This document provides information about a DC to DC converter (chopper) circuit and its operation. It discusses: 1. DC-DC converters are used to convert a fixed DC source into a variable DC source and can step up or step down voltages. Their applications include motor control and voltage regulation. 2. A step-down chopper circuit uses a switch (like a transistor) to alternately connect and disconnect a load from a DC source voltage. This produces a pulsed output voltage that can be averaged to a lower value. 3. The document describes the waveforms and equations for calculating the average and RMS output voltage and current values based on the duty cycle and frequency of the switch. It also

1. Shantilal Shah Engineering College

2. SUBJECT : POWER ELECTRONICS
TOPIC:DC TO DC CONVERTER
(CHOPPERS)
Branch : Electrical
Sem : 5th
Prepared By :
NO. NAME ENROLLMENT NO
1 MER VISHAL GIRISHBHAI 130430109031
2 PATEL BHAVIN 130430109039
3 SINGH SUDHIR 130430109052
GUIDED BY :
PROF. J.K.CHAVDA

3. 3
DC-DC Converters
 Convert a fixed DC Source into a Variable DC Source
 DC equivalent to an AC transformer with variable turns ratio
 Step-up and Step-down versions
 APPLICATION
 Motor Control
 Voltage Regulators

4. 4
 Step-down Operation
• Switch SW is known as a “Chopper”
• Use BJT, MOSFET, or IGBT
• Close for time t1
• VS appears across R
• Open for time t2
• Voltage across R = 0
• Repeat
• Period T = t1 + t2

5. 5
 Waveforms for the Step-Down Converter

6. 6
 Average Value of the Output Voltage
1
1
0
0
1
1
1
1
t
a O
t
a S
a S S
a S
V v dt
T
V V dt
T
t
V V ft V
T
V kV


 




7. 7
 Average Value of the Load Current
1
a S
a
V kV
I
R R
T period
t
k dutycycle
T
f frequency
 

 


8. 8
 RMS Value of the output voltage
1
2
2
0
1
2
2
0
1
1
kT
O O
kT
O S
O S
V v dt
T
V V dt
T
V kV
 
  
 
 
  
 




9. 9
 If the converter is “lossless”, Pin = Pout
0
2
0
2
2
1
1
1
kT
in O
kT
O
in
S
in
S
in
P v idt
T
v
P dt
T R
V
P kT
T R
V
P k
R







10. 10
 Modes of Operation
• Constant – frequency operation
• Period T held constant, t1 varied
• Width of the pulse changes
• “Pulse-width modulation”, PWM
• Variable -- frequency operation
• Change the chopping frequency (period T)
• Either t1 or t2 is kept constant
• “Frequency modulation”

11. G1
G2
VS
C
A2
T2
K2
L
A
D
K
AF
KF
FD
RL
LL
DC CHOPPER USING THE SCR
CIRCUIT DIAGRAM
 Working Principle For convenience the
chopper operation is divided into five
modes.
 1. Mode-1
 2. Mode-2
 3. Mode-3
 4. Mode-4
 5. Mode-5
T1

12. 30V
V
 MODE -1 OPERATION
G1
G2
VS
C
A2
T2
K2
L
A
D
K
AF
KF
FD
RL
LL
»»»
»»
»»»»
»»
»»»»
»»»
»»»»
»»»»
V
30V
Thyristor T1 is fired at t = 0.
• The supply voltage comes across the
load.
• Load current IL flows through T1 and
load.
• At the same time capacitor discharges
through T1, D1, L1, & ‘C’ and the
capacitor reverses its voltage.
• This reverse voltage on capacitor is
held constant by diode D1
T1

13. 30V
V
MODE -2 OPERATION
G1
G2
VS
C
A2
T2
K2
L
A
D
K
AF
KF
FD
RL
LL
»»»
»»
»»»»
»»
»»»»
»»
»»»»
V
30V
• Thyristor T2 is now fired to
commutate thyristor T1.
• When T2 is ON capacitor voltage
reverse biases T1 and turns if off.
• The capacitor discharges through
the load from –V to 0.
• Discharge time is known as
circuit turn-off time.
• Capacitor recharges back to the
supply voltage (with plate ‘a’
positive).
T1

14. 30V
V
MODE -3 OPERATION
G1
G2
VS
C
A2
T2
K2
L
A
D
K
AF
KF
FD
RL
LL
»»»
»»
»»»»
»»
»»»»
»»
»»»»
V
30V
FWD starts conducting and
the load current decays.
• Hence capacitor charges to a
voltage higher than supply
voltage, T2 naturally turns
off.
T1

15. 30V
V
MODE -4 OPERATION
G1
G2
VS
C
A2
T2
K2
L
A
D
K
AF
KF
FD
RL
LL
»»»
»»
»»»»
»»
»»»»
»»
»»»»
V
30V
 Capacitor has been overcharged i.e.
its voltage is above supply voltage.
 Capacitor starts discharging in
reverse direction.
 Hence capacitor current becomes
negative.
 The capacitor discharges through VS,
FWD, D1 and L.
 When this current reduces to zero D1
will stop conducting and the capacitor
voltage will be same as the supply
voltage
T1

16. 30V
V
MODE -5 OPERATION
G1
G2
VS
C
A2
T2
K2
L
A
D
K
AF
KF
FD
RL
LL
»»
»»»
V
30V
»»»
»»
 Both thyristors are off
and the load current
flows through
 the FWD.
 This mode will end once
thyristor T1 is fired.
T1

18. THANKFUL TO YOU !!