SLUAAP2 March   2023 LMG2610 , UCC28782

 

  1.   Abstract
  2.   Trademarks
  3. 1Introduction
    1. 1.1 Design Requirement 1: Managing Thermals Induced by Power Losses
    2. 1.2 Design Requirement 2: Reducing Energy Storage Requirement by Switching at High Frequency
  4. 2A Brief Introduction to GaN's Value
  5. 3The Active Clamp Flyback
    1. 3.1 Power Loss Saving 1: Zero-Clamp Loss
    2. 3.2 Power Loss Saving 2: Zero-Voltage-Switching
  6. 4The Value of GaN in Active Clamp Flyback
  7. 5Leveraging Integrated GaN to Simplify ACF Stage
  8. 6Physical Design Implementations Using LMG2610 Integrated Half-Bridge and UCC28782 ACF Controller
    1. 6.1 UCC28782EVM-030
    2. 6.2 PMP23146
  9. 7Leverage Design Tools for ACF
  10. 8Summary
  11. 9References

3.2 Power Loss Saving 2: Zero-Voltage-Switching

Since high switching frequency operation is required to reduce the size of the system, special attention must be given to the frequency-dependent switching losses, as shown in Equation 3.

Equation 3. P l o s s , s w i t c h i n g ,   t u r n - o n = 1 2 C p × V d s 2 × f s w

Here, it is important to note that the switching losses are linearly proportional to the switching frequency, fsw. These incurred switching losses must be mitigated through ZVS. To achieve ZVS, the energy stored in the device output capacitance ,Cp, of the low-side FET, Q1, must be discharged before Q1 is turned on. This is achieved by building a negative current, IM−, in the magnetizing inductance, LM, that is sourced from Cp immediately after Q2 is turned off. When it is time for Q1 to turn on, Cp is discharged and there are zero volts from drain to source, enabling a zero-loss turn-on transition as shown in Equation 4.

Equation 4. P l o s s , s w i t c h i n g ,   t u r n - o n , Z V S = 1 2 C p × V d s 2 × f s w = 0

As a result, since the frequency-dependent turn-on loss is eliminated with ZVS, there is more freedom to increase the switching frequency, enabling the goal of a smaller design.