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controlling an tungsten lamp using microcontrollers

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venkates2218

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I would like to control tungsten lamp using control...the lamp will operate at 12v dc from an battery...the lamp will take maximum 1.5A from power supply..
My doubt is we can use eitheir PNP or NPN transistor to control the lamp..?
 

if i used NPN transistor means the volatge will return to transistor another end..?
because we are using tungsten bulb so it will conduct the voltage on another side..?
It will damage the controller in anycase..?
we have to use freewheeling diode across the transistor for safety..?
 

I don't know what is your bulb characteristics , but if it has inductive effect , yes you can use free wheeling diodes across the transistor and across the bulb
 

Hi,

use a logic level N-Ch-Mosfet in low side switching configuration.
Free wheeling diode across the BJT/Mosfet is useless. --> connect it across the load.
Use a bulk capacitor and a fast ceramics capacitor close to Mosefet to stabilize 12V


Klaus
 

Whether you use NPN or PNP the current that flows through lamp is the collector current. The base will be connected to microcontroller through a 560 Ohm resistor say. Microcontroller will not damage. You need two power supplies, 5V for micrcontroller and 12V for lamp. As lamp is a resistive device you don't need a free wheeling diode. That diode is only needed for inductive loads.
 
When you say "controlling an tungsten lamp" do you mean just switching it on and off or do you mean to set different brightness levels?

For on/off switching you can use a bipolar or MOS transistor. A good MOSFET will have less voltage drop than a BJT so it will run cooler.
If you want to control the brightness, you can do it by limiting the conduction of the transistor or by using PWM. Both methods work equally well but limiting the conduction will result in considerable heat loss and PWM will be far more efficient.

Brian.
 
hello,


a Mosffet canal N could be the best to drive it .
I did it with a PIC MCU and a Mosfet IRZL14 .
A 12F1840 DIP9 could be used instead of 16F...
Power supply for buble lamp 12V.. test with a 12V 5W , and also with a car lamp of 40W
but need a car 12V battery to test it !
don't forget that the buble resistance could be 10 times less at cold start !
so you can get a spike of maxi intensity : 10x nominal Intensity
 
just switching on and off only but it will happen frequently like blinking lamp...
 

Use Logic gate N Channel Mosfet say 4A 50V type. Use Heatsink for mosfet. Use PWM to adjust the brightness of the bulb. Turn ON/OFF PWM to get blinking effect.

Datasheet of Mosfet attached. You can use this Mosfet.

The chipFET is better. Mosfet with low Rds(on) is better.

- - - Updated - - -

Edit:

Still better use PowerTrench Mosfet from fairchild. FDS4410A
 

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Last edited:
venkates2218 said:
just switching on and off only but it will happen frequently like blinking lamp...
Click to expand...

Tungsten lamps are not the best for turning on and off as in a blinking; fast blinking will be impossible for high blinking rates. For low rate of on/off, it may be better not to turn off the lamp completely (like in a car flasher) but switch the intensity between 10% and 90%...

That will prevent the filament from excessive thermal stress...
 
frequent switching will damage the bulb..?
LED means we can do frequent switching..?it won't affect LED..?
 

Tungsten lamps produce light as a by-product of heating the filament so each time the light turns on and off the filament has to go from hot to cold. The thermal shock from repeated expansion and contraction will shorten the lamp life. They also draw more current when the filament is cold so for a brief moment as it lights up, the current is more than the formula W/V would suggest.

LEDs produce light by a chemical process and although they do produce heat, it is far less than a tungsten filament lamp produces so the thermal shock is also much smaller. They also do not draw extra current when turned on from cold.

So basically, frequently blinking a tungsten lamp will shorten it's life considerably, blinking an LED has almost no effect on it's life.

Brian.
 
betwixt said:
LEDs produce light by a chemical process and although they do produce heat,
Click to expand...

In a LED, the light is produced by the electron hole recombination and that IS NOT a chemical process.

All forward biased semiconductor diodes cause electron hole recombination but the energy appears as heat only.

LEDs can be flashed millions of times /sec (but forget about the 220V LED bulbs that you use at home).
 
In a LED, the light is produced by the electron hole recombination and that IS NOT a chemical process.
Click to expand...

I was trying to keep it simple! I know how LEDs work but I wasn't sure someone who couldn't flash an incandescent lamp would understand.
As C_mitra explained, don't try domestic AC LED lamps, they contain extra circuits and won't work on 12V or DC at all and also can't be flashed rapidly.

Brian.
 
thank you for your support friends...I have to control 5 lamps each will consume 2A current...
I would like to use driver IC to control the lamps...
I palnned,we can connect positive supply from 12v battery directly to the lamp...
We can control negative side by driver IC...
Is my idea is correct..?
Driver ic can withstand 2A current lamp..?

Or is their any way to control the lamp in simple method..?
 

Are the 5 lamps in series. If yes then current will be still 2A

If lamps are in parallel then you need a power supply which can provide 2A * 5 + additional = 10+A

If lamps are in series then you have to provide more voltage because each lamp is 12V and 5x 12V lamp in series needs 12 * 5 = 60V 2+A supply.

What driver IC are you going to use ?

Mosfets are better than driver IC.

Use power mosfet with low Rds(on).

Connect lamps in parallel using 5 Mosfets. you then need a 12V 10+Amps power supply.
 
Hi,

it is already meantioned before: cold start current can be up to 10 times nominal current.

--> your driver peak current needs to be 10 times nominal current.
--> your driver continous current needs to be 1 x nominal current.

Klaus
 
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