12 Volt DC to 9 Volt DC?

[4123]

Can someone out there in electricland tell me how to make a permanent circuit that drops the voltage from 12 VDC to 9 VDC? I know that radio shack has multiple voltage power supplies etc. but I would like to make one of my own that's simple and only provides the 9 VDC without a bunch of extra stuff. I want to permanently mount it. This will be used to power an amplified TV antenna only. Thanks, Ron

[starleen2]

Can someone out there in electricland tell me how to make a permanent circuit that drops the voltage from 12 VDC to 9 VDC? I know that radio shack has multiple voltage power supplies etc. but I would like to make one of my own that's simple and only provides the 9 VDC without a bunch of extra stuff. I want to permanently mount it. This will be used to power an amplified TV antenna only. Thanks, Ron

Look for the power adapter on the antenna and give us the required amperage for the antenna - also where is your 12 volt power coming from? a converter, battery, or something else? Dropping voltage is one thing, but knowing the amps would be useful as well

[4123]

Hi starleen2,

It will be running off the 12 volt battery. I purchased the amplified antenna at a yard sale and it didn't come with the power supply. I looked the antenna up on Google and could only find the operating voltage (9VDC) but no amperage. I'm guessing it's measured in milliamps but can't be sure. I've got a number to call for tech assistance but they won't be open until tomorrow.

[starleen2]

something like this should work

This "buck," or voltage reducing DC/DC converter is designed to power CD players, walkmans, video games, portable TVs, tape recorders, GPS, hand scanners, and radios from automobile cigarette lighter power points.

It is an extremely reliable, full switchmode power supply. These are used extensively as OEM regulating power supplies when 6 to 30 volts is available, and a reduction in voltage is required

found at
http://www.powerstream.com/dc6.htm



Also Most wally worlds will have something similar - why try to recreate the wheel?

[4123]

Thanks for the heads up. I'm well aware of these. But as I said,
I would like to make one of my own that's simple and only provides the 9 VDC without a bunch of extra stuff, multiple connections, plugs, slider switches etc...I'm hoping that someone can tell me what I need to build one. A hard wired 12 volt pair going in, a hard wired 9 volt pair coming out.

[sdtripper2]

Ron:


Sense you want to be in the MacGyver tradition here is a link for you.

Happy tinkering and fists of smoldering iron joys

[Joanne]

An LM317 voltage regulator will do the trick for you. You should be able to pick one up at Radio Shack or any other electronics store. Here's a link to a simple circuit.

http://ourworld.compuserve.com/homepages/Bill_Bowden/page12.htm

Joanne

[sdtripper2]

Joanne:

Looks like we were on the same track with the LM317~

[starleen2]

Or you could use this one:


even has a resistor calculator on the page

http://www.reuk.co.uk/Using-The-LM317T-To-Regulate-Voltage.htm


Output Voltage Tables for Stock R1 and R2 Values

[Trackstriper]

Ron,

I'm definitely not an electronics jock, but here's something to ponder. You could call the manufacturer to see if the DC input is critical. Maybe you could get to a tech guy if you asked nice. It might be that the amp chip inside is actually running at say 5 volts or 7 volts and that this voltage is handled by an internal voltage regulating circuit already, limiting the DC voltage from the 9 volt output of the wall wart. Perhaps feeding the input jack 12 volts wouldn't make any difference, it's 30% higher than 9 volts, but with manufacturing tolerances etc.....

For instance, check out the specs for this battery powered antenna:

http://www.p4c.philips.com/files/s/sbct ... ss_eng.pdf

It will run off two AA batteries, or a 12V DC adapter. Perhaps regulated....maybe with a simple resistor though.

Might just be something to look into. But hey, don't try it without asking first.

[wannabefree]

Looking at Starleen's schematic - The LM7809 regulator will do the same thing without the resistors. You can probably get one at Rad Shack, or any local elex supply. The circuit is not complete, however. Voltage regulators can be unstable and break out in oscillation if not handled right. To fix that problem you need a 10uF and two 0.1uF capacitors. Put a 0.1uF cap from the input of the regulator to ground, and one from the output to ground. Solder these as close to the regulator pins as you can. Then put the 10uF cap from the input to ground, in parallel with the 0.1. Any doubts, go to www.national.com and look up the 7809, or 317, and they'll tell you how to hook it up.

[starleen2]

Looking at Starleen's schematic - The LM7809 regulator will do the same thing without the resistors. You can probably get one at Rad Shack, or any local elex supply. The circuit is not complete, however. Voltage regulators can be unstable and break out in oscillation if not handled right. To fix that problem you need a 10uF and two 0.1uF capacitors. Put a 0.1uF cap from the input of the regulator to ground, and one from the output to ground. Solder these as close to the regulator pins as you can. Then put the 10uF cap from the input to ground, in parallel with the 0.1. Any doubts, go to www.national.com and look up the 7809, or 317, and they'll tell you how to hook it up.

Here's a schematic with the capacitors gleened fron Joanne's post above - notice the diode to prevent flowback. Ignore the AC conveter part

[bgeddes]

an LM7809 would be a lot simpler

[TimJones]

[quote="starleen2"]something like this should work



Cut off the plug on end cut off the output on the other end,you got hard wire 12v going in and hard wire 9v coming out can get simpler but you dont get to build anything Tim

[starleen2]

an LM7809 would be a lot simpler

Could you please post a schematic?