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Direct Current Dimmer Schematic Circuit Diagram

Versatile 12-Volt Controller: Energy-Efficient Solution

This 12-Volt controller, designed for energy conservation, finds widespread utility. Its applications extend beyond managing battery-powered illumination in vehicles such as cars, boats, or caravans; it’s also adept at regulating the speed of model trains. Essentially, this circuit transforms 12-Volt direct current (DC) into a rectangular pulse train, allowing for adjustable duty cycles ranging from 0 to 100%. The circuit comprises four sub-circuits: a saw-tooth generator centered around IC1, the reference network P1/R3/C3, comparator IC2, and the driver stage T1/T2. The comparator evaluates the generated sawtooth voltage (1) against the reference voltage (2).

Adjustable Pulse Train Generation

The reference voltage is modifiable within the lower and upper limits of the sawtooth voltage through P1. When the saw-tooth voltage surpasses the reference, the comparator’s output goes ‘high’. Given the fixed frequency of the saw-tooth voltage continually crossing the reference voltage, a rectangular waveform (3) emerges at the comparator’s output. The duty cycle of this waveform can be finely tuned using P1. The driver stage, featuring significant current amplification, ensures that the voltage, up to a load current of 3.15 A, maintains a suitably square waveform. By adjusting the reference with P1, the pulse train’s pulse width can be altered, directly influencing the average voltage delivered to the load and, consequently, the power it consumes.

Direct Current Dimmer Schematic Circuit Diagram 1

Direct Current Dimmer Schematic Circuit Diagram 2

Optimizing T2’s Power Dissipation

The current flowing through T2 is at its peak when the voltage drop across it is minimal (during saturation) and at its lowest when the voltage drop is at its maximum. Consequently, T2 requires minimal power dissipation and cooling, except when dealing with highly inductive loads. Diode D2 plays a dual role: safeguarding against reverse connections and acting as a freewheeling diode for inductive loads.

Sawtooth Generation and Frequency Adjustment

The sawtooth generator employs IC1, a 555 timer configured as an AMV, set to 65 Hz with R2/C2. Although the square wave at pin 3 is typically used for AMVs, our focus here is on the charge/discharge voltage across C2. While not a pure sawtooth waveform, it is highly suitable for this controller. If the controlled lamp visibly flickers, the frequency can be increased by reducing the value of C2. However, due to load behavior and T2’s dissipation, it’s advisable not to exceed 200 Hz. Despite being capable of functioning at frequencies above 10 kHz, the circuit performs optimally within this range.

555 Timer and Frequency Adjustment Mechanism

The 555 timer, IC1, is configured to generate a stable frequency. Its upper limit is externally accessible via the control input (pin 5), offering adjustment possibilities. This voltage is stabilized by C3 and directly linked to P1. To set the lower limit, the resistance of P1 and R3 is equalized, ensuring the same voltage division as the internal resistors in the 555 timer, effectively in parallel with them.


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