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aadamson(at)highrf.com
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 Posted: Tue Jun 24, 2008 5:22 pm Post subject: Need a to-220 connector |
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Bob, etc all.
I need to use to TO-220 LM7812C as a simple voltage regulator to take 24V to
12V for a Bob Archer Antenna switch.
No problems with the circuit, the current is small enough (<10ma) that I
don't need any additional parts or heatshrink. But I did want to make it
such that I could replace the lm7812 without having to solder and
unsolder.... Yes I could solder and connector the who regulator, but I
thot... Hmm, wonder if the legs of the to-220 part would fit in regular DB25
female pins and yep, they do, pretty much like the male pin would with just
a smidge of snugness (new word btw)...
If I use heatshrink to keep this all together, does anyone see any issue
with using these 3 pins as a simple "to-220 socket"? I'd crimp up the wires
to the 3 db25 pins, heatshrink them full length, then slide them on the
to-220 and heatshrink it as a unit to the 3 pin wires. Tuck it away and
hope I never have to deal with it, but if I do, cut some heatshrink, replace
the lm7812 and re-heatshrink.
Let me know your thots please...
Thanks,
Alan Adamson
Atlanta, GA
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mrspudandcompany(at)veriz
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| Posted: Wed Jun 25, 2008 3:39 am Post subject: Need a to-220 connector |
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Alan,
Looks like an excellent way to connect, I would do it that way. You are
essentially putting a square pin (LM7812) into a round hole, but, the
"smidge of snugness" will give you a good secure connection. If, at a later
date, say 20 years from now, you have a problem with it, you still have the
option of solder.
Roger
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matronics(at)rtist.nl
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| Posted: Wed Jun 25, 2008 4:13 am Post subject: Need a to-220 connector |
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In general I'd not use a connector at all for this purpose. But if you want
to have a connector for this, why not use a 3-pin connector with the same
pin distance? Check out those 3-pin connectors that you find on computer
fans. They are designed to take flat pins and take a lot less space. Do try
to find a good quality connector for this so it doesn't develop problems
with corrosion. Especially the ground pin is critical, if it loses contact
your switch will get 24V direct.
Rob
---
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nuckolls.bob(at)cox.net
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| Posted: Wed Jun 25, 2008 4:26 am Post subject: Need a to-220 connector |
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At 09:18 PM 6/24/2008 -0400, you wrote:
| Quote: |
<aadamson(at)highrf.com>
Bob, etc all.
I need to use to TO-220 LM7812C as a simple voltage regulator to take 24V to
12V for a Bob Archer Antenna switch.
No problems with the circuit, the current is small enough (<10ma) that I
don't need any additional parts or heatshrink. But I did want to make it
such that I could replace the lm7812 without having to solder and
unsolder.... Yes I could solder and connector the who regulator, but I
thot... Hmm, wonder if the legs of the to-220 part would fit in regular DB25
female pins and yep, they do, pretty much like the male pin would with just
a smidge of snugness (new word btw)...
|
Hmmmm . . . the LM7812 series devices are not guaranteed
"stable" without a couple of capacitors from input and output
to ground.
| Quote: | If I use heatshrink to keep this all together, does anyone see any issue
with using these 3 pins as a simple "to-220 socket"? I'd crimp up the wires
to the 3 db25 pins, heatshrink them full length, then slide them on the
to-220 and heatshrink it as a unit to the 3 pin wires. Tuck it away and
hope I never have to deal with it, but if I do, cut some heatshrink, replace
the lm7812 and re-heatshrink.
Let me know your thots please...
|
For such a tiny amount of current, how about wiring a 1N4742 zener
in series with the switch. Doesn't need capacitors. You can splice
the zener into the switch's feed-wire with techniques illustrated
in . . .
http://aeroelectric.com/articles/Homeless/Homeless_Components.htm
Bob . . .
----------------------------------------)
( . . . a long habit of not thinking )
( a thing wrong, gives it a superficial )
( appearance of being right . . . )
( )
( -Thomas Paine 1776- )
----------------------------------------
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aadamson(at)highrf.com
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| Posted: Wed Jun 25, 2008 5:38 am Post subject: Need a to-220 connector |
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Thanks all for the comments, the one about the computer fans is an
especially good one...
Ok, now I need a bit of an education... Bob, the Zener, will that step the
voltage down from 24v to 12v?
That's all I really need is a reliable 12V out of 24v. The data sheet on
the LM7812C suggested that it didn't need any other components, but I'm
always open to better solutions and if the Zener will do it, then I'm all
for that.
