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I built a circuit that allows me to control a load current using logic by using a P16NF06L MOSFET. Here is the circuit:

TweetMonkey circuit
source

What I need now is something that does the same thing but has multiple channels so I can control multiple loads independently with separate logical inputs, has more safety handling built in (opto isolation? separate logic and driving grounds?), and is packaged better than my breadboard solution. My loads would be small - usually under 300mA and often under 1A.

I recently learned that this is called "gate driving". Is this something that I should design myself or is it common enough that others have already done it?

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closed as off-topic by Dave Tweed Apr 22 at 1:04

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  • \$\begingroup\$ Jeremy, you need to edit this fairly smartly to prevent it being closed as it looks like a direct shopping question and these are not allowed. Asking for the correct nomenclature or search terms is fine. Also, uploading the image into the question will attract a lot more readers and the question will still make sense when the link dies. \$\endgroup\$ – Transistor Apr 21 at 22:40
  • \$\begingroup\$ The device you selected is not suitable for use with an R'Pi and this is a good answer for the device selection: electronics.stackexchange.com/questions/81135/… You can get devices that will support 12-30V and more at several amps ….devices such as the AO3400 come to mind: aosmd.com/res/data_sheets/AO3400.pdf With this device direct connected to an R'Pi GPIO you could expect to support currents up to several amps. \$\endgroup\$ – Jack Creasey Apr 22 at 0:54
  • \$\begingroup\$ Pi-Face Digital has 2 relay outputs and 6-8 transistor outputs (ULN2803 driver) \$\endgroup\$ – Jasen Apr 22 at 6:12
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I'd like to suggest board mounted SSRs (solid state relays) as an easy to implement, albeit slightly more expensive ($2-3), solution to your problem. These devices could almost be thought of as a 'system-on-chip' for power switching as they integrate many discrete components which might be used into one convenient package.

To use one of these devices, you need to drive a (usually infrared) LED on the input side at a forward voltage of ~1-1.3V and ~2-5mA. This can be done directly from an Arduino GPIO pin (an maybe a Raspberry Pi pin, check the specifications for pin current capacity) using only an additional current limiting resistor. For example, to drive the input at 2mA from a 5V GPIO output configured pin: 5V - 1.3V / 0.002A = 1,750Ohm ~ 1.8kOhm

Here's an example part from Vishay Semiconductor, but there are many others that could meet the needs of you application: https://www.digikey.com/product-detail/en/vishay-semiconductor-opto-division/VO14642AT/VO14642AT-ND/4074374

SSR features:

  • High current and voltage capacity (2A 60VDC in the case of my example)
  • Optical isolation in the kilovolts
  • Low 'bounce' on outputs
  • Low on-state resistance (often < 100mOhm)
  • <1ms switching (fast compared to mechanical relays)
  • Lower discrete part count and sizing
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Enhancement FET's have a threshold voltage, Vt or Vgs(th) that must be exceeded by at least 2x above threshold to achieve rated current as a switch. This means as V+ switch or high-side-switch that Vgs must be;

  1. Vgs boosted with a charge pump well above the load V+
  2. replaced with a Pch FET and open drain Nch driver
  3. re-designed as a low side switch

The Nch switch needs a gate voltage higher at least twice it's switch threshold above the load voltage to be a high side (+) switch. Therefore it makes more sense to use it as a low side switch.

The error newbies, often make, is to assume the gate threshold is adequate to switch rated load current. Vgs(th) is just the threshold of conduction often rated at 250uA, hardly enough and has a wide Vgs range. Therefore choose Logic Level Nch FETs to switch on the low side of the load (-).

Choose a part with Vgs(th) is < 1/3 of your logic level output for good results. Thus if logic output is 3.3V consider an Nch FET with Vgs(th) < = 1.1V

schematic

simulate this circuit – Schematic created using CircuitLab

There is such an off-the-shelf multiple output IC as type 1. above with 8 separate logic level inputs and 8 power N ch outputs, 0 to 500 mA and up to 50V. enter image description here enter image description here

  • There also exist commercial 4ch and 8 ch opto-isolated relay cards that are inexpensive online.
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  • \$\begingroup\$ I didn't understand all of that. I neglected to mention that my load is going to be 12V. I'll look up "low side switch" and "high side switch" and some of the other terms you mentioned to see if I can figure this out. My inexperience is an argument for seeing if this is something that might already exist on the market. \$\endgroup\$ – Jeremy Foster Apr 22 at 0:15
  • \$\begingroup\$ This is how (low side) they often switch loads in Car smart switches which have additional protection. Given there are over 40k different FETs for different applications, a common one fits all is rare. but if you shop, you may find' \$\endgroup\$ – Tony Stewart Sunnyskyguy EE75 Apr 22 at 0:18
  • \$\begingroup\$ rohm.com/electronics-basics/transistors/what-is-a-load-switch (hi side) \$\endgroup\$ – Tony Stewart Sunnyskyguy EE75 Apr 22 at 0:22

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