Charge Pump

Topics: Charge pump, Capacitor, Phase-locked loop Pages: 3 (763 words) Published: March 25, 2011


What do you mean by charge pump? How does a charge pump supply power in a embedded system without using the power supply lines?

A charge pump is a kind of DC to DC converter that uses capacitors as energy storage elements to create either a higher or lower voltage power source. Charge pump circuits are capable of high efficiencies, sometimes as high as 90-95% while being electrically simple circuits.

Charge pumps use some form of switching device(s) to control the connection of voltages to the capacitor. For instance, to generate a higher voltage, the first stage involves the capacitor being connected across a voltage and charged up. In the second stage, the capacitor is disconnected from the original charging voltage and reconnected with its negative terminal to the original positive charging voltage. Because the capacitor retains the voltage across it (ignoring leakage effects) the positive terminal voltage is added to the original, effectively doubling the voltage. The pulsing nature of the higher voltage output is typically smoothed by the use of an output capacitor.

This is the charge pumping action, which typically operates at tens of kilohertz up to several megahertz to minimize the amount of capacitance required. The capacitor used as the charge pump is typically known as the "flying capacitor". Another way to explain the operation of a charge pump is to consider it as the combination of a DC to AC converter (the switches) followed by a voltage multiplier. The voltage is load-dependent; higher loads result in lower average voltages. Charge pumps can double voltages, triple voltages, halve voltages, invert voltages, fractionally multiply or scale voltages such as x3/2, x4/3, x2/3, etc. and generate arbitrary voltages, depending on the controller and circuit topology. The term 'charge pump' is also used in phase-locked loop (PLL) circuits. This is a completely different application. In a PLL the phase difference between...
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