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Topic: Switching on and off a 6.5V load (Read 191 times) previous topic - next topic

Rhydm

Hello. I'm quite rusty with electronics, so here's my task.

I need to switch on and off the power supply to a 6.5V device (another microcontroller) which will drain 100mA max. The frequency of switching will be a Hz or less. I'm thinking about using a MOSFET as a switch which would be controlled by Arduino.

If that's the way to go, any tips about what I should pay attention to when choosing the MOSFET.

Also I'd like to protect the load against voltage spikes that might occur during the switch. Would a zener diode suffice?

Thanks for your time and answers/tips.

Paul_KD7HB

Hello. I'm quite rusty with electronics, so here's my task.

I need to switch on and off the power supply to a 6.5V device (another microcontroller) which will drain 100mA max. The frequency of switching will be a Hz or less. I'm thinking about using a MOSFET as a switch which would be controlled by Arduino.

If that's the way to go, any tips about what I should pay attention to when choosing the MOSFET.

Also I'd like to protect the load against voltage spikes that might occur during the switch. Would a zener diode suffice?

Thanks for your time and answers/tips.
Unless there is some inductance in the circuit you failed to disclose, there are no voltage spikes.

Paul

FredScuttle

#2
Jul 12, 2018, 11:54 pm Last Edit: Jul 13, 2018, 01:28 am by FredScuttle Reason: Moved R2

Paul__B

What's the 220 Ohm resistor supposed to do?

FredScuttle

Ease my mind.  :)  I know it's not really needed, guess I have a mental aversion to hooking things directly to a transistor base, it can be dispensed with.

Rhydm

Thanks for the repplies.

Unless there is some inductance in the circuit you failed to disclose, there are no voltage spikes.

Paul
There isn't so I guess it should be fine without any special precautions.

Something like this might work.
https://www.digikey.com/products/en?keywords=vp2206
Thanks. I had something like that in my mind.

wvmarle

Low side switching with an n-channel MOSFET is easier. Normally you'd switch low side unless there's a very specific reason not to.
Quality of answers is related to the quality of questions. Good questions will get good answers. Useless answers are a sign of a poor question.

FredScuttle

OK marle, why don't you provide us with a comprehensive list of those reasons. I'll start my stopwatch... NOW.

Paul__B

Ease my mind.  I know it's not really needed, guess I have a mental aversion to hooking things directly to a transistor base, it can be dispensed with.

No, actually, it is not "it can be dispensed with", it is an error.  Albeit not particularly critical in this case.

I am taking a guess that you have been reading all about driving FETs from an Arduino output where it is desirable to limit the current the microcontroller output stage will transiently supply to charge or discharge the FET gate capacitance, particularly when used repetitively as  for PWM.

Now in this case, you are not switching all that often but in any case, the transistor is rated for 200 mA collector current, ten times that of an Arduino and that is arguably a continuous rating anyway, so there is no indication to restrict the gate current.  In fact, the 10k resistor may be a concern as it will slow the FET switching off, spending more time in a linear control mode and thus wasting power.  You may want a lower value resistor there but this will waste more power.  If this became a significant problem you would need to provide a proper totem pole driver to the FET.

Low side switching with an n-channel MOSFET is easier. Normally you'd switch low side unless there's a very specific reason not to.
Such as switching power to another microcontroller perhaps?  :smiley-eek:

You use low side switching when the device whose power is switched has only two connections.

wvmarle

#9
Jul 13, 2018, 07:14 am Last Edit: Jul 13, 2018, 07:15 am by wvmarle
Such as switching power to another microcontroller perhaps?  :smiley-eek:
Right. Missed that tidbit in the OP. Was put off with the generic "load" that was used for the rest of the discussion.
Quality of answers is related to the quality of questions. Good questions will get good answers. Useless answers are a sign of a poor question.

Rhydm

No, actually, it is not "it can be dispensed with", it is an error.  Albeit not particularly critical in this case.


Thanks for your input. Hopefully it all work well enough :)

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