Hello, I'm trying to design a simple circuit to convert a PWM signal to variable DC. The PWM signal is a 5.5vpeak 50Hz square wave of varying duty cycles. However, I want a clean DC output. So, at say, 10% duty cycle, I want a clean.6vDC; at 20% I want a clean 1.2vDC; and so on until at 90%, the DC output is a clean 5.4v DC. Really, what I'm trying to do is create a circuit to take the PWM signal from a remote control car (hobby class) receiver (which would normally go to a servo) and have the output on (~6v) or off (0v), but would be nice to have the variable aspect for other uses. DC-DC Converter Tutorial. When the current is unacceptably high, the PWM circuit shuts down, thereby protecting the circuit. The type of switching. Download free Amx To Pwm Converter. While this circuit is very simple, choosing the appropriate values for R & C encompass some design decisions. So far, I figured I'd use a basic op-amp input stage to buffer the signal against loading, use *something* (this is where I'm stuck) to filter the PWM signal to a clean DC level, and use another op-amp as a comparator to trigger the output. The buffer and the comparator works (easy enough), I'm just stuck on the PWM filtering part. I've searched here and googled for some clues but everything I've found talks about converting DV to a PWM signal, not the other way around. Any clues or anything would be greatly appreciated! Thanks in advance! To turn a PWM signal into a DC voltage, you could low-pass filter it. But at a frequency of 50Hz you would really need a huge time constant and it would be very slow to react to changes in duty cycle. In other words, not very practical. Personally, I would do it with a microcontroller, using a timer and an interrupt it wouldn't be that hard to measure the width of the pulse. That would eliminate the need for the buffer and comparator, just provide the digital output right from the microcontroller. Not to mention, examples of using microcontrollers to interpret servo signals are already out there so you'd have something to start from. Thanks for the reply. Since the output of the cap/resistor network is feeding the input of another high-impedance (10^12ohms) op-amp, I can use a smaller cap/resistor. That should solve the time constant issue. I was shooting for a simple circuit - a microcontroller setup is a little too complex for me to get into. ![]() Led Pwm CircuitI think I'll stick with analog for now. I'm goingo to borrow an oscilloscope from work tomorrow so I can see more of what's happening. There's only so much my old Fluke 87 will show me. Analog To Pwm ConverterYou need a lowpass filter. The tradeoffs are in complexity, delay, and ripple. For example, I tried a 3-pole active Bessel with cutoff frequency=5Hz. In this case, the ripple for your application would be 18mv p-p, and the delay from when the signal is applied to final value is around 120ms. You can get less ripple with a more complex filter, or with lower cutoff frequency, or both. Pwm To Voltage Converter CircuitThe price you pay is more delay from a change in duty cycle to the new value being settled. Perhaps we can zero in on a solution if you can clarify what you can tolerate in terms of ripple and delay.
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