# PCB Heaven

## General Category => Analog discussion => Topic started by: dvanpolanen on June 10, 2012, 15:18:55 PM

Title: Fade-in 12V Incandescent Light Bulb
Post by: dvanpolanen on June 10, 2012, 15:18:55 PM
Hi

Im trying to make a 12V Incandescent Light bulb fade-in when turned on with a flip switch, I'm not too fussed with a fade out. I will be using a 12V power supply.

Its similar to whats being shown in the first bit of this tutorial except i don't want to use LED's -  http://www.pcbheaven.com/circuitpages/LED_Fade_In_Fade_Out_Dimmer/

Is this possible with the bulb I'm using or can this only be done with LED's?
If it is possible what would i need to buy to make it work, and how do i put it together? A drawn diagram of the circuit would be amazing!

Thanks For Any Help

Daniel
Title: Re: Fade-in 12V Incandescent Light Bulb
Post by: kam on June 10, 2012, 20:03:01 PM
This circuit can be used for incandescent lams as well without any particular change (the first one). After all, it is just a linear power supply. There are 2 problems that you will have to face: During fade in process, the transistor will be called to dissipate a lot of power, which depends on the current drawn by your lamp. The BC548  is absolutely incapable to do this. You will definitely need the second stage with the BD243  as explained at the bottom of the page.

Second, each transistor will generate a voltage drop. The first one (BC548 ) about 0.7 volts and the second one (BD243) another 0.7 volts. If you plan to use a power darlington pair transistor instead of the BD243, then this number becomes some 1.3 volts. You will therefore need some 2 volts greater power supply than your lamp to achieve maximum power. If for example your lamp runs maximum at 12V, you will either need 1.4+12 = 13.4Volts if the transistor are simple transistors, or 2+12=14V if the second transistor is a darlington pair...