Hello,
I do have a PWM switch (breaking negative pole -) and was wondering if there is any device that can detect that switch is simply On or Off.

Thanks

 

An LED ??????
What Frequency is your PWM Circuit operating at ?
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@LowQCab
hello, yeah a LED stripe is connected to it.

PWM module:
frequency: 24 Khz
range: 1.5% ~ 99.6%


thanks

 

Much more information is required,
I have no idea about what your question is.
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@LowQCab
basically what i want to achieve is ... in case PWN switch / dimmer is on ie led stripe produces light,
i will be able to somehow using some device? send signal to the relay which is on in case there is 0V or 12V, and relay will turn on/off other circuit.

What info are u looking for?

As its PWM switch .. and breaking Minus pole, I am not able to get constant 0V.


Thanks

 

Maybe there is a language-translation problem ........
I don't understand your Post.

Please provide a Schematic-Diagram and an explanation.
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@LowQCab

well I can do it ... but isnt it simple?

PSU -> PWM Switch / dimmer -> LED STRIPE.

I will take out Negative pole from Led strip as controlling signal which will control other circuit ie Relay, in the following way
a) LED strip is on, controlling signal turn on the relay
b) LED strip is off, controlling signal turn off the relay

Circuit with a relay is connected on the same PSU as a Led stripe,
and has "controlling" port -> which activates relay based on the controlling signal

is that more clear?

 

Circuit with a relay is connected on the same PSU as a Led stripe,
and has "controlling" port -> which activates relay based on the controlling signal

What is this "controlling signal" to activate the relay?
This provides a constant 12 volt out when the PWM is ON.

 

What are the voltage and current specs of the LED strip?
Please post a link to the PWM module.

 

What we do need to know is the voltage across the switch when the PWM is in the off state.
Really, though, the simpler scheme will be to monitor the power feed to the LED strip using an LEd opto-isolater with an appropriate series resistor. Whenever the PWM is not off, the isolator will present some portion of ON.

 

What are the voltage and current specs of the LED strip?
Please post a link to the PWM module.

Hi,
LED strip is 12V, 2m, ~15W
this is the PWM Spec - in Czech language
https://www.t-led.cz/media/doc/prod/Instructions/Uživatelský návod stmívač 8AS 2023.pdf

 

What we do need to know is the voltage across the switch when the PWM is in the off state.
Really, though, the simpler scheme will be to monitor the power feed to the LED strip using an LEd opto-isolater with an appropriate series resistor. Whenever the PWM is not off, the isolator will present some portion of ON.

what do you mean by across the switch?

Thanks

 

What is this "controlling signal" to activate the relay?
This provides a constant 12 volt out when the PWM is ON.
View attachment 335074

by PWM out it means i have to attach there (-) pole which is connecting pwm <-> led stripe?

thanks!

 

by PWM out it means i have to attach there (-) pole which is connecting pwm <-> led stripe?
thanks!

Correct.

 

sghiato's circuit in post #8 should do what you want. D1 cathode is connected to the negative of the LED strip. C1 negative is connected to the negative of your 12 volt power supply. (Befor it is converted to a PWM signal.) The plus 12 volt to the source of the P channel mosfet Q1 is the +12 volts from the power supply. You will connect one side of the relay coil to the drain of Q1. The other side of the relay coil will go to the same place as the negative of C1.
This how it works. Any pulses of the PWM signal to ground will discharge C1 (Even when the PWM signal has a very low duty cycle.) C1 wil not charge up enough to cause Q1 to switch off during the off state of the PWM signal. When there is no PWM signal C1 will charge up enough for Q1 to turn off causing the relay coil to be de energised. (The will take about a second to happen after the PWM signal goes away. (If the time is too long you wil have to change the time constant of C1 R1.)
You will need to ad a diode in parallel with the relay coil to protect Q1 from the back EMF from the relay coil when it switches off.

Les.

 

@LesJones
hello appreciate your explanation,
and thank you so much @sghioto for the design of it!

Just one question regarding the need to add diode ,,,
https://dratek.cz/docs/produkty/1/1927/1700475986s_1700646270s_1476828250s.pdf

this is the relay module (again in Czech) - do I really need to add that diode? Its galv separated.


thanks!

 

No diode needed as it's on that relay module.

 

No diode needed as it's on that relay module.

@sghioto
they do that module in multiple variants 5/12/24V
I have the 12V one.

 

Changed C1 to 100nf, more then enough for 24Khz pwm.

 

That relay modules has other components on the input coil side of the relay. You will need to trace out the schematic of the input side of the board. We just need to get to the ends of the relay coil. I think there is a diode on the module so we need to know how it is wired.

Les.