Regulated 7VDC 2Amp power supply suggestions?

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kadams4458
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Regulated 7VDC 2Amp power supply suggestions?

Post by kadams4458 » Wed Feb 18, 2004 8:05 am

Hey, folks.<p>I'm currently trying to figure out a way to construct a fairly well regulated 7VDC 2A supply for my digital camera.<p>Up until now I've generally only had to tinker with 5 and 12 volt stuff, and have a herd of 7805 and 7812 regulators to prove it. I'm hoping that someone here can point me towards a few common component options that will fit the bill.

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MrAl
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Re: Regulated 7VDC 2Amp power supply suggestions?

Post by MrAl » Wed Feb 18, 2004 11:10 am

Hello,<p>There's a chip like the LM317 that goes up
to 2 amps. You would need a transformer,
rectifier bridge, and large value electrolytic
caps to go with it.
If you are interested i'll look up the part
number.<p>Alternately, you may be able to modify an
existing computer power supply to put out
7v instead of 12v.<p>Take care,
Al
LEDs vs Bulbs, LEDs are winning.

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Re: Regulated 7VDC 2Amp power supply suggestions?

Post by amuron » Wed Feb 18, 2004 11:50 am

Make sure you put a crowbar on the output....<p>The easiest way would be to use Nationals simple switchers and webbench. 2A at 7VDC with a linear regulator will require a huge heat sink unless you can find just the right transformer. The other possibility is to use 3-4 2N3055's as series pass transistors so you can spread the heat dissipation out across a wider surface area. You will be dissipating close to 10W. <p>Some LM317's may work, but it is really marginal. You would definitely need the TO3 package, and you'd have to run the thermal calculations to see if it would fly even with an ideal part.<p>Web bench makes switchers easy, and they generate the BOM for you as well.<p>Good luck,
Ron

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Re: Regulated 7VDC 2Amp power supply suggestions?

Post by myp71 » Wed Feb 18, 2004 4:13 pm

Wouldn't a 6vdc lead-acid battery work for this??<p>It would be simple :D

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jwax
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Re: Regulated 7VDC 2Amp power supply suggestions?

Post by jwax » Wed Feb 18, 2004 4:24 pm

Hook up your 12v and 5v so they fight it out!
12-5=7!<p>Sorry. Couldn't resist!

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Re: Regulated 7VDC 2Amp power supply suggestions?

Post by amuron » Wed Feb 18, 2004 6:01 pm

6VDC is probably a little too low for the camera's lcd switcher. It will be working very hard, and could go into shutdown, or worse be damaged.<p>As far as a computer supply, it really depends on how they handle the feedback. It the supply was not optimized for a heavy load on 5 and lighr on the 12, it might work. Be sure that you put on your own crowbar though, the internal 5V and 12V crowbar circuits would probably not offer enough protection.<p>Ron

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MrAl
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Re: Regulated 7VDC 2Amp power supply suggestions?

Post by MrAl » Thu Feb 19, 2004 10:10 am

Hello there,<p>I would be careful about using a switching
power supply using 12 volts minus 5 volts to get
7 volts. If the 5v line drops lower then
5 volts (say to 4 volts) you end up with
8 volts supply for a $200 device that really
requires 7 volts. Any lower and you might end
up with 12 volts feeding the camera :-)<p>Also, there is no spec that i know of that
guarantees that the +5v line comes up as
fast as the +12v line, so it's possible that
during turn on the camera sees the full 12
volts just before the +5 volt line comes up
fully. I think there is a power read output,
but you'd have to connect it to a relay or
something, then worry about how it powers
down next.<p>The chip i was talking about was not the
LM317, but a similar chip that goes up to
2 amps. Also, the power lost is related to
the input voltage level and wont be as high
as 10 watts if it's done right.<p>Since the camera cost might be high, you might
even consider a switcher/linear combo.
The switcher keeps the power lost in the linear
down to a minimum while you still get most
of the benefits of a linear supply.<p>
Take care,
Al
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Re: Regulated 7VDC 2Amp power supply suggestions?

