Constant voltage and current

[siddarth.ghaste]

Hi
For indicating lamp, I am giving min 12VDC and max 220VDC,For all these voltages brightness should be same can somebody HELP me....

 

[FvM]

A LED with a high voltage capable current source can work. A moderate current of 5 mA is already generating 1.1W power dissipation however.

 

[siddarth.ghaste]

okay thanks, do you know about LM317 IC?

 

[FvM]

LM317 has 40V voltage rating, thus I don't see it related to your original question.

 

[kripacharya]

12VDC and max 220VDC....

thats a very wide range. What could your actual application possibly be ?

 

[siddarth.ghaste]

Indicating led lamp which can give same brightness for all voltages.....

 

[kripacharya]

i meant - what sort of source are you using which has a range of 12v to 220v ?

 

[FvM]

Ultimately you may want to add 230 VAC to the specification.

I remember, that I previously designed industrial controllers with an e.g. 15 VDC to 230 VAC voltage range for binary signals. In some cases there might a similar specification for indicator lamps. The most serious argument against it is that you sometimes observe residual voltage levels of several ten volts in open 230 VAC circuits. Thus a wide range control input might be trigerred and an indicator lamp flicker in this situation.

I already mentioned a current source as straight forward solution, it would need a high voltage transistor as active element.

I also have an old Steinel VoltCheck 1A, a simple 4.5 to 380V AC/DC voltage indicator, using mainly a NTC to achieve an (almost) constant current.

 

[siddarth.ghaste]

Thanks for your help,can you tell me how NTC can be used in this application.....