Switching ON/OFF a 3.3V Regulator with propeller
Hi,
I need to switch a 3.3V regulator (LM2937-3.3) ON or OFF via the propeller to power a AEROCOMM RADIO MODULE ( AC4490 )
My regulator currently runs from the 5V supply of my board.
Which is more suitable, a transistor or a mosfet?
Thanks
Dave M
I need to switch a 3.3V regulator (LM2937-3.3) ON or OFF via the propeller to power a AEROCOMM RADIO MODULE ( AC4490 )
My regulator currently runs from the 5V supply of my board.
Which is more suitable, a transistor or a mosfet?
Thanks
Dave M
Comments
-Phil
Your idea of a regulator with enable pin is a good idea, it will take up less space!
I now just have to choose one from gazillions available!
regards
Dave M
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"A complex design is the sign of an inferior designer." - Jamie Hyneman, Myth Buster
DGSwaner
LP3875ET-3.3 1.5A - NATIONAL SEMICONDUCTOR — IC, REGULATOR LDO 3.3V
LP3964ET-3.3 — 0.8A - NATIONAL SEMICONDUCTOR — IC, REGULATOR ULTRA-LDO +3.3V
Are these overkill, I think they are expensive!
thanks
Dave M
Bugetary price is $1.20, so you can expect a street-price of $6 for low quantities.
Nick
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Never use force, just go for a bigger hammer!
The DIY Digital-Readout for mills, lathes etc.:
YADRO
Datasheet:
http://www.fairchildsemi.com/ds/FD/FDN304P.pdf
Mouser: ($.55)
http://www.mouser.com/Search/ProductDetail.aspx?qs=MA%2b40jw2YMpyjgZQyVD8yA==
You can see a schematic for how I use this via the attachment:
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Regards,
Ryan O'Hara
www.ohararp.com
Post Edited (ohararp) : 1/15/2008 6:20:39 PM GMT
I'd be very tempted to fit a pullup resistor to the gate, though. A half-turned-on SOT23 will desolder itself fast, if your output pin is floating for a while.
Even with the gate driven hard, I^2R losses in the FET are getting close to the thermal limits, if you're really hoping to switch the full 2.4A. Careful PCB layout would be called for.
It would be brave indeed to switch a 5V rail with a 3.3V IO pin from a propeller straight to the gate. Even when 'off', you'll have a Vgs of 2 volts or so. That's mostly on. Expect crispy smells. A second transistor stage to get the levels, and defaults, safe would be advisable, wouldn't it?
Steve
-Phil
Post Edited (Phil Pilgrim (PhiPi)) : 1/15/2008 8:46:46 PM GMT
Steve
Thanks guys for all the tips,
I think a regulator with enable pin is they way to go, As I can easily add this to my existing layout.
regards
Dave M.
Regards, David
I found this device FAIRCHILD KA378R33
http://www.mouser.com/Search/ProductDetail.aspx?qs=RAZo5F3HLrnWbTu8pZ2dtA==
Is it just a matter of connecting the enable pin to one pin on the PROPELLER , with a pulldown resistor to ground, so on start-up this regulator is OFF, and when I choose to, I ENABLE it via HI on the prop pin?
I guess I only need 1 output CAP as usual, I will be running this from a regulated 5V device which is about 8cm away from it . So I hope I don't need a HEAT-SINK as well.
What do you think?
thanks
Dave M