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[QUOTE=Real Gambler;747109]Yikes, I would not put them in parallel!   If they were perfect, this would not be a problem.  (Ex.  All three could give 6.0000000 volts).

The problem is they are not perfect.  So one my want to regulate at 6.1V, the second at 5.95V and the third at 6.0Volts (they would be closer to 6.0V, but I made it look worst so it's more obvious).

So, each is trying VERY hard to keep the output at their voltage, fighting the other two.  I think I would put a diode and a very low ohm resistor on each output (so end result would be about 5.2 volts to your RX and a little bit of voltage drop in each resistors to protect the regulators), or I would simply use one single bigger TO-3 version which can output 3 amps on it's own. Weight wise, it would probably be about the same as the 3 TO-220 you're using right now anyway.

In both case, make sure you have enough air going around them to cool them off.  Remember, the RX itself doesn't draw that much current, but with all servos, you do![/QUOTE]

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Topic Review (Newest First)

09-08-2010 10:16 AM

Dangaras

Re: 7806 voltage reg

Quote:

Originally Posted by cf-drg

So if I only used 1, it's not a problem.. It's if I need more than 1 amp and have to gang them up, that I will have to build the curcuit.. Thanks for the schematic Moo.. I did use heat shrink and made an oversized heatsink out of aluminum..

Unless you have all the parts lying around, the most economical thing to do is buy a few from Hobbyking or work with someone you know to add to their order to save on shipping. You will definitely get better results using a switching regulator than a linear in terms of power consumption/loss, reliability, space and weight saving..

For anything from foamies up to 60 size with 6 or 8 standard servos these 2 have been very reliable:

http://www.hobbyking.com/hobbyking/s..._5.5~23v_Input

http://www.hobbyking.com/hobbyking/s...oise_Reduction

If I need more than 3 amps, I can insert a 1N5820 in line with each +Ve output line and set the output to 6V to give me twice as much current at the 5.5V mark. It is amazing how well these guys work together.

I also remember using some TO-22x type packaged switching regulators that had 5 pins. The output voltages and currents were compatible with the 78xx series, just dont remember the exact specifics. They were available from Digikey.ca... Might help.

09-08-2010 08:39 AM

cf-drg

Re: 7806 voltage reg

09-07-2010 09:18 PM

Dangaras

Re: 7806 voltage reg

The best diode you would want is a 1N5820, 3A, 20V Schottky Rectifier with a voltage drop of 0.475V.

09-07-2010 07:57 PM

moo

Re: 7806 voltage reg

Quote:

Originally Posted by Real Gambler

Diode was simply extra safety since

unnecessary

it's internal circuitry is linear and bipolar
(and the internal circuitry includes a load resistor)

Quote:

Originally Posted by cf-drg

and thought I would tinker around with them on a foamy

one amp should be plenty on a foamy don't forget the heatsink ... also

12V-6V=6V
6Vx1A=6W
max temp - ambient temp = 60C - 25C = 35C
estimate air flow at 10m/s
pull out your heatsink data book ...

09-07-2010 03:56 PM

Real Gambler

Re: 7806 voltage reg

Quote:

Originally Posted by moo

This is true of switching regulators, but 7806 is a linear regulator.
A small value high power resistor on the output of each is suggested.
(maybe .1 to .47 Ohm, 1 Watt for R1, R2, R3)

That's what I basically said no? "I think I would put a diode and a very low ohm resistor on each output (so end result would be about 5.2 volts to your RX and a little bit of voltage drop in each resistors to protect the regulators)"

Diode was simply extra safety since we can afford going down to 5.2Volts. Most RX and servos are happy with anything between 5.0V to 6.0V.

09-07-2010 09:27 AM

cf-drg

Re: 7806 voltage reg

Thanks for the info.. Just that I had a few of these and thought I would tinker around with them on a foamy.. I can get a nice BEC from HK for $6 US, should probably just go that route.. It's not like I need 6-8 amps to my RX, scale floatplanes don't 3-D that well.. I think I will try and convert all my aircraft to a lipo rx packs though..

09-07-2010 12:36 AM

moo

Re: 7806 voltage reg

'headroom' is actually dropout voltage, up to 2 Volts for older devices
meaning they need two volts more in than out (at 1 Ampere)

09-07-2010 12:31 AM

moo

Re: 7806 voltage reg

Quote:

Originally Posted by Real Gambler

So, each is trying VERY hard to keep the output at their voltage, fighting the other two. I think I would put a diode and a very low ohm resistor on each output

This is true of switching regulators, but 7806 is a linear regulator.
A small value high power resistor on the output of each is suggested.
(maybe .1 to .47 Ohm, 1 Watt for R1, R2, R3)

09-06-2010 05:10 PM

Spitball

Re: 7806 voltage reg

The other issue with the '78' series of IC regulators is that they require quite a bit of headroom, ie. voltage above the output voltage. I believe the LM 2940 (I think it is) is much superior here but you can't beat a UBEC, they seem to called, in this application. Good regulation and much more efficient.
But '78's' can't be put in parallel just like that, but require extra components to ensure that they share the output load current equally, cf-drg.

09-06-2010 04:32 PM

Real Gambler

Re: 7806 voltage reg

Quote:

Originally Posted by GoodDad

Go look at this site: http://www.sentex.ca/~mec1995/circ/ampboost.html

GoodDad

Smart! I guess using something more powerful than a TIP2955 (adding weight but giving more current) and a very small regulator would be great.

Still, I think a good old BEC would likely be a better choice. But knowing myself, I could see myself using a regulator if I was stuck, so why not!

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