Go Down

Topic: linear regulator (Read 711 times) previous topic - next topic

arduinoPi

I have a 5 volt linear regulator that can give out 1 amp if I put say 5 regulators in parallel would I be able to get 5 amps?

mmcp42

noooooooooooooooooo
you would get 5 dead regulators!
if you need 5 amps get a bigger regulator
there are only 10 types of people
them that understands binary
and them that doesn't

majenko

It is possible, but you require extra circuitry around the regulators.  Plus, if the regulators aren't 100% matched then the load will be mismatched and you will find that they may start overheating.

For that kind of current draw you really need to go for a switching regulator.  The power wastage of a linear regulator at those kinds of current is massive.

Say you're dropping 12V to 5V with 5A.  That's a 7V - and 35W of power wasted.

A TO-220 packaged regulator with typical thermal resistances without additional heatsinking would reach a junction temperature of a whopping 1,915°C

Even a 1A regulator like yours with that kind of voltage drop and maxing out the 1A current would reach over 400°C.

pgmartin

#3
Jan 23, 2012, 02:37 pm Last Edit: Jan 23, 2012, 02:42 pm by pgmartin Reason: 1
You can add a power transistor to get more current. Look at the 78xx datasheet in the typycal applications section: http://www.datasheetcatalog.org/datasheet/nationalsemiconductor/LM78XX.pdf


Or more here:

cr0sh


You can add a power transistor to get more current. Look at the 78xx datasheet in the typycal applications section: http://www.datasheetcatalog.org/datasheet/nationalsemiconductor/LM78XX.pdf


Or more here:



...and this is the typical way of getting more current with a 78xx linear reg; just realize you are going to want to use a good heatsink on both (and the one on the transistor will be fairly large, depending on your current reqs)...
I will not respond to Arduino help PM's from random forum users; if you have such a question, start a new topic thread.

retrolefty

I'm of the opinion that now a days any regulator application requiring more then one amp output should be based on switching regulators, not linear regulators. The gains in efficiency and reduced need of size of heatsinks is just to high to ignore. The price of cheap Asian switching regulator modules up to around 3 amps even makes building your own regulator circuits or modules a questionable activity.

Lefty

jwatte

And of course those cheap Asian regulator modules will never self-oscillate when using miscellaneous reactive loads, right?
:-)

retrolefty


And of course those cheap Asian regulator modules will never self-oscillate when using miscellaneous reactive loads, right?
:-)



Maybe. I've bought both step-up and a step-down regulator modules and they worked fine to spec and quality seemed fine. I'm sure there may be variation between manfactures but that is always the case. The ones I have seemed to follow the recommended datasheet application designs, and one even added extra low pass filtering on it's output to keep ripple at lower then 2 mv.

So what is your point that a average person will be able to build their own switching regulator and not have such problems occur? We have seen here begineers that have had their DIY linear regulators go into self-oscillation usually as a result of not understanding the need and method of input and ouput caps around the chip.

Lefty

arduinoPi

is there any type of regulator circuit that can say take 12 volts down to 5 and take the 7 volts dropped and feed it to another device instead of heat for example a 12 volt motor

retrolefty


is there any type of regulator circuit that can say take 12 volts down to 5 and take the 7 volts dropped and feed it to another device instead of heat for example a 12 volt motor


No.


zoomkat

You need to go to hobbyking or ebay and search for UBEC
Google forum search: Use Google Advanced Search and use Http://forum.arduino.cc/index in the "site or domain:" box.

jwatte



is there any type of regulator circuit that can say take 12 volts down to 5 and take the 7 volts dropped and feed it to another device instead of heat for example a 12 volt motor


No.




The point of linear regulators is that they "burn" the over-voltage by the drawn current to make the voltage out very precise. It adjusts the amount of "burn" very quickly to changes in draw. If you draw a lot of current on the voltage out, it means it has to burn a lot of current, and it'll get warm. A load that it cannot control precisely (such as a motor) won't be useful to the regulator.

On the other hand, the point of a switching regulator is that it basically works as a low-pass filter on a PWM signal, where the duty cycle of the PWM is set to coincide with the voltage/current draw needed at the output.

It is possible to build a switching regulator that switches "to" something when it's switching "from" the regulated output. The available power (voltage) on the "to" output would then vary inversely with the draw of the regulated output. However, this is not really a win, because the "off" part of the PWM duty cycle doesn't really "cost" any power -- this is how well-designed switching power supplies can have > 95% efficiency in their sweet spot.

Go Up