Voltage regulator question

Bellerophon · Post by **Bellerophon** » Thu Jan 17, 2013 10:14 am

I have circuits requiring 9VDC and 4.5VDC in my KBoP and would like to power it externally with just 9V. I'm thinking of using a 7805 to provide the second voltage (5 volts probably wouldn't overdrive the 4.5V circuit). However, voltage regulators get HOT (I've gotten nasty burns from them) and the regulator has to go inside, and I don't want the plastic to melt. (Had a nightmare about that even!)

I was wondering what would happen if I put a load across from the line-in pin to the load-out pin to avoid having so much current passing through the regulator, so some LEDs would be on a 4V circuit (dropping from 9V to 5V). This could help prevent the regulator from getting so hot, but does anyone know if it would also mess with the function of the regulator? Anyone ever try this?

I'm going to breadboard this to find out.

RossW · Post by **RossW** » Thu Jan 17, 2013 5:08 pm

Are you just using the 7805 to drive the LEDs? If that's all you're using it for (i.e. not a PIC microcontroller, for example) then instead of using the voltage regulator think about putting 2 LEDs in series with a current-limiting resistor, and then parallel that out for as many as you need. No voltage regulator required.

If you do need the 5V for something else, then add a clip-on heat sink to the metal part of the voltage reg.

Mr. Engineer · Post by **Mr. Engineer** » Thu Jan 17, 2013 7:50 pm

I second that. And also, if you apply 9 volts or 12 volts to the 7805, the additional voltage is going to make it get hot.

If the KBoP are all LEDs, you might want to consider using current limiting resistors.

Bellerophon · Post by **Bellerophon** » Fri Jan 18, 2013 12:12 am

No, it's not just LEDs--there's a board for some of the LEDs that uses 3 AA cells. It's from a string of mini Christmas lights with effects. I'm using it for a pulsing glow for the engines. Everything else is 9V, mainly because other lighting effects require 2 LEDs in series (one flashing or flickering to vary the current in another LED of the desired color).

So I need two supply voltages, and would like to minimize the wiring coming into the ship, and a 5V regulator with 9V input would be great if it doesn't get hot. That's why I had the idea of putting a load across the 4V drop from the input to the output of the regulator, so less power is dissipated in the regulator. (If I tried to just put a load in series with the LEDs with the lighting effect, its voltage would fluctuate, so the regulator is necessary.) It may not work properly, though, and I was wondering if anyone had tried this. I'm going to breadboard it and find out.

Worst case, it doesn't work and I'll need three wires coming into the ship.

Sloucher · Post by **Sloucher** » Fri Jan 18, 2013 8:21 am

Do you know what sort of current you'll need for the 4.5v supply?

I can see two choices - if the current is less than 100mA you could use a L78L05 regulator, but if you need more current, I'd use a step down (Buck) converter such as the LM2575 which is good for up to 1A.

Checkout their respective data sheets to see which works best for you.

I use the LM2575 for my Enterprise Effects circuit now rather than the 7805 and it runs as cool as you like.

Bernie

Bellerophon · Post by **Bellerophon** » Fri Jan 18, 2013 10:49 am

Thanks for the info, Sloucher.

The board draws 58mA using 3 fresh AA cells (4.8V with no load). It's only driving 12 LEDs. I guess heat dissipation won't be an issue in this case, though I'm still curious to see what happens if I bypass current from the supply pin to the load pin.

A more efficient, adjustable regulator would be great for bigger projects. That's really useful information! Digikey has them in DIP and TO-220 packages at under $3 apiece, so I'll order some. (I like DIPs cause my soldering is just awful and I can use a socket so I don't fry the IC.)

RossW · Post by **RossW** » Fri Jan 18, 2013 11:05 am

Bernie - it looks like the LM2575 is an incredible chip; wide range in input voltages with up to 1A output and no heat. Is it really as good as it sounds? I've only ever used the 7805 but have been frustrated when I need to use a 12V power supply (for LED strip lighting) but 5V for my microcontrollers.

RossW · Post by **RossW** » Fri Jan 18, 2013 11:11 am

RossW wrote:Bernie - it looks like the LM2575 is an incredible chip; wide range in input voltages with up to 1A output and no heat. Is it really as good as it sounds? I've only ever used the 7805 but have been frustrated when I need to use a 12V power supply (for LED strip lighting) but 5V for my microcontrollers.

And would be a typical set up? I'd like to try this out so I need to know what components to get.

http://circuits.datasheetdir.com/386/LM ... rcuits.jpg

Sloucher · Post by **Sloucher** » Fri Jan 18, 2013 12:04 pm

This is the configuration and component values I use with an input voltage of 12v

http://www.flickr.com/photos/38926882@N ... hotostream

Bernie

PS Oooops C4 got truncated - its 100uF

RossW · Post by **RossW** » Fri Jan 18, 2013 12:46 pm

Thanks Bernie!

