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I've been looking at ways to drive a 4 A, 12 V solenoid valve from a tiny, 3.3 V, 0.33 mA (max) current output from a PIR module.

Whatever I try (MOSFETs, transistors etc), there never seems to be enough current or voltage from the PIR unit to drive enough current through the load.

The PIR has 3 connections: 0 V, 12 V and output.

Can anyone suggest a suitable MOSFET I could use, or an alternative circuit?

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    \$\begingroup\$ Which PIR module works at 3.3V? Show make, model, at the very least. \$\endgroup\$ – jonk Oct 14 '16 at 14:39
  • \$\begingroup\$ We don't really need that when we know the output specs... \$\endgroup\$ – Passerby Oct 14 '16 at 15:32
  • \$\begingroup\$ I think you mean "to control ..." rather than "to drive..." \$\endgroup\$ – Scott Seidman Oct 14 '16 at 15:52
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"Normal" mosfets wont work in this application. What you are looking for is a so called "Logic Level" fet. The devices you have likely tried have a typical gate-source voltage of 8 or so volts to get them to fully turn on. Logic level fets are far less common and and you will likely have to order one from an online supplier. IPP60R385CPXK from Mouser would work as its Vgs is only 3v.

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  • example 3V min PIR Analog sensor : Panasonic EKMC1601111

  • with suggested one shot solenoid or relay driver from PIR sensor.

  • Choose "Logic Level" MOSFET Driver with RdsOn or BJT as shown from One Shot and power source ESR to be < ~2% of coil DCR for good efficiency, load regulation and low heat loss. must not interfere with 3.3V supply and ground return, otherwise hysteresis effects or false switching may be seen.

enter image description here

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There are opto isolators that will drive with very small currents. I had an application that was 3.3Vdc @ < 1mA. In that case IXYS's CPC1301 was suitable. It might be possible to use it or a similar opto in your application.

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