Protocol generation using MOSFETS

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Hi,

The load are addresable smoke detectors which communicate with the controller using pulses over 24V pedestal.
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Why do you think it doesn't draw the power from the higher voltage pulses? ... with increased current...

I think it's quite expectable that the devices draw higher current to charge their capacitors from the higher voltage pulses.
Thus I'd rather use 24V on idle .... and drop the voltage to - lets say - 20V or 16V for the data pulses. With this you avoid increased current for the first bits of communication.

Klaus
 
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    d123

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Hi,
Unfortunately, 24V down to 20V or 16V will not work as per specs of the smoke detectors. It has working range of 34V to 28V. Also, I have to consider cable load that will be connected in real scenario. So 34V dropped to may 28V due to cable load is acceptable.
 

Hi,

I wonder... if the spec says 34V ...28V...why do you use 24V then? It's out of spec.

I wouldn't be surprised if you don't know the specifiaction for data transfer.
What is the specified idle state? High voltage or low voltage?
What are the voltage limits for LOW signal level?
What are the voltage limits for HIGH signal level?

Klaus
 

Hi,
Let me clear the confusion. The pedestal (base) voltage is 24V. The protocol pulses are anywhere between 5-10V. Hence, to get the 5-10V over 24V, I am switching 34V so that I get 10V pulses over 24V. The detector will recognize pulses over 24V as valid pulses. These pulses should be 5-10V amplitude.
As the cable load increases, the 10V amplitude may reduce, hence I said that it may work upto 28V, actually it should be 29V, so that pulse may be minimum 5V.
 

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