1

Quasi-square-wave ZVS converters

+– CrVg

D1

D2

Q1

+

v2(t)

–

i1(t) i2(t)

+

v1(t)

–

Lr

L

C R

+

V

–

I

0Ts

i2(t)

v2(t)V1

0t

0

Conductingdevices: D2X XQ1D1

A quasi-square-wave ZVS buck

Resonant transitions but transistor and diode conduction intervals are similar to PWM

Tank capacitor is in parallel with all semiconductor devices, hence all semiconductors operate with ZVS

Peak currents are increased, and are similar to DCM

Peak voltages applied to semiconductors are same as PWM

Magnetics are small, and are similar to DCM

2

Interleaved quasi-square-wave buck converters as VRM

3

Quasi-square-wave versions of other converters

Boost Flyback

Single transistor version of switch is restricted to 0.5 < µ < 1

So for boost, M > 2

For flyback, M > n

Boost inductor and flyback transformer are very small, and are similar to DCM devices

4

Quasi-square-wave ZVS converters

+– CrVg

D1

D2

Q1

+

v2(t)

–

i1(t) i2(t)

+

v1(t)

–

Lr

L

C R

+

V

–

I

0Ts

i2(t)

v2(t)V1

0t

0

Conductingdevices: D2X XQ1D1

A quasi-square-wave ZVS buck

Resonant transitions but transistor and diode conduction intervals are similar to PWM

Tank capacitor is in parallel with all semiconductor devices, hence all semiconductors operate with ZVS

Peak currents are increased, and are similar to DCM

Peak voltages applied to semiconductors are same as PWM

Magnetics are small, and are similar to DCM

5

Goal: Find steady-state solution for this resonant switch cellApproach: State plane analysis followed by averaging of

terminal waveforms

6

Interval 1Q1 conduction

Begins when Q1 starts to conductFor ZVS operation, this occurs when D1 had been previously conducting

CircuitInitial conditions

DynamicsWhat ends interval

EndpointsLength of interval

7

State plane

8

Interval 2Dead time

CircuitInitial conditions

DynamicsWhat ends interval

EndpointsLength of interval

9

Interval 3D2 conduction

CircuitInitial conditions

DynamicsWhat ends interval

EndpointsLength of interval

10

Interval 4Dead time

CircuitInitial conditions

DynamicsWhat ends interval

EndpointsLength of interval

11

Interval 5 (1)D1 conduction

CircuitInitial conditions

DynamicsWhat ends interval

EndpointsLength of interval

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Waveforms

13

Average switch input current

14

Average output current

15

Average output current, p. 2

16

Control input: transistor/diode conduction angle

17

A way to solve and plot the characteristics

18

Solving, p 2

19

Results: Switch conversion ratio µ vs. F

20

Switch conversion ratio µ vs.

Course website contains Excel spreadsheet (with function macros) that evaluates the above equations and can plot the above characteristics.

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