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Encyclopedia > Charge pump

A charge pump is an electronic circuit 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. An electronic circuit is an electrical circuit that also contains active electronic devices such as transistors or vacuum tubes. ... Capacitors: SMD ceramic at top left; SMD tantalum at bottom left; through-hole tantalum at top right; through-hole electrolytic at bottom right. ... International safety symbol Caution, risk of electric shock (ISO 3864), colloquially known as high voltage symbol. ... The efficiency of an entity (a device, component, or system) in electronics and electrical engineering is defined as useful power output divided by the total electrical power consumed (a fractional expression). ...


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. The term leakage has numerous definitions: In normal usage, leakage is the diffusion of energy or matter out of a container. ...


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". A kilohertz (kHz) is a unit of frequency equal to 1,000 hertz (1,000 cycles per second). ...


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. It has been suggested that this article or section be merged with charge pump. ...


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.


Applications

  • A common application for charge pump circuits is in RS-232 level shifters where they are used to derive positive and negative voltages (often +10 V and -10 V) from a single 5 V or 3 V power supply rail.
  • Charge pumps can also be used as LCD or white LED drivers, generating high bias voltages from a single low-voltage supply, such as a battery.
  • Charge pumps are a key component in EEPROM and flash memory devices. These devices require a high voltage pulse to "clean out" any existing data in a particular memory cell before it can be written with a new value. Early EEPROM and flash memory devices required two power supplies: +5V (for reading) and +12 V (for erasing). As of 2007, commercially available flash memory and EEPROM memory requires only one external power supply -- generally 1.8 or 3.3V. A higher voltage is used to erase cells, but that higher voltage is generated internally by an on-chip charge pump.

RS-232 (also referred to as EIA RS-232C or V.24) is a standard for serial binary data interchange between a DTE (Data terminal equipment) and a DCE (Data communication equipment). ... LCD redirects here. ... External links LEd Category: TeX ... An EEPROM (also called an E2PROM)[] or Electronically Erasable Programmable Read-Only Memory, is a non-volatile storage chip used in computers and other devices to store small amounts of volatile (configuration) data. ... A USB flash drive. ... 2007 is a common year starting on Monday of the Gregorian calendar. ...

External links and references

  • DC/DC Conversion without Inductors. General description of charge pump operation; example applications using Maxim controllers.
  • Charge-Pump and Step-Up DC-DC Converter Solutions for Powering White LEDs in Series or Parallel Connections
  • Circuit Board Layout Guidelines for White LED Charge Pumps
  • Build a Charge Pump with Ultra-Low Quiescent Current (Iq)

See also


  Results from FactBites:
 
CHARGE PUMP NOTES notes (814 words)
A charge pump looks similar to the voltage multiplier, but the voltage generated is much less than the peak to peak voltage out of the transformer.
I = C * delta in voltage on cap * 60 Hz The difficulty in using charge pumps is determining the "delta in voltage on the capacitor".
I prefer to think of the dual charge pump as doubling the frequency instead of doubling the capacitance because the ripple on the output voltage will be at 120 Hz, not 60 Hz, when a dual charge pump is used.
Charge pump - Wikipedia, the free encyclopedia (460 words)
Charge pump circuits are capable of high efficiencies, sometimes as high as 90-95% while being electrically simple circuits.
Charge pumps can also be used as LCD or white LED drivers, generating high bias voltages from a single low-voltage supply, such as a battery.
Charge pumps are a key component in Flash RAM memory devices.
  More results at FactBites »

 
 

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