Flyback Switching Power Supply Output Capacitance Calculator

Formulas

The formulas to calculate the minimum output capacitance are:

Calculate $T_{on}$ :

$T_{on} = \frac{1}{f} \times D_{max}$

Calculate $I_{pk}$ :

$I_{pk} = 2 \times \frac{I_o}{1 - D_{max}}$

Calculate Minimum Output Capacitance $C_{min}$ :

$C_{min} = \frac{I_{pk} \times T_{on}}{V_{ripple}} \times 10^6 \, (\mu F)$

Calculate ESR:

$ESR = \frac{65}{C_{min} \times 10^6} \, (\Omega)$

Switching Frequency (f): The frequency at which the switch operates, measured in kHz.

Output Current (Io): The current delivered to the load, measured in amperes (A).

Maximum Duty Cycle (Dmax): The maximum duty cycle of the switch.

Output Ripple Voltage (Vripple): The acceptable peak-to-peak ripple voltage at the output, measured in millivolts (mV).

T_on: The on-time of the switch, measured in microseconds (µs).

I_pk: The peak current, measured in amperes (A).

C_min: The minimum output capacitance, measured in microfarads (µF).

ESR: Equivalent series resistance, measured in milliohms (mΩ).

Example: Calculate the minimum output capacitance

Step 1: Calculate $T_{on}$ :

$T_{on} = \frac{1}{60,000} \times 0.457 = 7.62 \, \mu s$

Step 2: Calculate $I_{pk}$ :

$I_{pk} = 2 \times \frac{1}{1 - 0.457} = 3.68 \, A$

Step 3: Calculate $C_{min}$ :

$C_{min} = \frac{3.68 \times 7.62 \times 10^{-6}}{0.12} \times 10^6 = 233.68 \, \mu F$

Step 4: Calculate ESR:

$ESR = \frac{65}{233.68 \times 10^6} \times 10^3 = 0.00028 \ = 0.28 \, \Omega$