I have an opto-isolator driven by PWM which is smoothed out by a low pass filter. The high voltage side of the isolator
is tied to a separate 10 VDC power supply. I'm attempting to modulate a proportional Belimo actuator from the high voltage
side of the opto-isolator. The funny thing is, when no load is connected to the output of the opto-isolator the output is linear to the input signal. For example 2.5VDC input from the UNO equals 5 volts. The problem is, any time the actuator is connected, my voltage drops dramatically.
Is the load on the isolator to much causing a voltage drop?
Hopefully a diagram will explain it better than I can.
C and R need to be mirrored, R needs to be on the PWM pin and C on the far side of R bypassing to ground. However your opto circuit is going to try to be on or off. Try this circuit:
Opto isolators work better at transmitting digital signals, so you would be better off smoothing the signal on the actuator side, not the Arduino side.
Can someone help me size a low pass filter for this circuit on the actuator side?
I've found many sites telling how this is done yet i dont understand sizing the cap or resistor.
It depends on now fast you want to operate the actuator and how tolerant it is of ripple in the input voltage. I suggest something like this:
increase the 10v DC supply to 12v
2K resistor between Q2 collector and +12v
18K resistor between Q2 collector and actuator input
10uF capacitor between actuator input and local 0V (Q2 emitter)
This give a time constant of around 0.2 seconds. If the actuator chatters or its current consumption remains high even when it has moved to the correct position, use a bigger capacitor. If you need faster response, use a smaller capacitor, and increase the PWM frequency if neccessary.
I would like to thank all who replied to this thread.
With your wealth of knowledge I've successfully completed my
analog circuit and utilizing the actuator.
