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Topic: Which Transistor Wiring is Better? (Read 248 times) previous topic - next topic

pseudoresonance

Mar 16, 2020, 11:43 am Last Edit: Mar 16, 2020, 11:47 am by pseudoresonance
I've seen many tutorials on how to wire up 5050 LEDs with some MOSFETs, but almost all tutorials I've seen are showing the output of the MOSFET connected to ground through a 10k resistor, however from what I've read about transistors in general and from what I've seen on another tutorial, shouldn't the resistor be connecting the input from the Arduino to ground?

Here is a diagram to demonstrate the first method I talked about:


And what I think makes more sense:


Is there a correct way of wiring this up? And if so, why?

Sorry if I missed something, thank you!

TomGeorge

I've seen many tutorials on how to wire up 5050 LEDs with some MOSFETs, but almost all tutorials I've seen are showing the output of the MOSFET connected to ground through a 10k resistor, however from what I've read about transistors in general and from what I've seen on another tutorial, shouldn't the resistor be connecting the input from the Arduino to ground?

Here is a diagram to demonstrate the first method I talked about:


And what I think makes more sense:


Is there a correct way of wiring this up? And if so, why?

Sorry if I missed something, thank you!
The output is not connected to gnd through a 10K resistor.
LOOK the Fritzy, the 10K is connected to gnd and the GATE INPUT OF THE MOSFET.
The input of the MOSFET is connected to a pin of the UNO, it will be configured as an OUTPUT to apply control to the MOSFET.
Tom... :)
Everything runs on smoke, let the smoke out, it stops running....

TomGeorge

Hi,
However this diagram has the 10K in the wrong place;


Tom... :)
PS. Can I suggest you stop looking at Fritzy picture and convert to proper schematics.
Everything runs on smoke, let the smoke out, it stops running....

TomGeorge

#3
Mar 16, 2020, 12:21 pm Last Edit: Mar 16, 2020, 12:21 pm by TomGeorge
Hi,
This is more informative;

Tom... :)
Everything runs on smoke, let the smoke out, it stops running....

pseudoresonance

Hi,
However this diagram has the 10K in the wrong place;


Tom... :)
PS. Can I suggest you stop looking at Fritzy picture and convert to proper schematics.

Thank you for the fast response.

I also just noticed that the resistor placement is inconsistent within that first picture... That is mainly what I was referring to initially, however despite your efforts to use nice diagrams, I also found another picture from Adafruit..



This one is putting a resistor between the Arduino and gate, not to ground... Isn't that just incorrect? I see no point.

Thanks!

TomGeorge

Hi,
Putting a resistor in series with the gate is another thing you can do.

The gate of the MOSFET acts like a capacitor, when you PWM or pulse it, there is a current pulse that occurs as you increase frequency, this resistor limits the current pulse magnitude to protect the  Arduino output.

So if you like , certainly place a 220R or 470R resistor in the gate wire.

Tom.. :)
Everything runs on smoke, let the smoke out, it stops running....

Ron_Blain

The attached illustrates a single section of a 5050 LED string I have. As can be seen they are common anode so the MOSFETs are used to switch the cathodes making for low side switching.  While the MOSFET Gates reflect 100 K Ohm to common (Ground) the use of 10 K Ohm would be fine.



The DIO points are digital outputs from a uC. The LED series resistors are integral to the LED strip.

Ron


pseudoresonance

Hi,
Putting a resistor in series with the gate is another thing you can do.

The gate of the MOSFET acts like a capacitor, when you PWM or pulse it, there is a current pulse that occurs as you increase frequency, this resistor limits the current pulse magnitude to protect the  Arduino output.

So if you like , certainly place a 220R or 470R resistor in the gate wire.

Tom.. :)
Ah, I see, thank you. Do you think it would be important to add that resistor with an Arduino Nano for longevity? Or is the difference negligible.

Thanks again for your help!

Smajdalf

The resistor between Arduino output and MOSFET gate protects Arduino and stresses the transistor. IMHO it does not matter for simple switching, it may be important for PWM. I would say it is better not to use it but many people here would say you will die in pain if you forget to add the gate resistor.
How to insert images: https://forum.arduino.cc/index.php?topic=519037.0

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