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

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

3

Interleaved quasi-square-wave buck converters as VRM

4

Waveforms

5

State plane

6

Interval 1Q1 conduction

7

Interval 2Resonant transition

8

Interval 3Diode D2 conduction

9

Interval 4Resonant Transition

10

Interval 5D1 conduction

11

Average switch input current

12

Length of switching period

13

Another approach: Find dc component of output current

14

Average output current, p. 2

15

Control input: transistor/diode conduction angle

16

A way to solve and plot the characteristics

17

Solving, p 2

18

Results: Switch conversion ratio µ vs. F

19

Switch conversion ratio µ vs.

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