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We are using MC33035 for controlling the BLDC motor. Currently we are connecting a Potentiometer between reference output and Error non-inverting input.We like to control the Speed using the PWM of micrcontroller. Let me know how we can do this.

You did not specify the desired precision of the speed-set function. So I am going to assume, moderate? precision, not high-precision, since he is now using a potentiometer. Refer to Figure 39 on page 20 of the MC33035 datasheet. The Error Amp is part of a control loop that compares two DC voltages (representing set-speed and actual speed), and outputs a DC voltage to the input of the PWM comparator. The set-speed input must therefore be DC. The requirement therefore becomes how to generate a DC voltage that is proportional to a PWM signal duty cycle. To describe the functional requirement as a simple table: = duty cycle ==== output V ==================== == 0% ========= 0V == == 100% ====== Vreg (MC33035 Pin 8) == 50% ======= Vreg / 2 Step one is to make the PWM signal vary between 0 and Vreg, independent of actual amplitude. This could be a comparator, single transistor amplifier, or operational amplifier (all of these would have Vcc / Vdd connected to Vreg, thus setting the maximum output voltage at Vreg. Step two to is to average the output, this could be a simple RC integrator, or better, an inverting op amp configured with an input resistor to set a charge current, and a parallel-connected RC between output and (inverting) input. The non-inverting input would be connected to Vreg. The output is connected to Pin 11 of the MC33035. A dual op-amp could be used to manage both functions. It must be single-supply ?rail-to-rail? type because common-mode input range is 0 to Vreg, and the amplifiers are powered by Vreg. Answered by:
ON Semiconductor
2011-06-15 17:58:36.0