I've never bought inductors before - do you have a part #?

Also, I'm assuming the caps are polarized electrolytic - is that right?

Sloucher · Post by **Sloucher** » Fri Jan 18, 2013 2:09 pm

I bought my inductors from Ebay (http://stores.ebay.co.uk/sunsphere-comp ... 7675.l2563 (I'm in the UK)).

I'd calculate for your application you'd need a 1H (1 Henry, or 1000uH) inductor part# FALGA0307-102K or check page 17 of the LM2575 data sheet, its got several manufacturers part#s there.

Your output cap should be between 100 and 470uF and be at least rated at least 10, 15 or 25v.

Oh, and yes you're quite right, both the caps are electrolytics.

Don't forget the catch diode as well! Most the useful info is on page 13 of the datasheet.

Cheers
Bernie

RossW · Post by **RossW** » Fri Jan 18, 2013 2:47 pm

Is it this kind of inductor?

http://www.ebay.co.uk/itm/10x-Axial-Mag ... 82686c6fb6

Sloucher · Post by **Sloucher** » Fri Jan 18, 2013 3:08 pm

Those are the ones

Just choose the 1mH choice from the dropdown.
Are you UK based?

Bernie

RossW · Post by **RossW** » Fri Jan 18, 2013 3:09 pm

No, I'm in Canada but have had good luck with ordering from UK.

I'll try DigiKey.ca and Mouser.

Mr. Engineer · Post by **Mr. Engineer** » Sat Jan 19, 2013 10:00 pm

Thanks RossW for the LM2572 tip. Just some time ago, I got these nice little PSU step-down modules from eBay. They're running on LM2596. Being a sucker for LEDs, I chose the one with a small Voltmeter attached. It costs quite a bit from where I am but I just love the concept:

You feed it any voltage from 4 volts to 40 volts and it churns out 5volts for me and runs 2Amps.

Over the next few weeks, I'll try to get a circuit to run on this and if its good, I might want to incorporate this on my products. Yeah, I am so 'out of touch' with these stuff

Anyway, here is the photo taken from my FB page, Piscean Works.
https://fbcdn-sphotos-e-a.akamaihd.net/ ... 5572_n.jpg

Bellerophon · Post by **Bellerophon** » Sun Jan 20, 2013 1:23 am

Wow, that's neat! I just checked eBay and didn't find any with the built in voltmeter, but they do have some dirt cheap power supplies.

Meanwhile I'm waiting on parts. There's a Radio Shack walking distance from my house, but no surprise 7805 was out of stock. So instead of paying $2 for one 7805, I'm paying $2.55 for 30 78L05 from Jameco.

I'm also going to try out zener diodes for regulating the voltage to LEDs. It's interesting that the forward voltage for LEDs generally goes up as the wavelength decreases.

Mr. Engineer · Post by **Mr. Engineer** » Sun Jan 20, 2013 8:50 am

OK, this is what I did.

1. I used the text, "DC step down power supply +voltmeter"
2. Select Sort by, "Lowest first" *ahem*

You'll find a few from there.

Tchail · Post by **Tchail** » Sun Jan 20, 2013 10:35 am

What about something like this?

https://www.sparkfun.com/products/9370

I've bought one, but have not had the chance to hook it up yet.

Best,

-Tchail

Bellerophon · Post by **Bellerophon** » Sun Jan 20, 2013 2:20 pm

Mr. Engineer wrote:OK, this is what I did.

1. I used the text, "DC step down power supply +voltmeter"
2. Select Sort by, "Lowest first" *ahem*

You'll find a few from there.

Yeah, last time I pasted in your phrase "PSU step down module."

Wow, $8 plus free shipping. For $24 they come with ammeters. There are boost step up power supplies with voltmeters from $15. All very handy for figuring out your power requirements so you can build your own power supply.

RossW · Post by **RossW** » Mon Jan 21, 2013 10:31 am

RossW wrote:No, I'm in Canada but have had good luck with ordering from UK.

I'll try DigiKey.ca and Mouser.

No luck at either of those suppliers. I've gone over the LM2575's datasheet but the recommended inductors aren't available at DigiKey, Mouser or Jameco. And if I can find the right inductance (e.g. 330 uH), it's non-stock.

UPDATE
Bernie - this is a full list of 330uH inductors (axial lead) at DigiKey. There aren't that many, but with many different specs. Do any of them look like they'd match the ones you get from the UK?

