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can anyone help me design a transformer for low voltages?

can anyone help me design a step-up transformer where the input voltage is around 100 mV (AC) and to be converted around 2.5V (AC)?

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orksecurity6 years ago
The basic formula can be found, among other places, at https://secure.wikimedia.org/wikipedia/en/wiki/Transformer

That assumes perfect coupling between the two coils. Real-world transformers always lose some of the power. Physical design and choice of core material and configuration can affect that.

Remember that even in the ideal case, a transformer gives you at most the same power (volts times amps) out that you put in. By stepping up the voltage 25 times, you reduce the current available by the same amount. If you only have 100mV, I suspect you also have almost no current available, and reducing that by 25 times ... well, you can't do much with that except feed it into a high-input-impedance amplifier.

So why not just feed your 100mV signal into an amplifier?
... Actually, transformers do sometimes get used for low voltages. I've seen folks "split" a microphone signal using an isolation transformer with two output coils -- same voltage but half the power at each of two outputs. If that's going directly into a sufficiently good input stage -- preferably op-amp, which can be very high input impedance and thus not require much power.

But I remain skeptical about whether that's really better than feeding the signal to a single preamp stage and then splitting the amplified signal. Depends on just how much you do or don't like that preamp, I guess.

So the real question here is: What are you trying to do? A transformer may be the right answer or may not... and if it is, odds are pretty good that you can buy one for not-unreasonable amounts of money.
jeromekang (author)  orksecurity6 years ago
The application we are working on is with regards to energy harvesting. We were advised to use a transformer to amplify our sources which are piezoceramics, magnets and micro motors. The power we plan to harvest comes from the typing motion in computer keyboards and mouse scrolls and clicks so that is somewhat only parasitic. Would an amplifier be better for our application? What kind of amplifier? We are currently at a lost on how to proceed with this project.
(Reposting to correct a typo.)

An amplifier is just a valve -- it uses one signal to control another, usually larger, signal -- and so draws power; it would not be useful to you.

A transformer doesn't "amplify" power either. It increases or decreases voltage, but it decreases or increases available current to the same degree. Since power is volts times amps, this theoretically means the power remains unchanged -- though actually, since no transformer is 100% efficient, you will lose some power.

What a transformer may do, by giving you the greater voltage, is make "stacking up" power in a capacitor somewhat easier. Of course you'd need a blocking diode to keep that power from discharging back through the transformer.

Experts have been playing with parasitic energy gathering for a while. It's hard to gather enough energy to do much. You might want to start by searching the literature to see what they've tried.
> We are currently at a lost on how to proceed with this project.
.  If no one on your team understands transformers, piezoceramics, and magnets, then you need to find someone who does. It doesn't require a full-blown engineer; just about any college freshman EE student (maybe even a HS student) should already know about such things.
seandogue6 years ago
Although it admittedly doesn't answer your question, I'm curious why you're trying to amplify a low level AC signal using a transformer rather than using a simple gain of 25 opamp circuit.

Unless you have isolation issues from a high voltage setting, it seems a bit silly to me to be screwing around with transformers for the task.
I dunno, its certainly novel, and if you have a source of low voltage AC at high currents....

Steve
Well, they are used for isolation, but usually as just that, not for amplification. We routinely used isolated amplifiers for fuel test stands, since flammability regulations required their use, but even then they weren't used as amplifiers, simply as isolators.

The law of transformers (not really a "law", but I think you'll get my drift) says that any amplification of voltage results in a corresponding attenuation in current, so any such amplification circuit would likely be more susceptible to external noise sources.

I'd be more inclined to use a diff in amp for syphoning off a high current line
I've got to thinking though what LOW voltage POWER source you could have that needs boosting up to usability
imo, that's for the author to provide, since he's the one who wants assistance
jeromekang (author)  seandogue6 years ago
The application we are working on is with regards to energy harvesting. We were advised to use a transformer to amplify our sources which are piezoceramics, magnets and micro motors. The power we plan to harvest comes from the typing motion in computer keyboards and mouse scrolls and clicks so that is somewhat only parasitic. Would an amplifier be better for our application? What kind of amplifier? We are currently at a lost on how to proceed with this project.
In terms of power harvesting, yes, I suppose a transformer might be more applicable than an amplifier. Sorry to have misled you. I thought you were literally trying to amplify the signal. For energy harvesting, the idea would be to boost the signal level to one that could be converted into a usable source for charging a battery or similar, parasitically "stealing" a tiny amount of energy from some source.

The basic relationship starts here (minus any losses in the transformer)

1:1 same voltage in and out same current
1:2 Vout is twice V in, Iout is half Iin
1:4 Vout is four times Vin, Iout is 1/4th Iin
etc etc

Steve surmised your usage correctly.