Was Once A Beginner


4. 4
Agenda.
Lesson (6):
Control High Power Devices By MC.
Lesson (7):
Interfacing DC Motor and Control Its Direction.
© Mohamed F.A.B 2015
Lesson (8):
Interfacing Stepper Motor.

5. 5
Lesson(6).
© Mohamed F.A.B 2015
Lesson (6):
Control High Power Devices By MC.

6. 6
Lesson (6) Topics.
© Mohamed F.A.B 2015
►Transistor Overview.
►Using Transistor as a Switch.
►Darlington transistor array (ULN2003 & ULN 2803).
►Opto-coupler Overview.
►Control 12VDC with MC.
►Relay Overview.
►Control High Power Devices 220 VAC.

7. 7
Transistor Overview.
© Mohamed F.A.B 2015
o There are two types of transistors:
PNP TransistorNPN Transistor
NPN is the most common used transistor, so we only
cover it in our tutorial.
NOTE:
o There are two Applications of transistors Usage:
o Transistor as a switch.
o Transistor as an Amplifier.

8. 8
Transistor Parameters.
© Mohamed F.A.B 2015
IC
IE
IB VCE
VBE
+
-
+
-
IE=IB+IC
IB is very small
So, IE=IC
VBE(sat)=0.7 Volt(Datasheet).

9. 9
Transistor Operation Regions.
© Mohamed F.A.B 2015
Cut-OFF Region
 The input and Base are grounded ( 0v ).
 Transistor is “fully-OFF” (Cut-off region).
 No Collector current flows ( IC = 0 ).
 VOUT = VCE = VCC.
 Transistor operates as an “open switch”.
Saturation Region
 The input and Base are connected to VCC.
 Transistor is “fully-ON” (saturation region).
 Max Collector current flows ( IC = Vcc/RL ).
 VCE = 0 ( ideal saturation ).
 VOUT = VCE.
 Transistor operates as a “closed switch”.
In this two regions, transistor Work as a switch.
NOTE:

10. 10
Cont’
© Mohamed F.A.B 2015
VBE
0.7
IB
Ic
Cut-OFF
Saturation

11. 11
Transistor As a switch?
© Mohamed F.A.B 2015
 Most of microcontrollers work within 5
volt environment and the I/O port
can only handle current up to 20mA.
 if we want to attach the
microcontroller’s I/O port to different
voltage level circuit or to drive
devices with more than 40mA, we
need to use the interface circuit.
 There are Popular methods:
 Transistor as a switch.
 Opto-Coupler.
 Relay.
 Contactor.

12. 12
Designing Transistor as a switch circuit .
© Mohamed F.A.B 2015
find the minimum Base current required to turn the transistor
“fully-ON” (saturated) for a load that requires 200mA of
current when the input voltage is increased to 5.0V. Also
calculate the new value of RB.
Ic Is the current needed for switching the load.
ß Founded in Datasheet for transistor.
NOTE:
Example.

13. 13
NPN Transistors.
© Mohamed F.A.B 2015
Transistor V IC ß
BC547 45V 100mA 110
2N3904 40V 200mA 100
BC517 30V 500mA 30000
BC337 45V 800mA 100
2N2222 40V 1A 200
BD139 80V 1.5A 40
TIP31A 60V 3A 100
TIP41A 60V 6A 30
TIP120 60V 5A 1000
TIP142 100V 10A 500
2N3055 60V 15A 10

14. 14
Example.
© Mohamed F.A.B 2015
Vin
5V
We need to control LED which work with 3V and 20mA DC by
small signal 3.3v.
Here, we can choose BC547 (Vce =45V, Ic=100mA, ß=110).
=
20𝑚𝐴
110
= 0.182𝑚𝐴
=
3.3 − 0.7
5 ∗ 0.182
= 2.857𝐾Ω
Here, result is IB in active region, to get IB
in saturation we need to multiply IB by 5
or 10.
NOTE:
Typical Value for 2.857 𝑲𝜴 is 2.7 𝑲𝜴
P(RB)=RB * (𝐼𝐵)2 𝑤𝑎𝑡𝑡

15. 15
Example.
© Mohamed F.A.B 2015
We need to control a DC Motor Work with 24V by small signal(5V).
Vin
24VIc(max for motor)=
24
𝑅(𝑚𝑜𝑡𝑜𝑟 𝑐𝑜𝑖𝑙)
=
24𝑉
17Ω
=1.4A
Here, we will choose TIP41.(Vce=60V, Ic=6A, ß=30).
=
1.5
30
= 0.05𝐴
=
5 − 1.8
5 ∗ 0.05
= 12.8Ω
Typical Value for 12.8𝜴 is 10𝜴
P(RB)=RB * (𝐼𝐵)2 = 10 ∗ (0.25)2 = 0.625 𝑤𝑎𝑡𝑡
So, we must choose 1 watt Resistor.
Why using Flywheel Diode?

