In this video, prof. Sam Ben-Yaakov explains principle of switched capacitor converter operation and its features.
Introduction
Switched Capacitor Converters (SCCs) are pivotal in modern power electronics due to their high efficiency and design flexibility. Prof. Sam Ben-Yaakov provides an in-depth exploration of SCC operations, focusing on resonant switching, loss mechanisms, and advanced converter configurations such as Google’s innovative topology.
Basic Principles of Switched Capacitor Converters
SCCs operate by transferring charge between capacitors through controlled switching. The fundamental operation exhibits similarities to basic switched capacitor converters, albeit with sinusoidal waveforms during charging and discharging phases. This sinusoidal behavior influences the analysis of power loss and efficiency.
Power Loss Analysis
Power loss in SCCs is predominantly a function of:
- Total Resistance (R<sub>total</sub>): Comprising R<sub>DS(on)</sub>, ESR, and ESL contributions from capacitors and inductors.
- Current Characteristics: RMS current squared (I<sub>RMS</sub>²) and average output current.
The average current relates to the peak current in a half-sinusoidal waveform as 1/π, and RMS current is I<sub>peak</sub>/√2. Consequently, the losses are proportional to the equivalent resistance and the square of the average output current.
Resonant Switched Capacitor Converters
Resonant SCCs mitigate conduction losses through zero current switching (ZCS). However, ZCS doesn’t entirely eliminate switching losses due to the charging and discharging of output capacitors during transitions, resulting in current spikes at switch transitions.
Moving Towards Zero Voltage Switching
Advanced designs, such as Google’s switch tank converter, shift towards zero voltage switching (ZVS) to further reduce switching losses. ZVS minimizes voltage stress on MOSFETs, reducing R<sub>DS(on)</sub> and improving overall efficiency.
Google’s 4:1 Step-Down Converter
Google’s converter topology exemplifies innovation in SCC design:
- Operation: Involves sequential control of switches (S1 and S2) to achieve a 4:1 step-down ratio.
- Voltage Stress Reduction: Transistor voltages are limited to 2V<sub>out</sub>, significantly reducing R<sub>DS(on)</sub>.
Experimental Results and Efficiency
Experimental units demonstrated impressive efficiency:
- High Efficiency: Up to 99% at optimal load conditions.
- Loss Distribution: Predominantly due to MOSFET conduction, with minimal switching and inductor losses.
Future Developments
Ongoing modifications target ZVS implementation, leveraging GaN transistors to further reduce losses. This approach is promising for widespread adoption in practical circuits.
Conclusion
Switched Capacitor Converters continue to evolve, with resonant designs and advanced topologies like Google’s converter pushing efficiency boundaries. Prof. Ben-Yaakov’s insights video highlight the potential for SCCs in future power electronics applications.