Regulators

[GregSilver]

Alex, looked at the specs of both. Did i read them incorrectly...

looks like the uA7812 shows 12.5V min and the uA78m12 14.5V min

[ssassen]

Alex, looked at the specs of both. Did i read them incorrectly...

looks like the uA7812 shows 12.5V min and the uA78m12 14.5V min

An LM2940-12 will do the trick, is this for a camera or a Vtx? In the former case you only need to add an LC filter in front of it and some decoupling caps, in the latter case it will require a heatsink for cooling.

[IBCrazy]

The LM2940 is a bit better than the uA7812 series. It has a better regulation voltage. They are similar chips. Here is where you can get it: http://www.jameco.com/webapp/wcs/sto...0001_837476_-1

Basically with the uA7812 you need 14.2V or more to hold 12V. Once you drop below 14.2, the output is 2.2V lower than the input voltage.

With the LM2940-12 you only need 13.6 volts. Once you drop below that, the output and input voltage separate by 1.6 volts.

Most every camera and VTX I have tried work fine all the way down to 9.5V. Cameras usually work down to 7.5V. Video transmitters lose frequency lock between 9.5V and 7.5V depending on the VTX. Transmit power decreases about 30% by this time, which really isn't a big deal.

In other words, if you take your 4S down to 12V (which is a bad idea, btw), your video system will be running at 10.4volts with the 2940-12. This is plenty to sustain your video system.

-Alex

[ssassen]

In other words, if you take your 4S down to 12V (which is a bad idea, btw), your video system will be running at 10.4volts with the 2940-12. This is plenty to sustain your video system.

Close, but no sigar!

The voltage drop you quote is usually with the maximum current delivered by the regulator. If you are powering a camera, or a Vtx not requiring the full 1A (for example) the voltage drop is less. In reality once the Vin = Vout the output transistor in the regulator will driven be open fully, which means that typically the drop is about 200mV at most, but typically ~100mV (when Iout < Imax), this is due to the fact that feedback loop governing the output voltage is tied around an internal reference (usually 1.25V) which obviously is a long way from 12V and thus the regulator's circuitry can provide ample voltage to drive the output transistor.

[JiP]

Maybe a stupid question (but I don't have the answer so I'm thinking it's still worth asking): what's wrong with using the balance plug of the 4s lipo to get the 12v ? I mean, as long as the camera, osd, etc... can work from 3 full cells to 3 empty cells ?

Don't want to be a burden but is it wrong taking three cells from a 4s lipo to get the 3s voltage ? (assuming you're filtering it) ?
I'd really use an educated advice as I'm building a zephyr, wanting a 4s lipo but trying to transpose the 3s video gear from my maxiswift,

Thanks guys :-)
JiP

[GregSilver]

An LM2940-12 will do the trick, is this for a camera or a Vtx? In the former case you only need to add an LC filter in front of it and some decoupling caps, in the latter case it will require a heatsink for cooling.

Sander, this is for vTX AND Camera coming from single battery 4S setup.

Would it be best to use separate regulators for each or is it ok to use 1 for both of them (I want best usage..not, "its ok....but....")

[ssassen]

Sander, this is for vTX AND Camera coming from single battery 4S setup.

Would it be best to use separate regulators for each or is it ok to use 1 for both of them (I want best usage..not, "its ok....but....")

I would take two, put the one for the Vtx on a heatsink and position that in the airflow over the fuse/wing, the one for the camera won't need a heatsink.

[GregSilver]

Thank you Sander.

[ssassen]

To avoid a plethora of 'how do I hook this up', 'what goes where' and questions of similar nature, here's how you make this work and no, I'm not making anyone a Digikey or Mouser partslist, nor will I draft a PCB for it.

[GregSilver]

Does this look good so far?
Item Quantity Qty to Ship Unit Cost Total +12V/1.5A TO-220 LDO


Part no. 837476 Manufacturer NATIONAL SEMICONDUCTOR Manufacturer no. LM2940T-12.0/NOPB This item is Non-Cancelable
and Non-Returnable Remove
5 on 3/22/12 $1.19 $5.95 INDUCTOR,TORID,VERTICAL,
470.0 uH,1.6 IDC,0.28 OHM,

Part no. 371936 Manufacturer JAMECO VALUEPRO Manufacturer no. 2120-V-VP Remove
4 on 3/19/12 $0.49 $1.96 @ RES,CF,1K OHM,1/4 WATT,5%,
(100 BAG)

Part no. 690865 Manufacturer JAMECO VALUEPRO Manufacturer no. CF1/4W102JRC Remove
100 on 3/19/12 $0.03 $3.00 @DIODE SCHOTTKY,1N5817,1.0A
20V (10)

Part no. 177949 Manufacturer MAJOR BRANDS Manufacturer no. 1N5817. Remove
10 on 3/19/12 $0.14 $1.40 @CAP,RADIAL,330uF,35V,
! 20%,105C,10x16x5mm(10)

Part no. 609721 Manufacturer JAMECO VALUEPRO Manufacturer no. UVZ1V331MPD Remove
10 on 3/19/12 $0.19 $1.90 @CAP,CER,RADIAL,100000PF,
100V,10%,X7R,INCREMENT of 10

Part no. 544884 Manufacturer JAMECO VALUEPRO Manufacturer no. SR211C104KAA-VP Remove
10 on 3/19/12 $0.15 $1.50 Subtotal: $15.71