Capacitors perform a number of functions in electronics. One major function is simple energy storage, where charge from an applied current is stored within the capacitor and later released back into the circuit as useful current. The rate of charging and discharging can be controlled by placing a resistor in series with the capacitor. This effect is often used in high-current discharge circuits (photoflashes, actuators, etc.), as well as small energy backup supplies for low-power memory ICs. It is also used to smooth out power supply ripple, control timing in ICs, and alter the shape of waveforms.