Best Diode and Transistor for 12V 4.5Amp Circuit

Thread Starter

maxvit99

Joined Jan 20, 2017
4
Hi! I am building a project where I have a pump (needs 12V, 4.5Amp Max) connected to a power source (12V, 5Amp) and to an electronic switch (a transistor). That switch is controlled by a much lower power Arduino Uno. The Arduino is basically turning the pump circuit on and off. I am new to electronics, so I have no idea how to do this. I found this article: https://itp.nyu.edu/physcomp/labs/m...o-control-high-current-loads-with-an-arduino/ and it explains the steps pretty clearly.

However, it says to use the TIP120 Transistor, but it later says that you can also use an IRF510 or IRF520 MOSFET Transistor. According to this website, TIP120 is a terrible option: http://sensitiveresearch.com/elec/DoNotTIP/index.html So my first question is, should I choose the IRF510 or IRF520? This site says that they are not interchangeable: http://www.redwaveradio.com/5_55856568f12dc970_1.htm

My second question is that the website for the Arduino electronic switch says that I have to use a diode because the motor can generate a back voltage. I wasn't able to find one that has the specs I need (12V, 5Amp). Are there any that can work for me? If not, then are there any replacements? I assume it can be higher Amp than I need just in case, right?

Also, I didn't quite understand what the second diode is for and when to use it. Can someone help me with that?

My final question is more of a conceptual one. The diagram for the Arduino shows that the high power battery is connected to the black wires and that eventually goes to the Arduino after a series of other black wires. Is that a problem, or is something in the circuit protecting the Arduino? I know it also says to add a separate battery for the Arduino.

Thanks for any help!
Max
 

shteii01

Joined Feb 19, 2010
4,644
1. Make your life easy. Use LOGIC LEVEL MOSFET. Here how to choose one: http://electronics.stackexchange.com/questions/36098/selecting-a-mosfet-for-driving-load-from-logic

2. The back emf diode. This diode is placed in parallel with the motor, but the polarity of the diode is opposite of the motor. This means that it will have 12 volts across it. But. It's polarity is opposite. So the 12 volts will try to break the diode. Each diode has a break down voltage. So. Look for diode that has breakdown voltage greater than 12 volts. The next thing about this diode is that it provides the "escape" path for the current when motor is turned off. You know that your motor will have 4.5 amperes. So. You need diode that will conduct 4.5 or more amperes. Those are the two criteria that you need to meet:
a. diode break down voltage greater than 12 volts
b. conduct current of 4.5 or more amperes
You can read the explanations here: http://electronics.stackexchange.com/questions/110574/how-to-choose-a-flyback-diode-for-a-relay

3. Arduino Foundation uses ATmel chips. Uno uses ATmel ATmega328 chip. This chip needs 5 volts to work. To provide ATmega328 with 5 volts, Arduino Foundation placed 5 volt regulator onto the Uno board. This voltage regulator can take as much as 20 volts. However, Arduino Foundation does not recommend using 20 volt power supply, that will stress the voltage regulator and shorten its life, which is not desirable. They recommend 9-12 volt power supply for their boards. As you can see, you can easily power Uno with anything up to 18 or 19 volts dc.

4. For motor to mosfet, then mosfet to ground I would recommend using 18 AWG wire. The 18 AWG stranded wire is rated for 7 amperes.
 
Last edited:

GopherT

Joined Nov 23, 2012
8,012
I would pick this one.

It can handle a Pwm control from your arduino, it can be driven directly from the arduino pin (use a 100 to 330 ohm resistor between arduino pin and gate).

This transistor doesn't not need a heat sink at 5 amps.

If it feels warm, turn down the Pwm frequency (I don't think standard Pwm commands will generate anything over 20kHz on arduino).

price is only $1.50 each.

http://www.vishay.com/docs/90416/90416.pdf
 

AnalogKid

Joined Aug 1, 2013
9,615
Rather than believe some ranting stranger on the innergoogle, believe me - a non-ranting stranger on the innergoogle. The TIP120 page ignores some of the realities of semiconductor physics. First is that they have not changed since the 70's. The TIP series of power components is still being manufactured in the billions by a dozen companies around the world because THEY WORK <gasp>. Also, because they were designed from the ground up for industrial applications, they are nearly indestructible ***during assembly***. Handling a MOSFET (as in touching it with your fingers) without destroying it requires an awareness of static electricity protection measures (called ESD protocols), grounding straps, etc. The heart of a MOSFET is a sheet of glass about 10-50 atoms thick. It can handle 20 V during operation. The teeniest little static charge will puncture it. The TIP does not have this sensitivity because A) it's very different device physics, and b) it has a couple of resistors built-in that help drain away static charges.

