140W Rompower Valley Detection USB-PD
About
Scope and purpose
This document describes the 140 W with power delivery protocol 5V to 28V and the maximum output current 5A at 20V/28V and 3A for 5-15V, 90VAC ~ 265VAC input off-line. The unit has several operation modes: forced quasi-resonant (FQR), burst mode, zero voltage switching (ZVS) flyback converter in a compact unit. It uses a PFC controller with two voltage level regulations to minimize the PFC inductor and maximize efficiency above to 97%. The semiconductors power devices that are used are: IGLR70R140D2S (Flyback switch), ISC032N12LM6 (SR switch), IGLD65R110D2 (PFC switch), ISZ330N12LM6 (ZVS switch), BSC011N03LS (PD load switch).
Intended audience
This document is addressed to users who want to use an Ideal flyback topology in an adapter market who requires a very compact package, good thermal behavior due to very high efficiency. This flyback topology could be adapted to any other power level and formfactor, to have the best performance (the efficiency could be above 97% if it is used PFC to increase the input voltage to 250V) and to integrate in many other applications: AC-DC and DC-DC.
1 Introduction
This design shows the highest power density and efficiency that is possible due to implementing the Rompower technology applying to the flyback converter and transforming it into an Ideal Flyback topology.
By the Rompower passive clamp the energy from the leakage inductance of the transformer is recycled to obtain ZVS and modified the shape of current in the secondary side minimizing the body diode losses before turning on the SR.
With Rompower current injection the ZVS is guaranteed in any condition of input, output voltage and at any output load (even at light load and standby). Due to this feature could be eliminated any snubber from the converter.
Due to Rompower noise canceling technology implemented inside the transformer the EMI filter is smaller and more efficient with a smaller Ycap and a smaller EMI filter.
Features:
› Passive clamp technology with recycling energy to obtain ZVS
› Valley detection & adaptive ZVS
› Forward mode current injection technology
› True soft switching with no spikes/no ringing across SR
› Simplicity in design compared to ACF
› EMI suppression technology
Benefits:
› Maximize efficiency up to 94.41% through leakage energy harvesting
› Very high and flat efficiency curve independent of line/load condition
› Lower SR MOSFET voltage rating (120V device)
› Less EMI filtering effort due to Rompower noise suppression technic inside the transformer
2 Abstract
This reference design outlines a highly efficient and compact 140W USB Power Delivery (USB-PD) Switched-Mode Power Supply (SMPS) based on Rompower’s advanced Ideal Flyback topology. Designed for universal AC input (90–265 VAC) and compliant with USB-PD output voltage levels (5V, 9V, 15V at 3A and 20V – 28V at 5A), the system demonstrates superior power density and performance, making it ideal for modern high-efficiency AC-DC adapters and power conversion applications. The core innovation lies in the integration of Rompower’s passive clamp technology, which recycles transformer leakage energy and enables zero-voltage switching (ZVS) across all load conditions, including light load and standby. This feature eliminates the need for traditional snubber circuits and significantly reduces switching losses.
Additional efficiency gains are achieved using a forward-mode current injection circuit and valley detection with adaptive ZVS, ensuring optimal soft-switching behavior without voltage spikes or ringing on the synchronous rectifier (SR). Rompower's proprietary EMI suppression techniques are embedded within the transformer itself, minimizing the size of the EMI filter components and maintaining conducted emissions well within EN 55022 Class B limits.
The design supports multiple operation modes—burst mode, discontinuous conduction mode (DCM), quasi-resonant (QR), and active burst mode (ABM)—and leverages dual-voltage PFC regulation to reduce PFC inductor size and boost system efficiency beyond 97% at optimal conditions. Thermal performance and power density are enhanced by a compact layout (78cc volume) with a power density of above 29.5 W/in³.
Comprehensive testing confirms consistent efficiency above 94.4% at full load (28V, 5A), with low standby power consumption below 50 mW and touch current under 60 µA. The reference design includes extensive performance measurements, such as efficiency data, ripple voltage and thermal behavior under worst-case conditions. This design illustrates a scalable, high-performance flyback solution that can be adapted for a wide range of applications where size, efficiency, and reliability are critical.
3 Specifications of the demo board
4 Reference board
This document contains the list of features, power supply specifications and measurements performance. Typical operating characteristics such as performance curves and oscilloscope waveforms are shown at the end of the document.
Figure 1: 140W PFC+Ideal flyback converter (top view)
Figure 2: 140W PFC+Ideal flyback converter (bottom view)
Figure 3: 100W PFC+Ideal flyback converter (side view)
5 Features of Rompower 140W PFC+Ideal flyback topology
6 Circuit description
6.1 Introduction
The demonstrator board accepts a wide input range from 90VAC to 265VAC, and the output is 5 V to 28 V, maximum 140 W. The circuit is like PFC with two output voltage regulations depending on input line and an ideal flyback converter which includes some rompower functionalities to eliminate the disadvantage of a classical flyback topology.
In figure 4. show a principal diagram block of the unit, to the input to output of unit. The input filter includes the input fuse, the Xcap which depends on the specification could be from 470nF to 680nF. As the input bridge we place a classical one, but if it is needed a higher efficiency could be replaced with a half active bridge with a higher cost and integrating the Xcap discharge function. After rectifying the input voltage, we have a differential mode filter to eliminate the DM noise.
