Driver circuit for 8 LED in series

[tuty]

I am looking for a driver circuit or any simple circuit to glow 8 green LED in series/parallel using 9 Volt battery ..

i have attached the LED datasheet

its forward Current 20 mA.
forward Voltage 3.1V

 

[Diver300]

You need a boost converter, something like this:-

http://cds.linear.com/docs/en/datasheet/1937f.pdf

 

[jjw]

Put two leds in series with a 150 ohm resistor and four of these parallel.

 

[Diver300]

With a simple resistor circuit, and with the variation in the voltage on the LEDs and the battery, you would not know what LED current you would get with much accuracy. If you put typical numbers into an LED current calculator like this:-https://www.mtrak.co.uk/led_calculator.html you will find that the worst case current could be far from what you expect.

If you allow ±10% for the battery, and ±0.1 V for the LED, then if you don't mind the current being anywhere between 10 mA and 28 mA, then the 150 Ω resistors will work.

With a boost converter and a 5% current sense resistor, all the LEDs will have the same current, the current will be within ±15% of what you want, the efficiency will be better, and the current will be constant over the whole life of the battery.

If you are using a PP3 battery, the voltage will fall to 8 V fairly quickly, and you need to be able to use the battery down to around 6 V if you are to get the best use out of it, so with resistors the LED current will be far less than what you want for most of the life of the battery.

 

[Colin]

Here's a circuit:

 

[ronv]

Here's a circuit:

View attachment 95815

Maybe you could draw a schematic. It's not clear there are 2 windings on the bolt and which goes where or how many turns.

 

[misterR]

HOW we can light 8 leds in series with just 9V supply?

 

[Diver300]

HOW we can light 8 leds in series with just 9V supply?

The voltage is increased by using an inductor and a switching circuit.

It is a method similar to a vehicle ignition system. Colin's circuit is a slight variation on the "Joule theif" circuit, which you can google or search for on this forum.

 

[audioguru]

All of my solar garden lights use a voltage stepup IC so that a single Ni-MH battery cell voltage can drop as low as 0.7V and the 3.5V LED still lights.

 

[Gasboss775]

Put two leds in series with a 150 ohm resistor and four of these parallel.

I vote for this solution, sometimes the simplest things are the best.

That being said, the ability to work off one 1.2 / 1.5 volt cell can be useful.

 

[misterR]

The voltage is increased by using an inductor and a switching circuit.

How this circuit work.

 

[Diver300]

How this circuit work.

https://en.wikipedia.org/wiki/Joule_thief#Description_of_operation