Hold-Up Capacitor: Calculations And Uses

What Is Hold-Up Time?

Hold-Up is when the power supply keeps supplying power to load before it drops below the specified voltage level. This voltage level and the corresponding hold-up time differ for different power supplies.

Generally, linear supplies have very short hold-up times and go to zero almost instantaneously. However, the switched-mode supplies can hold up until the power comes back on or the UPS gets connected.

This is because switched-mode power supplies have hold-up capacitors after the rectification stage that keep the power within given levels.

How To Calculate The Value Of Hold-Up Capacitor?

It has been established earlier that switched-mode power supplies use hold-up capacitors to hold the power level above a specific level in case of power cuts.

Now to calculate the value of such a capacitor, the supply's hold-up time is set first. Secondly, the output voltage and current values are to be known to calculate power. This power value is to be used later for capacitor value calculation.