Charge pump
Encyclopedia
A charge pump is a kind of DC to DC converter
that uses capacitor
s 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, a two-stage cycle can be used to generate a higher pulsed voltage from a lower-voltage supply. In the first stage of the cycle, a capacitor is connected across the supply, charging it to that same voltage. In the second stage of the cycle, the circuit is reconfigured so that the capacitor is in series with the supply to the load. Ignoring leakage
effects, this effectively provides double the supply voltage to the load (the sum of the original supply and the capacitor). The pulsing nature of the higher voltage output is typically smoothed by the use of an output capacitor.
An external or secondary circuit drives the switching, typically at tens of kilohertz up to several megahertz. The high frequency minimizes the amount of capacitance required as less charge needs to be stored and dumped in a shorter cycle. 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 the reference signal (often from a crystal oscillator) and the output signal is translated into two signals – UP and DN. The two signals control switches to steer current into or out of a capacitor, causing the voltage across the capacitor to increase or decrease. In each cycle, the time during which the switch is turned on is proportional to the phase difference, hence the charge delivered is dependent on the phase difference also. The voltage on the capacitor is used to tune a voltage-controlled oscillator (VCO), generating the desired output signal frequency. The use of a charge pump naturally adds a pole at the origin in the loop transfer function of the PLL, since the charge-pump current is driven into a capacitor to generate a voltage (V=I/(sC)). The additional pole at the origin is desirable because when considering the closed-loop transfer function of the PLL, this pole at the origin integrates the error signal and causes the system to track the input with one more order. The charge pump in a PLL design is constructed in integrated-circuit (IC) technology, consisting of pull-up, pull-down transistors and on-chip capacitors. A resistor is also added to stabilize the closed-loop PLL.
DC to DC converter
A DC-to-DC converter is an electronic circuit which converts a source of direct current from one voltage level to another. It is a class of power converter.- Usage :...
that uses capacitor
Capacitor
A capacitor is a passive two-terminal electrical component used to store energy in an electric field. The forms of practical capacitors vary widely, but all contain at least two electrical conductors separated by a dielectric ; for example, one common construction consists of metal foils separated...
s as energy storage elements to create either a higher or lower voltage
Voltage
Voltage, otherwise known as electrical potential difference or electric tension is the difference in electric potential between two points — or the difference in electric potential energy per unit charge between two points...
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, a two-stage cycle can be used to generate a higher pulsed voltage from a lower-voltage supply. In the first stage of the cycle, a capacitor is connected across the supply, charging it to that same voltage. In the second stage of the cycle, the circuit is reconfigured so that the capacitor is in series with the supply to the load. Ignoring leakage
Leakage
Leakage may refer to:*Leakage *Memory leak, in computer science*Leakage *Leakage *Leakage *Leakage...
effects, this effectively provides double the supply voltage to the load (the sum of the original supply and the capacitor). The pulsing nature of the higher voltage output is typically smoothed by the use of an output capacitor.
An external or secondary circuit drives the switching, typically at tens of kilohertz up to several megahertz. The high frequency minimizes the amount of capacitance required as less charge needs to be stored and dumped in a shorter cycle. 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
Voltage multiplier
thumb|right|280px|Villard cascade voltage multiplier.A voltage multiplier is an electrical circuit that converts AC electrical power from a lower voltage to a higher DC voltage, typically by means of a network of capacitors and diodes....
.
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
Phase-locked loop
A phase-locked loop or phase lock loop is a control system that generates an output signal whose phase is related to the phase of an input "reference" signal. It is an electronic circuit consisting of a variable frequency oscillator and a phase detector...
(PLL) circuits. This is a completely different application. In a PLL the phase difference between the reference signal (often from a crystal oscillator) and the output signal is translated into two signals – UP and DN. The two signals control switches to steer current into or out of a capacitor, causing the voltage across the capacitor to increase or decrease. In each cycle, the time during which the switch is turned on is proportional to the phase difference, hence the charge delivered is dependent on the phase difference also. The voltage on the capacitor is used to tune a voltage-controlled oscillator (VCO), generating the desired output signal frequency. The use of a charge pump naturally adds a pole at the origin in the loop transfer function of the PLL, since the charge-pump current is driven into a capacitor to generate a voltage (V=I/(sC)). The additional pole at the origin is desirable because when considering the closed-loop transfer function of the PLL, this pole at the origin integrates the error signal and causes the system to track the input with one more order. The charge pump in a PLL design is constructed in integrated-circuit (IC) technology, consisting of pull-up, pull-down transistors and on-chip capacitors. A resistor is also added to stabilize the closed-loop PLL.