The writer is correct that a TIP120 is less efficient in that it takes more energy to turn it on (though the arduino can supply that easily) and it has a higher saturation (on) voltage. But it's not as bad as he says; he's using the worst-case datasheet value rather than a real world number which is about half of that. Still, when switching a 5 A load it will need a small heatsink to dissipate the heat.

MOSFETs are great in many applications, but those are things built in a production facility that understands MOSFETs. I've never thought of them as a beginner's device because they are not forgiving. My vote is stay with a bipolar power transistor and deal with the excess heat. It is what I would do, and I've been designing with both TIPs and MOSFETs for over 40 years.

As for 510 and 520 interchangeability, you have to read the fine print. That article is talking about radio power amplifier applications, not motor drive. So it is correct for the question it is answering, but not applicable to your situation.

The diode across the transistor probably is not needed, since it sounds like your motor will not be spun backwards by an external force, making it act as a generator. The diode across the motor is important, but it's requirements are not directly related to the specs of the load. When the driver transistor is turned off, the inductance of the motor coils generates a high voltage spike that lasts a few milliseconds. This is similar to the action of an automobile ignition coil. The diode "shorts out" this spike. The diode voltage rating should be at least twice that of the system power voltage. As for the diode current rating... The right way is to know the inductance of the motor windings and calculate the total energy in the inductive kick blah blah blah. Or, load current divided by 3 as a minimum starting point. 5 A load = 2 A diode. Something in the 1N5400 series will be fine.

ak
 
Last edited:

Thread Starter

maxvit99

Joined Jan 20, 2017
4
Ok, thanks for the replies!

So, the reply from AnalogKid is the most logical for me and with most evidence so I will use a TIP120 with a heatsink. Transistors figured out!

As for the diode, I would believe AnalogKid, but it seems weird that this would work because if the diode is parallel to the motor, the current will go both ways and if 5 amps goes into a 2 amp diode, it will surely blow it out... Right? Or am I missing something?

I will hope that the Arduino article was correct and that the 12V will it will not blow out the Arduino. (I assume that it is somehow not connected directly to the Arduino circuit... a 12V motor battery AND a 5V battery for the Arduino circuit seems too much to me even if it COULD handle one at a time...)

Also, I will make sure to use 18AWG wires just to be safe. :)
 

ian field

Joined Oct 27, 2012
6,539
Hi! I am building a project where I have a pump (needs 12V, 4.5Amp Max) connected to a power source (12V, 5Amp) and to an electronic switch (a transistor). That switch is controlled by a much lower power Arduino Uno. The Arduino is basically turning the pump circuit on and off. I am new to electronics, so I have no idea how to do this. I found this article: https://itp.nyu.edu/physcomp/labs/m...o-control-high-current-loads-with-an-arduino/ and it explains the steps pretty clearly.

However, it says to use the TIP120 Transistor, but it later says that you can also use an IRF510 or IRF520 MOSFET Transistor. According to this website, TIP120 is a terrible option: http://sensitiveresearch.com/elec/DoNotTIP/index.html So my first question is, should I choose the IRF510 or IRF520? This site says that they are not interchangeable: http://www.redwaveradio.com/5_55856568f12dc970_1.htm

My second question is that the website for the Arduino electronic switch says that I have to use a diode because the motor can generate a back voltage. I wasn't able to find one that has the specs I need (12V, 5Amp). Are there any that can work for me? If not, then are there any replacements? I assume it can be higher Amp than I need just in case, right?

Also, I didn't quite understand what the second diode is for and when to use it. Can someone help me with that?

My final question is more of a conceptual one. The diagram for the Arduino shows that the high power battery is connected to the black wires and that eventually goes to the Arduino after a series of other black wires. Is that a problem, or is something in the circuit protecting the Arduino? I know it also says to add a separate battery for the Arduino.

Thanks for any help!
Max
You probably need an IRFL510 logic-level MOSFET. 6A leaded diodes exist, but not many stockists carry them - you can get higher than that in a TO220 package. I'd try a 1N5401 - its only rated 3A, but the back emf pulse is short duration, so you can probably get away with it. The peak pulse rating is probably around 30 or more A for the duration of a mains half-cycle.
 

