Anyone used this "optical MOSFET relay" ?

Jump to Latest
#21
These optical MOSFET relays are incredible and they got so much potential (just to be sure: metaphorically). They are real problem solvers for countless uses. They are very tempting for getting nice main power switches and (cheaper & nicer) power buttons. They have a major drawback though: When they fry, they shorten the output, unlike real relays, which are then simply open. So, especally, if you use them for main power switch purposes, look very critically at the usage if it's really what you want - especally in a power supply - in case of failure.
 
#22
timpert said:
I read something a but different in RyhthMick's description. As I see it, he only wants his amp to turn HV on when the bias is present, so he wishes to use the "relay" to switch the B+ on once there is bias.

If you want to go for that, a better solution would be to use a photovoltaic optocoupler, and an external MOSFET which is beefy enough to handle the load and surge. It is basically the same part, but without the built-in switch MOSFET.
Click to expand...

Thats right Tim. OK thanks I guess that makes sense to separate the optocoupler providing the sensor function driving a "beefy" MOSFET switch. I'll go look at those, though if you have any recommendations that would be helpful.
 
#23
You could, for example, use a TLP3906 (just search for a photovoltaic optocoupler) to drive a MOSFET with sufficient voltage rating and an apperently excessive current rating. Because the proposed optocoupler puts out 7 V, while many MOSFETs are characterized at 10 V gate drive, you should look at lowish threshold voltage types, with a voltage rating of around 600 V. The STP12N60M2 looks suitable, rugged and cheap. Up to about 8 A it behaves like a 0.5 Ohms resistor, and it only "lets go" above 16 A at 7 V drive. So it can take quite a bit of inrush, and the inrush current will not flow for long. The device doesn't need a heatsink, as it's own heat capacity is enough to absorb the heat dissipated during switching. That is, unless you wish to switch several times per second continuously...
 
#24
timpert said:
You could, for example, use a TLP3906 (just search for a photovoltaic optocoupler) to drive a MOSFET with sufficient voltage rating and an apperently excessive current rating. Because the proposed optocoupler puts out 7 V, while many MOSFETs are characterized at 10 V gate drive, you should look at lowish threshold voltage types, with a voltage rating of around 600 V. The STP12N60M2 looks suitable, rugged and cheap. Up to about 8 A it behaves like a 0.5 Ohms resistor, and it only "lets go" above 16 A at 7 V drive. So it can take quite a bit of inrush, and the inrush current will not flow for long. The device doesn't need a heatsink, as it's own heat capacity is enough to absorb the heat dissipated during switching. That is, unless you wish to switch several times per second continuously...
Click to expand...

Thanks Tim that's really helpful
 
#25
I have seen switching Mosfets in 4 pin TO-220, with the opto-coupler built in.
This is simply an ordinary enough solid state relay, the ones sold here have switching control input at 5-32 V DC, and the mains side is 440 V . Single as well as three phase ones are available.

The short circuit protected ones rated 50A are about 5 GBP here, single phase.

The DC control supply operates a photo switch, which then turns the switching element on or off.
Mosfet or thyristor based, how does it matter? Unless you are switching particular wave forms...if it is a mains frequency switch, simply buy the appropriate rated item.
 
Last edited:
You must log in or register to reply here.
Top Bottom