USB power > 8 vdc

[HarveyH42]

I've got a a small wireless camera that runs off a 9 v battery, or 8 v wallwart. I also have several USB chargers (built in rechargeable batteries). Unfortunately, 5 volts isn't enough to run the camera, a 9 v battery doesn't last long, and a wallwart kind of defeats the 'Wireless' aspect. Looking for a simple method of boosting the USB 5volts up to 8 volts, any ideas?

 

[gootee]

You didn't mention how much CURRENT the camera draws.

You could connect the 5V from one USB charger to the 0V of a second one, and have 10V between the remaining 0V and 5V terminals. Then you could use an LDO (Low Drop-Out) three-terminal regulator to bring it down to 8 Volts.

Alternatively, you could design and build a 5V-to-8V boost-mode switching power supply. Go to national.com and look for the Webench automatic power supply designer. Linear.com also has SwitcherCadIII (not IV) that includes an automatic power supply design feature (File --> Switch Selector Guide).

 

[tcmtech]

If your in the 100 Ma range or so a basic 555 timer running a charge pump voltage doubler will likely work just fine. You will need to use a low ESR capacitor and find what frequency it works best at.

Given that 555 based charge pumps are not perfect voltage doublers the .5 volt loss on the charge side from the 555 timer plus the .5 volt drop from the diode at the output should should put you close enough to 8 - 9 volts to work without problems.

If you need more than a 100 ma or so then use a second two transistor half bridge output running 180 degrees out of phase from the 555's output to boost the current capacity and double the charging cycle frequency as well.

 

[AtomSoft]

since you have several usb chargers why not series 2 of them for 10v and add a diode to drop it 1.5v down and you will have 8.5v which is almost perfect.

Or similar get a hold of a 9.1v zener and use that to drop the 10v

 

[HarveyH42]

Sorry been busy lately, but order some ICL7660 regulators. Most of the newer stuff is surface mount, which I haven't attempted yet. Built the attached circuit, taken out of the data sheet on a breadboard. C1 and C2 are 10 µf, and D1 and D2 are 1N914 (have literally thousands of them). I get about 9 volts out, using the intended USB charger as the supply, which is great. The problem though, is it doesn't seem to provide enough current. The camera draws 112 mAs, and will work down to 7.2 volts. Is there anyway to adjust the values/circuit to get the current up, or did I miss read the data sheet, and expecting too much from this chip?

 

[Externet]

I don't get it
A wallwart defeats the wireless aspect but one or two USB chargers do not ?
What is wireless on it; the video signal or the power supply ?
Get a motorcycle battery and regulate to 9V with a low drop circuit.

 

[AtomSoft]

i think he means 2 usb rechargable battery type devices.. those things are like for cellular phones...

 

[Sceadwian]

Externet, read his post again, he said his USB chargers were battery based.
Harvey, are you sure your USB devices are going to have enough battery power to supply the camera for a decent length of time? I'd cut all this middle man stuff out and simply build a high capacity pack using 9 NiMH cells and a low dropout regulator. Atomsoft's idea of using two of your USB device in series might work as well but that seems like a bit of a cludge to me. It wouldn't hurt to find out if the camera has any kind of protection from over voltage as well, you may simply be able to use 9 NiMH cells straight without a regulator, if it has one built in.

 

[Externet]

You are very right. Read it several times and still missed the battery part in brackets
Thanks.

 

[HarveyH42]

Mostly, I was hoping there was a simple solution, since I don't need a huge voltage boost. The USB power sources are lithium rechargeable, pretty good capacity 2 & 3 Ah. The 2 Ah chargers are solar, and will charge the battery and power the USB at the same time, sun available. I haven't fooled around with lithium ion batteries, so a little skeptical about the series idea for a couple of reasons. First they are something like 3.6 volts, and need a boost circuit to get 5 volts out for the USB, not sure enough to risk frying something, or burning down my house, if the aren't friendly that way. The camera will work off a 9 volt battery (clip with plug included). I could provide power a number of alternate ways, but the USB packs have good capacity and small size. The solar ones would be perfect with a little boost.

Back to the 7660... I hooked my meter in series with the camera, and it's drawing on 54 mA, about half of what I need. The unloaded output of the circuit was 9.7 volts (little higher than expected). Thought those diodes would have a higher drop. My brother dropped by for a visit, need help on his laptop. Got my first look ad Windows 7, and not a fan, maybe it gets better with use. Finally left, after relieving me of a printer cable, and a few other odds and ends. Will do some more measurements later, maybe re-wire the circuit. Only a few parts, and does double the voltage. Have to check my USB voltage, could be 5.5 volts, and would explain the higher than expected output.

 

[Sceadwian]

Harvey you don't need a huge voltage boost? Only 200% of the incoming voltage? I'd consider that huge =)
You still haven't stated exactly what the voltage tolerances of the camera are, does it have an internal regulator? If it does you could be over analyzing this.

The 7660 is not capable of directly supplying the current you need, according to the PDF it's maximum limit is 45ma, if you're drawing 54 then you're already over the max limit. Might not hurt to look into some of Linears switch mode converters, they'll buck/boost (giving you WIDE input voltage allowances) 100ma or more pretty easily using only a single IC and a couple external components and they're reasonably priced.

Go to linears website and use the parametric search. They have a LOT of switch mode regulators.

 

[HarveyH42]

Will probably look into the 555 charge pump this weekend, but had some thoughts about paralleling the output of 3 x 7660 . Figured I got the chips, simple circuit, and already one on the breadboard. If it works as planned, should provide 135 mA, which gives a little room for losses, not much though. I thought I'd post this, and see if I need to isolate the 7660 in some way for protection or function, maybe some more diodes.

 

[Sceadwian]

If your device is similar to this one you shouldn't have any trouble. This is obviously not ideal, but as you said you already have the chips.
http://www.datasheetcatalog.org/datasheet/microchip/21465b.pdf

 

[HarveyH42]

I just hooked up three 7660 chips in parallel, and it works. Used 3 x 10 uf, 6 1N914, and a 100 uf on the shared output. Will have to see how long it goes off the battery now. Should work out nicely though, if the battery solar charges and powers the camera at the same time. The camera isn't very good in the dark, so perfect for daytime use. Have to read the data sheet a little closer, and see if I can improve a little, before making a PCB.