Q&A(FAQ) How to calculate external capacitor value from required hold-up time?
1. Requirement of the extension of hold-up time
Demand for longer hold-up times is increasing in order to maintain the output voltage during instantaneous interruptions. Adding a smoothing capacitor extends the hold-up time (Th), while adding an output capacitor increases the fall time (Tf).
2． Extension method of hold-up time
1) In the case of AC-DC converter
To achieve a longer hold-up time, it is necessary to increase the capacitance of the smoothing capacitor on the primary side. The TU series offers design flexibility, allowing the hold-up time to be extended by adding an external smoothing capacitor. For the LFP240F and LFP300F models, an external capacitor unit is available as an optional accessory (available only with the -U1Y option).
2) In the case of DC-DC converter
It is necessary to add an external capacitor between +Vin and -Vin to extend hold-up time.
3．Calculation formula of required capacitance for hold-up time
External capacitor (Cbc) value can be calculated with following formula.
Calculation example
-Product: TUHS10F05
-Input voltage: 100Vac
-Output power: 4W
-Required hold-up time: 200ms
-Ambient temperature: -20ºC
- 1)Efficiency(η) and minimum input voltage for regulated output voltage(Vh) of TUHS10F05 are listed in test data.
η：Efficiency (by Load Current) of P.4 at test data, at 100Vac, 0.8Aout, Efficiency is 80.6%.
Vh：Minimum Input Voltage for Regulated Output Voltage of P.21 at test data, at 50%out, -20ºC,
Minimum Input Voltage for Regulated Output Voltage is 38Vac. - 2)Cbc value can be calculated by above formula.
