Resonant Converters
EE 442-642
9-1
Voltage and Current Waveforms across the switch of a Buck Converter
id
9-2
Turn-on and Turn-off Snubber Circuits
Power loss is shifted to snubber circuits.
9-3
Switching Trajectories of Hard and Soft Switching
9-4
Undamped Series-Resonant Circuit
Vbase  Vd ,
I base  Vd / Z o
Vd  Vco
iL (t )  I Lo cos(ot ) 
sin(ot ),
Zo
vc (t )  Vd  (Vd  Vco ) cos(ot )  Z o I Lo sin(ot )
where
o 
1
,
Lr Cr
Lr
Zo 
Cr
9-5
Series-Resonant Circuit with Capacitor-Parallel Load
Vbase  Vd ,
I base  Vd / Z o
iL (t )  I o  ( I Lo  I o ) cos(ot ) 
Vd  Vco
sin(ot ),
Zo
vc (t )  Vd  (Vd  Vco ) cos(ot )  Z o ( I Lo  I o ) sin(ot )
where
o 
1
,
Lr Cr
Lr
Zo 
Cr
9-6
Impedance of a Series-Resonant Circuit
o Lr
Zo
1
Quality Factor : Q 


R
oCR R
9-7
Undamped Parallel-Resonant Circuit
Vco
iL (t )  I d  ( I Lo  I d ) cos(ot ) 
sin(ot ),
Zo
vc (t )  Vco cos(ot )  Z o ( I d  I lo ) sin(ot )
where
o 
1
,
Lr Cr
Lr
Zo 
Cr
9-8
Impedance of a Parallel-Resonant Circuit
R
R
Quality Factor : Q  o RC r 

o Lr Z o
9-9
Resonant Switch DC-DC Converters
ZCS
ZVS
9-10
ZCS Resonant-Switch Converter
Necessary
condition for iT to
come back to zero:
I o  (Vd / Z o )
9-11
ZCS Resonant-Switch Converter
By controlling the switch-off time (t4 - t3), i.e., the switching frequency,
the average value of voi, hence the average power supplied to the load
can be controlled.
9-12
ZCS Resonant-Switch Converter- Alternate Config.
9-13
ZVS Resonant-Switch Converter
Necessary
condition for vc to
come back to zero:
I o  (Vd / Z o )
9-14
ZVS Resonant-Switch Converter
By controlling the switch-on time (t4 - t3), i.e., the switching frequency,
the average value of voi, hence the average power supplied to the load
can be controlled.
9-15