DESIGN OF DC-DC CONVERTER FOR SMPS WITH MULTIPLE ISOLATED OUTPUTS

PRAJWAL RAJ M B

Content

1. SMPS2. DC-DC Converter Topologies3. SEPIC Converter, Operation and simulation results4. Flyback Converter, Operation and Simulation

results5. Forward Converter , Operation and Simulation

results6. Closed Loop circuit for the SEPIC Converter, PI

controller and Simulation results.7. Conclusion.

SMPS

What is SMPS?• An electrical power supply that incorporates a switching

regulator to convert electrical power efficiently.• Voltage regulation is achieved by varying the ratio of on-

to-off time• The SMPS has dc-to-dc switching converter for

conversion from unregulated dc input to regulated dc output voltage.

• Typical frequency range of SMPS is from 50 kHz to several MHz.

Switched-mode power supply

• The input supply drawn from ac mains is first rectified to get a unregulated dc voltage.

• The unregulated dc voltage then fed to a high frequency dc- to dc converter.

• Most of the dc-dc converters used in SMPS circuits have high frequency transformer for voltage scaling & isolation.

• Output voltage is again filtered at the secondary side.

Advantages of SMPS

• Lower weight• Smaller size• Higher efficiency• Reduced costs• Lower power dissipation• Provide isolation between multiple outputs.

Disadvantages of SMPS• Greater circuit complexity.

Applications of SMPS

• Personal computers• Space stations• Electric vehicles• Mobile battery chargers• Security Systems (Closed circuit cameras) etc

DC-DC CONVERTER TOPOLOGIES

• SEPIC Converter• Flyback Converter• Forward Converter

Objective :• To design multiple isolated outputs. • The output voltages is designed for 12V, 5V

and 3.3V for an input voltage of the order of 200-400V input supply.

• The simulation of the circuits is done in Matlab.

1. SEPIC CONVERTER

Operation of SEPIC Converter

Two modes of operation • Mode1: when ‘Sw’ is ON• Mode2 :when Sw is off

Parameters

Input voltage 357.8V

Output voltage V1=12V, V2=3.3V, V3=5V

Inductor L1=12mH

Capacitors C1=40nf, C01=150mf, C02=40mf, C03=100mf

Duty cycle 50%

Switching frequency 61923.381Hz

Simulation Results

• Input Voltage :357.8V

• 12V output0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

-400

-300

-200

-100

0

100

200

300

400

Time(s)

V(in

)

0 1 2 3 4 5 6 7 8 9 100

2

4

6

8

10

12

14

Time(s)

V1(

V)

• 5V output

• 3.3V output0 1 2 3 4 5 6 7 8 9 10

0

1

2

3

4

5

6

Time(s)

Vol

tage

(v3)

V

0 1 2 3 4 5 6 7 8 9 100

1

2

3

4

Time(s)

V(2

) V

Flyback Converter

Operation of Flyback Converter

Two modes of operation• Mode1: when ‘Sw’ is ON• Mode2: when ‘Sw’ is off

Parameters for Flyback Converter

Input voltage 357.8V

Output voltages V1=12V, V2=5V and V3=3.3V

Inductor Lm=15mH

Capacitor C01=150mf, C02=100mf, C03=50mf

Duty cycle 50%

Switching frequency 50kHz

Simulation Results

• Input Voltage :357.8V

• 12V output

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2

x 105

0

2

4

6

8

10

12

14

Time(s)

V1(

V)

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1-400

-300

-200

-100

0

100

200

300

400

Time(s)

V(in

)

• 5V output

• 3.3V output0 1 2 3 4 5 6 7 8 9 10

0

1

2

3

4

5

6

Time(s)

V(2

)

0 1 2 3 4 5 6 7 8 9 100

1

2

3

4

5

Time(s)

V(3

) V

Forward Converter

Operation of the Forward Convereter

Two modes of operation:• When switch ‘sw’ is on• When switch ’sw’ is off

Parameters for the forward Converter

Input Voltage 200V

Output Voltage V1=12V, V2=3.3V

Inductance L1=8.5µH, L2=19.2mH

Capacitance C1=385mf, C2=120mf

Switching Frequency 100kHz

Duty ratio 50%

Simulation Results• Input voltage:200V

• Output Voltage: 3.3V0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

-200

-150

-100

-50

0

50

100

150

200

Time(s)

Vin

(V)

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 50

0.5

1

1.5

2

2.5

3

3.5

Time(s)

V1(

V)

• 12V output:

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 50

2

4

6

8

10

12

14

Time(s)

V2(

V)

Closed Loop Circuit for SEPIC Converter Using PI Controller

• The Kp and Ki values selected for PI Controller

Kp Ki

PI Controller 0.4 2

PI Controller 1 0.2 5

PI Controller 2 0.1 8

Simulation Results

• Input voltage:357.8

• 12V output

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 50

2

4

6

8

10

12

14

Time(S)

V1(

V)

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1-400

-300

-200

-100

0

100

200

300

400

Time(s)

V(in

)

• 5V output

• 3.3V output

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 50

1

2

3

4

5

Time(s)

V2(

V)

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 50

1

2

3

4

5

6

Time(s)

V3(

V)

Conclusion

• The closed loop circuit is more efficient in terms of settling time when compared to open loop condition which is verified in the SEPIC Converter.

• Constant voltage can be maintained even though there is variation in the load if closed loop control circuit is employed.

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