Navitas Semiconductor - World's First & Fastest GaN Power IC
Navitas Semiconductor - World's First & Fastest GaN Power IC

Active Clamp Flyback Using GaN Power IC for Power Adapter Applications

Active Clamp Flyback Using GaN Power IC for
Power Adapter Applications

Linqxiao (Lincoln) Xue, Staff Applications Engineer, [email protected]
Jason Zhang,
VP Applications, [email protected]
March 29th 2017

How to Improve Power Adapter Density?

Traditional Travel Adapter and Chargers

USB PD and Quick Charge

• Added power in USB PD and Quick Charge requires dramatically higher power density (>20 W/in3)
• Higher efficiency and lower power loss are required in high density adapters
• How to dramatically improve the power density?

Outline

• Added power in USB PD and Quick Charge requires dramatically higher power density (>20 W/in3)
• Higher efficiency and lower power loss are required in high density adapters
• How to dramatically improve the power density?

QR Flyback Hits Performance Ceiling

• Frequency-dependent losses

• Leakage inductance loss
• Snubber/clamp losses
• Partial hard-switching loss at high line
• Slow turn-on loss to minimize EMI

• Difficult to improve efficiency at high frequency

ACF Enables ZVS and High Frequency Switching

• No snubber losses, all leakage energy is recovered
• ZVS soft switching over entire operation range
• ZCS soft turn-off for output rectifier
• Clean waveforms reduce EMI
• Enable small adapter design with high-frequency switching

ACF Operation

• Lr resonates with Cr during S2 ON interval
• ZVS is achieved by magnetizing inductance current
• Rectifier current is the difference between iLm and iLr
• iLr returns to iLm by the end of S2 ON interval for rectifier ZCS

Drawbacks of Traditional ACF

• Difficult to shape the current to achieve ZCS and minimize rms current
• Conduction loss is high
• Not compatible with SR controllers

New ACF Using Secondary Resonance

• S1 ON interval is the same as primary resonant
• In S2 ON interval

• Co/n2 << Cr , Co resonates with Lr
• iLr centers around a line lower but in parallel with iLm
• ZCS is easily achieved. No rectifier current double dipping

New ACF Simplifies SR and Reduces Current RMS

• iLr current can be easily shaped
• No rectifier current dipping issue. Simplifies SR
• Reduced rms current and conduction loss

Experimental Result of RMS Reduction

Efficiency Benefit of New ACF

• 0.4 W power loss reduction
• ~0.8% efficiency improvement

Advantages of Using GaN in ACF

• GaN ACF needs only 0.2A negative current for ZVS vs. Si’s 0.5A
• GaN ACF RMS is only 0.9A vs. Si’s 1.1A
• GaN has no body diode loss
• Low high-frequency gate-charge loss

Half-Bridge iDrive GaN Power IC

• Internal level-shift, bootstrap
• Range from 150-600 mOhm (650V)
• Single component
• Ground-referenced PWM signals
• Active Clamp Flyback, Half-Bridge, LLC, etc.

GaN Power IC Simplifies ACF

GaN Power IC Efficiency Advantage

• GaN reduces power loss by 0.6W
• GaN boosts efficiency by 1.2%

High Density 65W Adapter Using ACF and GaN

Conclusion

• USB-PD and QC demand high density solutions
• QR flyback hits performance ceiling
• ACF overcomes QR limitations and enables high frequency operation
• New ACF using secondary resonance improves ACF’s operation and
efficiency
• GaN is uniquely suitable for high frequency operation
• Half-Bridge GaN Power IC simplifies ACF design and improves density
• An example of 65W ACF adapter using GaN and secondary resonance
achieves 22W/in3 density, while meeting thermal and EMI requirement

Benchmark Power Density Today

• AC-19VDC 150W
• GaN Power ICs
• 1 MHz – DSP-controlled

• Not optimized for light-load operation

• Power Density : 26.4 W/in3 = > 2x increase vs. best-in-class

650V AllGaN™ Power IC
for Power Supply Applications

4th IEEE Workshop on Wide Bandgap Power Devices and Applications (WiPDA)
Fayetteville, NC, USA. November 9th 2016.

Marco Giandalia, VP IC Design
Marco.giandalia@navitassemi