# filament lamp

Discussion in 'General Electronics Chat' started by Alho, Mar 28, 2012.

1. ### Alho Thread Starter New Member

Nov 3, 2011
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I am designing a certain circuit which uses a filament lamp, 6.3V, 200mA. Can I use a 9V or 12V power supply for this lamp instead of 6.3V?

2. ### Stuntman Active Member

Mar 28, 2011
181
47
I don't see why not. However, remember that this extra power (9V-6.3V= 2.7V 2.7V*.2A=.54W) will have to be bled off through the system in some way if you want to use simple linear voltage regulation. (a consideration if this is a battery powered design)

A simple adjustable voltage regulator will give you where you need to get with no trouble.

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3. ### Alho Thread Starter New Member

Nov 3, 2011
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As long as i maintain the rated power (6.3V x 0.2A = 1.26W), i can adjust the current and voltage?

4. ### Stuntman Active Member

Mar 28, 2011
181
47
If it's a filament lamp, (ie, not some kind of discharge lamp that requires an external ballast) just get an adustable regulator that can handle >200ma (go 250mA at a minimum IMO) , then read the datasheet on how to set the voltage (usually a simple voltage divider) to 6.3V and you should be a go.

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5. ### Ron H AAC Fanatic!

Apr 14, 2005
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If you adjust the voltage, the current will change, which will cause the power dissipation to change. If you drive it with a current source, and adjust the current, the voltage will change, which will cause the power dissipation to change.
The most efficient way to get 6.3V from a higher voltage is to use a switching (buck, in this case) regulator.

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6. ### Alho Thread Starter New Member

Nov 3, 2011
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actually i am designing a transistor (2N2222A) switch circuit. The transistor turns ON this 6.3V, 200mA lamp. Transistor base receives 5V from a PIC microcontroller. Instead of 6.3V i wanted to use 9V.

I also have some confusion in choosing the value for Hfe from the 2N2222A datasheet for calculating the base resistance. the datasheet gives so many values for Hfe. Which Hfe should I use? In this case we have Ic = 200mA.

7. ### Audioguru New Member

Dec 20, 2007
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The datasheet for the 2N2222A and for most other transistors specify a base current that is 1/10th the collector current for the transistor to be used as a saturated switch. HFE is only used only when the transistor has plenty of collector to emitter voltage (used in an amplifier) so it is not saturated.

The HFE is rated when the VCE is 10V. It saturates with a VCE of only 0.3V to 1V.

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