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Transformer

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JoeWawaw

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hi, is it possible to step up a very low AC voltage (0.5-2V) with a transformer?
My question here is not how to do it, but i was wondering if 1V is too little to be stepped up by a transformer
thanks
 
There really isn't a minimum voltage that can be stepped up by a transformer. However, the transformer will only have a small inductance so you may need quite a lot of current to supply the transformer.

Current transformers typically have very small input voltages, but large input currents.

What is the application?
 
Thanks,
I want to step-up a small water turbine actually, the output would then go to a mosfet to turn on external components. the mosfet itself requires 1.5V gate voltage, and after the diode bridge there isnt enough voltage to power it
 
You've said that the AC signal is 0.5 - 2.0 V. Have you got any idea of what the impedance is? If you measured the short-circuit current of the turbine that would give a good idea.

I assume that you mean a really small turbine, and you are trying to detect water flow rather than get power from the water. Have you got more details?
 
From what you wrote it seems that you're just wanting to increase the voltage to drive the mosfet gate. You could use an NPN transistor, which can be turned on with around half a volt. The NPN can be used to control a larger voltage to switch your mosfet.

Another way is to use a Cockcroft-Walton multiplier to boost the voltage. With 0.5VAC, you have 1.4Vpp so each multiplier stage can provide 1V (using Schottky diodes)

You could use a transformer to boost the voltage as you said.
 
.... You could use an NPN transistor, which can be turned on with around half a volt. The NPN can be used to control a larger voltage to switch your mosfet....

Bias the NPN to turn it into AC-coupled amplifier and it will have a voltage gain of >50. A passive diode detector and a filter capacitor can turn the amplified AC into a voltage to control the gate of a FET. mV of an AC signal can easily produce a few Vdc at the gate.
 
Diver3000: yes it is a small turbine, mainly to detect water flow, rather than produce electricity from it
dougy83: Thanks! ill look into the Cockcroft-Walton generator and see how it works
MikeMl: yes i could do that, although i would need minimum 1.5V also (two schottky diodes from the bridge recitifier, then 0.7V for the transistor), if i had a peak of 2V, it would be on only after passing 1.5V, which isn't a great duty cycle
 
This is a version of the NPN switching thing I mentioned.. it is pretty crappy, but should turn the FET on if the input voltage is described.
 

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... although i would need minimum 1.5V also (two schottky diodes from the bridge recitifier, then 0.7V for the transistor), if i had a peak of 2V, it would be on only after passing 1.5V, which isn't a great duty cycle

I was assuming that you have a DC supply available, in which case I can make ~7V at the gate of the FET when the input signal is ~100mV.
 
dougy83: whats the use of the capacitor in the circuit?
MikeMl: yes it does have an external power supply, 9V actually. I'll see how it works, thanks
 
The capacitor smooths out the pulses from the transistor (1 pulse per input AC cycle) to keep the fet on constantly while the motor is turning.
 
ahh ok thanks
one other thing: this circuit only takes the positive part of the AC voltage from the coils... would putting a PNP allow me to also use the negative part of it?
 
You can use a PNP as well, but on first thoughts you will need to isolate the DC component from the NPN and PNP e.g. with capacitors.
 
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