Voltage regulator question

Ask and answer questions, share tips and resources for installing lighting and other electronics in your models.

Moderators: Sparky, Moderators

User avatar
Bellerophon
Posts: 2543
Joined: Fri Oct 16, 2009 10:00 pm
Location: 13 miles southwest of Grovers Mill
Contact:

Voltage regulator question

Post by Bellerophon »

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.
But isn't it all Klingon opera?

http://bellerophon-modeler.blogspot.com/
RossW
Posts: 198
Joined: Wed Oct 02, 2002 1:04 pm
Location: Toronto, ON

Post by RossW »

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.
User avatar
Mr. Engineer
Posts: 440
Joined: Mon Dec 10, 2007 6:01 am
Location: Malaysia
Contact:

Post by Mr. Engineer »

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.
What can I take apart today?

https://www.facebook.com/PisceanWorks
User avatar
Bellerophon
Posts: 2543
Joined: Fri Oct 16, 2009 10:00 pm
Location: 13 miles southwest of Grovers Mill
Contact:

Post by Bellerophon »

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.
But isn't it all Klingon opera?

http://bellerophon-modeler.blogspot.com/
Sloucher
Posts: 72
Joined: Mon Dec 07, 2009 5:49 pm
Location: UK

Post by Sloucher »

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
WiredFX

Small Lighting and Effects UK
User avatar
Bellerophon
Posts: 2543
Joined: Fri Oct 16, 2009 10:00 pm
Location: 13 miles southwest of Grovers Mill
Contact:

Post by Bellerophon »

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.)
But isn't it all Klingon opera?

http://bellerophon-modeler.blogspot.com/
RossW
Posts: 198
Joined: Wed Oct 02, 2002 1:04 pm
Location: Toronto, ON

Post by RossW »

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
Posts: 198
Joined: Wed Oct 02, 2002 1:04 pm
Location: Toronto, ON

Post by RossW »

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
Posts: 72
Joined: Mon Dec 07, 2009 5:49 pm
Location: UK

Post by Sloucher »

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
WiredFX

Small Lighting and Effects UK
RossW
Posts: 198
Joined: Wed Oct 02, 2002 1:04 pm
Location: Toronto, ON

Post by RossW »

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
Posts: 72
Joined: Mon Dec 07, 2009 5:49 pm
Location: UK

Post by Sloucher »

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
WiredFX

Small Lighting and Effects UK
RossW
Posts: 198
Joined: Wed Oct 02, 2002 1:04 pm
Location: Toronto, ON

Post by RossW »

Sloucher
Posts: 72
Joined: Mon Dec 07, 2009 5:49 pm
Location: UK

Post by Sloucher »

Those are the ones :)

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

Bernie
WiredFX

Small Lighting and Effects UK
RossW
Posts: 198
Joined: Wed Oct 02, 2002 1:04 pm
Location: Toronto, ON

Post by RossW »

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

I'll try DigiKey.ca and Mouser.
User avatar
Mr. Engineer
Posts: 440
Joined: Mon Dec 10, 2007 6:01 am
Location: Malaysia
Contact:

Post by Mr. Engineer »

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 :oops:

Anyway, here is the photo taken from my FB page, Piscean Works.
https://fbcdn-sphotos-e-a.akamaihd.net/ ... 5572_n.jpg
What can I take apart today?

https://www.facebook.com/PisceanWorks
User avatar
Bellerophon
Posts: 2543
Joined: Fri Oct 16, 2009 10:00 pm
Location: 13 miles southwest of Grovers Mill
Contact:

Post by Bellerophon »

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.
But isn't it all Klingon opera?

http://bellerophon-modeler.blogspot.com/
User avatar
Mr. Engineer
Posts: 440
Joined: Mon Dec 10, 2007 6:01 am
Location: Malaysia
Contact:

Post by Mr. Engineer »

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.
What can I take apart today?

https://www.facebook.com/PisceanWorks
User avatar
Tchail
Posts: 4330
Joined: Tue Mar 04, 2003 8:40 pm
Location: Nowhere in Particular

Post by Tchail »

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
“In the beginning the universe was created. This made a lot of people angry, and has generally been regarded as a bad move." Episode 5, The Hitchhiker's Guide to the Galaxy
User avatar
Bellerophon
Posts: 2543
Joined: Fri Oct 16, 2009 10:00 pm
Location: 13 miles southwest of Grovers Mill
Contact:

Post by Bellerophon »

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.
But isn't it all Klingon opera?

http://bellerophon-modeler.blogspot.com/
RossW
Posts: 198
Joined: Wed Oct 02, 2002 1:04 pm
Location: Toronto, ON

Post by RossW »

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
Posts: 72
Joined: Mon Dec 07, 2009 5:49 pm
Location: UK

Post by Sloucher »

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
WiredFX

Small Lighting and Effects UK
RossW
Posts: 198
Joined: Wed Oct 02, 2002 1:04 pm
Location: Toronto, ON

Post by RossW »

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? :oops:

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
Posts: 198
Joined: Wed Oct 02, 2002 1:04 pm
Location: Toronto, ON

Post by RossW »

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
Posts: 72
Joined: Mon Dec 07, 2009 5:49 pm
Location: UK

Post by Sloucher »

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
WiredFX

Small Lighting and Effects UK
User avatar
Bellerophon
Posts: 2543
Joined: Fri Oct 16, 2009 10:00 pm
Location: 13 miles southwest of Grovers Mill
Contact:

Post by Bellerophon »

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!
Last edited by Bellerophon on Thu Jan 24, 2013 10:28 pm, edited 1 time in total.
But isn't it all Klingon opera?

http://bellerophon-modeler.blogspot.com/
User avatar
Mr. Engineer
Posts: 440
Joined: Mon Dec 10, 2007 6:01 am
Location: Malaysia
Contact:

Post by Mr. Engineer »

Cool! Glad it worked out for you can't wait to see your video! :D
What can I take apart today?

https://www.facebook.com/PisceanWorks
Sloucher
Posts: 72
Joined: Mon Dec 07, 2009 5:49 pm
Location: UK

Post by Sloucher »

what Mr Engineer said :wink:

Bernie
WiredFX

Small Lighting and Effects UK
User avatar
Bellerophon
Posts: 2543
Joined: Fri Oct 16, 2009 10:00 pm
Location: 13 miles southwest of Grovers Mill
Contact:

Post by Bellerophon »

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.
But isn't it all Klingon opera?

http://bellerophon-modeler.blogspot.com/
User avatar
Mr. Engineer
Posts: 440
Joined: Mon Dec 10, 2007 6:01 am
Location: Malaysia
Contact:

Post by Mr. Engineer »

Wow! That is amazing! :shock:
What can I take apart today?

https://www.facebook.com/PisceanWorks
User avatar
Bellerophon
Posts: 2543
Joined: Fri Oct 16, 2009 10:00 pm
Location: 13 miles southwest of Grovers Mill
Contact:

Post by Bellerophon »

Thanks, glad you liked it. It's fun to cobble together some electronics to see what lighting effects you can come up with.
But isn't it all Klingon opera?

http://bellerophon-modeler.blogspot.com/
Post Reply