SLVUBB4B November   2017  – February 2023

 

  1.   Abstract
  2.   Trademarks
  3. 1 Topologies Window
  4. 2 FET Losses Calculator
  5. 3 Load Step Calculator
  6. 4 Capacitor Current Sharing Calculator
  7. 5 AC/DC Bulk Capacitor Calculator
  8. 6 RCD-Snubber Calculator for Flyback Converters
  9. 7 RC-Snubber Calculator
  10. 8 Output Voltage Resistor Divider
  11. 9 Dynamic Analog Output Voltage Scaling
  12. 10Dynamic Digital Output Voltage Scaling
  13. 11Unit Converter
  14. 12Loop Calculator
    1. 12.1 Inputs
    2. 12.2 Transfer Functions
      1. 12.2.1  Output Impedance Transfer Function
      2. 12.2.2  Transfer Function VMC Buck Power Stage
      3. 12.2.3  Transfer Function CMC Buck Power Stage
      4. 12.2.4  Transfer Function CMC Boost Power Stage
      5. 12.2.5  Transfer Function CMC Inverting Buck-Boost Power Stage
      6. 12.2.6  Transfer Function CMC Forward Power Stage
      7. 12.2.7  Transfer Function CMC Flyback Power Stage
      8. 12.2.8  Transfer Function Closed Loop
        1. 12.2.8.1 Transfer Function Type II Compensation Network
        2. 12.2.8.2 Transfer Function Type II Transconductance Compensation Network
        3. 12.2.8.3 Transfer Function Type III Compensation Network
      9. 12.2.9  Transfer Function Isolated Type II Compensation Network With a Zener Clamp
      10. 12.2.10 Transfer Function Isolated Type II Compensation Network Without a Zener Clamp
  15. 13Filter Designer
    1. 13.1 Impedances
    2. 13.2 Transfer Functions
    3. 13.3 Filter Output Impedance
    4. 13.4 Damping Factor
  16. 14Additional Information
  17. 15Revision History

7 RC-Snubber Calculator

An RC-Snubber circuit is one option to reduce ringing in a switch mode power supply. Alternatives are the use of MOSFET gate resistors or a resistor in series with the bootstrap capacitor to slow down rise and/or fall times. With the RC-Snubber Calculator, Power Stage Designer helps the designer determine starting values for the snubber resistor and capacitor.

#T5147377-13 shows the RC-Snubber Calculator window.

GUID-C1D299D3-8CD5-448E-A799-76C655025235-low.png Figure 7-1 RC-Snubber Calculator Window
  • Measure the oscillation frequency f0 of the circuit without a snubber network.
  • Add a capacitor C1 in parallel with the rectifier or FET and measure the shifted oscillation frequency f1. Select a C1 value that is several times larger than the stated typical capacitance of the rectifier at full reverse voltage or the output capacitance of the FET.
  • After entering these three values, the tool will propose starting values for the R-C Snubber network.

Frequency shift ratio:

Equation 17. m = f 0 f 1

Parasitic capacitance:

Equation 18. C 0 = C 1 m 2 - 1

Parasitic inductance:

Equation 19. L = m 2 - 1 2 × π × f 0 2 × C 1

Initial Snubber capacitance:

Equation 20. C s n u b = 3 × C 0

Initial Snubber resistance:

Equation 21. R s n u b = L C 0