Computing stuff tied to the physical world

Meet the MOSFET Plug

In Hardware on Aug 16, 2010 at 00:01

There’s a new plug at Jee Labs – one I’ve been waiting to use myself for quite some time – a dual MOSFET plug:

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The IRLZ34N’s used here should be able to drive over 5A @ 50V, but this will require a heatsink. For use without heatsink, a maximum currrent of 1 .. 3 amps should work fine. Just keep in mind that MOSFETs can generate a few watts of heat when used continuously at 2A or more. You can tie the MOSFETs in parallel for larger currents. You’ll need to add protection diodes to switch inductive loads, such as DC motors, relays, and solenoids.

This plug was designed for driving LED strips, but other loads can be driven as well. With two MOSFET Plugs, there are 4 individually controllable switches – to drive an RGB strip and a white strip, for example.

The terminal blocks used on this plug are heavy duty and detachable and use a standard 0.2″ grid (5.08 mm). They are much more convenient than fixed terminal block, particularly if the plug is mounted high or in some remote spot behind a book case or curtain. The two outputs have separate connectors.

The traces on this board have been made extra wide to be able to handle large currents flowing through the terminal block pins. The pins are laid out as two pairs: one side must be tied to ground, the other side (+A or +D) is then tied to the load, which in turn gets connected to a positive supply voltage (3..50V). Note that the positive supply voltage used by the load is not connected to the plug. A pulldown resistor is used to keep the MOSFETs switched off when the I/O pins are not connected, or not set up as outputs. Also, keep in mind that this plug ties the plug signal ground and the load ground together – it is not isolated from the load power supply.

The length of the plugs is 34 mm, making them a perfect fit for the Carrier Board + Box:

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Note that a closed box provides little airflow to cool the MOSFETs, so this setup is not recommended for high-current use. Having said that, I’ve been driving a few meters of RGB LEDs with these MOSFETs without them even getting warm. See this earlier weblog post.

For dimmer use, there’s example code for a remote-controlled JN and 4 MOSFETs using software PWM.

I’ve set up a documentation page in the cafĂ© and an order page in the shop. Since the prototypes worked on first try, these MOSFET Plugs are available as simple through-hole part kits right away.

A Murphy-less plug, so to speak :)

  1. Nice plug, but isn’t the STP80NF03L-04 better? R_DS = 0.004 ohm, I_D = 80 A, V_DSS = 30V I guess you shouldn’t have issue with heat dissipation.

  2. Isn’t the TO-220 package fine for through-hole PCB’s? See

    A few others: ISL9N302AP3, ISL9N303AP3, and IRL540NPbF. I’m not sure they are all suitable.

    • Ah, great – I was looking at another datasheet with only a D-PAK version on it. Well, as long as the pinout matches, you could use the PCB and pick your own MOSFETs.

  3. What switching frequencies can the mosfet accomodate ? I need to switch a piezo (as far as I understand a capacitive load) with high(-er than 5) voltage at 200khz.

    • I’m sorry… I don’t know. Couldn’t find decisive info with a quick Google search either :(

      Switching those same MOSFETs @ 97 KHz with a Dimmer Plug seems to work fine (I only did a quick check).

      Not sure about piezo… you may need a push-pull setup to get them to also discharge quickly. Then again, it’s low power – perhaps you could simply add a resistor across the piezo for getting rid of the charge when the MOSFET is open.

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