I tryed to run my 10 led vu meter with AC 10V,2A adaptor and I heard cracking sound, the lm3915 got very hot and apparently its not even working even with my 9V battery anymore.. Can anyone explain why this circuit wont work with alternating current? whats bad about it I mean i know the differences between alternating and direct current in the theoretical way but i cant use it the practical things

 

That chip is not designed for its power supply voltage to become more negative than its ground pin. Try feeding it AC for a power supply and it's going to die suddenly.

 

Well, you just learned one thing about the practical differences between AC and DC: Things meant for DC will be destroyed by AC!

 

I mean i know the differences between alternating and direct current in the theoretical way but i cant use it the practical things

Now you know it matters and can use this experience as an opportunity to learn from your mistake.

 

Yeah definately thats some good experience. So u guys mean lm3915 cant go any more down than 0V or it will be destroyed?

 

Most parts won't tolerate reversed power connections.

 

Yeah definately thats some good experience. So u guys mean lm3915 cant go any more down than 0V or it will be destroyed?

Exactly.
If you apply a reverse voltage to most IC power pins it forward biases the substrate isolation diode and large currents will flow, zapping the IC.
Most semiconductors require a steady DC voltage of one polarity and not AC voltage which is constantly varying and reverses polarity every half cycle.
Only a few devices are designed to directly operate with AC voltages such as SCRs and TRIACs.

 

Cool guys, thanks so much for quick answers!