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ilikebbs
Joined: 30 Nov 2002
Posts: 101
Helped: 2
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 20 Sep 2008 5:14 how to use moset to control on/off high voltage |
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the processor is power by 3.3v.
LCd is powed by 15V.
How to use mosfet to control the on/off of 15v?
Thanks
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MAK-1
Joined: 26 Jun 2008
Posts: 49
Helped: 3
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20 Sep 2008 5:48 how to use moset to control on/off high voltage |
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Mosfet gate voltage gradually open with the increase of gate voltage. You can check it proactically when Mosfet start conducting while increasing gate voltage.
For low voltage scenario, you can use npn transistor. Please search yourself to get approperiate npn transistor for your application
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nandhu015
Joined: 11 Feb 2006
Posts: 640
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Location: Tamilnadu, India
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20 Sep 2008 7:52 Re: how to use moset to control on/off high voltage |
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there is no need for an mosfet unless you are driving high current (say more in amps).
Just a common transistor is enough for the job i think
Regards
Nandhu
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ilikebbs
Joined: 30 Nov 2002
Posts: 101
Helped: 2
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20 Sep 2008 14:34 how to use moset to control on/off high voltage |
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| Could you give the reference schematic??
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nandhu015
Joined: 11 Feb 2006
Posts: 640
Helped: 46
Location: Tamilnadu, India
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20 Sep 2008 16:58 Re: how to use moset to control on/off high voltage |
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Google for level converters
You can find a lot
Nandhu
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sujojk
Joined: 22 Jun 2008
Posts: 14
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22 Sep 2008 8:16 Re: how to use moset to control on/off high voltage |
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If your LED power requirement is very low, then you can use a transistor itself directly. Thing to remember is : transistor is a current driven device. Larger the output current (here LED current) larger the input driving current, which the processor may not be able to deliver.
Generally MOSFETs have a threshold voltage around 4V. Since your processor is working at 3.3V, you have to use a low power transistor in between the processor and mosfet.
Optocoupler is another option which will give you perfect isolation.
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22 Sep 2008 8:16 Ads |
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fsmyth
Joined: 15 Nov 2004
Posts: 68
Helped: 1
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22 Sep 2008 8:56 Re: how to use moset to control on/off high voltage |
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A few driver examples:
http://hmin.tripod.com/als/fsmyth/pages/drivers.html
<als>
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angelote
Joined: 28 Apr 2005
Posts: 106
Helped: 11
Location: Spain
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23 Sep 2008 6:51 Re: how to use moset to control on/off high voltage |
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I use theese circuits to switch on/off power supply, and control signal is 3,3V from a processor.
Q6 controls a power supply lower than 3,3V.
Q5 and Q7 can control a power supply from 3,3V to the maximum Vds of Q7. Use the Q5 that meets your specifications.
I current is high, check Q6 and Q5 Rds(on).
I find less difficult and more power efficient to use mosfet better that BJT.
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