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Circut to leave fans on when xbox turned off

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mgeno216

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I want to build a circut that leaves the fans on on an xbox 360 for like 5 minutes after the console is turned off. So this is a block diagram I made in paint (so excuse the sloppiness)

**broken link removed**

The 5v is a standby voltage the remains even if the xbox is power down, as long as the xbox is plugged in. The 3.3v is only on when the xbox is powered. The 555 is set up in a monostable setupDo I need all the resistors, they are only there as current limiting resistors. I chose the nessacary current following the 10:1 saturation rule. I drew the transistor with bottom as base left as collector and right as the emitter. I am not to familiar with transisors or how to use them properly so could someone tell me if the transistors are set up properly.

Mike
 
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I've attached something which i think should work for you. It'll save you a transistor too lol...

when Vcc is applied (in your case 3.3v) the transistor is on and current is "shorted" to earth via a resistor obviously, but when Vcc is not applied the transistor is off and current flows to the 555 to trigger the monostable.

you'll just have to figure out values for that capacitor discharge...
I didn't add it, but you'll prob need to use diodes to control the charge and discharge times.

Hope this helps...
 

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I am not sure what you linked me to. It was just one page in the catalog and nothing jump out at me as being useful for the purpose I need. Personally, I don't find the circut too complicated, or did you mean it was too complicated to read. I already have to make one PCB to add in the console, adding this to the PCB won't be that big of deal.

Thanks
Mike
 
Normally open thermostat; make on temperature rise. Pick your temperature. Wire it between an always-on power supply and the fan(s).
 
@MikeMI
I don't want to use the 5v until the console is turned off and I want to use it for x minutes (I will decide after some testing) regardless of the temperature.

@bychon
I appreciate the time it took for you to make that schematic, but why wouldn't mine work. I noticed what you added, but why was it nessacary

Thanks to both of you

Mike
 
Your left pnp is on all the time, so the 555 is too, a 555 has 6 more pins than you accounted for, the 555 goes positive when it's clocking, which will turn the fan off, not on, you didn't allow for a negative trigger pulse...and that's all the time I intend to spend after handing you everything you wanted.
 
I didn't ask you to make a schematic for me. And I am aware that the 555 has eight pins. I was just showing more of a block diagram, just the input and output. I was under the impression that with a PNP transistor the transistor only lets current though when the base has no current. If that is true then the first transistor would give power to the 555 when the 3.3v turns off (aka. when the console is off). I am aware that you are smarter than me, maybe I didn't explain what I am doing properly, but I guess this is coming down to my understanding of PNP transistors.

I am thankful for the schematic you posted, but it is also better that you don't do my work for me. I should learn and I know that. My googling has taught me what I know so far, so excuse errors.

Mike
 
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If you are offended by this I am sorry, but you were trying to give me a bit of a hard time:
and that's all the time I intend to spend after handing you everything you wanted.

If you don't want to help me, fine just don't post. If you do, my question is if my understanding of PNP transistors is correct.

Mike
 
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Hi Ya Mike

You may want to give this thread a lookie and see if it fits into your scheme of things.

On a side note if you are in the US is the 216 by chance your area code? :)

Ron
 
My area code is 630. I am in Wheaton, Illinois.

I have seen that version. It seems alittle over complicated.

I have put more thought in mine and this is what I think

**broken link removed**

I added the 3.3v to the base of the 2nd PNP inorder to have the transisto only let the 5v standby through when the console was off.
Does any1 know if a protection diode would be needed where is specified in the pic. Because when the console is on 3.3v would be flowing into the output pin.

Mike
 
A 555 has 8 legs. You need to connect most of them. Which ones are shown here? Is anything hooked to the others?
Maybe you could label EBC on the transistors so we don't have to guess.
If I'm guessing the EBC pins correctly, the 3.3V is being supplied with (5V-.65 =) 4.35V through both emitter-base junctions all the time.
How much does the fan draw? Is it a 5V or 3.3V fan?
 
Thanks Mike.

I hate it when posters split a topic into two threads. I usually check when someone is new, but I figured this one would have known better.
 
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