Energy Storage in Capacitors

crutschow

Joined Mar 14, 2008
25,133
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
25,133
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.
 
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