What is H-Bridge
An H bridge is an electronic circuit that
enables a voltage to be applied across a load
in either direction. These circuits are often
used in robotics and other applications to
allow DC motors to run forwards and
backwards. H bridges are available as
integrated circuits, or can be built from
discrete components
Basic Circuit
High side
High side
low side
low side
Basic Working
Basic Working Braking
How to makeH-bridge
Using a simple switch(manual operation)
Using electro-mechaical Relays
Using BJTs
Using Mosfects
Electromechanical Relays
Used as a switch
Electromechaical Relays
Electromechaical Relays
Free Wheeling
Electromechanical Relay based Hbridge
Free wheeling diode
A flyback diode (sometimes called a snubber
diode, freewheeling diode, suppressor diode, or
catch diode) is a diode used to eliminate flyback,
which is the sudden voltage spike seen across an
inductive load when its supply voltage is suddenly
reduced or removed.
Flyback diodes are used whenever inductive
loads are switched off by silicon components: in
relay drivers, H-bridge motor drivers, and so on
Free wheeling diode
H
Free wheeling diode
H
Electromechanical Relay based Hbridge
Pros n Cons
Relay based circuit are cheaper
Easy to control
Can handle high current and voltage easily
Slow switching not suitable when using PWM
DE bouncing problems
Example :Relay (Panasonic)
Example :Relay (Panasonic)
Example :Relay (Panasonic)
Bipolar Junction Transistor
Can be used as switch
amplifiers ,oscillators
BJT H-bridge
Resistors used to limit current passing through base
e.g to prevent too much current from/to microcontroller pins
BJT H-bridge
R1
R2
R3
R4
GND
GND
GND
GND
Brake/off
GNG
GND
forward
GND
GND
reverse
Brake/off
GND
GND
Short
circuit
GND
GND
off
BJT H-bridge
forward
Reverse
GND
GND
off
GND
forwar
d
GND
Reverse
short
BJT H-bridge
Q1
Q2
Q3
Q4
opt couplers or Buffer ICs can also be used to provide a high current to base. Opt couplers has
additional advantage of complete isolation of circuit . Power and Logics Ground can be kept
separated easily
How to select appropriate BJT for you
Second letter in transistors marking describes its primary use:
C - low and medium power LF transistor,
D - high power LF transistor,
F - low power HF transistor,
G - other transistors,
L - high power HF transistors,
P - photo transistor,
S - switch transistor,
U - high voltage transistor.
Examples
AC540 - germanium core, LF, low power,
AF125 - germanium core, HF, low power,
BC107 - silicon, LF, low power (0.3W),
BD675 - silicon, LF, high power (40W),
BF199 - silicon, HF (to 550 MHz),
BU208 - silicon (for voltages up to 700V),
BSY54 - silicon, switching transistor.
There is a possibility of a third letter (R and Q - microwave transistors, or X - switch transistor),
but these letters vary from manufacturer to manufacturer.The number following the letter is of
no importance to users.
American transistor manufacturers have different marks, with a 2N prefix followed by a number
(2N3055, for example). This mark is similar to diode marks, which have a 1N prefix (e.g.
1N4004).
Japanese bipolar transistor are prefixed with a: 2SA, 2SB, 2SC or 2SD, and FET-s with 3S:
2SA - PNP, HF transistors,
2SB - PNP, LF transistors,
2SC - NPN, HF transistors,
2SD - NPN, HF transistors
How to select appropriate BJT for you
= &
= &
= =
= =
How to select appropriate BJT for you
Typical connection diagram for pnp and npn transistors
MOSFECTS
MOSFECTS
MOSFECTS
MOSFECTS
MOSFECTS
Choosing right MOSFECT
MOSFECT
MOSFECT
MOSFECT
MOSFECT
MOSFECT
MOSFECT
MOSFECT
H-bridge using Power Mosfect
Assignment
Construct physically an H-bridge circuit using
Relays<Powertransitor<Mosfect
On Vero boards or PCBs
5 members each group
Submit circuit along with report containing
circuit diagram and your calculations
Due date 25th April,2013
