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Designing cIsolated circuit to be contrroled by Active and Passive dimmers (Problem using Active Dimmer)

juanGuzman182

New Member
Hi to all

I have been trying to come up with a solution to a problem that I'm having with a circuit that I designed, I have not been able to come up with a solution and i would appreciate it any help.

So, I'm trying to basically isolate the input of my circuit from the rest of my circuit.
The input is a Passive and active input (0-10V Dimmer- 0-10V power source) and the (0-10V) signal is being isolated and transmitted using an optoisolator.
The isolation has been successful and the range of dimming for active and passive input is fine.
The problem arises when I connect more than one of my circuits to the same Active dimmer. The Voltage range for the active dimmer when one circuit is connected is (0.6v-10V), however when two circuits are connected the range is (1.2V -10V), connecting a third circuit would make the range (1.8-10V).

I have uploaded the schematics of the circuits that I'm using.

It seems that when I connect the active dimmer to control multiple circuits the voltage difference of each controller is adding up .
I tried to include a diode, which helped me to reduce it but it makes that my circuit doesn't work with the passive dimmer.

So my ultimate goal is to be able to isolate the active/Passive dimmer input in my circuit and being able to connect multiple circuits using just one Active or passive dimmer, as of now i have been able to achieve everything but the part of connecting the Active dimmer to multiple circuits because the range gets reduced.

Any help, advice or comment would be appreciated
 

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rjenkinsgb

Well-Known Member
Most Helpful Member
Each of the 15K bias resistors in the opto-isolator part is in effect connected in parallel between the input voltage and +10V.

Without knowing what's providing that 0-10V source, my guess would be that the additional current from each bias resistor is causing the voltage to rise across all the isolators.
 

juanGuzman182

New Member
Each of the 15K bias resistors in the opto-isolator part is in effect connected in parallel between the input voltage and +10V.

Without knowing what's providing that 0-10V source, my guess would be that the additional current from each bias resistor is causing the voltage to rise across all the isolators.
Hi rjenkinsgb
Thank you for helping me.
So basically what Im trying to do is to isolate the input from the rest of the circuit (right side of the opto-isolator)
But the input could be either a 0-10V power supply or a Passive Dimmer (potentiometer).
I am using the +10V in order for the passive Dimmer to work (producing current to transfer through the opto-isolator)
The design should be able to work either by connecting the power source or the passive dimmer.
That is how i designed my circuit as the picture attached but i would like to know if there is a way to get rid of that risen voltage (some electronic component) or maybe a different approach to the design?
Any advice would be very helpful
 

ChrisP58

Well-Known Member
Is the 0-10 Volt signal on the left side of your schematic a low impedance voltage source? If so, then you shouldn't need the 15K pullup resistors on each LED. If it is not a low imedence source, and the pullups are needed, then you change the effective impedance of that net with each additional pullup resistor. That may explain the behavior that you're seeing.


It looks to me that you're expecting the opto couplers to work in a linear fashion, where the collector current will vary proportionally to the LED current.

Most optos don't work very well in this mode. There are some that are intended to do this, but the ones I've seen have two transistors and require some extra circuitry to make it work.

What is the part number of the opto you're using?

Is the current limiting resistor connected to the LED and ISO_GND really 100K?
 

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