Automatic AC Bulb Fuse Detection Circuit

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Hello !

I have an AC bulb operating at 220v 50Hz , i want a circuit that determines automatically either the bulb is fused or not. I need 5v and 0v logic for this purpose as i need this feedback for the micro-controller.

I have considered several solutions for this purpose :

1. When the bulb is fused circuit becomes open so we can add a current sensing op-amp circuit in the path.
2. Convert the AC to DC without transformer configuration and make 5v DC from 220v AC and directly give it to mcu.

But these are not the best optimized ways. Can some-one guide me the best solution for this purpose along with schematic diagram.
I want the solution to use minimum components.

Thanks
 

barry said:
how about a current transformer? A hall effect sensor?
Click to expand...
Thank you for replying. Yes well transformer and hall effect sensor can be used but transformer is bulky device and more over there are 8 bulbs and i want to know to status of each bulb separately n this means if i use transformer or hall effect sensor then i need 8 transformers/sensors for this purpose which will make the circuit too heavy and costly.

I want a very simple solution using a simple diode/zener diode if possible. I know that zener diode of 5v always drops 5v across itself when it is attached in series with load, so when AC voltage is applied on it it will drop 5v across itself and by using comparator i can determine the logic. Is it ok ?
 

That doesn't sound good, because:
1) Your zener is going to have to carry all of the load current; you'll be dissipating 2.5 Watts in your poor zener for a 100W bulb, for example. You'll need a heatsink.
2) You're going to need either some isolation or a diff amp with a high-common mode rating.
3) Some other reasons I'm too lazy to go into.

How about a light detector?
 

How about an LDR and series resistor across the 5V supply, the connection between them will give you a logic level output depending on whether light was being emitted or not.

Brian.
 


Ok, so you've got an LED lit. What are you going to do with that? You've still got dangerous high voltage floating around. However, if that LED was the input of an optoisolator, you'd be fine.
 

I see the problem that a lamp short (can happen when the bulb burns out) will brobably burn the schottky diodes or the LED/optocoupler if no current limiting elements are added.

A current transformer (can be a small 6 or 10 mm core) would be still my favourite solution.
 

How are you powering the micro-controller? Remember that everything will be not isolated from the mains if you don't use any isolator between your sense circuit and the micro-controller which creates a lethal shock hazard.
 

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