Thread Starter

maxvit99

Joined Jan 20, 2017
4
You probably need an IRFL510 logic-level MOSFET. 6A leaded diodes exist, but not many stockists carry them - you can get higher than that in a TO220 package. I'd try a 1N5401 - its only rated 3A, but the back emf pulse is short duration, so you can probably get away with it. The peak pulse rating is probably around 30 or more A for the duration of a mains half-cycle.
Ok, if two people recommend a diode, I will try it. 1N5401 Diode it is!

As for the transistor, I though AnalogKid said that MOSFET are hard to handle for a beginner due to static electricity.

The TIP120 page ignores some of the realities of semiconductor physics. First is that they have not changed since the 70's. The TIP series of power components is still being manufactured in the billions by a dozen companies around the world because THEY WORK <gasp>. Also, because they were designed from the ground up for industrial applications, they are nearly indestructible ***during assembly***. Handling a MOSFET (as in touching it with your fingers) without destroying it requires an awareness of static electricity protection measures (called ESD protocols), grounding straps, etc. The heart of a MOSFET is a sheet of glass about 10-50 atoms thick. It can handle 20 V during operation. The teeniest little static charge will puncture it. The TIP does not have this sensitivity because A) it's very different device physics, and b) it has a couple of resistors built-in that help drain away static charges.

The writer is correct that a TIP120 is less efficient in that it takes more energy to turn it on (though the arduino can supply that easily) and it has a higher saturation (on) voltage. But it's not as bad as he says; he's using the worst-case datasheet value rather than a real world number which is about half of that. Still, when switching a 5 A load it will need a small heatsink to dissipate the heat.

MOSFETs are great in many applications, but those are things built in a production facility that understands MOSFETs. I've never thought of them as a beginner's device because they are not forgiving. My vote is stay with a bipolar power transistor and deal with the excess heat. It is what I would do, and I've been designing with both TIPs and MOSFETs for over 40 years.
 

ian field

Joined Oct 27, 2012
6,539
Ok, if two people recommend a diode, I will try it. 1N5401 Diode it is!

As for the transistor, I though AnalogKid said that MOSFET are hard to handle for a beginner due to static electricity.
They're not that bad.

If you walk across a plush carpet and then pick up the device; you can have a big static charge and zap it.

Most well designed circuits will prevent static build up once the MOSFET is soldered in, leave it in the anti-static bag till you're ready to solder it in place. Handle it by the plastic part of the body so you avoid touching the pins. If you breathe on it like you would when cleaning spectacles - the moisture in your breath gently leaks away any static.

Once or twice; I've soldered a physically small bleed resistor onto the tops of the G/S pins to bleed away static, but if you leave it on, it mustn't be such low resistance that it interferes with circuit operation.
 

Thread Starter

maxvit99

Joined Jan 20, 2017
4
Ok, so what are the pros and cons of using each (TIP120 vs IRFL510/520)? Or is it just a matter of personal preference? I am planning to have a heatsink, in either case, just to avoid any accidents.
 

AnalogKid

Joined Aug 1, 2013
9,615
As for the diode, I would believe AnalogKid, but it seems weird that this would work because if the diode is parallel to the motor, the current will go both ways and if 5 amps goes into a 2 amp diode, it will surely blow it out... Right? Or am I missing something?
Missing something. With a DC motor connected to a positive voltage, and the - end of the motor connected to ground through a switch (electronic, relay, big-ass knife switch out of a horror movie; whatever), and the diode across the motor with the anode connected to the + end, then when the motor is on, the diode is reverse biased. No current is flowing through the diode when the motor is on and none is flowing through the diode a few milliseconds after the motor is off. So as long as the reverse voltage rating of the diode is at least twice (for margin) the system power voltage, that's the easy part. Now, about those few milliseconds. This is when the magnetic energy stored in the motor coils comes out to greet you. Because of a minus sign in Faraday's Law, the voltage that appears across the motor's terminals when one of then is rapidly disconnected is the opposite polarity from the voltage that was running the motor. To this voltage spike, the diode is now forward biased and clamps the spike to around 1 to 2 V, depending on the diode type and construction. Yes, this is higher than the rated Vf for the diode, more of that real world physics stuff.

ak
 
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