SLYT877 April   2026 LMG3427R030 , TMS320F280039C

 

  1.   1
  2. 1 Introduction
  3. 2 How to let PFC enter TCM at light loads
  4. 3 How to detect zero current
  5. 4 How to achieve ZVS at TCM
  6. 5 Transitioning between CCM and TCM
  7. 6 Dynamic dead time
  8. 7 Control law and PWM generation
  9. 8 Test results
  10. 9 Conclusion
  11. 10References
  12. 11About the author

8 Test results

This control method was implemented in a 3.6KW totem pole bridgeless PFC [1]. Its maximum switching frequency is 65KHz, the minimum switching frequency is set at 45KHz. The controller uses TI's TMS320F280039C real-time MCU. High-frequency switches use the LMG3427R030 GaN FET, which has a built-in ZCD circuit. A 65KHz interrupt service routine 1 (ISR1) implements the current loop and ZCD delay-time calculation, while a 10KHz interrupt service routine 2 (ISR2) implements the voltage loop. The ZCD delay, ENABLE window, AND logic, and actual switching period measurement are implemented through the TMS320F280039C's configurable logic block (CLB). After configuration, the CLB runs independently without involving the CPU.

The design achieved >180W/in3 power density and has excellent light-load efficiency. Figure 10 and Figure 11 show the efficiency comparison (tested on the same board) between this proposed control method and traditional CCM control, with light-load efficiency improving by as much as 2%.


Efficiency comparison at low line

Figure 10 Efficiency comparison at low line

Efficiency comparison at high line

Figure 11 Efficiency comparison at high line

Figure 12 shows the input current waveform at a 50% load, with no current distortion observed during the mode transition.


Input current waveform at a 50% load

Figure 12 Input current waveform at a 50% load