Frequently Asked Questions...
I need an emergency light circuit diagram?
I need an led emergency light circuit diagram which would charge a 6v battery and turns on itself when power is out.
Answer:
Okay, you need three pieces. First, you need a charger that will charge the 6V battery while the power is applied. Second, you need a control circuit that turns the light on when the power goes off. Last, you need the driver needed for the LEDs (to supply them the right amount of current).
If you want a test button, it must only disable the input power. That is, a test button should simulate a blackout. That way, it tests everything. (The battery, the LED, and the control circuit.)
All of these pieces are simple, and they go together simply. You can use any battery charging circuit that is safe to trickle charge continuously. You don't want a fast charger (it will cause the battery to fail prematurely through overcharging).
The LED driver can be a simple as a resistor, but it should be appropriate for your chosen LED assembly. If you are using a simple LED that only needs a resistor, the equation for the resistor value is:
R = (Vb - Vl) / Cl
Where R is the value of the resistor placed in series with the LED in ohms. Vb is the battery voltage in volts. Vl is the LED dropping voltage in volts. Cl is the desired resistor current in amperes. So, for a 6 volt battery, 2.3 volt LED, and 150mA LED current, you get (6-2.3)/.015 = 246, so a 250 ohm resister will do fine.
If you use two LEDs in series, their voltages add. So that would be, in my example, 4.6 volts instead of 2.3 in the equation. If you use LEDs in parallel, you should just give each one its own dropping resistor and connect the LED/resistor circuits in parallel to each other.
The only tricky part is the control circuit that turns the light off when the power is on. I recommend the KISS approach (keep it simple). Just get a normally-closed relay that can be opened by either the 110 AC input or the DC that goes to the power supply for the charger. Connect the battery positive output to one contact on the relay and the supply input to the LED driver to the other. That way, when the power goes out, the relay will close, connecting the battery to the LED driver.
The link below shows a simple example of an emergency light constructed this way. I would recommend using a more conventional AC input circuit, with a transformer.
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Led Emergency
Blue LED Glow Stick / Emergency Flashlight
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