SLVAFE0 February   2023 TPS62441-Q1 , TPS62442-Q1 , TPS62810-Q1 , TPS62811-Q1 , TPS62812-Q1 , TPS62813-Q1 , TPS628501-Q1 , TPS628502-Q1 , TPS628503-Q1 , TPS62870 , TPS62870-Q1 , TPS62871 , TPS62871-Q1 , TPS62872 , TPS62872-Q1 , TPS62873 , TPS62873-Q1 , TPS62874-Q1 , TPS62875-Q1 , TPS62876-Q1 , TPS62877-Q1 , TPSM8287A06 , TPSM8287A12 , TPSM8287A15

 

  1.   Abstract
  2.   Trademarks
  3. 1Overview
  4. 2Detailed Description
    1. 2.1 Input Filter Design
    2. 2.2 Output Filter Design (Second Stage)
  5. 3Measurement and Analysis
  6. 4Damping of the Filters
  7. 5Further Analysis with Damped Filters
  8. 6Conclusion
  9. 7Reference

4 Damping of the Filters

There are two different ways of damping the filter which can help in reducing the quality factor of filter resonance. Figure 4-1(a) is the filter model without damping. Figure 4-1(b) is the damping technique with series damping resistor Rd and Figure 4-1(c) is the damping method with parallel Rd-Cd branch with filter.



Figure 4-1 Models of an Input Filter Without Damping, as Well as With Two Different Damping Techniques

Quality factor Q is the parameter which determines the damping of any resonance. High quality factor gives sharper resonance peak. Equation 9 helps to determine the quality factor of series RLC circuit.

Equation 9. Q = 1 R d L C

Rd is the damping resistor which can be calculated for particular value of Q which is chosen according to the damping required in the system. Q is taken as 1 for critically damped system. After inserting the Q value in Equation 9, it transforms the equation to Equation 10.

Equation 10. R d = L C

Here the input filter is taken as an example. With the help of Lf,in and Cf,in, Rd is determined with Equation 11 which is 0.23 Ω. In the second method, parallel Rd-Cd is used with the filter to dampen the resonance of the filter. Damping resistor Rd value is already calculated. To avoid affecting the filter cut-off frequency, the damping capacitor Cd needs to be larger than the filter capacitor. At least five times of filter capacitor seems a reasonable value.

Equation 11.                 C d = 5 C i n = 75   μ F


Figure 4-2 Frequency Plots of Filter Model with Different Damping Techniques

It can be observed in the gain-frequency plot in Figure 4-2 that extra series damping capacitor and resistor in parallel to the filter capacitor helps to damp the resonance peak without impacting the attenuation level of the designed filter while technique (b) in Figure 4-1 dampens the resonance peak but it also affects the attenuation level after the cutoff frequency of the filter. After adding the damping branch with the input and output filter, all measurement results are observed again in next section.