White LED driver circuit

Hi..

I am trying to build a circuit using an LDR and timer-555 ic, the circuit is intended to turn on 10 white LEDs when it gets dark and i wish to power the circuit using a 3.7v battery, but the problem i am facing is the output(pin 3) of 555 cannot drive 10 white LEDs In their full power! But LEDs can glow in their full power when i connect them directly to 3.7v battery!! Are there any ideas or circuits to light the LEDs in their full power? (maybe a transistor amplifer?).

The posted circuit have some errors that it turns on leds in daylight instead of darkness..so i fixed them by changing the LDR and VR in opposite

A npn transistor would be all you need, and a resistor between the 555 output and the base pin of the transistor (maybe around 1K)

10 x 30mA = 300mA so a transistor rated at 0.5 - 1 amp would do fine.

Pete.

SABorn said:

A npn transistor would be all you need, and a resistor between the 555 output and the base pin of the transistor (maybe around 1K)

10 x 30mA = 300mA so a transistor rated at 0.5 - 1 amp would do fine.

Pete.

Click to expand...

thanx pete.. When i tried bc548 the LEDs worked in full power but glows in opposite mode(leds turn on when light falls on LDR instead of darkness)..so i tried a PNP transistor then it worked as same as it worked before without a transistor.. I have no idead what to do..

Maybe i don't know how to connect a transistor, can u post a circuit showing how to connect a transistor in this circuit?

hi Z,
Try swapping over the LDR and 50Kpot, add the 10K

ericgibbs said:

hi Z,
Try swapping over the LDR and 50Kpot, add the 10K

Click to expand...

thank u eric..

I will try

ericgibbs said:

hi Z,
Try swapping over the LDR and 50Kpot, add the 10K

Click to expand...

hi eric

i tried to fix the circuit as you said, but its still in opposite mode! So i think i have connected the transistor in a wrong way.. Here is a picture of how i connected the LEDs.. May be a worst pic bcuz i drew it using my mobilephone

You could try a simple transistor inverter by using 2 transistors, like this.

Pete.

SABorn said:

You could try a simple transistor inverter by using 2 transistors, like this.

Pete.

Click to expand...

it works!!! I reconnected the LDR n pot as shown in the original diagram and The problems have been fixed! Thanx pete that inverter works really good n thanx eric for fixing the schematic.