DC to DC Converter

Very difficult as most components need more than 0.2 volts for switching, and drop more than that when saturated.
I'd look for a comercial chip, or if it's a fun/educational project I'd set a more acheivable task, say getting a single battery, say AAA (0.8-1.5v depending on how discharged it is) up to say 3 or 5volts.

Del

Del,

I did not see any assumption re power so I thought along the lines of your first post on this topic - use a battery. Ok I MAY need two!

I just wanted to point out that the starting voltage issue only applies for a single transistor input. Ok and without a power source!!

Enjoy

Sleepy

Do you not have any other voltage sources available that would allow you to use something like an Op Amp to boost the 0.2V signal to 1V? A power supply or battery may not be suitable (if your circuit is located away from a regular grid-connected power supply and designed for low or zero maintenance) but what about a small solar panel or vibration or heat energy harvesting circuit and super capacitor energy storage.

What's the application, is it an energy harvesting circuit?

Jack - (Post 2000 and still going strong)

My guess is that the source is a thermocouple...

what about our good old opamps viz μ741 ?

Theoritically it should serve 0.2V but not sure (long back worked and then too not on these sub-voltage ranges)

I was asked to design an energy scavenging project where something like this would have been required. My suggestion was to us a small lithium battery to run a very low power control that would be able to then use standard conversion methods to boost the low voltage but presumably substantial power source. In this instance they wanted to extract power from a microvolt source and that just wasn't realistic. 0.2 volts I can work with but not 0.0002!

I don't think you've described the problem very well. Any chance of a circuit diagram?

You can draw it using TinyCad which is free, then capture it to a file using a free screen capture utility like this one, then post it on CR4 using the little green camera:-

Like this: I've just drawn this; of course you just need to capture the circuit not the whole TinyCad window

EDIT POST: when you use the screen capture utility save the file as a .jpg

If you can use a different transistor, you could substitute a germanium transistor. The Vbe voltage is about .2 volts versus .6 volts.

nganpet,

first thoughts are to use an Op Amp ina differential situation.

That should work downn to verly low input voltages, you can even trim the (zero) input out with the offset.

Good Luck

Sleepy

I was assuming the unit was to be self powered wich precludes the use of op amps etc...

nganpet: Is this a 0.2V signal that you're using to switch something which has "proper" power supplies available, or is the 0.2V your only source of power?

Please clarify.

You can look at a voltage pump circuit similar to the ones used on transceiver circuits. The circuit stores the energy in a capacitor and pass the voltage along to another cap to increase the voltage potential. This is what they do in a RS232 circuit to change 5V to 25V.

Good Luck

Another posed question with insufficient information for us to help. So here's a list of questions the OP should answer so we can help. (Some have already been posted.) I'll add an asterisk * after any that must be answered, try to answer as many of the others as you can.

• Does the transistor circuit have its own power available or are you getting all of the power from the 0.2V signal? *
• How fast is the pulse?
• Is the input signal just a pulse?
• Do you want your transistor circuit to square this signal into a pulse?
• How long is the cable between the pulse producing device and your pulse detecting device?
• What is the output impedance of the pulse producing device? In other words, when you measured 0.2V what instrument did you measure this signal with and what else was this signal connected to at the time?
• Are you committed to using this BJT and which transistor is it?
• What voltage swing are you looking for after this transistor?

Ok, that should give us some grist for this mill.

Recalculate your voltage divider, the transistor is obviously drawing more current than you presumed and the upper resistor is dropping 0.8 volts instead of the required 0.4 volts. What is the current gain of your transistor? What is the transistor load current? You must know approximately how much base drive you need to drive the transistor on! Additionally, the lower resistor's value may also be too low and is drawing too much current away from the transistor's base.

What sort of transistor are you using?

Have you got the base and collector mixed up?

This is one of those posts that amazes me. Mostly posts that are bad to just wrong by people who likely have never designed a switching supply from scratch nor have ultra-low power experience and it just goes on and on with no subsequent posts by the original poster. Sorry guys, I call this pointless.

I agree. This is precisely why I listed a collection of questions for the OP to answer hoping for either a quarter of my questions answered or revelation that they are over their head. Instead, only the question I indicated to be mandatory was answered. Apparently the OP thought that I had asked the other questions just for fun.

Well you cannot help people who refuse to be helped.

For those of you that aren't too familiar with English (or your fingers), please use the spell checker.

I didn't reply to the second line in the op's post which is the crux of the matter, operation in the field with 0.2 volts. 0.2 volts is insufficient to drive a transistor on with either type of transistor. Your only solution is to provide a higher voltage source in the field, i.e. a small battery or a small voltage up-verter to boost the drive signal.. Both National Semi and Linear Tech make excellent chips for this purpose.

0.2 volts is way too marginal even for Germanium transistors. Nganpet, you must give us more information about your circuit, there just isn't enough here to give you a good answer with. What is powering your drive signal and do you know why you are only getting 0.2 volts in the field instead of 1.0 volt? Refred's questions are a good place to start with answers to get good good answers. Please shed some more light on your problem.

E Wiz,

While the OP's lack of cooperation will mean we may never be able to generate a suitable answer, I disagree that 0.2V is insufficient to drive a transistor. While it is true that a BJT must have 0.6V from base to emitter to effectively start conduction, nothing says that the input signal must be the only source for this voltage. Also if one uses a depletion mode MOSFET by definition with no voltage applied to the gate, conduction occurs and can be modulated between source and drain.

Redfred:

Given the sparse information, Nganpet did say 'transistor' and 'Vbe of 0.6 volt', given these two parameters, direct drive of a 'transistor' is not possible. If he would tell us what his drive signal is, it may very well be capable of producing enough voltage to drive a BJT, we don't know. I certainly agree that a MOSFET could operate with 0.2 volts gate drive but he doesn't appear to be using one. That may be a possible 'fix' for him.

He did mention that on the bench, he had 1.0 volt drive and was using a voltage divider to reduce it to 0.6 volts, but in the 'field' he only has 0.2 volts, what happened to his drive voltage? Was the circuit on his bench different in some manner from the field circuit? We don't know, just cryptic replies.

I'm not disagreeing with you, just trying not to second guess this person's circuitry.

Agreed

Nganpet:

You say you have "proper power supplies" available, okay. Now tell us about your 0.2 volt signal source, what is producing it and what is it driving? If you have higher voltages available, why is your driving signal so small? Your postings so far are of no help to us, we need DETAILS, other wise we aren't going to be able to give you answers!

We would like to help you but so far you haven't given us much of anything to work with. We are waiting for information, otherwise we are not going to get anywhere with this.

JohnDG....it wasn't me either, perhaps the wrong button was hit by mistake.

"What we've got here is a failure to communicate."

(Paul Newman as Luke in the movie "Cool Hand Luke")

I thing all the responders missed the OPs #23 comment.

It is a control signal.

And he got it right using an OAPS (I think that means OPAMP?)

<Pat Pat #6>

You may be correct, but we're still guessing, he is still not giving up details.