DC/DC converter

  • Thread starter mrjeffy321
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  • #1
mrjeffy321
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Hello,
I want to make a DC to DC voltage converter so that I can "step up" the output voltage from what it is to something a little more useable.

Right now it outputs about .5 volts, I was thinking that is I could step that up to around 1 or 2 (or higher, higher is no problem) volts, I could use it for something practical.

I know that when you increase the voltage, the current will drop, but this really isnt that big of a concern for me.

I have seen these DC/DC converters sold, but range in price and functionality, I would build one, but I have no clue on how to do it, and I have searched all over the web, but have found little that will help me.
 

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  • #2
enigma
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Is there a reason why you can't use an amplifier?
 
  • #3
mrjeffy321
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I suppose I could, but I know very little about them, could you explain in a little more detail, or tell me some place that could
 
  • #4
Integral
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What kind of device are you starting with? Simply giving output voltage does not say much, what is your current capabilities? What are your current needs? More information cannot hurt.

DC step up is not as easy as AC step up, it requires some form of circuitry which involves cost and some knowledge to create.
 
  • #5
Cliff_J
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And are you sure its only .5V?? Most semiconductors have more voltage drop. Why not use a AAA or AA battery instead?

Cliff
 
  • #6
mrjeffy321
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my voltage source is a PEM Hydrogen fuel cell that I built, it is not very impressive with its current output, I would like to increase it, through some form of circuitry so that it will be a little more impressive during a demonstration, or during practical use.
I have no definite device decided on to use the fuel cell to power, but anything practical will need a little more juice than .5 v.

In my mind, stepping up/down AC voltage couldnt be easier, just built a transformer with the desired coil ratio, tada, you changed the voltage (while changing the current also). but DC isnt that easy, thats why I need help finding out how to do it. I can follow insrtuctions pretty well, so I could built it myself, providing it doesnt get too complicated.

but this idea of increasing a voltage souce's voltage does not nesesarily need to apply to a fuel cell, it could be used to step up any DC voltage source to a greater voltage.
 
  • #7
Cliff_J
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Well a switching power supply can take DC and pulse it through a transformer as pseudo-AC and voila! Or for small currents there are even ICs all ready to go to double or even triple a voltage with minimal parts. Here's some info on switching power supplies:
http://www.smpstech.com/tutorial/t03top.htm#BUCK

But you'd almost need a mechanical switch like a relay vibrating back and forth to pulse the DC because any regular transistor's voltage drop would be greater than or a large percentage of the .5V you have to work with.

Is there any way to build multiple cells that can be wired in series to increase the voltage? (probably too late but never the less an idea)

Maybe find a small DC fan or some other device that can run on your .5V and whatever current is available. Maybe a small DC motor from a slot car or something. Much simpler, wouldn't need to bother with circuitry at all then.

Cliff
 
  • #8
chroot
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You can buy many, many, many switch-mode IC boost converters. The problem is that few of them will function on an input as low as 0.5V..

And you can't use an amplifier, enigma, because an amplifier does not derive power from its input.

You can certainly build a chopper-transformer-rectifier boost converter yourself, but it'll be ugly and very lossy.

- Warren
 
  • #9
mrjeffy321
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I could build more than one cell and hook them up together, building a new cell (while not impossible) does require a little bit of redesigning of the cell I allready have, not to mention that it may cost anywhere from $40 to $60 to make a new cell.

what do they use in cars, they use transformers, but they only have a DC battery.

This is where I origianlly got the idea to make one of these things:
http://www.fuelcellstore.com/cgi-bin/fuelweb/view=NavPage/cat=13 [Broken]
but their prices are a bit high
 
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  • #10
enigma
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chroot said:
And you can't use an amplifier, enigma, because an amplifier does not derive power from its input.
Yes, of course. I didn't realise that the .5V output was the actual power being provided.

I thought it was some sort of signal which needed to be boosted.
 
  • #11
chroot
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Most devices in cars are designed to operate off 12V. Linear or switch-mode boost or buck converters are used for devices that need larger or smaller voltages.

A simple IC boost converter would be ideal for your application, but you'll need more than 0.5V to get them to work. There are many available that will work from 1V, however.

- Warren
 
  • #12
mrjeffy321
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so these IC boost converter, do I buy them, built them, how do I get a hold of one or more?

I would like to build as much of it as possible, as long as it stays simple, I have seen some circuit diagrams of them,they look pretty complicated.
 
  • #13
Cliff_J
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If you look here:
http://www.micrel.com/_PDF/mic2571.pdf
They have a diagram with 4 external parts. No DIP package to make for an easy solder/breadboard, but one of a few ICs that will go down to .9V Mouser.com part number is 803-MIC2571-1BMM and its in stock for $2.28.

Cliff
 
  • #14
mrjeffy321
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I think that is what I am going to end up doing, getting one of these MIC2571-1BMM IC to increase the voltage. We'll see how it works when I get it and try to assemble it.
 
  • #15
chroot
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That Micrel IC will not function with a Vin of 0.5V.

- Warren
 
  • #16
Integral
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Any such circuitry will require an external power supply to operate, doesn't this sort of defeat the purpose of a fuel cell? Seems to me that you need to make several cells and tie them together for more current and higher voltage. If you get something over a volt you can drive a LED.
 
  • #17
chroot
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Integral,

Actually all you need is a diode drop (only about 0.6V for the standard GaAs LED) to make a LED work. It'll be dim, but it'll work off 0.5V.

In general, a switch-mode boost converter does not need an additional power supply -- it is powered off the of the input voltage supplied to it.

- Warren
 
  • #18
mrjeffy321
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I will try to increase the output of my fuel cell, and/or add a small 1.5 volt battery to push it up to the minimun voltage
 
  • #19
chroot
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Adding a battery will of course work, but you'll be drawing power from the battery as well as from the cell.

- Warren
 
  • #20
mrjeffy321
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yes, I know, but that is what I will have to do, untill I find a substitute
 
  • #21
I was reading about ignition coils used in older cars. They operate on DC current and create about 25,000 volts from 12 volts. From what I understand the current builds up in the coil, but nothing happens until the distributor rotates into the right position at which time a magnetic field collapses in the primary winding in the coil inducing a high-voltage current in the secondary winding of the coil. (I'm not clear on just how it happens.) The point is that it is one way to get a repetative 'burst' of higher voltage which you could do something with, like make sparks.

Just an idea.
 
  • #22
chroot
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The operation of an ignition coil is actually similar to that of a switch-mode inductive boost converter. The idea is simple: inductors (coils) refuse to allow currents to change instantaneously through them. When you allow current to flow through an inductor, then suddenly open a switch and break the circuit, the inductor will develop enormous voltages in a desperate attempt to keep the current from dropping instantaneously to zero. This is known as inductive "kick."

The distributor in a car is nothing more than a repetitive switch that opens and closes once per revolution for each spark plug. When the switch is closed, current flows, building up a magnetic field and storing energy in the ignition coil. When the circuit is broken, the inductor generates large voltages and forces a spark across the switch, and thus across the spark plug gap as well.

The "points" of the distributor are the switch contacts. Over time, the arcing destroys them, and they must be replaced.

- Warren
 
  • #23
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what is the total power output from the fuel cell stack?
is t a single fuel cell or stack of cells?
 

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