High Current Voltage Regulation
High Current Voltage Regulation
Connect voltage regulators in parallel to increase the current which can be regulated
electric circuit | electronics | generalVoltage regulators are available as easy to use three terminal integrated circuits - one terminal for the input voltage, one for the output voltage, and one for the ground (0V). The most commonly used are from the
78XX series - 7812 for 12 Volts, and 7805 for 5 Volts etc. Also of particular use for
renewable energy generators are very efficient
low dropout regulators such as the
LM2940 series - LM2940CT-12 for 12 Volt etc.
One common shortfall of these common regulators is they are rated at just
1 Amp output current. It is usually possible to use them with higher currents, but a large heatsink and/or fan is essential. Regulators for higher currents than 1 Amp are available, but tend to be expensive, and still require good heatsinking.
Pictured above is a circuit from the
Fairchild LM7812 datasheet. This uses a
power transistor and a
power resistor to take on some of the workload enabling higher currents to be regulated. With this set up, the power transistor and power resistor need
heatsinking, and selecting the correct specification of transistor and resistor, and getting everything set up is not particularly easy.
One alternative is instead to
parallel connect multiple three terminal regulators, with each regulator handling up to 1 Amp of current.
Parallel Connecting Mulitple Voltage Regulators
Voltage regulators such as the LM7812 cannot just be connected in parallel without additional circuitry. Each voltage regulator, though nominally rated at the same voltage, will in practice output a slightly different voltage - for example, three LM7812's could output 11.98, 12.01, and 12.06 respectively.
This tiny difference in voltage has the disastrous consequence of making the regulator with the lowest output voltage trying to carry
all of the current. This will cause it's internal
thermal protection to trigger (as the regulator overheats)
effectively removing that regulator from the circuit and kicking off a chain reaction up through the remaining parallel-connected regulators.
The circuit shown above* (from the
EDN article
High-Current Supply uses Standard Three-terminal Regulator) has two
LM7812 voltage regulators connected in parallel for a maximum total output current of 2 Amps - double the rated current of one LM7812.
*
Diodes D1, D2, and D are 1N4007; C=47,000uF, C1 and C2 are 4,700uF.
An even simpler way to parallel multiple voltage regulators together is to add very low (below 1 Ohm)
ballast/
equalising resistors in series with the regulator outputs. Doing so should make the regulators
share current equally and therefore operate together without problems. It is worth noting however that this approach to
load balancing makes regulation a bit less accurate.
An example of this simplistic approach in use can be seen on the following web page
Experimental 12V/6A Power Supply in which six LM7812 regulators were connected in parallel with
0.25 Ohm load balancing resistors (made up of four 1 Ohm resistors in parallel) connected in series with the output from each 7812 regulator. The above image shows the key elements in this 6 Amp 12 Volt regulator.
Article Last Modified: 17:16, 5th Dec 2007
Recommended Related Articles
People who read this article also enjoyed the following articles:
Using The LM317T To Regulate VoltageUse an LM317T to regulate voltage in renewable energy projects
Article Last Modified: 15:04, 7th Mar 2008electric circuit | electronicsLM317T Voltage Regulator ChipLearn about the LM317T and its uses in renewable energy projects
Article Last Modified: 09:34, 30th Mar 2007electronics | electric circuitUsing The LM317T With LED LightingUse an LM317T to regulate the current in LED lighting projects
Article Last Modified: 12:47, 12th Mar 2008lighting | electric circuitMake a Simple Battery Status MonitorMonitor battery status with this easy electric circuit project - no skill required!
Article Last Modified: 12:33, 16th Mar 2007storage | electric circuitHigh Capacity Alternative to 9 Volt BatteryGet ten times the capacity of a 9 Volt battery to power your devices
Article Last Modified: 09:39, 7th Jun 2008general | electric circuit | solarZener Diode Voltage RegulatorMake a simple zener diode voltage regulator
Article Last Modified: 17:31, 7th Mar 2008electric circuit | educationSolar Battery Charger With LM317TFind out how to make a current controlled solar battery charger using an LM317T
Article Last Modified: 09:34, 30th Mar 2007solar | education | electric circuitLM317 Current CalculatorA handy online output current calculator for the LM317, LM338, and other linear voltage regulators
Article Last Modified: 12:47, 12th Mar 2008electric circuit | electronics | generalSolar Greenhouse Heat SinkFind out how to make a solar powered heatsink for your greenhouse
Article Last Modified: 11:32, 24th Jun 2008solar | general200W 12V Immersion HeaterUse a wind turbine to heat water for your home via an immersion heater element
Article Last Modified: 13:18, 30th Jun 2008heating | wind
|
|
