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Topic: Combining the Ampere of two voltage regulator? (Read 5005 times) previous topic - next topic

eloso

I need a 12VDC voltage regulator that can produce at least 3A. My DC Source is 18.5volts 3.5A. I'm powering gsm shield, arduino, solenoids and etc. I only have here two LM317 regulator and their max current is only 1.5a based on the datasheet. The electronic shop near me doesn't have regulator that can produce more than or equal to 3A. My circuit has a master switch and backup battery that will turn on when the main supply is off. This is the schematic if i will use two regulators with master switch and back up, it is very complicated, and i want to reduce it as shown in the left of the picture by using only one regulator.


eloso

my bad, i forgot the voltage drop of zener diode. so the left schematic in the picture is invalid. -_-

be80be

You don't want to do that there not going to do what you think. One will try to put out more the it should and basically cutoff the second one. See there not going to supply the same voltage.

I would do this use a PNP to get you more current

retrolefty

Well the following are 12vdc 3 amp linear regulators in TO-3 package:
78H12
NTE933

and lambda sometime ago use to have a 12vdc 5 amp regulator in a TO-3 package that you can sometimes find sold as new old stock:

http://www.ebay.com/itm/LAMBDA-LAS1912-12-VOLT-5-AMP-TO-3-REGULATOR-NOS-78H12-NTE933-EQUIVALENT-/380547135339?pt=LH_DefaultDomain_0&hash=item589a60776b

Lefty

eloso


You don't want to do that there not going to do what you think. One will try to put out more the it should and basically cutoff the second one. See there not going to supply the same voltage.

I would do this use a PNP to get you more current


can i use npn transistor only? i have a couple  of TIP120 here.

eloso


Well the following are 12vdc 3 amp linear regulators in TO-3 package:
78H12
NTE933

and lambda sometime ago use to have a 12vdc 5 amp regulator in a TO-3 package that you can sometimes find sold as new old stock:

http://www.ebay.com/itm/LAMBDA-LAS1912-12-VOLT-5-AMP-TO-3-REGULATOR-NOS-78H12-NTE933-EQUIVALENT-/380547135339?pt=LH_DefaultDomain_0&hash=item589a60776b

Lefty


do you have alternative solutions than buying a new regulator? :D



eloso


You don't want to do that there not going to do what you think. One will try to put out more the it should and basically cutoff the second one. See there not going to supply the same voltage.

I would do this use a PNP to get you more current


i simulate that circuit using circuit wizard and it is not working.

be80be

I guess they put that in there data sheet for looks It works.

jackrae

#10
Jan 04, 2013, 12:44 pm Last Edit: Jan 04, 2013, 12:48 pm by jackrae Reason: 1
Let's go back a few steps

Question - Why do you think you need a 3A regulated supply ?  What is your actual load ?  Just because the power supply can provide 3A+ doesn't mean your regulator has to be rated at that figure.  If 6 volts meets you back-up needs than "losing" 12.5 across a linear regulator is a shear waste of power  (12.5 x 3 = 37.5 watts).  If you really need 6 or 12 volts  (you seem to be a bit mixed on voltages) then I'd suggest a switched mode regulator that offers over 90% efficiency with very little heat.

dhenry

Quote
my bad, i forgot the voltage drop of zener diode.


Not to mention that finding zeners that can flow 1.5a/each is quite hard.

If you really need 3amp, you can look into the datasheet of your voltage regulator to see  how to expand their current capabilities.

be80be

Quote
If you really need 3amp, you can look into the datasheet of your voltage regulator to see  how to expand their current capabilities.


I posted that for the OP he said in some kind of simulator it didn't work

dhenry

Quote
it didn't work


thank god we don't live in a simulator.

Quote
so i cannot use npn transistor?


Yes, you can.

eloso


Let's go back a few steps

Question - Why do you think you need a 3A regulated supply ?  What is your actual load ?  Just because the power supply can provide 3A+ doesn't mean your regulator has to be rated at that figure.  If 6 volts meets you back-up needs than "losing" 12.5 across a linear regulator is a shear waste of power  (12.5 x 3 = 37.5 watts).  If you really need 6 or 12 volts  (you seem to be a bit mixed on voltages) then I'd suggest a switched mode regulator that offers over 90% efficiency with very little heat.


I have a solenoid lock,alarm,relay rated at 12v. A couple of 5 inputs to arduino. The gsm shield required is 1.5A. Assuming the arduino is 500mA, gsm is 1.5A, the solenoid lock is 200mA, alarm is 300mA, relay is 50mA then the total is 2550mA or 2.5A. The remaining 500ma is just for extra. The purpose of the back up battery is not to power them all but to only power the arduino and gsm, so that the gsm can still send message and call.

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