Introduction: MOSFET Touch Lamp

This Instructable shows you how to make a touch lamp with the use of MOSFET.

You can see the circuit working in the video.


parts: n-channel MOSFET, 5.6 kohm resistor, bright LEd, 100-ohm resistor, heat sink, heat transfer paste, encasement, wires, bolt, nuts, washer, 2 AA/AAA batteries, 3 V/6 V or 9 V battery harness.

tools: wire stripper, pliers, screwdriver.

optional parts: solder.

optional tools: soldering iron, multimeter, voltmeter.

Step 1: Design the Circuits

You can attach a small capacitor between MOSFET Gate terminal input and ground to filter the noise. However, testing of this circuit showed that even a small capacitor might prevent MOSFET from turning on.

The cutoff frequency of the input low pass filter will equal:

fl = 1/(2*pi*Ri*Ci)

The maximum LED current will equal to:

Imax = (Vs - Vled) / Rd = (3 V - 2 V) / 100 = 10 mA

Keep in mind that bigger LEDs might need 15 mA or 20 mA, not 10 mA of current. There are smaller LEDs that consume 5 mA current.

The minimum n-channel MOSFET turn ON gate voltage could be above 2 V. Thus you will need to raise the power supply to at least 6 V. With the LEDs needing 2 V potential voltage you can connect three LEDs in series and thus eliminate the need for the Rd resistor. However, I cannot guarantee that the LED light will not be dim. The LEDs might need 2.1 V to reach full brightness. You can also try connecting four LEDs in series and use a 9 V battery harness. Then the maximum LED current will equal to:

Imax = (Vs - 4*Vled) / Rd = (9 V - 8 V) / 100 = 10 mA

This is a well known circuit that you can find on the internet. You can click on:

Step 2: Build the Circuit

I did use a soldering iron because I thought the wires were loose. However, not all joints were soldered together.

You do not need high power resistors for this circuit. You can see that I never included the input capacitor.

Step 3: Put in Encasement

I used an old foam packaging material and a high power wire to secure the components to the encasement.