MOSFET replacement

[Rajinder1268]

Hi all,

I have attached a picture, where SSR fet relays are used to pass signals to vehicle Comms.
Is there an alternative to SSR fet relays? That would be a cheaper option.
The relay is a single pole normally open form A.

 

[dick_freebird]

"Can you?" and "Should you?" are separated by "Stuff goes
wrong" in an electrically-filthy and distributed automotive
electrical system. You may think it's "12VDC" but that is
hardly ever true and sometimes very much not.

You must understand what abnormalities must be dealt
with on the signal source and control sides of the problem,
if you mean to select something like an analog switch / mux
IC to do the job - gross under / overvoltage can easily ruin
such parts or what's on the other side of them. And
sometimes "big, tough and dumb" is exactly who you want
on the offensive line close to the violence. A $2 part that
outlasts the vehicle is better than a $0.49 one that won't.
Especially if it ruins your demo or allows your potential
customer to break your evaluation sample.

 

[BradtheRad]

Are your signals Audio? There's the 4066 quad bilateral switch which works similar to a relay.

Or are your signals pulsed DC? Then you can use a plain AND gate. Apply signal to one input. Transmit or block by applying Hi/Lo to the other input.

Waveforms may need to be conditioned to be robust in an automotive environment.

 

[Rajinder1268]

Are your signals Audio? There's the 4066 quad bilateral switch which works similar to a relay.

Or are your signals pulsed DC? Then you can use a plain AND gate. Apply signal to one input. Transmit or block by applying Hi/Lo to the other input.

Waveforms may need to be conditioned to be robust in an automotive environment.

View attachment 182696

The signals are pulsed DC. For vehicle Comms such as KLine and Lline, CAN etc.
My concern is will using an alternative method comprise the integrity of the signal and work in a noisy automotive environment. Could I use FETs?

 

[KlausST]

Hi,

in electronics design we use specifications, like: Volts, amperes, frequency, waveform, ohms ...
I don´t find any specification. Thus - for me - it´s impossible to give any recommendation.

Oh, I´m wrong, there is a specification: it says "1k". But nothing about the input voltage, nothing about the diode current (which should be a LED, I guess)..

In SSR´s there is no functional electrical connection between "control" and "load".
But analog switches and FETs refer to the same voltage system (you may call it GND). Control and load are not galvanically isolated.
As long as you don´t provide informations about your application it´s impossible to decide whether a FET or an analog switch is suitable.

Klaus

 

[Rajinder1268]

Hi,

in electronics design we use specifications, like: Volts, amperes, frequency, waveform, ohms ...
I don´t find any specification. Thus - for me - it´s impossible to give any recommendation.

Oh, I´m wrong, there is a specification: it says "1k". But nothing about the input voltage, nothing about the diode current (which should be a LED, I guess)..

In SSR´s there is no functional electrical connection between "control" and "load".
But analog switches and FETs refer to the same voltage system (you may call it GND). Control and load are not galvanically isolated.
As long as you don´t provide informations about your application it´s impossible to decide whether a FET or an analog switch is suitable.

Klaus

Hi,
The application is for automotive vehicle Comms such as CAN, K-Line.etc.
Input to the SSR are from GPIO of microcontroller operating from 3V3 supply. Input to the LED is 3V3 driven from the microcontroller. The SSR device is CPC1117N.

--- Updated May 9, 2023 ---

Hi,
The application is for automotive vehicle Comms such as CAN, K-Line.etc.
Input to the SSR are from GPIO of microcontroller operating from 3V3 supply. Input to the LED is 3V3 driven from the microcontroller. The SSR device is CPC1117N.

1mA LED current.

 

[KlausST]

Hi,


Let´s say 10 people want to help you.
* Then 10 people need to do the internet search for datasheets. Often there are different datasheets of different brands and different versions. --> May lead to different results

* Then 10 people need to find out what specifications apply for your project. It´s like guessing. 10 people may come to 10 different guessing results.

* 10 people need to...

Aren´t you interested that it´s easy to help you, that all have the same source of informations, don´t need to guess, can give fast and precise feedback?

.. And you as the designer - don´t you already have all these informations by hand?

Klaus

 

[Rajinder1268]

Hi,


Let´s say 10 people want to help you.
* Then 10 people need to do the internet search for datasheets. Often there are different datasheets of different brands and different versions. --> May lead to different results

* Then 10 people need to find out what specifications apply for your project. It´s like guessing. 10 people may come to 10 different guessing results.

* 10 people need to...

Aren´t you interested that it´s easy to help you, that all have the same source of informations, don´t need to guess, can give fast and precise feedback?

.. And you as the designer - don´t you already have all these informations by hand?

Klaus

Hi
Unfortunately I did not do the original design but told to find an cheaper alternative.

 

[danadakk]

Accurate to say Kline, Lline, all have to meet the CAN buss physical layer
specs ? Per :

https://www.ti.com/lit/an/slla270/slla270.pdf?ts=1683601987468#:~:text=The%20Physical%20Layer%20is%20the,CAN%20message%20entering%20a%20node.

ISO-11898

Application one specific vehicle or any/all vehicles on the planet ?


Regards, Dana.

 

[Rajinder1268]

Accurate to say Kline, Lline, all have to meet the CAN buss physical layer
specs ? Per :

https://www.ti.com/lit/an/slla270/slla270.pdf?ts=1683601987468#:~:text=The%20Physical%20Layer%20is%20the,CAN%20message%20entering%20a%20node.

ISO-11898

Application one specific vehicle or any/all vehicles on the planet ?


Regards, Dana.

It would be for the majority of newer vehicles that have CAN capability. My concern is, if we use analog switches we may not get the isolation offered with an Opto.

 

[dick_freebird]

If you mean to find cheaper, you need to know what you can do without.

Isolation is a big one. There are cheaper isolation products now than
"PhotoMOS" hybrids I do believe. But whether these are (a) capable and
(b) "blessed" are two questions if your product incorporates industry
spec compliance.