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Topic: Arduino controlled mosfet driverwont switch. (Read 3990 times) previous topic - next topic

esgeroth

You wouldn't say that if you could see the waveforms on an oscilloscope.  Decoupling is mandatory
for reliable operation.
The light still won't turn off. So it does not make any difference that matters.

Why are you using DigitalWrite (blinking) , instead of AnalogWrite (PWM) ?

Like I said, I just wrote the blink sketch so that I can see the light blink. How is this going to make a difference?

It's hard to tell, when looking at your photo, because of parallax, but it looks like the Orange lead is connected to pin 2 (on the Arduino), yet, your sketch is pulsing pin 3.

Regarding the "decoupling capacitor" that some are screaming about.  Yes, for "proper" operation, it is required, but it's not going to make all that much difference at such low frequencies -- but, to make everyone happy, and to remove one of the variables, I suggest to include it in your test circuit.
It does look like that in the picture but it's definitely in pin 3. I have added the recommended capacitor as I posted in my last post so hopefully everyone should be happy.

I'm not finding very many circuit designs using this chip. Should the signal input pin be pulled down with a resistor? The arduino has an internal pull down resistor right?

ReverseEMF

#31
Apr 24, 2018, 07:19 pm Last Edit: Apr 24, 2018, 07:24 pm by ReverseEMF
Should the signal input pin be pulled down with a resistor? The arduino has an internal pull down resistor right?
This is quite a perplexing problem. 

Regarding the Arduino output, and whether it has a "pull down resistor" or not.  The ATmega8 datasheet doesn't seem to reveal the exact electronics of the output [only shows a "buffer" symbol], but more than likely it's an arrangement of a p-channel FET and an n-channel FET in a "totem-pole" like arrangement [not sure if totem pole is the proper term for this kind of circuit -- but it's similar to the old TTL totem pole outputs].  So, I doubt there's an internal pull down resistor, but there is a pull down action, probably via an n-channel FET (so no need to add a pull down resistor).

So, have you watched, with a scope, the Arduino output, as it toggles, while it's connected to pin 2 on the TC4427?  To make sure the line is actually toggling (when the TC4427 output [on pin 7] remains high)?  What about if you place the probe right on pin 2?  Do you still see the toggling signal?

It's so odd, that manually manipulating the voltage on the TC4427 input, causes the LED to indicate a change, yet the Arduino output has no effect.

What if you try the other driver -- pin 4 and pin 5 (on the TC4427?
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raschemmel

Quote
Like I said, I just wrote the blink sketch so that I can see the light blink. How is this going to make a difference?
FYI,
If you want to DIM the LED, use PWM (AnalogWrite)

ReverseEMF

You wouldn't say that if you could see the waveforms on an oscilloscope.  Decoupling is mandatory
for reliable operation.
This statement indicates a lack of understanding of the role of a decoupling capacitor.  It does two things.  It decouples (i.e. removes) the noise caused by transitions in digital output circuitry [more of an issue in the days of TTL], and it supplies immediate current [that would not, otherwise, be available due to inductance in the supply lines] for each digital transition.  And, the decoupling effect can, actually, be considered a side effect of the latter function.  This is only an issue at higher speeds and when there are other circuits that could be affected by these current spikes.  It may alter the rise or fall time, but at 10Hz, this just isn't significant.

For what the OP is doing, this is a minor effect that plays no role in debugging the issue.  The TC4427, will function well enough to provide a credible result -- which was proven by the OPs experiment where he/she manually applied high and low voltage to the TC4427 input, which produced an observable change in the LED's brightness.  

When the OP says "has not changed anything", he/she means within the context of the experiment -- i.e. still fails to produce the expected indication in the LED.  The fact that the LED failed to pulse, even with the capacitor, excludes the capacitor as a determining factor.
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ReverseEMF

#34
Apr 24, 2018, 07:45 pm Last Edit: Apr 24, 2018, 07:47 pm by ReverseEMF
FYI,
If you want to DIM the LED, use PWM (AnalogWrite)
This is not about dimming the LED.  The OP is trying to determine why the TC4427 is not driving the LED, when the Arduino is applied to it's input.  He/she wants a clear indication of actual transitions, not a dimming of the LED.
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raschemmel

#35
Apr 24, 2018, 09:37 pm Last Edit: Apr 24, 2018, 09:50 pm by raschemmel
Wouldn't a voltmeter tell you that ?

You don't need a scope to determine that,
nor do you need to 'blink' it. A simple on/off test should suffice. I don't see how any of the tests done do far are as good as a voltage meadurement with s meter. The fact a DMM has not been mention should tell you something. All of the questions about voltages have been ignored so it would seem the OP either doesn't have a DMM or doesn't know when and where (or how?) to use it.
How about providing  a schematic with voltage measurements ?

