DC to DC converter
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In electronics engineering, a DC to DC converter is a circuit which converts a source of Direct Current from one voltage to another. It is a class of power converter.
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[edit] Usage
DC to DC converters are important in portable electronic devices such as cellular phones and laptop computers, which are supplied with power from batteries. Such electronic devices often contain several sub-circuits with each sub-circuit requiring a unique voltage level different than that supplied by the battery (sometimes higher or lower than the battery voltage, and possibly even negative voltage). Additionally, the battery voltage declines as its stored power is drained. DC to DC converters offer a method of generating multiple controlled voltages from a single variable battery voltage, thereby saving space instead of using multiple batteries to supply different parts of the device.
[edit] Conversion methods
[edit] Linear
A simple method of converting one voltage to another is a circuit known as a voltage divider. This technique uses resistors in series with the voltage supply to provide a lower voltage. However, this method suffers serious drawbacks:
- Provides no voltage regulation
- Requires knowledge of the resistance of the load
- Poor efficiency, which also leads to excess heat dissipation
- Impossible to generate voltages higher than the supply voltage
- Impossible to generate negative voltages, unless the system ground is defined by a node in the resistor network.
Any kind of voltage regulator solves the first two problems, however, linear regulators still have the last three problems.
[edit] Switched-mode conversion
Electronic switch-mode DC to DC converters are available to convert one DC voltage level to another. These circuits, very similar to a switched-mode power supply, generally perform the conversion by applying a DC voltage across an inductor or transformer for a period of time (usually in the 100 kHz to 5 MHz range) which causes current to flow through it and store energy magnetically, then switching this voltage off and causing the stored energy to be transferred to the voltage output in a controlled manner. By adjusting the ratio of on/off time, the output voltage can be regulated even as the current demand changes. This conversion method is more power efficient (often 80% to 95%) than linear voltage conversion which must dissipate unwanted power. This efficiency is beneficial to increasing the running time of battery operated devices. A drawback to switching converters is the electronic noise they generate at high frequencies, which must sometimes be filtered.
Isolated DC-DC converters convert a DC input power source to a DC output power while maintaining isolation between the input and the output, generally allowing differences in the input-output ground potentials in the range of hundreds or thousands of volts. They can be an exception to the definition of DC-DC converters in that their output voltage is often (but not always) the same as the input voltage.
A current-output DC-DC converter accepts a DC power input, and produces as its output a constant current, while the output voltage depends on the impedance of the load. The various topologies of the DC to DC converter can generate voltages higher, lower, higher and lower or negative of the input voltage; their names are:
- Buck
- Boost
- Buck-boost
- Inverting
- Forward
- Flyback converter
- Push-pull
- Half bridge
- Full bridge
- Ćuk
- SEPIC
In general, the term "DC to DC converter" almost always refers to one of these switching converters.
Switching DC to DC converters are available in a wide variety of input and fixed or adjustable output voltages.
DC to DC converters are now available as integrated circuits needing minimal extra components to build a complete converter. DC to DC converters are also available as complete hybrid circuits, ready for use within an electronic device.
[edit] Electrochemical
A further means of DC to DC conversion in the kW to many MW range is presented by using redox flow batteries such as the vanadium redox battery, although this technique has not been applied commercially to date.
[edit] References
- Fang Lin Luo, Hong Ye, Muhammad H. Rashid (2005). Power Digital Power Electronics and Applications. Elsevier. ISBN 0-12-088757-6.
- Abraham I. Pressman (1997). Switching Power Supply Design. McGraw-Hill. ISBN 0-07-052236-7.
- Ned Mohan, Tore M. Undeland, William P. Robbins (2002). Power Electronics : Converters, Applications, and Design. Wiley. ISBN 0-471-22693-9.
- Mingliang Liu (2006). Demystifying Switched-Capacitor Circuits. Elsevier. ISBN 0-7506-7907-7.
- Fang Lin Luo, Hong Ye (2004). Advanced DC/DC Converters. CRC Press. ISBN 0-8493-1956-0.
