SLUSDD4B April 2019 – December 2020 UC1843B-SP

PRODUCTION DATA

- 1 Features
- 2 Applications
- 3 Description
- 4 Revision History
- 5 Pin Configuration and Functions
- 6 Specifications
- 7 Detailed Description
- 8 Application Information Disclaimer
- 9 Power Supply Recommendations
- 10Layout
- 11Device and Documentation Support
- 12Mechanical, Packaging, and Orderable Information

- KGD|0
- HKU|10

The poles and zeros of a flyback converter can be found with the following equations:

Equation 36. ${f}_{ZESR}=\frac{1+D}{2\pi \times {C}_{out}\times {R}_{ESR}}$

Equation 37. ${f}_{ZESR}=\frac{1+0.5}{2\pi \times 1146\mu F\times 0.009\Omega}=23.15kHz$

Equation 38. ${f}_{P}=\frac{1}{2\pi \times {C}_{out}\times {R}_{o}}$

Equation 39. ${f}_{P}=\frac{1}{2\pi \times 1146\mu F\times 0.5}=278Hz$

Equation 40. ${f}_{RHPZ}=\frac{{R}_{out}\times (1-{D}_{MAX}{)}^{2}}{2\pi \times \frac{{L}_{PRI}}{{{N}_{ps}}^{2}}\times {D}_{MAX}}$

Equation 41. ${f}_{RHPZ}=\frac{0.5\times (1-0.5{)}^{2}}{2\pi \times \frac{21\mu H}{3.{33}^{2}}\times 0.5}=21kHz$

Equation 42. ${f}_{CompensationZero}=\frac{1}{2\pi \times {R}_{COMP}\times {C}_{COMP}}=\frac{1}{2\pi \times 5.11k\Omega \times 0.22\mu F}=142Hz$

Equation 43. ${f}_{CompensationPole}=\frac{1}{2\pi \times {R}_{COMP}\times {C}_{HF}}=\frac{1}{2\pi \times 5.11k\Omega \times 1500pF}=20.76kHz$

Type IIB compensation was selected to compensate the poles and zeros of the flyback converter for the design. Since the right half plane zero (RHPZ) of the flyback converter is unable to be compensated, the crossover frequency of the converter should be between one fourth to a whole decade below the RHPZ of the converter. Type IIB compensation has 1 pole and 1 zero to help compensate the converter. The pole from the compensation is suggested to be placed by the RHPZ of the converter and the zero from compensation is suggested to be placed a decade before the expected crossover frequency. Using these guidelines the compensation values for the converter were picked for the converter. For the non-isolated portion of the board this means choosing the value of the compensation resistors and capacitors along these guidelines. Increasing or decreasing the gain of the design can be compensated for by dividing the resistor from compensation down and increasing the values of the capacitors by the same amount. This allows for the gain to be controlled in the system without changing the poles and zeros of the system. Optimization is needed for compensation values, and those values can be validated through testing.