16. 16
Darlington Transistor.
© Mohamed F.A.B 2015
Vcc Sometimes the DC current gain of the
bipolar transistor is too low to directly
switch the load current or voltage, so
multiple switching transistors are used.
 the current gain of the first transistor is
multiplied with that of the current gain
of the second transistor to produce a
device which acts like a single
transistor with a very high current gain
for a much smaller Base current.
if the first input transistor has a current gain of 100 and the second switching
transistor has a current gain of 50 then the total current gain will be
100 x 50 = 5000. So for example, if our load current from above is 200mA, then the
Darlington base current is only 200mA/5000 = 40uA. A huge reduction from the
previous 1mA for a single transistor. Ic=IB* ß
Example.

17. 17
ULN2003 & ULN2803.
© Mohamed F.A.B 2015
 It is an array of some Darlington transistors in one package.
 ULN2003 contains 7 channels but ULN2803 contains 8 channels.
We can use diode connected to COM as a flywheel diode.
NOTE:

18. 18
Opto-Coupler (Optoisolator).
© Mohamed F.A.B 2015
 An Optocoupler, also known as an Optoisolator
or Photo-coupler, is an electronic components
that interconnects two separate electrical
circuits by means of a light sensitive optical
interface.
 for example driving motors, motors can
produce what is called back E.M.F and a high
voltage spike produced by a sudden change
of current.
 An opto-isolator has a LED transmitter and
photo-sensor receiver separated from each
other by a gap.
 Optocoupler is equivalent to previous transistor
circuit but only differ in the way of transistor
biasing.

19. 19
Relay.
© Mohamed F.A.B 2015
 A relay is an electromagnetic switch which is used to switch
High Voltage/Current using Low power circuits.
 Relay isolates low power circuits from high power circuits.
 It is activated by energizing a coil wounded on a soft iron core.
 A relay should not be directly connected to a microcontroller,
it needs a driving circuit.
 A relay should not be connected directly to a microcontroller
due to following reasons:
 A microcontroller is not able to supply current required
for the working of a relay.
 A relay is activated by energizing its coil. Microcontroller
may stop working by the negative voltages produced in
the relay due to its back E.M.F.

20. 20
Relay Interface Circuit.
© Mohamed F.A.B 2015
220V
Load
We need to control 220VAC Lamp using
small signal from MC.
I(relay coil) =25mA.
Vin=5V.
VBE=0.7V.
=
25𝑚𝐴
100
= 0.25𝑚𝐴 (𝐴𝑐𝑡𝑖𝑣𝑒)
=
5 − 0.7
5 ∗ 0.25
= 3.44 𝐾Ω
Typical Value for 3.44 K𝜴 is 3.4 K𝜴
We can connect contactor (coil) instead of 220V Lamp and control 3
phase motor or another high power device   .
NOTE:
Example(3).

21. 21
Relay Advantage and disadvantage.
© Mohamed F.A.B 2015
Advantages:
1- It can pass both AC and DC current.
2- It can work with high voltage and high current.
3- One relay can control multiple device.
Dis-advantages:
1- It has a bigger package than transistor.
2- It can not be ON and OFF rapidly.
3- It need higher current than transistor to work.
4- Digital ICs or micro-controller can not active it.

22. 22
Lesson (7).
© Mohamed F.A.B 2015
Lesson (7):
Interfacing DC Motor and Control Its Direction.

23. 23
Lesson (7) Topics.
© Mohamed F.A.B 2015
►Motor Direction Control Theory.
►H-Bridge Theory.
►H-Bridge Using Relays.
►H-Bridge Using NPN Transistors.

24. 24
DC Motor Direction Control Theory.
© Mohamed F.A.B 2015
 Simply, We can control DC Motor Direction
by changing Power Source Polarity.
Clockwise Direction. Anti-Clockwise Direction.
M-+
M+-

25. 25
H-Bridge Circuit Theory.
© Mohamed F.A.B 2015
 It is so hard to control its direction with mechanical switches as we
need to press two switches for one direction.
 So, we can use relay or transistor instead of mechanical switches.
NOTE:

26. 26
H-Bridge Circuit Using Relays.
© Mohamed F.A.B 2015
 Don't Be Confused Between Motor Power Supply and
Relay Coil Power Supply.
NOTE:

27. 27
H-Bridge Using NPN Transistors.
© Mohamed F.A.B 2015
12V
A B Direction
0 0 STOP
0 1 CCW
1 0 CW
1 1 STOP
 For High power Motors we can use TIP122 or TIP 120
Transistors or MOSFET Transistors.
NOTE:

28. 28
H-Bridge Using L298N.
© Mohamed F.A.B 2015
Specifications of L298N
 Double H bridge Drive Chip (Two Motors).
 Logical voltage: 5V (MC Control Signal).
 Drive voltage: 5V-35V (Motor Voltage Source).
 Logical current: 0-36mA (MC Control Signal).
 Drive current: 2A (MAX single bridge).
 Max power: 25W.

29. 29
H-Bridge Using L298N.
© Mohamed F.A.B 2015

30. 30
Questions:
© Mohamed F.A.B 2015

31. Thank You All 
31
mo7amed.fawzy33@gmail.com
01006032792
fawzy.fab@gmail.com
© Mohamed F.A.B 2015