Sloucher · Post by **Sloucher** » Mon Jan 21, 2013 3:21 pm

Bernie - this is a full list of 330uH inductors (axial lead) at DigiKey. There aren't that many, but with many different specs. Do any of them look like they'd match the ones you get from the UK?

Don't see any list RossW

Actually, going from your original 58mA @ 5v output requirement, you don't need 330uH, what you actually need is 1000uH (or 1mH), but anything from about 680 to 1000 would be ok.
If you can't source any, drop me a PM and I'll get some from SunSphere here in the UK and send them to you. I think they're about C $ 2.50 for 10 units plus a bit for postage.

Bernie

RossW · Post by **RossW** » Mon Jan 21, 2013 4:06 pm

Sloucher wrote:
Bernie - this is a full list of 330uH inductors (axial lead) at DigiKey. There aren't that many, but with many different specs. Do any of them look like they'd match the ones you get from the UK?
Don't see any list RossW
Actually, going from your original 58mA @ 5v output requirement, you don't need 330uH, what you actually need is 1000uH (or 1mH), but anything from about 680 to 1000 would be ok.
If you can't source any, drop me a PM and I'll get some from SunSphere here in the UK and send them to you. I think they're about C $ 2.50 for 10 units plus a bit for postage.

Bernie

That would help, wouldn't it?

Here it is: http://www.digikey.com/scripts/dksearch ... y=0&PV80=8

BTW, I need up to 1A so I think I'm in the 150uH range for an input of 9V.

RossW · Post by **RossW** » Mon Jan 21, 2013 4:50 pm

In particular part #445-3602-1-ND's datasheet ([/img]http://www.delevan.com/seriesPDFs/SPD125.pdf) makes the part look just like the one in this EEEvilBae DC-DC power converter:

http://www.ebay.com/itm/LED-Voltage-and ... 232111a49d

Sloucher · Post by **Sloucher** » Mon Jan 21, 2013 6:41 pm

The only downside of that one seems to be the fact that its smd. If you're happy soldering smd components then it shouldn't be a problem.

I would think that from the graph on the LM2575 data sheet that at 1A, an inductor of 120uH would do the job. The reason I mention that value is that I can get it from the place I mentioned before (same price) and they are axial lead type components about the size of a 1W resistor - a bit easier to incorporate into a home brew circuit!

Even though I use smd components in the main in most of the circuits I build, on my Enterprise Effects circuit board, I use the axial type of inductor in conjunction with the LM2575 because its a much lower profile and fits into confined spaces a bit easier!!

Bernie

Bellerophon · Post by **Bellerophon** » Thu Jan 24, 2013 10:20 pm

My 78L05 (and other goodies) came from Jameco today so I was able to try out my idea of putting a load between the input of the voltage regulator and its output to reduce the heat dissipation in the regulator.

So the 78L05 had two loads connected to it. The regulated 5V output went to the lighting effects module, which draws a variable amount of current. A second load was between the input pin (9V) and the output pin: a string of the LEDs mentioned above (about 20) in series with a 10 ohm resistor. The 5V output of the 78L05 did not appear to be disrupted, but the lighting effects module was happy to draw more current through the other string of LEDs causing it to vary in brightness.

So it's a dumb idea if the load using the regulated voltage varies, and it's not very useful even if the load is constant. It worked okay when the lighting effects module was set to constant output, but the 78L05 wasn't going to get hot anyway. Maybe it'd get hot if the input was 35V and the load was 100mA, so it had to dissipate 3W.

I'm going to take some video of the lighting effects (they're pretty cool if I do say so) and post them in Star Trek Modeling.

Thanks Sloucher and Mr. Engineer for some good tips!

Mr. Engineer · Post by **Mr. Engineer** » Thu Jan 24, 2013 10:27 pm

Cool! Glad it worked out for you can't wait to see your video!

Sloucher · Post by **Sloucher** » Fri Jan 25, 2013 2:47 am

what Mr Engineer said

Bernie

Bellerophon · Post by **Bellerophon** » Sat Jan 26, 2013 2:27 pm

Okay, I linked to the post in the WIP thread for this project: http://www.starshipmodeler.net/talk/vie ... highlight= Scroll down page two, thirteenth post.

It was a PITA to video the lighting effects as some of the wires were just twisted together or plugged into the breadboard, but all the lighting effects seem to show up okay in the video.

Mr. Engineer · Post by **Mr. Engineer** » Sat Jan 26, 2013 11:34 pm

Wow! That is amazing!

Bellerophon · Post by **Bellerophon** » Sun Jan 27, 2013 10:39 am

Thanks, glad you liked it. It's fun to cobble together some electronics to see what lighting effects you can come up with.