Using multiple MOSFET as switches controlled by Arduino

Thread Starter

mewerlof

Joined Sep 21, 2020
3
Hi!
Im trying to build the circuit in the attached image. But i cant figure out how i would replace the switches with MOSFETS so that i can controll them with my arduino uno.

I have some N-channel MOSFETS (IRF7010PbF) laying around which is hope to use. But maybe i need some other components to make this work.
ive been thinking about using opto-couplers to isolate the arduino. But still i cant figure out how to connect everything to the arduino.

Below is a description of the system:
1: S1 turns on to charge the first capacitor.
2: S1 turns off.
3: S2 turns on. current goes though the inductor.
4: S2 turns off. Back EMF is collected in the second capacitor.
5: S3 turns on. current goes though the inductor in the opposite direction.
6: S3 turns off. Back EMF is collected in the first capacitor.

And here is a link to my attempt in the falstad.com simulator. The inductive load seam to interfere with the MOSFET's or maybe its the simulator that isn't accurate? http://tinyurl.com/y35yp7r4
 

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djsfantasi

Joined Apr 11, 2010
6,811
I don’t think your IRF7010PbF MOSFETs will work, as they don’t appear to be “logic level”. 2N7000s or IRL540s are N channel logic level MOSFETs.

You need a logic level component because a microprocessor / Arduino does not have enough voltage to drive a standard MISFET.
 

BobTPH

Joined Jun 5, 2013
2,541
Your project is ill-coceived. The first switch will indeed charge the capacitor. The second will connect the indictor and capacitor in a tank circuit. It will oscillate at the resonant frequency and lose energy. It will not produce a higher voltage than the capacitor started with.


Try looking up “boost converter” if you want to know how to use a single switch, capacitor and inductor to create a high voltage.

Bob
 

Thread Starter

mewerlof

Joined Sep 21, 2020
3
Thanks for the replies!

I don’t think your IRF7010PbF MOSFETs will work, as they don’t appear to be “logic level”. 2N7000s or IRL540s are N channel logic level MOSFETs.
You are right, the IRF7010PbF ins't specified to be logic level. but they do accually work when i use them with the arduino. i guess the mosfet ins't fully saturated at 5v. But the VGS graph in the datasheet suggest that the max current at 5v is around 60A(15v). Or am i missing something there?

After digging some more into this i concluded that isolating the controller from the high side probably is a good idea.
I found this Opto-coupler (VOM1271) that can be used as a direct drive for mosfets as it outputs 8.4 volts. And the MOSFET should be fully saturated at that potential right? One question remains tho. The VOM1271 only supply 15uA output current. I know that mosfets are voltage driven, but will 15uA be enough? from what i read the current would charge the gate. Lower current would increse the turn on time. And the expression is as follows:
Ig=Qg/time

The mosfet spec is Qg = 130. so 130/15uA = 8.66, But i dont know what unit this is? is it us, ms, s or what?
https://toshiba.semicon-storage.com/ap-en/semiconductor/knowledge/faq/mosfet/is-the-mosfet-drive-current-necessary.html

If i can use the VOM1271 i think that the bidirectional circuit below could be inserted into my original circuit drawing.

Datasheet for VOM1271: https://www.vishay.com/docs/83469/vom1271.pdf
 

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Thread Starter

mewerlof

Joined Sep 21, 2020
3
Your project is ill-coceived. The first switch will indeed charge the capacitor. The second will connect the indictor and capacitor in a tank circuit. It will oscillate at the resonant frequency and lose energy. It will not produce a higher voltage than the capacitor started with.
Thanks for the input. i wasnt really clear about what the circuit is ment to do. and its not a buck converter. im just doing som experiments with back EMF. And yeah, if i leave S2 closed for too long it would oscillate. But S2 will be closed before the potential in the first cap reaches 0.
 

Irving

Joined Jan 30, 2016
1,017
Thanks for the replies!



You are right, the IRF7010PbF ins't specified to be logic level. but they do accually work when i use them with the arduino. i guess the mosfet ins't fully saturated at 5v. But the VGS graph in the datasheet suggest that the max current at 5v is around 60A(15v). Or am i missing something there?

After digging some more into this i concluded that isolating the controller from the high side probably is a good idea.
I found this Opto-coupler (VOM1271) that can be used as a direct drive for mosfets as it outputs 8.4 volts. And the MOSFET should be fully saturated at that potential right? One question remains tho. The VOM1271 only supply 15uA output current. I know that mosfets are voltage driven, but will 15uA be enough? from what i read the current would charge the gate. Lower current would increse the turn on time. And the expression is as follows:
Ig=Qg/time

The mosfet spec is Qg = 130. so 130/15uA = 8.66, But i dont know what unit this is? is it us, ms, s or what?
https://toshiba.semicon-storage.com/ap-en/semiconductor/knowledge/faq/mosfet/is-the-mosfet-drive-current-necessary.html

If i can use the VOM1271 i think that the bidirectional circuit below could be inserted into my original circuit drawing.

Datasheet for VOM1271: https://www.vishay.com/docs/83469/vom1271.pdf
The VOM1271 is no good for application in wat is effectively a switching supply. Its turn on/off times are measured in tens of microseconds not nanoseconds, and that gate drive current of 15uA with your MOSFET gate charge of 130nanoColumbs gives a turn-on time of 130e-9/15e-6 = 8.66e-3S ie 8.7mS , though with higher LED current you could get 50uA giving 2.6mS. Basically the VOM1271 is intended to switch MOSFETs in solid-state relays where switching time isn't a criteria. Completely useless for this application...
 

butch28

Joined Oct 14, 2020
12
Hi!
Im trying to build the circuit in the attached image. But i cant figure out how i would replace the switches with MOSFETS so that i can controll them with my arduino uno.

I have some N-channel MOSFETS (IRF7010PbF) laying around which is hope to use. But maybe i need some other components to make this work.
ive been thinking about using opto-couplers to isolate the arduino. But still i cant figure out how to connect everything to the arduino.

Below is a description of the system:
1: S1 turns on to charge the first capacitor.
2: S1 turns off.
3: S2 turns on. current goes though the inductor.
4: S2 turns off. Back EMF is collected in the second capacitor.
5: S3 turns on. current goes though the inductor in the opposite direction.
6: S3 turns off. Back EMF is collected in the first capacitor.

And here is a link to my attempt in the falstad.com simulator. The inductive load seam to interfere with the MOSFET's or maybe its the simulator that isn't accurate? http://tinyurl.com/y35yp7r4
use the arduino to relays relays will handle the power and arduino only needs enough power to energize the relay. if you want to ramp the voltage! if i am right you need a 0 to 5 volt to turn on a mosfet to send a larger voltage from another leg. i am kinda doing the same thing. using low voltage to control high voltage and amps. mosfets use 0 to 5 volts to turn on a 12 volts from 0 to 12 volts as the 0 moves up to 1 so does the 0 of the 12 volts so 1 volt of pot makes the mosfet send 20% of 12 volts 2 volts = 40% and so on! hope it helps out! you will probly need heat sinks on the mosfets. you will need a diode to stop the electric from reversing and a relay to recharge! not sure what you are doing! a cap only stores electric. once spent! you have to charge it again! the bigger the cap the longer it takes to charge it!
 
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