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Topic: Flyback Diode limiting motor running power (Read 1 time) previous topic - next topic

red913

I have a flyback diode. I'm using this https://www.sparkfun.com/products/8589 one. It's reversed as I was told. You can see how it's connected to the motor here: https://www.circuitlab.com/circuit/gewe4c/screenshot/1024x768/

So when it's connected, the motor doesn't really run. It just kind of sputters and makes a little noise. I remove it, the motor runs fine. Any ideas? Am I using the wrong part?

retrolefty

Quote
So when it's connected, the motor doesn't really run. It just kind of sputters and makes a little noise. I remove it, the motor runs fine. Any ideas? Am I using the wrong part?


Sure sounds like you have the diode wired in backwards. It's draw correctly in your link.

Lefty

red913

I believe the side of the diode with the strip on it is the cathode(+) so I've got that in parallel with the negative and the other side of the diode (-) with the positive on the motor.

Erdin

#3
Apr 09, 2013, 02:38 am Last Edit: Apr 09, 2013, 02:41 am by Erdin Reason: 1
A P-Channel mosfet ? How is that possible. Do you happen to have a "logic level" N-Channel mosfet ?

Read 'card5', http://www.pighixxx.com/abc-english-version/

retrolefty


I believe the side of the diode with the strip on it is the cathode(+) so I've got that in parallel with the negative and the other side of the diode (-) with the positive on the motor.


The cathode end (striped end) should wire to the positive voltage source/motor lead, the anode lead should wire to the motor lead/drain lead of the mosfet. Sounds like you have it wired backwards. Wire it like it's drawn in that drawing you posted.

Lefty

red913


A P-Channel mosfet ? How is that possible. Do you happen to have a "logic level" N-Channel mosfet ?

Read 'card5', http://www.pighixxx.com/abc-english-version/


been meaning to fix that. Thanks. It's a n channel I'm using by the way. Yes it is logic level.

red913



I believe the side of the diode with the strip on it is the cathode(+) so I've got that in parallel with the negative and the other side of the diode (-) with the positive on the motor.


The cathode end (striped end) should wire to the positive voltage source/motor lead, the anode lead should wire to the motor lead/drain lead of the mosfet. Sounds like you have it wired backwards. Wire it like it's drawn in that drawing you posted.

Lefty


ha ha what stupid mistake. Cathode is negative not positive. ok. thanks. works now. lol

retrolefty

#7
Apr 09, 2013, 02:55 am Last Edit: Apr 09, 2013, 02:57 am by retrolefty Reason: 1
Quote
ha ha what stupid mistake. Cathode is negative not positive. ok. thanks. works now. lol


Your doing yourself a disservice by thinking negative and positive when using diodes, they are just cathode and anode. How they are wired depends on the function of the diode, usually you wire then so that they are forward biased (turn on) with the applied voltage, but in this case you want the diode to be wired in reverse bias for normal applied voltages. So it is at times valid to wire diodes one way or the other depending on it's function in the circuit. Thinking that one end is always positive and the other negative fails to understand the basic theory of operation of a simple diode.

Your failure was in not wiring the diode as shown and drawn correctly in the schematic, you tried to 'out think' the schematic.

Lefty

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