dc to dc (1.5V to 5V)

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I want to run an atmega8 and some LEDs on 1 AA battery. So, I want to make a step-up circuit. I've looked into using a MC34063A converter IC, but my tragically inadequate electronics experience has made this difficult. I know there's a de facto 1.5V to 5V circuit somewhere out there (not in module form); any info on what that might be?

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The MC34063 is a no go: doesn't run @ 1.5V

Have a look at Linear Technology devices, and National Semiconductor. Both will most likely have a parametric selection table.

Fellow freaks may jump in with some direct answers .... that I don't have :)

A GIF is worth a thousend words   They are called Rosa, Sylvia, Tricia, and Ulyana. You can find them https://www.linuxmint.com/

Dragon broken ? http://aplomb.nl/TechStuff/Dragon/Dragon.html for how-to-fix tips

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Perhaps this one..

http://www.linear.com/pc/productDetail.jsp?navId=H0,C1,C1003,C1042,C1031,C1060,P90287

You need to add up the supply current requirements for Mega8 and the LEDs and any other loads and see where you go from there. The Linear part is available with fixed 5 volt output. I did not review the data sheet but it looks like its in the right area.

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TPS61200,TPS61010,REG710,MAX756,MAX1674,MAX1678.

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Awesome, especially the built-in 5V out ICs. Any chance any of these are through-hole variety?

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LT1073

this?

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What about Microchip MCP1640 ? Work's from 0.65V.
But i don't have one to test it.

Computers don't make errors - What they do they do on purpose.

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And ... just for somewhere to "park" an interesting circuit for anyone else, this circuit, with a 100 turn centre-tapped trannie, converts 800 millivolts to 3 volts. The output is set by the 0.6 of the Vbe junction plus the 2.4 volt zener.

I cannot remember where I found it ... I am not claiming any rights or lefts.

Cheers,

Ross

Attachment(s): 

Ross McKenzie, Melbourne Australia

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I would do something like Ross but very cheap, just so it can start the mega8 (perhaps use a low volt version). When the cpu is running I would use a portpin for the convertion(switch). (and a ADC to test the 5V (as I remember the maga8 can read ref. voltages with the ADC))

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ICs like MCP1640 might be more ideal in later (more learned) applications, but for now, I’d like through-hole, as SMD seems inconvenient to experiment with.

Ross’s circuit might work, but again, I’d like to get my hands on a basic IC-based circuit first. For me, learning is as much an objective as anything at this point. So, I’d like to try a more fundamental approach before branching off towards more complex (and probably more application-optimized) methods.

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Maybe I’m asking too much out of 1 AA alkaline battery. Really, I only have 3 LEDs, a button, and an atmega8 (w/ crystal ideally, though not necessarily). The LEDs operate at 20mA, but only at 3.2V. Does this mean that I can get by with 3.3V, provided I supply somewhere around 80-100mA? And to reiterate, I am shooting for a DIP.

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Ross's contribution looks alot like one of the many variations of the joule thief...

Also, finding a DIP boost IC will be tricky, the newer ones that operate at higher frequencies are somewhat layout dependent...
I might have saw one the other day for sample online but it would take some serious digging to find it...

What's the reason for hating on the SMDs??
You might be able to get a breakout PCB for SMD...

Michael

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How about this:
UCC3941N-5

I’d be okay with a breakout PCB for experimentation, but I’m not sure that I’d want to implement a breakout in a “final product”. My definition of “final product” includes a small protoboard, as I’ve just started working with microcontrollers and the like about a month ago, and merely on a hobbyist basis. So, DIPs are manageable, at least for now.

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That's a good find.
Compared to most other boost converters the input is relatively low.

It looks like it's been replaced with an SMD soic version.
As long as you don't need to many, it's a good choice.
TI doesn't stock any and no free samples are available.

Unfortunately there is no layout info in the datasheet.
If you are designing a pcb you will want to be careful of the layout.
You might want to check other datasheets to get an idea of the layout.

As for SMD vs. DIP, if you are making your own PCB, you won't have to drill as many holes.
SMD soldering is pretty easy, especially for soic size...

