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Topic: How to increase the output current 10-20x over. (Read 652 times) previous topic - next topic

lonehunt

Hi, I have a Nano connected to four 74hc595 shift registers. They work beautifully when it comes to outputing the right voltages for testing with LEDs. My issue is that the current they output is not nearly what I need. They output approximately .01 to .02 amps, when I need much higher, maybe in the range of .2A to 1A. Whats the smallest/lightest way of amplifying the current of an output based on the voltage given by the shift registers? I've heard suggestions of transistors, and relays from various sources but without any solid pointers to a particular model. I am willing to add another power source as well.

If I am not giving enough information, please let me know.

Wawa

The TPIC6x595 shift register family, e.g. the TPIC6B595, can sink 100-150mA per output.
If that's not enough, then drive logic level mosfets with the 74HC595.

That sort of current always needs an external supply.
What are you planning to switch.
Leo..

MarkT

The ULN2803 octal darlington might be useful for this too.
[ I will NOT respond to personal messages, I WILL delete them, use the forum please ]

lonehunt

Ahh okay. Thank you for the advice. Is there any particular model/type I should look at, or should any MOSFET work? Im more of a software person so I am a bit clueless on this.

We are trying to drive electromagnets in different directions with the current. Don't think I should say too much more than that. :)


@MarkT, I will look at the darlington as well and reply with any additional questions after my exam tomorrow. Thank you!

Wawa

Is there any particular model/type I should look at, or should any MOSFET work?

Don't think I should say too much more than that. :)


@MarkT, I will look at the darlington as well and reply with any additional questions after my exam tomorrow. Thank you!
Only "LOGIC LEVEL" mosfets will work with 5volt gate drive.

Maybe we also should have that attitude.

Note that TPIC and ULN chips also have a total current limit, and related temp limit.
Better tell us exactly what you're trying to do, before you make mistakes.
Leo..

CrossRoads

"The ULN2803 octal darlington might be useful for this too."
Not really it has a large voltage drop across its outputs.

If you want them all in parallel, this one would be good
https://www.digikey.com/product-detail/en/infineon-technologies/IRL540NPBF/IRL540NPBF-ND/812000

If you want them more controllable, individually, or small parallel groups then TPIC6A595, TPIC6B595, or TPIC6C595

Designing & building electrical circuits for over 25 years.  Screw Shield for Mega/Due/Uno,  Bobuino with ATMega1284P, & other '328P & '1284P creations & offerings at  my website.

lonehunt

Thank you for all of your inputs. After doing some tests with the solenoid we are trying to drive, it seems that we need approximately 700mA worth of current. I looked up a particular Darlington array that has a maximum output 1.5A on the collector.

https://www.mitsubishielectric-mesh.com/products/pdf/m54532p_e.pdf

Can someone more experienced let me know which value on the datasheet I should look at to decide what kind of power the chip needs?

@CrossRoads, thank you so much for the suggestions. Can you explain what it means when you say that the Darlington has a large voltage drop? For the solenoid that we are trying to drive, only the current matters.

Thank you again for all of your responses, I really appreciate it.

MorganS

If your power supply is 5V and the darlington drops 1.2V then you only have 3.8V left to drive the solenoid. Additionally, a big fraction of your power is wasted heating up the darlington.

I like to use pre-packaged driver chips. They put a lot more inside the chip than just a simple MOSFET. Something like a BTS716G gives 4 outputs protected from short circuits and other overloads. A BTS5012 is a single device but it controls higher current and gives you a nice current feedback so the Arduino can see how much current is going out the output.

If you need to drive the solenoids both directions then motor driver chips are good. The TB6612FNG can drive two solenoids or you can parallel its outputs for double the current. The VNH5019 (replacement for VNH2SP30) is good for currents up to 30A with no heatsink.
"The problem is in the code you didn't post."

lonehunt

@MorganS The issue is we are trying to drive 6-24 of them in a relatively small device. :/

I am looking into transistor that CrossRoads listed as it seems that the Darlingtons give too low of an output, or is ridiculously expensive.

MorganS

24 devices at 700mA is a LOT of power. That is unlikely to be a pocket-sized device.
"The problem is in the code you didn't post."

lonehunt

#10
Apr 12, 2018, 02:50 am Last Edit: Apr 12, 2018, 02:51 am by lonehunt
Yeah, we realized that recently :(

We are going to try to do just 6 of them now.

On a good note, we found a bunch of IRL540NPBF that CrossRoads mentioned in our school lab. We are having issues getting it to work.

We connected our solenoid to the Drain, with a diode in parallel to the solenoid, and we connected the other end of the solenoid/diode to VCC (another power supply separate from the Arduino). We connected the Source to the ground and the Gate to the logic output of the shift register. However, it seems that the Drain reflects what the power supply gives off without reacting to the Logic input at the gate. How can I make it so that the NMOS cuts off any current going into the Drain when there is a logic "0" from the shift register.

A quick note: Our shift register gives off approximately 4 volts, and 20mA when "on".

If a picture would help visualize this better, please let me know. 

Wawa

We connected the Source to the ground... 
To solenoid supply(-) AND shift register ground?
Leo..

lonehunt

#12
Apr 12, 2018, 03:23 am Last Edit: Apr 12, 2018, 03:24 am by lonehunt
So I connected the ground of the solenoid supply and the ground of the shift registers/Arduino. So I only connected the transistor to both by proxy I guess. Was I not meant to do this?

Wawa

Yes, source connects to supply(-) and shift register/Arduino ground.

Maybe the (ESD sensitive) mosfets were not used/handled properly before you 'found' them.
Leo..

lonehunt

#14
Apr 12, 2018, 04:03 am Last Edit: Apr 12, 2018, 04:05 am by lonehunt
I will try further debugging tomorrow. Could the issue be the diode? I know Im supposed to have it to absorb some of the current from the Solenoid when the Mosfet is turned off. I have seen some diagrams that have the diode parallel to the Source and Drain instead.

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