Question: Driving a relay directly with a PIC?

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William At MyBlueRoom

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Are there any brands of small signal coil based relays (reed or magnetic) that can be directly hooked up to a PIC I/O pin without a driving transistor?
 
<25 ma relays

Some miniature PCB mount DIP relays are <30ma. But is it prudent enough to load the Pic port with an inductive load??
Correct clamping of the transients is essential to guarantee the Pic' s life-cycle!
 
What about those solid state relays? I've never actually used one, or felt the need to actually investigate them. I assume they are just some sort of transistor mod.
 
SS Relay

Solid-State relays are Opto-coupled SCR/Triac switches. They are also expensive and a little bulky.
 
I've used the Fairchild versions in the DIP-8 package, but usually for driving relays (grin)...

The LED input side requires about 1.6v at 3.0-ma and the output side is good for 250-vdc at around 300-ma (parallel drains) or 250-vac (peak) at around 190-ma... The 400v versions provide about 200-ma (dc parallel) or 120-ma (ac)...

If switching AC loads, you might look at the Teccor series of Sensitive Gate Triacs with current capability up to about 8-amps... Most of these can be driven directly by a PIC output pin though I'm not sure I'd recommend it...

Regards, Mike
 
SS relay

SS relays can be safely used with micros. But the post was for a relay without even a transistor but direct drive.
 
Re: <25 ma relays

docel said:
Some miniature PCB mount DIP relays are <30ma. But is it prudent enough to load the Pic port with an inductive load??
Correct clamping of the transients is essential to guarantee the Pic' s life-cycle!
Click to expand...
there are internal diodes that can act as clamping diodes
 
Re: <25 ma relays


No prob at all, either hook up a small diode or get a PCB relay with a diode already built in (a bit uncommon, but not hard to find).

MOSFET's often a better idea if the load can be switched by grounding.
 
Just the thing...

**broken link removed**

This will take you to a data sheet for a SIP (Single Inline Package) relay. This can be activated with less than 5V. Since the coil is 500 Ohms, this means your activation current is well within the PIC's capabilities.
These are available with an optional protective diode. DigiKey has them. Their P/N is 306-1066-ND, $4.00 each.

Hope this is what you wanted.
kenjj
 
Re: Just the thing...


Ken,

Good find... Perfect for one of my projects... Thank you for sharing Sir...

Regards, Mike
 
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