Applications
- A common application for charge pump circuits is in RS-232RS-232In telecommunications, RS-232 is the traditional name for a series of standards for serial binary single-ended data and control signals connecting between a DTE and a DCE . It is commonly used in computer serial ports...
level shiftLogic levelIn digital circuits, a logic level is one of a finite number of states that a signal can have. Logic levels are usually represented by the voltage difference between the signal and ground , although other standards exist...
ers 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 LEDLEdLEd is a TeX/LaTeX editing software working under Microsoft Windows. It is a freeware product....
drivers, generating high bias voltages from a single low-voltage supply, such as a battery. - A charge pump providing a negative voltage spikeVoltage spikeIn electrical engineering, spikes are fast, short duration electrical transients in voltage , current , or transferred energy in an electrical circuit....
has been used in NES-compatible games not licensed by Nintendo in order to stun the Nintendo Entertainment System lockout chip10NESThe 10NES system is a lock-out system designed for the American version of the Nintendo Entertainment System video game console. Various companies found ways to bypass the authorization chip.-Design:...
. - As of 2007, charge pumps are integrated into nearly all EEPROMEEPROMEEPROM stands for Electrically Erasable Programmable Read-Only Memory and is a type of non-volatile memory used in computers and other electronic devices to store small amounts of data that must be saved when power is removed, e.g., calibration...
and flash memoryFlash memoryFlash memory is a non-volatile computer storage chip that can be electrically erased and reprogrammed. It was developed from EEPROM and must be erased in fairly large blocks before these can be rewritten with new data...
integrated circuits. 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). , commercially available flash memory and EEPROM memory requires only one external power supply – generally 1.8 or 3.3V. A higher voltage, used to erase cells, is generated internally by an on-chip charge pump. However, some researchers say that a solid-state driveSolid-state driveA solid-state drive , sometimes called a solid-state disk or electronic disk, is a data storage device that uses solid-state memory to store persistent data with the intention of providing access in the same manner of a traditional block i/o hard disk drive...
using a single large boost converterBoost converterA boost converter is a power converter with an output DC voltage greater than its input DC voltage. It is a class of switching-mode power supply containing at least two semiconductor switches and at least one energy storage element...
will cost less and use 33 percent less power than current SSDs which use a charge pump on every flash chip.
External links
- Charge Pump DC/DC Converters. Applications, circuits and solutions using inductorless (charge pump) dc/dc converters.
- 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
- Linearized three state phase detector by Steven F. Gillig (patent filed 1990, awarded 1990, assigned to MotorolaMotorolaMotorola, Inc. was an American multinational telecommunications company based in Schaumburg, Illinois, which was eventually divided into two independent public companies, Motorola Mobility and Motorola Solutions on January 4, 2011, after losing $4.3 billion from 2007 to 2009...
) - Linearized digital phase and frequency detector by John D. Hatchett and Andrew S. Olesin (patent filed 1980, awarded 1983, assigned to MotorolaMotorolaMotorola, Inc. was an American multinational telecommunications company based in Schaumburg, Illinois, which was eventually divided into two independent public companies, Motorola Mobility and Motorola Solutions on January 4, 2011, after losing $4.3 billion from 2007 to 2009...
)
See also
- Cockcroft-Walton generatorCockcroft-Walton generatorThe Cockcroft–Walton generator, or multiplier, is an electric circuit which generates a high DC voltage from a low voltage AC or pulsing DC input...
- Voltage multiplierVoltage multiplierthumb|right|280px|Villard cascade voltage multiplier.A voltage multiplier is an electrical circuit that converts AC electrical power from a lower voltage to a higher DC voltage, typically by means of a network of capacitors and diodes....
- Switched capacitorSwitched capacitorA switched capacitor is an electronic circuit element used for discrete time signal processing. It works by moving charges into and out of capacitors when switches are opened and closed. Usually, non-overlapping signals are used to control the switches, so that not all switches are closed...
- Charge Transfer SwitchCharge transfer switchA charge transfer switch OR CTS charge pump is a charge pump that offers better low-voltage performance and "a better voltage pumping gain and a higher output voltage" than previous charge pumps such as the Dickson charge pump....
- Voltage doublerVoltage doublerA voltage doubler is an electronic circuit which charges capacitors from the input voltage and switches these charges in such a way that, in the ideal case, exactly twice the voltage is produced at the output as at its input....