Solid state relay replacement

[Signumx]

Hi,

I'm currently using a photovoltaic solid state relay (Fairchild
HSR312L) to open or close the path of a square wave signal. It works
fine but at over a 1$ per unit it's rather hard on my circuit budget.
I tried to replicate the internal circuitry of the chip (see datasheet:
http://www.fairchildsemi.com/ds/HS/HSR312L.pdf) by using two MOSFETs
with their sources connected together but I can't seem to turn off the
switch (open the path). Anyhow, would anyone have a suggestion of a
low cost, low current consuming solution to replace the HSR312L?

Thanks!

 

[Robert Scott]

On 17 Aug 2005 08:01:27 -0700, "Signumx"
<jf.morin@ggi-international.com> wrote:

Hi,

I'm currently using a photovoltaic solid state relay (Fairchild
HSR312L) to open or close the path of a square wave signal. It works
fine but at over a 1$ per unit it's rather hard on my circuit budget.
I tried to replicate the internal circuitry of the chip..

It is exceedingly rare that you can build something with discrete
components for less money than a large-scale manufacturer has already
built as an integrated circuit.


-Robert Scott
Ypsilanti, Michigan

 

[Mook Johnson]

I don''t think you'll get isolation for less than $1 each. If the isolation
requirement was removed, it might be possible but still kinda tight.

Maybe if you shared more about what the circuit is attempting to do we could
be of more help.





"Signumx" <jf.morin@ggi-international.com> wrote in message
news:1124290887.952509.273350@f14g2000cwb.googlegroups.com...

Hi,

I'm currently using a photovoltaic solid state relay (Fairchild
HSR312L) to open or close the path of a square wave signal. It works
fine but at over a 1$ per unit it's rather hard on my circuit budget.
I tried to replicate the internal circuitry of the chip (see datasheet:
http://www.fairchildsemi.com/ds/HS/HSR312L.pdf) by using two MOSFETs
with their sources connected together but I can't seem to turn off the
switch (open the path). Anyhow, would anyone have a suggestion of a
low cost, low current consuming solution to replace the HSR312L?

Thanks!

 

[Signumx]

I forgot to mention that the isolation is not required. Here is a
summary of my project. We buy a unit that controls DC motor. Right
now we also buy an off-shelf wired remote control which has simple SPST
switches to open or close what seems to be current loops (I measure
40mA when a loop is closed). We want to add a module between the
remote and the control unit to allow or prevent some of the remote keys
to function. This needs to be managed electronically (or digitally).
A 0-5V signal would take care this. Also, I've been told that the the
return path of the control signals is not connected to the unit's GND.
Therefore, I can't put my module to the same ground reference as the
unit.

In brief, a HI signal would allow the loop to close and current to flow
and a LOW signal would open (or put in high impedance) the loop.

Thanks.

 

[Mook Johnson]

If you need to get a singal that is referenced to one ground to appear on
another non-connected ground, you need isolation.

I think you're at about as cheap as you can get for this part.



"Signumx" <jf.morin@ggi-international.com> wrote in message
news:1124330201.816106.203010@g14g2000cwa.googlegroups.com...

I forgot to mention that the isolation is not required. Here is a
summary of my project. We buy a unit that controls DC motor. Right
now we also buy an off-shelf wired remote control which has simple SPST
switches to open or close what seems to be current loops (I measure
40mA when a loop is closed). We want to add a module between the
remote and the control unit to allow or prevent some of the remote keys
to function. This needs to be managed electronically (or digitally).
A 0-5V signal would take care this. Also, I've been told that the the
return path of the control signals is not connected to the unit's GND.
Therefore, I can't put my module to the same ground reference as the
unit.

In brief, a HI signal would allow the loop to close and current to flow
and a LOW signal would open (or put in high impedance) the loop.

Thanks.