Question on using power MOSFET & PICAXE

Thread Starter

izon

Joined Mar 17, 2013
195
Hi,
I'm trying to connect a power MOSFET (BS270) to one output pin on a PICAXE
controller chip. The device the MOSFET is to turn on is an LED array that is constructed to look like a beacon light. It uses 24vdc and the PICAXE uses 5vdc.

I've connected things as shown on my attached drawing. When I power on my
project, the LED array immediately operates for about 10-15 seconds and then goes off.
It should not come on at all. It must be running at about half the normal voltage during
this time since I see only about half the LEDs lighting.

What am I doing wrong here.... how can I get it to stay off even when just applying
power to the project via a wal-wart? I can tolerate this but I'm concerned maybe Ive
done something wrong that will cause a failure later. Since the light is a warning, I
don't want it to ever be on falsely.

Thanks!
 

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crutschow

Joined Mar 14, 2008
24,084
What is the gate connected to when you ran your test? A MOSFET gate cannot ever be open (floating).
The gate must be connected to ground, either through a resistor, or the PICAXE output has to be in the logic low state, for the MOSFET to be fully off.
 

Thread Starter

izon

Joined Mar 17, 2013
195
Sorry my details and drawing were not the best. The gate is connected directly to one of the
PICAXE output pins. I guess I would have thought the output upon initially applying power
would be logic low and fully off. Maybe there is some stored up voltage until everything
gets into normal state.
Thanks for trying to help...the PICAXE is a 20M2.
 

AnalogKid

Joined Aug 1, 2013
8,251
Connect a resistor from the gate to GND, something between 10 K and 100 K. This will prevent the gate from floating if the picaxe output is in tri-state.

ak
 

Thread Starter

izon

Joined Mar 17, 2013
195
Hey thanks fellas ! Put in a 10k and it solved the problem and all else seems to work ok too..thanks again!
 
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