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Operating Modes
of the Series Resonant Converter
Lecture 23
Resonant and Soft-Switching Techniques
in Power Electronics
ECEN 5817
ECEN 5817 Resonant and Soft-Switching
Techniques in Power Electronics
1
Lecture 23
Next Homework Assignment
Problem 1
Conventional hard-switched flyback converter
Ringing caused by transformer
leakage inductance
Limit peak transistor voltage using a
dissipative snubber circuit
Analyze performance via state plane analysis
ECEN 5817 Resonant and Soft-Switching
Techniques in Power Electronics
2
Lecture 23
Series resonant converter
ECEN 5817 Resonant and Soft-Switching
Techniques in Power Electronics
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Lecture 23
Discontinuous Conduction Modes
In the “type k” discontinuous conduction mode, the tank rings through k complete
half cycles during each half switching period. The output diode rectifiers then
become reverse-biased, and remain off until the input bridge transistors switch to
initiate the next half switching period.
Q: Why do
the diodes
decide to
interrupt the
ringing after
k half-cycles,
instead of k–
1, or k+1, or
...?
ECEN 5817 Resonant and Soft-Switching
Techniques in Power Electronics
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Lecture 23
The k = 1 DCM
ECEN 5817 Resonant and Soft-Switching
Techniques in Power Electronics
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Lecture 23
Why the diodes become
reverse-biased
State-plane explanation
ECEN 5817 Resonant and Soft-Switching
Techniques in Power Electronics
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Lecture 23
Why the diodes
become reversebiased
Inductor voltage waveform
explanation
ECEN 5817 Resonant and Soft-Switching
Techniques in Power Electronics
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Lecture 23
Summary of results
k = 1 DCM
M=1
J < 4/
ECEN 5817 Resonant and Soft-Switching
Techniques in Power Electronics
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Lecture 23
The k = 2
DCM
ECEN 5817 Resonant and Soft-Switching
Techniques in Power Electronics
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Lecture 23
Charge Arguments and Averaging
ECEN 5817 Resonant and Soft-Switching
Techniques in Power Electronics
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Lecture 23
State Plane Diagram
k = 2 DCM
ECEN 5817 Resonant and Soft-Switching
Techniques in Power Electronics
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Lecture 23
Summary of Results: k = 2 DCM
Solution for radii
Output plane
characteristics
ECEN 5817 Resonant and Soft-Switching
Techniques in Power Electronics
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Control plane characteristics
Lecture 23
19.5 General Solution for the Steady-State
Characteristics of the Series Resonant
Converter
Mode index k and subharmonic number 
ECEN 5817 Resonant and Soft-Switching
Techniques in Power Electronics
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Lecture 23
Type k CCM
Steady-State Solution
Elliptical output
characteristic
with
Control plane characteristic
ECEN 5817 Resonant and Soft-Switching
Techniques in Power Electronics
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Lecture 23
Type k CCM
Waveforms
Switch network
output voltage
Tank inductor current,
odd k (ZCS)
Tank inductor current,
even k (ZVS)
ECEN 5817 Resonant and Soft-Switching
Techniques in Power Electronics
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Lecture 23
Type k DCM
Steady State Solution
Type k DCM, odd k
Output voltage
Mode boundaries
Type k DCM, even k
and
Output current
Mode boundaries
and
Steady-state equivalent circuit model for
even DCM: an effective gyrator. The
converter exhibits current source
characteristics.
ECEN 5817 Resonant and Soft-Switching
Techniques in Power Electronics
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Lecture 23
CCM and DCM Boundaries
ECEN 5817 Resonant and Soft-Switching
Techniques in Power Electronics
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Lecture 23
Complete SRC Characteristics
Control Plane
ECEN 5817 Resonant and Soft-Switching
Techniques in Power Electronics
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Lecture 23
SCR Output Characteristics
Above Resonance
ECEN 5817 Resonant and Soft-Switching
Techniques in Power Electronics
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Lecture 23
SRC Output Characteristics
Selected Modes Below Resonance
ECEN 5817 Resonant and Soft-Switching
Techniques in Power Electronics
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Lecture 23
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