Michael

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No through hole versions but the price and feature set look good. ST Micro's L6920DB .8V needed for startup.

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1.5V alkalines are not 1.5V for very long. They start at ~1.7 volts and steadily fall until they're dead at approx 0.8V. The ability to support a certain voltage is also current dependent. ~65mA @ 3.3V ~= 214mA @ 1V But some boost converters are notoriously inefficient. Some switched capacitor efficiencies are as low as 50%. So that 214mA turns into 428mA. That AA cell won't last long.

Jim M., Rank amateur AVR guy.

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JimmyM,
I’m not -exactly- sure how much current I need. I know I have 3 LEDs with forward voltages of 2V, 3.2V and 3.2V, with forward current at 20mA each. If I’m correct (please let me know), that’s about 51mA at 3.3V. I don’t know how much the atmega8 draws, with or without a crystal oscillator. If I use your 65mA at 3.3V, and 214mA at 1V, and assume maybe 80% efficiency, that’s 257mA at 1V. That’s about 9.3h...

That’s not too bad, but I’ve seen circuits involving few LEDs and a micro, and they run weeks at a time. Even if I add a battery and assume PWM only draws half the power than 20mA all the time, that’s about 36h (if my math is correct). How do they do it?

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odriew wrote:
JimmyM,
I’m not -exactly- sure how much current I need. I know I have 3 LEDs with forward voltages of 2V, 3.2V and 3.2V, with forward current at 20mA each.
Are all three leds ON at the same time ... 100% of the time? Your maths should include an allowance for led operational duty cycle. If they are only on for 50% of the time ... your battery may last twice as long. And that 20 mA figure is used to allow you to compare one device with another. It is not a "must do" figure.

odriew wrote:
How do they do it?
I don't know about "them", but I usually run my leds at about 5 mA and they are "plenty bright" for their indoor applications.

Cheers,

Ross

Ross McKenzie, Melbourne Australia

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Valuesoft is right. Run your LEDs at 5mA, or try using 25% PWM at 15mA. Figure out which one uses less power but appears brighter. Also, run your mega8 as slow as possible. You can drop your current requirements by running the chip as slow as possible.

Jim M., Rank amateur AVR guy.

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Another contender for a 1.5 > 5.0V step-up circuits http://www.onsemi.com/pub_link/Collateral/NCP1400A-D.PDF

Charles Darwin, Lord Kelvin & Murphy are always lurking about!
Lee -.-
Riddle me this...How did the serpent move around before the fall?

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I think that going to 3.3V would be better. The mega8 can run on 3.3 and the LEDs won't need as large dripping resistors. Going from 1.5->5.0->3.2(Vled) is not as efficient as going from 1.5->3.3->3.2V. I know the OP was originally looking for 1.5-5.0V, but as it turns out, 3.3V looks like it will suit his needs and forward is goal of having good battery life.

Jim M., Rank amateur AVR guy.

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How much power does the atmega8 use at different speeds? Does the divide by 8 fuse save power when on? What about using a crystal oscillator at 16MHz?

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The power consumption data is usually on the first page of the datasheet..

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The MAX756 is available as both DIP and SMD, but probably won't run on a single AA battery. The only other problem is choosing the right coil as none of the parts mentioned in the AppNote appear to be available anymore.

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just pick one from here.
http://www.austriamicrosystems.c...

have used them, simple as hell to use. very few external components. and easy to obtain samples for prototyping.

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This is Gareth Jones

$ Spam gone- JS $

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Why do you want 5V anyway? if you're running on 1AA cell, then you probably don't need the 20MHz speed or anything... so just use 3.3V as a supply voltage. Then go to the austriamicrosystems.com website, look for AS1322, take the schematic from page one and be done with it. if 160mA is too little for you, select a higher current one (AS1326 for example, but those generally need 1.5V or higher as input voltage.

for 5V output most of them need 2AA cells or a lithium cell to work properly as otherwise the current that they can supply is too little to be useful for you (especially if you want to drive LEDs with them)

just for once, read the posts that are posted here. Most of the time they ARE helpful!

-Rain-

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Gareth,

You could also google "joule thief".

Cheers,

Ross

Ross McKenzie, Melbourne Australia