Component for driving 8 low power motors

Other Hardware Motors, Mechanics, Power and CNC
1

Hello,

I'm looking to build a multi-plant watering rig and need to drive up to 8 small water pumps rated at 3-5V < 200ma, possibly 500ma. Link to Motor

I plan on using 5V DC input voltage, which I also want to use to power the motors, controlled by a 3.3V microcontroller (Adafruit Feather 32u4).

I was initially planning to use several 2N7000-G MOSFETs, but this would require me to wire in many additional pull-down resistors and kickback diodes (based on this tutorial)

I was wondering whether there are any other options, ideally in a DIP package which can also give me 8 channels to switch these motors. I was looking at something like ULN2803A, but I'm worried about the voltage drop which seems to be up to 1.6V max, and as I understand my motors will only be getting 5V-1.6V -> 3.4., Although this is within the range for my motors, I was hoping for something with a lower voltage drop.

Can anyone suggest a good component for my needs?

Thanks in advance,
eyjohn

2

Relay contacts have almost zero voltage drop.
Paul

3

Paul_KD7HB:
Relay contacts have almost zero voltage drop.
Paul

Thanks for the suggestion, looks like a good option, a bit larger than I was hoping for but is definitely a good fallback

4

Darlington's like the ULN2803 indeed drop a lot of voltage. Single BJT's are much
better for this, though more limited in current handling:

2N2222A switching transistors can handle upto 600mA or so - use a 100 ohm base
resistor.

If that's not enough the rather more exotic ZTX851's can handle significantly more
current as they are super-beta devices able to switch upto 50 times the base current
(most switching transistors can handle 10 to 20 times the base current).

With 30mA from the microcontroller pin, that's 1.5A rather than just 600mA for
the ZTX851's.

Logic level MOSFETs are the other choice.

5

MarkT:
Darlington's like the ULN2803 indeed drop a lot of voltage. Single BJT's are much
better for this, though more limited in current handling:

2N2222A switching transistors can handle upto 600mA or so - use a 100 ohm base
resistor.

If that's not enough the rather more exotic ZTX851's can handle significantly more
current as they are super-beta devices able to switch upto 50 times the base current
(most switching transistors can handle 10 to 20 times the base current).

With 30mA from the microcontroller pin, that's 1.5A rather than just 600mA for
the ZTX851's.

Logic level MOSFETs are the other choice.

Thanks for the input MarkT

6

How about using a FET type transistor array?
e.g. TBD62381APG
It has lower on-resistance than bipolar type.
And built-in freewheel diode on all channels.
Furthermore, it's included an input circuit and can be directly connected to a 5V microcontroller.
Additional external component needed is a capacitor only.

7

The TBD62381APG has a worst-case on-resistance rating of 2.5 ohms, which isn't great, with 8 devices
in one package that might have the same thermal issues as an octal darlington.

It has lower on-resistance than bipolar type.

Well that's a bit moot, its best/worst case seems to straddle the 2N2222A's performance.
The best bipolar I know (ZTX851) is more expensive but has about 0.1 ohms at 1A - if only
you could get an array of those in one package(!).

If thermal issues might be a problem, 8 separate 2N2222's should be able dissipate more heat than
one DIP18, given suitable PCB area.

8

This topic was automatically closed 120 days after the last reply. New replies are no longer allowed.