DC Motor Speed Controller: 1.4V Variable Voltage Circuit

Description

This circuit leverages the voltage decline across bridge rectifier diodes to generate a 5-position adjustable voltage source for a DC fan or a small DC motor. It's not as effective as a switching-mode circuit, nevertheless, it boasts the advantages of straightforward construction and the absence of switching transients. The four full-wave bridges are arranged such that each consists of two diode pairs in parallel, resulting in an approximate voltage drop of 1.4V, contingent upon the load current.

Circuit diagram:

The rotary switch should feature “make before break” contacts that should be rated for current handling up to approximately one amp, or more. For higher current levels, upgraded bridge rectifiers and a more robust rotary switch (or solenoids) are necessary. To achieve finer voltage adjustments, the commoned AC inputs on the bridge rectifiers can be utilized, enabling intermediate speed settings on the control switch.

More about components

1N4004 diode is a general-purpose silicon diode, frequently employed for rectification and reverse polarity protection. It allows current to flow easily in one direction and blocks it in the other. The 1N4148 diode is a similar component, often utilized for similar applications due to its fast switching speed and low forward voltage drop. Both diodes are crucial for managing the flow of electricity within the circuit, protecting components from damage and ensuring proper circuit operation. They are indispensable for any circuit employing DC power.