Post by kadams4458 » Thu Feb 19, 2004 3:11 pm

Hello again,<p>First off, thanks for all the responses. I really appreciate the input.<p>I got to thinking about the amp rating of the proposed power supply last night, and I have concluded that I am an idiot. There's no way I need anywhere close to 2 amps to operate this thing. <p>Here's my reasoning, correct me if I'm screwing something up, but I really am a novice, and a dangerous one at that. :) <p>Ordinarily the camera runs off of four AA NiMH batteries wired in series. These, of course, are only rated to put out 1.2 volts/1800 mAh each, so I have 4.8 volts/1800 mAh, right? There is also the option of running off of standard alkalines which I've noticed tend to pump out around 1.6 volts per cell on average. Now that's pretty simple math as far as I know. <p>What I have powering the camera is around 4.8 volts. Apparently anything between 4.8 and 6.4 will work, so why is it the original power supply for the camera listed as being 7 volt? <p>So, correct me if I'm wrong, but what I reallyneed is a power supply capable of putting out 6 volts. I still don't know how much current it needs to produce, though. Argh. Has anyone measured the current of a 1.2 volt NiMH lately?<p>Maybe I'm going about this all wrong. I need more coffee. if something here doesn't make sense, blame it on the lack of caffeine! :)

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MrAl
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Re: Regulated 7VDC 2Amp power supply suggestions?

Post by MrAl » Thu Feb 19, 2004 4:09 pm

Hello again kadams,<p>No, that sounds right!<p>You may be able to run this thing off of a
regular 5 volt supply, like a computer
supply or something. There are lots of
5v regulators out there too.<p>Take care,
Al
LEDs vs Bulbs, LEDs are winning.

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Re: Regulated 7VDC 2Amp power supply suggestions?

Post by duratech34 » Thu Feb 19, 2004 5:04 pm

a 7 volt dc powersupply is needed in order to charge the 6 volt NiMH batteries you are not an idiot. The use of a 12 volt dc powerpack with a 7805 voltage regulator will work at 1amp. You wanted 7 volts. The 7805 can boost the volts to higher volts. My Sony needed 7.6 volts If you need help I can give you the resistors and pin conections. higher amps need a series by pass transistor. a 2N3055 transistor 2 amps or more.
Keep me posted
duratech34

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Re: Regulated 7VDC 2Amp power supply suggestions?

Post by amuron » Thu Feb 19, 2004 8:23 pm

Most likely they use 7V in order to save some headaches and deal with the cameras internal charger and switcher circuit. At 5V, the duty cycle may get so high as to overheat the core or other disastrous effects. <p>I cannot stress a 7.5V or smaller crowbar enough.<p>I've never had success with a 7805 providing 1A with a 12V input. May I ask how you go about acheiving that. You are correct that you can easily raise the 7805's output voltage, or add series pass transistors to get more current capability.<p>Still curious about the 1A out of the 7805. I've been doing this a long time, had a major failure in the early eighties with a 7805 providing close to an amp. Since then I have always kept away from them except for low power apps. Its quite likely I could have used the 7805 a bunch of times though, so I'm super receptive to your approach. <p>Today it seems I use switches 90% of the time due to cost, space, or heat constraints. For lower volume applications where a few hundred hours of switcher design and qual can't be justified, the 7805 might be just the trick I need.<p>Thanks in advance
Ron

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Chris Smith
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Re: Regulated 7VDC 2Amp power supply suggestions?

Post by Chris Smith » Thu Feb 19, 2004 9:33 pm

After all that Id go with a small 6 volt gel cell as a fanny pack on a belt. it will Run the camera for days. I doubt the camera actually runs at the high amperage, and simply uses the high current batteries for starts and stops as a safe buffer against surges that drop below a certain point and lose things like memory.

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MrAl
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Re: Regulated 7VDC 2Amp power supply suggestions?

Post by MrAl » Thu Feb 19, 2004 10:13 pm

Hello again,<p>Im sorry, I was talking about mainly a
'battery eliminator' which would run just fine
at 5v for that device.<p>Take care,
Al
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Re: Regulated 7VDC 2Amp power supply suggestions?

Post by myp71 » Thu Feb 19, 2004 11:13 pm

<blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr>Originally posted by Chris Smith:
After all that Id go with a small 6 volt gel cell as a fanny pack on a belt. it will Run the camera for days. I doubt the camera actually runs at the high amperage, and simply uses the high current batteries for starts and stops as a safe buffer against surges that drop below a certain point and lose things like memory.<hr></blockquote><p>Ah, told you so :D

kadams4458
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Re: Regulated 7VDC 2Amp power supply suggestions?

Post by kadams4458 » Tue Feb 24, 2004 11:52 am

Most interesting. :) <p>The camera doesn't have any circuitry for charging the battery, so I'm not certain if 7 volts are truly necessary. However, the original AC adapter, which is not easily available, does in fact put out 7 volts.<p>So, I reckon I'll go with at least part of my original figure. <p>I'm doing a little designing now, I'll let you all know what I come up with so that someone can smack me if I make a mistake in the design phase.

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