Problem with BUZ11

Using Arduino General Electronics
1

Hey there,

for my project (I have to power a peltier element with an external power supply (12v, 6w)), I needed a mosfet and bought the BUZ11.
Normally you should wire the GND of the peltier element to the middle leg, the GND of the power suppy (connected to the arduino) to the right leg and the arduino pin (I used 3) to the left leg (possibly with a 10k resistor to GND).
But although I did that (and tried out other wirings (with 220 Ohm, etc.) I wasn't able to control my peltier element (it was always "on", so the current wasn't blocked).

Any suggestions?

2

Any suggestions?

Maybe think a little longer about which would be the most appropriate section of the forum to post your question?

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(deleted)

4

Yup that's exactly how I connected it

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(deleted)

6

Yeah it does (so the MOSFET doesn't block the current even when gate = source)

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(deleted)

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Sorry... pic was to large, here it comes

IMG_20170205_185922.jpg
IMG_20170205_185922.jpg2468×1838 657 KB

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(deleted)

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11

Unfortunately I'm from Germany, but thank you for the offer!

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A BUZ11 is NOT a logic level fet, and should not be used with a 5volt Arduino.
Leo..

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(deleted)

15

Okay, thanks again for the replies :smiley:

I found a TIP120 transistor (still not a logic-level mosfet, but better than the BUZ11) and wired that one, but that doesn't work too.
(Again common GND to right leg, GND of the device (here peltier) to the middle leg and Arduino Pin to right (10k to GND behind)).

That also it doesn't work indicates that it is not a problem with the transistor.
Did I wire everything correctly? - I think so
So, is there any other problem? Maybe a problem with the digitalWrite() of the Arduino?

16

Okay I checked if the problem was with the digitalWrite-funktion but that isn't the problem (tried with an LED and it emitts 5v perfectly)

So do you have any idea what might be the solution?

17

spycatcher2k:
Vgs - 4V Max , should work fine.

That is threshold, when the MOSFET begins to conduct.
Tom.... :slight_smile:

18

james_no:
Okay, thanks again for the replies :smiley:

I found a TIP120 transistor (still not a logic-level mosfet, but better than the BUZ11) and wired that one, but that doesn't work too.
(Again common GND to right leg, GND of the device (here peltier) to the middle leg and Arduino Pin to right (10k to GND behind)).

That also it doesn't work indicates that it is not a problem with the transistor.
Did I wire everything correctly? - I think so
So, is there any other problem? Maybe a problem with the digitalWrite() of the Arduino?

TIP120 is not a MosFET and you cannot connect it like it was one.

If you have no resistor between the base of the transistor and Arduino output you will short the output of the Arduino, destroying both the transistor and possibly the Arduino in the process.

You need to look into difference between BJT (Bipolar Junction Transistor) and MosFET (Metal Oxide Field Effect Transistor) - they are not the same.

// Per.

19

spycatcher2k:
Vgs - 4V Max , should work fine.

Wrong.

The BUZ11 is NOT a logic-level MOSFET and requires 10V gate drive.

Perhaps you think the threshold voltage is when the device is on? It isn't.

20

TomGeorge:
That is threshold, when the MOSFET begins to conduct.
Tom.... :slight_smile:

Don't think of it like that for a MOSFET used as a switch, the plateau is when it starts
to conduct (as opposed to leaking a little).

The threshold voltage is useful if using the MOSFET in an analog circuit, it is not useful
for use as a switch.