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interior light dimming to off


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i am an idiot 
Platinum - Posts: 13,672
Platinum spaceThis member consistently provides reliable informationspace
Joined: September 21, 2006
Location: Louisiana, United States
Posted: May 21, 2010 at 6:57 AM / IP Logged  

2n3055 is a transistor, it is available at Radio Shack. 

How many lights are you going to have that are controlled by this circuit?  Do you happen to know the wattage of the lamps or the part number of them.  Also how long do you want them to remain on after the door is closed?

akuhead 
Member - Posts: 17
Member spacespace
Joined: January 18, 2006
Location: United States
Posted: May 25, 2010 at 3:54 PM / IP Logged  

There are going to be three light bulbs controlled by this circuit. Probably all three will be 3 watts. I don't know about the time to off function. Maybe 5-10 seconds, no more. I'm not particular. Just thought it would be kinda cool.

You guys are great and have a super forum. I really appreciate you all taking the time to give me suggestions, etc.

Thanks again

Jim

oldspark 
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Joined: November 03, 2008
Location: Australia
Posted: May 25, 2010 at 8:33 PM / IP Logged  
I'm still looking....
I know I also saw the real device recently - a T03 packaged 2N3055 with the components bird's-nested on (no PCB etc). If I find that, I can reconstruct the circuit diagram.
The 2N3055 handles a max of 15A; 10A is reasonably common.
Mine wasn't heatsinked, but was covered in araldyte (because the case of the 2N3055 is "live") and it would get warm-hot with a 10W bulb whilst actually dimming. (That's why I wrote "live" instead of "hot" - ie, +12V.)
Anyhow, 1A of load is no problem, but higher requires a heatsink.
These days dimming id done with PWM circuits so there is minimal heat.   
Of course, it's probably easier designing from scratch...
oldspark 
Gold - Posts: 4,913
Gold spacespace
Joined: November 03, 2008
Location: Australia
Posted: July 12, 2010 at 4:37 AM / IP Logged  
Victory to the patient! (Read: As a foggy photographic memory clears...)
From "Simple Projects from Electronics Today" page 85 (Published 1975):
The circuit:
interior light dimming to off - Page 2 - Last Post -- posted image.
And its birdsnest layout:
interior light dimming to off - Page 2 - Last Post -- posted image.
It is connected in parallel with the grounding door switch (ie "+VE" to switch & "-VE" to GND/chassis).
Be aware that the 2N3055 body is hot - both in terms of being +12V (but thru the dome/courtesy light) when the door switch is open, and also during operation depending on the load.
The circuit could be on the hot-side of the lamp provided the switch shorts out +VE & -VE (as in +ve chassis/GND vehicles).
When off, there should be no battery drain.
Operation:
The door switch closes (& turns the light on), C1 is discharged through D1. (REM - the door switch shorts the circuit's +VE to -VE)
The door is closed (door switch opens) & transistors Q1&Q2 are turned on.   
C1 charges via R1 & R2 gradually turning off Q1 (which turns of Q2).
C1 is chosen for ~full brightness for ~4 seconds followed by ~10 seconds of dimming. But the timing depends on transistor gains and the load so different C1 values could be used.
Resistors are 1/2W. EM401 ca be IN4004 etc. C1 can be 25V etc.
The 2N3055 gets hot mainly when dimming. Depending on frequency of use & lamp load, a heatsink may be required. The 2N3055 handles up to 15A. (Someone else can do a di/dv & time integrate to determine max loads without heatsinking (Ptot=115W).)   
Now to add a soft turn-on (for whoever wanted it....)
Page of 2

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