DC Relay.. Mosfet or Coil

[Eugene Onishi]

I've been making projects that require a DC dry contact. In some cases I use an opo-isolator with a high current Mosfet. It seems to work fine. Sometimes I use a ULN2803 in line with relays..

Most of the applications work fine either way and the cost is about the same. Any suggetions or comments on this?
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This message was ported from CCS's old forum
Original Post ID: 11884

[jim]

i dont know if you use your contacts in harsh enviroments but i would be concerned about any Spikes that could come down the line. the relays can handle allot but not the fet.


:=I've been making projects that require a DC dry contact. In some cases I use an opo-isolator with a high current Mosfet. It seems to work fine. Sometimes I use a ULN2803 in line with relays..
:=
:=Most of the applications work fine either way and the cost is about the same. Any suggetions or comments on this?
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This message was ported from CCS's old forum
Original Post ID: 11890

[Neutone]

:=I've been making projects that require a DC dry contact. In some cases I use an opo-isolator with a high current Mosfet. It seems to work fine. Sometimes I use a ULN2803 in line with relays..
:=
:=Most of the applications work fine either way and the cost is about the same. Any suggetions or comments on this?

Most relays dont surface mount.
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This message was ported from CCS's old forum
Original Post ID: 11898

[Shane Rowell]

If you use a relay you need to make sure you have supression diodes in place. I like the mosfet solution (low Rds devices)for currents that are on the order of an amp or two. You need to make sure that the gate capacitance is not too high. I have seen times when a pic will reset when changing the outputs to a fet input. You can add some series resistance, or pick a fet with a low gate capacitance. The datasheets from Microchip will give you a recommended max.
Mosfets in a SMT package are typically great.

-Shane

:=I've been making projects that require a DC dry contact. In some cases I use an opo-isolator with a high current Mosfet. It seems to work fine. Sometimes I use a ULN2803 in line with relays..
:=
:=Most of the applications work fine either way and the cost is about the same. Any suggetions or comments on this?
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This message was ported from CCS's old forum
Original Post ID: 11901

[ajt]

We use Omron surface mount relays. They are a bit pricey but we've had no problems.

:=:=I've been making projects that require a DC dry contact. In some cases I use an opo-isolator with a high current Mosfet. It seems to work fine. Sometimes I use a ULN2803 in line with relays..
:=:=
:=:=Most of the applications work fine either way and the cost is about the same. Any suggetions or comments on this?
:=
:=Most relays dont surface mount.
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This message was ported from CCS's old forum
Original Post ID: 11902
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Al Testani

[mcafzap]

Depending upon requirements, you can directly drive some relays - though you will still need protection diodes. I have used latching relays (NAIS TN2-L-5v) driven from 2 outputs for on and off. From memory, these required about a 1mS pulse @ about 20mA.
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This message was ported from CCS's old forum
Original Post ID: 11909