VOLTAGE REGULATOR CIRCUIT CHEAP
10-04-2004, 04:42 PM
#3
RE: VOLTAGE REGULATOR CIRCUIT CHEAP
do not try this circuit, you'll get into trouble with it. the LM78XX regulators need an input of about 3 volts more than the output.
instead try the LM2940 which is "low dropout" and only needs 0.5 volts more at the input. best to use a 5 volt model so you'll be safe when the batteries drop to around 6 volts. good for 1 amp. do a google and you'll find the data sheet, the same circuit as posted above with the addition of two caps
dave
instead try the LM2940 which is "low dropout" and only needs 0.5 volts more at the input. best to use a 5 volt model so you'll be safe when the batteries drop to around 6 volts. good for 1 amp. do a google and you'll find the data sheet, the same circuit as posted above with the addition of two caps
dave
10-04-2004, 05:07 PM
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RE: VOLTAGE REGULATOR CIRCUIT CHEAP
HO29
If you use this circuit, be sure to add the required capacitors to the input and output of the 78XX series regulators. If you don't they can break into oscillation and burn up. Check the data sheet for values. I think they were supposed to be 2.2 ufd tantalums.
Bill S. (the other Bill)
If you use this circuit, be sure to add the required capacitors to the input and output of the 78XX series regulators. If you don't they can break into oscillation and burn up. Check the data sheet for values. I think they were supposed to be 2.2 ufd tantalums.
Bill S. (the other Bill)
10-05-2004, 01:16 PM
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RE: VOLTAGE REGULATOR CIRCUIT CHEAP
7806 selection based on drop out voltage is a misnomer
The voltage regulator will work until there is not enough voltage to drive the internal components inside of it. That area is around 3-3.5 volts Hmmm... (If you are crazy enough to let your batteries get to that level then go for it) I'm not going to draw my 2S LI-PO batteries down to that level.
The whole drop out voltage thing is the voltage level that the chip is not guaranteed to output the stated output voltage.
My Li-polys output has always been way above what is needed to get the 6 volts out or close to it, then again I do not let my batteries get to a danger level
Flying my 1/2A equipped with 3 pico servos & receiver on a 250mAh 2S LI-POLY battery I've managed to fly over an hour & checked the battery output voltage to be 6.33-6.44 consistently.
The current draw of the componets (servos, receiver) are minimual.
I know this because the chip does not get warm to the touch.
Upon testing, I loaded the chip with a low resistance load & boy OH boy did that chip heat up. If you are driving 1A of current or even close to it you may want to consider heat sinking the chip.
The 7806 I tested maintained regulated 6 volts until the source voltage dropped below 7 volts, see attached pics
So, if you run 3S polys you will never see a drop in your regulated output.
You can add the caps but I do not use them. I have never had a problem.
I fly 1/2A & my airplane is not that expensive.
It's all what you feel comfortable with
Good luck & I hope this saves you a buck or two seeing as a 7806 costs about 50 cent.
The voltage regulator will work until there is not enough voltage to drive the internal components inside of it. That area is around 3-3.5 volts Hmmm... (If you are crazy enough to let your batteries get to that level then go for it) I'm not going to draw my 2S LI-PO batteries down to that level.
The whole drop out voltage thing is the voltage level that the chip is not guaranteed to output the stated output voltage.
My Li-polys output has always been way above what is needed to get the 6 volts out or close to it, then again I do not let my batteries get to a danger level
Flying my 1/2A equipped with 3 pico servos & receiver on a 250mAh 2S LI-POLY battery I've managed to fly over an hour & checked the battery output voltage to be 6.33-6.44 consistently.
The current draw of the componets (servos, receiver) are minimual.
I know this because the chip does not get warm to the touch.
Upon testing, I loaded the chip with a low resistance load & boy OH boy did that chip heat up. If you are driving 1A of current or even close to it you may want to consider heat sinking the chip.
The 7806 I tested maintained regulated 6 volts until the source voltage dropped below 7 volts, see attached pics
So, if you run 3S polys you will never see a drop in your regulated output.
You can add the caps but I do not use them. I have never had a problem.
I fly 1/2A & my airplane is not that expensive.
It's all what you feel comfortable with
Good luck & I hope this saves you a buck or two seeing as a 7806 costs about 50 cent.
