# Energy Storage in Capacitors

#### paul_alan

Joined Nov 5, 2011
43
What is the formula to calculate power in a capacitor circiit?

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#### Jony130

Joined Feb 17, 2009
5,484
W = 0.5*C*V^2 --> divide both sides by 0.5*V^2

W/(0.5*V^2) = C

C = 180J/ (0.5 * 450V^2) = 1777uF

Q = C*V = 0.8C

#### crutschow

Joined Mar 14, 2008
34,021
W = 0.5*C*V^2 --> divide both sides by 0.5*V^2

W/(0.5*V^2) = C

C = 180J/ (0.5 * 450V^2) = 1777uF

Q = C*V = 0.8C
Just to be clear, W in these equations is energy in Joules stored on the capacitor, not power (which is energy per unit time).

If the capacitor is being charged and discharged at a specific frequency (f) then the power dissipated in the charge and discharge circuit in watts is f*C*V^2.

#### bountyhunter

Joined Sep 7, 2009
2,512
If the capacitor is being charged and discharged at a specific frequency (f) then the power dissipated in the charge and discharge circuit in watts is f*C*V^2.
Yep, any R-C snubber used in a switcher has power dissipation in the snubber resistor given by:

Freq x C x V (squared)

Doesn't matter what the Ohmic value of the resistor is, same power.

#### crutschow

Joined Mar 14, 2008
34,021
Yep, any R-C snubber used in a switcher has power dissipation in the snubber resistor given by:

Freq x C x V (squared)

Doesn't matter what the Ohmic value of the resistor is, same power.
It's also the power dissipated by an amplifier or digital circuit driving a capacitive load. Charging and discharging the stray capacitance on a circuit board or internally in an IC is the primary cause of power dissipation in CMOS circuits.