12V Halogen Dimmer

A 12V 20W halogen lamp (MR16) and a 4.2Ah SLA battery are utilized in a bike light system. Due to the limited lifespan of the battery at this power rating, a cost-effective light dimmer was designed to reduce battery consumption and extend nighttime riding duration. The dimmer is based on a simple 555 timer circuit and a MOSFET switch (Q1), which operates by pulse-width modulation (PWM) of the 12V supply to the lamp. The 555 timer (IC1) is configured as a free-running oscillator, with two selectable mark/space ratios through a 2-pole, 5-position rotary switch (S1). The third position of the switch bypasses the electronic circuitry, connecting the lamp directly to the battery negative, providing three power levels of approximately 7W, 13W, and 20W. A logic-level IRL530N MOSFET, with a drain-source on-resistance of only 0.1 ohms, ensures minimal losses and negates the need for a heatsink. An alternative suitable MOSFET is the STP30NE06L (Jaycar Cat. ZT-2271).

The circuit design incorporates a 555 timer integrated circuit configured as an astable multivibrator, generating a continuous square wave output that modulates the power supplied to the halogen lamp. The frequency of this PWM signal can be adjusted by changing the resistive and capacitive components connected to the 555 timer, allowing for fine-tuning of the light output. The rotary switch (S1) provides the user with the ability to select different duty cycles, effectively controlling the average power delivered to the lamp.

When the switch is in the bypass position, the lamp receives full battery voltage, enabling maximum brightness for situations requiring high illumination. Conversely, the other positions of the rotary switch provide reduced power outputs, which are beneficial for conserving battery life during extended rides.

The choice of the IRL530N MOSFET is crucial for this application due to its low on-resistance, which minimizes heat generation during operation. This feature is particularly important in portable applications where weight and space are at a premium. The alternative MOSFET, STP30NE06L, offers similar characteristics and can be interchanged depending on availability or specific design requirements.

Overall, this circuit design presents an efficient solution for controlling the brightness of a halogen lamp while optimizing battery usage, making it ideal for bicycle lighting systems that require reliable performance over extended periods.A 12V 20W halogen lamp (MR16) and a 4. 2Ah SLA battery for my bike light system. The battery has only limited life at this power rating, so I designed this cheap light dimmer to reduce the battery drain and allow for longer rides at night. Based on a simple 555 timer circuit and Mosfet switch Q1, it works by pulse-width modulating the 12V supply to the lamp.

The 555 (IC1) is wired as a free-running oscillator, with two different mark/space ratios selectable via a 2-pole, 5-position rotary switch (S1). The third switch position bypasses the electronic circuitry and connects the lamp directly to battery negative.

This gives three power levels of about 7W, 13W and 20W. A logic-level IRL530N Mosfet with a drain-source on  resistance of only 0. 1 © ensures low losses and eliminates the need for a heatsink. An STP30NE06L Mosfet (Jaycar Cat. ZT-2271) would also be suitable. 🔗 External reference