Voltage multiplier circuit required

[srisms]

Hi all,

I need a DC to DC voltage multiplier circuit which should be stable and highly energy efficient. The input would be 0.5V @ 8amp and the output required is 12V with upto 400mA. Hope to receive good updates asap.

Thanks in advance.

Kumar

 

[Harald Kapp]

What you request is impossible.
Input power is 0.5 V * 8 A = 4 W
Output power is 12 V * 0.4 A = 4.8 W
Even a perfect (read 100 % efficiency) step up regulator could generate only 4 W, but real regulators have an efficiency of 75 % ... 90 % which means that from 4 W input power you can generate 3 W ...3.6 W

Apart from that discrepancy look up any standard step-up (or boost) switch mode regulator. There are many vendors of suitable chips.

Harald

 

[srisms]

DC to DC voltage multiplier

Dear Harald,

I do understand the issue. I said upto 400ma. I am happy with a 75% efficiency. Pl do provide if you have one.

Thanks in advance.

Kumar

What you request is impossible.
Input power is 0.5 V * 8 A = 4 W
Output power is 12 V * 0.4 A = 4.8 W
Even a perfect (read 100 % efficiency) step up regulator could generate only 4 W, but real regulators have an efficiency of 75 % ... 90 % which means that from 4 W input power you can generate 3 W ...3.6 W

Apart from that discrepancy look up any standard step-up (or boost) switch mode regulator. There are many vendors of suitable chips.

Harald

 

[mattsains]

unless I'm mistaken, 0.4A=400mA

 

[mattsains]

What Harald said is that it is impossible to get more than 333mA @12V from the given supply

 

[BobK]

Not to mention that you are unlikely to get high efficiency at 0.5V input.

Bob

 

[srisms]

Yes 0.4A is 400milli amperes. The said circuit need to pump UPTO 400ma if necessary.

unless I'm mistaken, 0.4A=400mA

 

[srisms]

Dear Matt,

I do understand. If in case I could not get a 0.5V and 8Amp source I may have to jump for a higher input rating hence the desired output current.

Kumar

What Harald said is that it is impossible to get more than 333mA @12V from the given supply

 

[srisms]

Dear Bob,

Pl try to provide the best efficient one. I can change the input power but the input voltage is not more than 0.5V

Thanks in advance.

Kumar

Not to mention that you are unlikely to get high efficiency at 0.5V input.

Bob

 

[mattsains]

Assuming an efficiency of 75%, you'd need 0.5V @ 12.8A to supply max 400mA @ 12V.
I'll leave it up to someone more experienced to do a google search to find a multiplier for you

 

[BobK]

What you need is a Joule Thief on steroids.

Bob

 

[Mongrel Shark]

Even I don't think I can make a joule thief that powerful. There are only a few silicon transistors that will go down to .5v. Even then you need special coil windings, and it's efficiency is horrible. Think more like 20%... output would be Pulses around the 1-50 khz range.

May I ask where you intend to get 8 amps or more at half a volt?

I know little about dc-dc step up's. But I would think you will have trouble finding one that takes an input less than 1.2v as that's about as low as single cell battery's go.

What you ask is not impossible, But it's a stretch with the technology available in 2012...

Perhaps a custom made Joule Ringer (ie 3 or more coils harmonically tuned)?

I can make 25v from 1v, But under a volt things really start to drop off.

I could charge a 1.5v battery (in theroy, still working on this) from .5v then use a step up from there... Getting a lot of losses though... Might need 10-20 amps....

I would need to know more about your power supply and intended load to help more. Sorry.

 

[Mongrel Shark]

Disregard my above statement. There are no transistors I know of that can run form the low voltage and handle the high currant at the same time. I don't think it can be done with a joule thief or ringer.

 

[CocaCola]

I know little about dc-dc step up's. But I would think you will have trouble finding one that takes an input less than 1.2v as that's about as low as single cell battery's go.

There are low voltage harvesting ICs and/or circuits out there, but IMO the final output requirements are unrealistic, or at the very least impractical...

And as stated by Mongrel, where are you going to get a 8+ amp 0.5v source and I asked why is the source limited to a 0.5 volts?

 

[(*steve*)]

Imagine I have 2 solar cells in my hand. They have an open circuit voltage of around 0.55V and a short circuit current of 4A

With some number of these (probably more than 2 of them) I can easily make a supply capable of 0.5V at 8A.

However, if this were the source, I'd probably put them in series.

MS, there's no insurmountable problem in creating a boost converter that can take 0.5V and pump it up to 12V. Doing it at high efficiency is another problem.

There are any number of mosfets with on resistances in the miliohm range that would drop only a tiny fraction of the voltage at the current contemplated.

Now it is true that it is difficult to consider a "joule thief" since these are essentially relaxation devices powered from the low voltage input, but it doesn't need to be so!

All you need is a low power source to bootstrap the device into operation (after which it may well be powered from it's output voltage).

There are significant technical challenges, your mosfet must have very low resistance, as must your inductor to allow the current to rise to 8A without losing a large fraction of the power to resistive losses.

Let's say that your combined mosfet, wiring, and inductor resistance would need to be below 6 milliohms -- that is the real challenge.

 

[CocaCola]

Imagine I have 2 solar cells in my hand. They have an open circuit voltage of around 0.55V and a short circuit current of 4A

More so I was thinking/talking about a single source that locked you into 0.5 volts... If you are going to use multiple 'cells' then as you said put them in series and up the voltage, it will make life easier and depending on the overall design you might not even need a boost... Either way the closer you get to 12 volts the easier/more economical it is to boost to 12 volts...

 

[(*steve*)]

100% true CocaCola. Even if a single large cell was available (the best I've seen are around 4A I think) I would have investigated smaller cells in series for this very reason.

Knowing the source of the power is probably an important issue because then we can discuss alternatives that will reduce the level of technical challenge.

Now, it's entirely possible that the source of power is exactly as stated, and cannot be placed in series with others to get a higher voltage, but it's such a fundamental issue that knowing this for certain (either way) would help focus us on a solution rather than potential problems.

 

[CocaCola]

Knowing the source of the power is probably an important issue because then we can discuss alternatives that will reduce the level of technical challenge.

From this comment below, I'm left feeling that the power source is not locked in, and IMO other source options are certainly something to consider...

If in case I could not get a 0.5V and 8Amp source I may have to jump for a higher input rating hence the desired output current.

 

[Mongrel Shark]

I have been googling in an attempt to better edumacate myself.

This is the best I can find. http://cds.linear.com/docs/Datasheet/1073fa.pdf

Needs 1v though. Is there any reason not to use two step up's?

Go from .5 to 1-3v then use a second converter to step that up to 12v.

If both are 90% efficient. and my maths is right it would be 81% efficient.

 

[john monks]

I believe the most efficient way is to use a flyback arrangement that uses a coil that is energiszed from the 0.5 volts through a power mosfet, rectified and filtered.