3W LED Hat Lamp Update (PWM Dimmer Circuit)

The hat lamp I previously designed had three brightness settings. I thought including a PWM dimmer would make it useful for dark adaptation and extending battery life. Using a dim setting for a warm colour would be melatonin friendly when reading at night.

In this circuit, I selected SMD components, which made the board compact enough to fit into an AA battery slot. The small switch of the holder was used to power the 7555 timer. Because we needed more current for the LED, I soldered ground directly to the source of the MOSFET.

Since I selected only low power components, the battery can last for months if you accidentally left the switch on with the LED disconnected or dimmed to 0%, assuming that you use low self-discharge batteries. The circuit uses only 250 uA is used on standby.

Materials

• IRLM6402 or AO3401 SMD P-channel MOSFET (SOT-23 package)
• Copper clad board
• 7555 timer (SMD package)
• 2.2nF, 100 nF, and 10 nF capacitors (0805 package)
• 10k and 10M resistors (0805 packages)
• 2-1N4148 diodes
• 500k potentiometer with a dial
• 4 AA battery holder
• Two core connector
• 3W LED (any colour) with heatsink
• LED lens (optional)
• Velcro (to attach the heatsink to a hat)
• 2 ohm 2W resistor (needed if using red or yellow LEDs)
• Heat shrink tubes
• Two core wire (3 to 4 ft)