# Build a Miniature High-Rate Speed Control with Battery Eliminator Circuit (BEC)

Posted on Feb 5, 2014

This design is based on one published by Milan Lulic in the German magazine elektroModell. Mr. Lulic`s design is for surface mount technology (SMT) construction, whereas mine uses standard off-the-shelf components, and is therefore better suited to construction by the hobbyist. If you`re interested in a non-BEC speed control with higher current

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capacity, and a brake, please see my other article, A Miniature High-Rate Speed Control with Brake. The circuit begins with a buffer, consisting of C1, R1, and Q1. This provides some isolation between the receiver and the rest of the circuit, and makes circuit operation somewhat independent of the model of receiver (although you may have to adjust R8 if you change receiver types). R2, R3, and C2 form an integrator, which produces an output voltage proportional to the pulse width of the input signal. This output voltage varies from approximately 1. 15V for a 1ms input to 1. 45V for a 2ms input (at 50 pulses per second). Z1A, together with R4 through R8, and C3, form a 2. 5kHz triangle wave generator. R8 adjusts the upper and lower bounds of the triangle wave (it also affects the frequency, but within the range over which R8 must be adjusted, this is not significant). When properly adjusted, the triangle wave (which appears across C3) will oscillate between about 1. 2V and 1. 4V. This covers the middle 2/3 of the range that the integrator voltage covers. Z1B is used as a comparator, which compares the integrator voltage with the triangle wave. When the integrator voltage is above the voltage of the triangle wave, the output of Z1B is high; when it is below, it is low. At zero throttle, the integrator voltage (1. 15V) is always below the triangle wave voltage (1. 2V to 1. 4V), so Z1B remains low. At full throttle, the...

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