Thanks
Alan
--
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rampil
Joined: 04 May 2007
Posts: 870
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| Posted: Wed Jun 25, 2008 1:15 pm Post subject: Re: Need a to-220 connector |
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Another connector solution is to use quality connector machined crimp
pins on the three leads with mating gender crimp pins on the wiring.
Very thin heat shrink on the bare leads and exposed wires. Heat shrink
over the mated connections, then a wide piece over the regulator and the
whole set of connections.
I agree with Bob regarding the stability (e.g. oscillations) of the 78/7900
family without the input bypass cap and the output filter cap.
Are you very sure that the Archer thingy will object to 24V? If you
have not done so, try calling them to find out.
I'm not an EE, I just played one through 4 years of grad school 
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aadamson(at)highrf.com
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| Posted: Wed Jun 25, 2008 3:00 pm Post subject: Need a to-220 connector |
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Yep, I'm sure, the TR switch won't work with 24v, it's got relays that
switch when the intercomm says one radio or the other is active.
I picked up the Zener as mentioned, but I'm still unclear, it's it just in
series with the switch, in the 24V line and it magically limits (drops) the
voltage to 12v? What a great solution for small current needs if that
assumption is true. The Zeners that I have are good to 1A, what is the max
current you could expect one to operate as a voltage limiter (regulator) I
might have one other item that could use the same thing, but I think it
draws more like 500mils
Alan
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retasker(at)optonline.net
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| Posted: Wed Jun 25, 2008 4:44 pm Post subject: Need a to-220 connector |
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The zener does NOT drop 24V to 12V. It subtracts whatever the zener rating is from whatever the higher voltage is. If you truly have 24V (more likely 28V if the "24V" is the alternator supply), then it would work fine. However, if the situation is that you have a 28V supply from your alternator, then the zener will subtract from that and you will have not 12V but 16V - possibly outside of the allowable tolerance of the TR switch.
The LM7812 does need capacitors for stability, but will supply 12 regardless of the input voltage (until you exceed its ratings).
You could use the zener Bob suggests in a slightly different way to get the 12V you want. If you truly need less than 10mA, you can use a resistor in series with a 12V (1N4742) zener and tap off the voltage you need across the 12V zener. Use a 620 ohm, 0.5W (or greater) resistor. This wastes about 10mA more than if you used an LM7812, but there is no need for capacitors.
Crude schematic follows (use fixed with font to see it):
24V ----RRRR-------ZZZZ---- GND
| |< |
12V GND
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To TR Switch
By the way, if you do decide to use an LM7812, I wouldn't worry about soldering it in. With the minimal load you will be drawing, I suspect it will still be going strong long after your plane turns to dust...
Dick Tasker
Alan Adamson wrote: [quote] [quote]--> AeroElectric-List message posted by: "Alan Adamson" <aadamson(at)highrf.com> (aadamson(at)highrf.com) Yep, I'm sure, the TR switch won't work with 24v, it's got relays that switch when the intercomm says one radio or the other is active. I picked up the Zener as mentioned, but I'm still unclear, it's it just in series with the switch, in the 24V line and it magically limits (drops) the voltage to 12v? What a great solution for small current needs if that assumption is true. The Zeners that I have are good to 1A, what is the max current you could expect one to operate as a voltage limiter (regulator) I might have one other item that could use the same thing, but I think it draws more like 500mils Alan --
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nuckolls.bob(at)cox.net
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| Posted: Wed Jun 25, 2008 6:50 pm Post subject: Need a to-220 connector |
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At 09:34 AM 6/25/2008 -0400, you wrote:
| Quote: |
Thanks all for the comments, the one about the computer fans is an
especially good one...
Ok, now I need a bit of an education... Bob, the Zener, will that step the
voltage down from 24v to 12v?
That's all I really need is a reliable 12V out of 24v. The data sheet on
the LM7812C suggested that it didn't need any other components . . .
|
If you look at the typical application schematics in the
last pages of . . .
http://www.aeroelectric.com/Mfgr_Data/Semiconductors/LM7812.pdf
. . . you will see capacitors to ground on both the input and
output leads of the device. These critters can go into oscillation
at rather high frequencies when they resonate with ship's wiring.
| Quote: | but I'm
always open to better solutions and if the Zener will do it, then I'm all
for that.
|
The zener inserts a constant 12V DROP in the supply voltage
24 becomes 12, 28 becomes 16, etc.
The 7812 is a good choice. I'd SOLDER leads to input and
output leads. Solder the smallest capacitors you can find
directly to the leads of the device. Epoxy the caps to
the regulator. Use same epoxy to beef up lead wires. Bolt
the device right to structure for grounding.
Bob . . .
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