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Constant voltage supply with a MOSFET

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FrAxl93

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Good morning.

I am in the need of powering my dsPIC with a 3.3 Volts supply but I don't have any generator around this value. I tried with the 3.3V ouput from Arduino but I think that it doesn't provide sufficient current*.

It happens that I am a bit short of components and I don't have access to any market. I don't have any voltage regulator and I have only 2 power MOSFET, 3 OPAMP, a 9V battery and an 12V power supply. I can't just create a voltage divider to create my 3.3 source since it will drop as soon as I connect the PIC, so I'll need something more reliable.

I decided to DC bias the MOSFET but in the **broken link removed** there is no trace of the parameters for the well known formula:

ID = 1/2µnCoxW/L (Vgs - Vt)2.

I know that such parameters are very temperature dependent so some datasheets just don't provide them, but how can I design the correct resistances if I don't know how to calculate the drain Current? This is the design I'd like to realize:

IMG_3402.jpg

I read on the internet that serious analog projects involve designs that don't rely on those parameters, may you provide some fixed design for such stiff voltage source?

Big thanks for your help,
regards, Francesco.

*In order to prevent this question becoming too broad I won't talk about the issues with the pic that make me think that I have a problem with the maximum current, if you are interested ask me and I will add details.
 

Hi,

A 3.3V voltage regulator is one of the most simple, most common and cheap devices. I can´t believe that there´s no such thing around you.
Open any defective electronic device and disassemble one. I have a lot of electronic parts around.. I´m sure there is a voltage regulator ...

I think that it doesn't provide sufficient current
You need to know the current comsumption. Independent if you use a ready to buy suppl, use a voltage regulator or design one on your own.
You need to find out from datasheet or measure it.
For any work with electronics you need a voltmeter and an amperemeter.

The given circuit won´t work, because the outout voltage is not stable.. it is too weak.

If you want to build one on your own, then you need some kind of voltage as reference. Maybe a zener, or even a LED may work.
Then you have an OPAMP, a FET or a BJT and some resistors and capacitors. With this parts you can build some kind of power supply.

Klaus
 

You forgot to tell us the current needed for the 3.3V output.
Mosfets have a range of gate to source voltage where one barely turns on (0.25mA) when the voltage is 4V and another one with the same part number turns on very well with a few volts. Then you must buy a few hundred Mosfets and test them all. You might be lucky to find one with a voltage you can use (maybe with a divider voltage of 9V for your 3.3V output).

Or you can use an opamp to measure the output voltage from the Mosfet and adjust the gate voltage so that the output voltage is the same as your 3.3V reference voltage.
 

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