ReverseEMF

Wouldn't a voltmeter tell you that ?

You don't need a scope to determine that,
nor do you need to 'blink' it. A simple on/off test should suffice. I don't see how any of the tests done do far are as good as a voltage meadurement with s meter. The fact a DMM has not been mention should tell you something. All of the questions about voltages have been ignored so it would seem the OP either doesn't have a DMM or doesn't know when and where (or how?) to use it.
How about providing  a schematic with voltage measurements ?
You make very good points -- with all the charm of a robot ;)   Heard from Dr. Morbius, lately?
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esgeroth

Wouldn't a voltmeter tell you that ?

You don't need a scope to determine that,
nor do you need to 'blink' it. A simple on/off test should suffice. I don't see how any of the tests done do far are as good as a voltage meadurement with s meter. The fact a DMM has not been mention should tell you something. All of the questions about voltages have been ignored so it would seem the OP either doesn't have a DMM or doesn't know when and where (or how?) to use it.
How about providing  a schematic with voltage measurements ?
A DMM has been mentioned and I provided the measurements in post #15.

ReverseEMF

A DMM has been mentioned and I provided the measurements in post #15.
Don't let the "haters" get to you.  

Based on those measurements, I'm wondering if the jumper wire could be open -- that's why I suggested you measure right on the pin -- i.e. pin 2 of the TC4427.  
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raschemmel

@ReverseEMF,
Quote
Don't let the "haters" get to you. 
The only one getting emotional here is you.

Try leaving it out and just discussing the technical details , like the fact that the TC4427 was  designed
to drive mosfets. It works fine when used that way.

Put 12V on Vdd and drive it with a 5V output from the arduino and you will see 12V on the output. 

ReverseEMF

...the TC4427 was  designed to drive mosfets. It works fine when used that way.

Put 12V on Vdd and drive it with a 5V output from the arduino and you will see 12V on the output.  
The TC4427 datasheet specifies the "Supply Voltage Operating Range" as 4.5V to 18V.  So, it should work at 5V.  And it should drive an LED the way the OP is attempting.
"It's a big galaxy, Mr. Scott"

Please DON'T PM me regarding what should be part of the Public Conversation -- Let it ALL hang out!!
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esgeroth

@ReverseEMF,The only one getting emotional here is you.

Try leaving it out and just discussing the technical details , like the fact that the TC4427 was  designed
to drive mosfets. It works fine when used that way.

Put 12V on Vdd and drive it with a 5V output from the arduino and you will see 12V on the output. 
There is no reason to be so argumentative. No one is being emotional at all.
As has been posted several times 5v is within the operating range of the TC4427 driver. I also had originally posted that I started with a mosfet on the output with 12v on Vdd and it would not turn off the mosfet when switched off. That's why I posted the test circuit above with the LED as a test. If it wont turn off an LED how can I expect it to turn off a mosfet?
I'm thinking that ReverseEMF is the only one here who has actually read the entire thread.

raschemmel

#42
Apr 25, 2018, 12:52 am Last Edit: Apr 25, 2018, 01:54 am by raschemmel
Did you read the datasheet for the mosfet ?
If you read it I think you will find that you need -10V to turn it off.
That's been your problem since the beginning. Only a logic level mosfet will turn off with 0V.
Most require at least -7V to turn off.
If you try connecting -10V to the mosfet gate I think you will find it turns off.
The TC4427 is not a bipolar device so you would need one that runs off a +/- power supply voltage.
The TC4427 has been a waste of time if you are trying to drive a mosfet that requires a negative
voltage to turn off. Try turning off the mosfet with a 9V battery connected with the "+" to GND.'
I don't know why the TC4427 won't turn off the led but I believe that is a different issue than why it
won't turn off the mosfet.

TomGeorge

#43
Apr 25, 2018, 02:06 am Last Edit: Apr 25, 2018, 02:08 am by TomGeorge
Hi,
Can  you verify how you have the LED connected on the protoboard.
In you picture it looks like you have positioned so both its pins are shorted at pin3 of the 4427.
Shouldn't the resistor and diode connection be on a separate row?


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

Wawa

#44
Apr 25, 2018, 02:18 am Last Edit: Apr 25, 2018, 02:21 am by Wawa
Seems correct.
Pin3 of the chip is ground, and the LED/resistor is connected between output(7) and ground.

Pin4 (second unused input) should be grounded too.

I think it's time to try a new chip.
Like all mosfet parts, handle it with ESD precautions.
Leo..

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