Power Supply Topologies

Switching Waveforms

Ajit & Arash

POWER SUPPLY TOPOLOGIES

There are several power supply topologies including Buck, Boost, Buck Boost(inverting), Sepic , Flyback , Forward, Active Clamp Forward, and half bridge to name a few.

In the next few slides few of the most popular topologies are reviewed and examples from WEBENCH are provided

Buck

Circuit Configurationtest

DT

t

Vin

Vout

p

ON

Drain Current

Ideal Transfer Function)1(1 DII outD

outQ II (max)1

VinVDS

Drain Voltage

Ave. Diode Current

Diode Reverse Voltage

VinVD 1

Buck

• Voltage and Current Waveforms

Buck Topology ExampleVin = 12.5 V, Vout = 5V, Iout = 0.5A , IC = LM2842Y

Output voltage

Buck TopologyVin = 12.5 V, Vout = 5V, Iout = 0.5A , IC = LM2842Y

Switch current

Inductor current and Diode current

Switch node voltage

Boost

Circuit Configurationtest

DtT

T

Vin

Vout

ONp

p

1

1

Drain Current

Ideal Transfer Function

outD II 1

DII outQ

1

1(max)1

outDS VV

Drain Voltage

Ave. Diode Current

Diode Reverse Voltage

outD VV 1

Boost

• Voltage and Current Waveforms

Boost Topology Example

Vout = 30V in steady state

Vin = 12.5 V, Vout = 30V, Iout = 3A , IC = LM3478

Boost Topology - waveforms

Inductor current

Diode current

Switch node voltage

Switch current

Buck Boost

Circuit Configurationtest

D

D

tT

t

Vin

Vout

ONp

ON

1

Drain Current

Ideal Transfer Function

outD II 1

DII outQ

1

1(max)1

outinDS VVV

Drain Voltage

Ave. Diode Current

Diode Reverse Voltage

outinD VVV 1

Buck Boost

• Voltage and Current Waveforms

Buck-Boost example Vin = 16, Vout = 12V, Iout = 3A , IC = LM5118-Q1

Output voltage

Buck-Boost Topology Vin = 16 V, Vout = 12V, Iout = 3A , IC = LM5118-Q1

Inductor current Switch node voltage

SEPIC

Circuit Configurationtest

D

D

Vin

Vout

1

Drain Current

Ideal Transfer Function

outD II 1

D

DII outQ

1

(max)1

outinDS VVV

Drain Voltage

Ave. Diode Current

Diode Reverse Voltage

outinD VVV 1

SEPIC

• Voltage and Current Waveforms

SEPIC Example Vin = 17.5 V, Vout = 12V, Iout = 0.5A , IC = LM3478

Output voltage (Vout)

SEPIC Topology Vin = 17.5 V, Vout = 12V, Iout = 0.5A , IC = LM3478

Inductor current and Switch current Switch node voltage (Vsw)

FLYBACK

Circuit Configurationtest

pout

p

LI

VoutTD

Vin

Vout

2

Drain Current

Ideal Transfer Function

outD II 1

p

ONQ L

tVinI

(max)1

s

poutinDS N

NVVV

Drain Voltage

Ave. Diode Current

Diode Reverse Voltage

s

pINoutD N

NVVV 1

FLYBACK

• Voltage and Current Waveforms

Flyback exampleVin = 5 V, Vout = 12V, Iout = 0.5A , IC = LM2587

Output voltage (Vout)

Flyback exampleVin = 5 V, Vout = 12V, Iout = 0.5A , IC = LM2587

MOSFET current (ISwitch )( same as Transformer primary current, Ipri)Secondary Diode current (ID1)Load current (Iout)

MOS Drain voltage (Vswitch)