The PFC stage is based on the PFC controller from ONsemi (NCP1623). The advantage of this controller is that it has two regulated voltage level (250V and 395V) and will help to have a smaller PFC inductor and could better optimize the efficiency of the PFC and set the flyback convert to maximum efficiency.
The flyback topology was converted with rompower passive clamp and ZVS circuit in an ideal flyback by eliminating all disadvantages of classical topology. With Rompower passive clamp, the energy from leakage inductance of transformer is transferred to the ZVS circuit, and part of it is returned to the secondary side and changed to the secondary side current. When the secondary side current is changed, the SR body diode conduction is reduced a lot because the current shape is smaller until the SR turns ON.
With energy harvesting from leakage inductance, we achieve ZVS for Flyback mosfet (Q4) and eliminating any spike voltage across the SR in the secondary side. Having these advantages, the frequency operation could be increased, and the snubber circuit could be removed (or place one very small only for back-up). By operating in two input voltage settings by PFC controller, the flyback efficiency could be optimized to the maximum points (above 97% for flyback stage).
Another advantage comes from rompower shield, which decreases the common mode filter dimension a lot, because the shield from inside the transformer reduce significantly the common mode noise which comes from secondary to primary through the windings.
Figure 4: Simplified demo circuit
7 Measurement results
7.1 Efficiency
Efficiency was measured with the unit outside of the enclosure and by sensing the output voltage directly on the PCB terminals. The input AC voltage was fed to the device under test (DUT) by a BK Precision AC voltage source. An electronic load was used in constant current (CC) mode.
The efficiency of 10%, 25%, 50%, 75% and 100% load is measured at nominal and extreme cases of input voltage. The average efficiency is calculated from four points of efficiency at 25%, 50%, 75% and 100%. The efficiency measurements were calculated with voltage reading before the PD connector (do not include the PD connector losses and the cable loss).
Figure 5: Test setup for efficiency measurements
Table 2: Measured efficiency over line and load range at PCB end for 140W
Table 3: Measured efficiency over line and load range at PCB end for 100W
Figure 6: Efficiency over line for 100W (20Vout) and 140W (28Vout)
The following efficiency measurements are the function of output current and based on it are plotted the graphs of efficiency vs output current. Also, based on these evaluated the average and 10% efficiency.
Table 4: Low input voltage
Table 5: High input voltage
Figure 7: Efficiency vs output current at 5V
Table 6: Low input voltage
Table 7: High input voltage
Figure 8: Efficiency vs output current at 9V
Table 8: Low input voltage
Table 9: High input voltage
Figure 9: Efficiency vs output current at 15V
Table 10: Low input voltage
Table 11: High input voltage
Figure 10: Efficiency vs output current at 20V
Table 12: Low input voltage
Table 13: High input voltage
Figure 11: Efficiency vs output current at 28V
Table 14: Summarized the efficiency data
Figure 12 : Average efficiency at different input voltages
Figure 13: 10% efficiency at different input voltages
7.2 Standby power
The standby power consumptions are measured at 230VAC at default 5 V output with cable unplugged. They are less than 60 mW. Standby power is measured with a Voltech Power Analyzer PM1000+ and integrated in one minute.
7.3 Output ripple – steady-state operation
The output ripple is measured at the PD cable end at full power (the worst case is at maximum output power) with input voltages of 90 VAC, 115VAC, 230VAC and 264 VAC.
0.1 µF and 10 µF electric capacitors are used. Measured output ripple voltage is in steady state (DC load current).
Figure 14: 28 V output voltage ripples
7.4 Dynamic load steps
The dynamic load steps from 0.5 A to 5 A, with slew rate 1 A/µs are measured at 115 VAC and 230VAC.
Figure 15: Dynamic load test
7.5 Measurement results
Thermal results were checked at the worst-case condition where the efficiency is lower input voltages 90Vac at 20V/5A after one hour’s burn-in at room temperature.
Figure 16: Thermal results
7.6 Conducted emissions (EN 55022 class B)
The conducted EMI was measured by a certified safety laboratory according to the test standard of EN 55022 (CISPR 22) class B. The demo board was setup at a different output full load with an input voltage of 115 VAC and 230 VAC. The system passed CISPR 22 class B.
Figure 17: Conducted emissions at 115 V AC and 28V/5 A load; Average (left), Qpeak (right) measurements
Figure 18: Conducted emissions at 230 V AC and 28V/5 A load; Average (left), Qpeak (right) measurements
7.7 Operational waveforms – Derating factor
By Rompower passive clamp technology it was able to achieve the lower voltage spike on the primary switch device and the energy recovered from leakage inductance/clamp, it is used in the current injection circuit to guarantee the lower power dissipation in main sw. At low line, where the converter is in QR mode and the voltage on the main SW is lower, the energy from clamp is returned to the input through current injection circuit and the energy stored to the clamp capacitor, it can return in the secondary through the reverse recovery time of the clamp diodes.
By current injection circuit (ZVS circuit), it was achieved no spike on the SR switch in any condition (bust mode, QR or DCM)
Figure 19: Switching waveforms for flyback stage
Figure 20: Switching waveforms PFC stage
