Power IC supports efficient and high power density 140W PD3.1 adapter design

Infineon / Mitsubishi / Fuji / Semikron / Eupec / IXYS

Power IC supports efficient and high power density 140W PD3.1 adapter design

Posted Date: 2024-01-23

GaNSense half-bridge IC enables the ZVS AHB flyback topology to operate at higher frequencies with smaller transformers and higher efficiency. The 140 W PD 3.1 evaluation board demonstrates the functionality and performance of a complete system design. The evaluation board achieves 94.5% efficiency at 90 VAC and 95.8% efficiency at 230 VAC, improving efficiency by at least 1% and saving up to 20% compared to the previous design. The case size is expected to be 100 cc and the power density is 1.4 W/cc.

Higher speed + higher efficiency = smaller size

The growing demand for reduced power supply size continues to challenge the industry to produce ever higher efficiencies and power densities. As silicon devices reach their frequency limits (

Figure 1. Simplified block diagram and key features of GaNSense power IC and GaNSense half-bridge IC.Image courtesy of Hakata Electric Power Systems
GaNSense improves PFC frequency and efficiency

Figure 2. Silicon-based boost PFC (left) and lossless GaNSense boost PFC (right).Image courtesy of Hakata Electric Power Systems

A boost follower function can be added to further increase efficiency so that the DC bus operates at a lower voltage during low voltage line AC input. This results in lower peak current levels, lower negative current and circulating energy, and lower core losses (Figure 3). All these improvements combine to deliver an additional +0.3% efficiency benefit.

Figure 3. Peak inductor current ramp during the AC half cycle at full load and different DC link voltage levels (90 VAC/400 V (left) and 90 VAC/260 V (right)).Image courtesy of Hakata Electric Power Systems [PDF]

GaNSense supports AHB, and AHB supports PD 3.1

Quasi-resonant flyback is a popular topology for downstream converters due to its wide voltage gain capability. However, when the power level increases above 100 W, the transformer leakage energy increases significantly. As leakage energy increases, voltage stress on the primary switch and secondary SR switch increases, including higher voltage spikes and EMI noise. Additionally, USB Power Delivery Specification Revision 3.1 supports higher output voltage levels, such as 28V to 48V, which makes flyback transformer turns ratio design more difficult. The voltage stress on the primary and secondary is much higher than conventional 20 V output conditions. The asymmetric half-bridge flyback converter operates with zero-voltage switching (ZVS) of the primary-side switch and zero-current switching (ZCS) of the secondary-side rectifier. Additionally, the primary switch is clamped at the PFC to an output voltage typically around 400 V, so stress and voltage ringing issues are significantly mitigated. For these reasons, the AHB topology is suitable for PD 3.1 applications, and the GaNSense half-bridge IC enables high-frequency operation and lossless current sensing in a small transformer size, resulting in higher efficiency (Figure 4).

Figure 4. Silicon-based QR flyback (left) and lossless GaNSense AHB flyback (right).Image courtesy of Hakata Electric Power Systems
140 W, PD 3.1 Evaluation Board

The complete PFC+AHB 140 W, PD 3.1 Evaluation Board (EVB) (Figure 5) has been built and tested for functionality and performance. The design achieves an impressive 100 cc estimated case size with a power density of 1.4 W/cc. EVB includes optimized PFC, AHB and SR power stages and magnetics and uses off-the-shelf controllers. The PFC and AHB power supplies are designed around the NV6138A GaNSense power IC and NV6245C GaNSense half-bridge IC. EVB also includes EMI filtering and operates through conducted and radiated emissions.

Figure 5. 140 W, PD 3.1 evaluation board, efficiency = 94.5%, estimated case size = 100 cc.Image courtesy of Hakata Electric Power Systems [PDF]

The full load boost PFC waveform is shown in Figure 6. During 115 VAC line input, the boost circuit operates under zero-voltage switching (ZVS) conditions, where the boost switch node voltage (VSW) drops to zero before the GaN power FET turns on. every switching cycle. During 230 VAC line input, the boost circuit operates at partial ZVS conditions where VSW drops to approximately 100 V and then hard switches from there to zero. The controller automatically detects the valley of the VSW node during shutdown in order to turn it back on every switching cycle to optimize the turn-on point of the voltage level as much as possible to minimize hard switching losses. Since GaN power ICs have very low output capacitance, the drain voltage will quickly drop to valley value each cycle. The controller must have fast valley detection to ensure that the VSW voltage is turned on before the voltage recovers. The boost follower function also works when the DC bus voltage decreases to 300 VDC for low line conditions and increases to 400 VDC for high line conditions.

Figure 6. Boost PFC switching waveforms at full load, 115 VAC input (left), 230 VAC input (right), IL=blue (1 A/div), VDS=yellow (100 V/div).Image courtesy of Hakata Electric Power Systems

Figure 7. AHB switching waveforms at 115 VAC input and full load conditions, IL = blue (2 A/div), VSW = yellow (100 V/div).Image courtesy of Hakata Electric Power Systems

Figure 7 shows the AHB half-bridge switch node (VSW) and tank current (IL) waveforms at 115 VAC input and full load conditions. The resonant tank current rises linearly during the on-time of the low-side of each half-bridge, and then resonates on time at the high-voltage side of each half-bridge. This enables the GaNSense half-bridge IC VSW output node to achieve clean, smooth ZVS operation during every switching cycle. The AHB operating frequency range is 125 to 300 kHz, depending on input line and output load conditions.

The efficiency curve (Figure 8) shows 4-point efficiency and load efficiency. The design achieves an astonishing 94.5% full-load efficiency at 90 VAC input, which is at least 1% higher than other products and saves up to 20% energy. Efficiency at 90 VAC and full load determines the case size and case contact temperature of the final adapter product.

Figure 8.4 Point efficiency (left) and load efficiency (right) curves.Image courtesy of Hakata Electric Power Systems

Conducted and radiated EMI is always a major issue in power supply design. New designs using GaN are continually challenged by EMI challenges due to faster switching speeds and frequencies. Designers often do not address the EMI portion of their designs until they are near completion, only to be surprised to find that emissions far exceed allowable limits. An EMI scan of this design (Figure 9) shows that both conducted and radiated EMI are well below the limits, with adequate manufacturing tolerance margins. These results can be achieved by implementing appropriate EMI guidelines early in the design phase, which include good practices such as PCB ground planes, inductor shielding, properly designed EMI filter components, proper PCB floorplanning, and component location and proximity.

Figure 9. Conducted emissions at 115 VAC/140 W (left) and radiated emissions at 230 VAC/140 W (right).Image courtesy of Hakata Electric Power Systems

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