Need help on DIY circuit for LED lighting

[ngwanhoe]

Hi any expert please help. Thanks

I have DIY a lighting system with LED. Anything wrong with my work?

Using 4 X 1.5V Alkeline batteries connected 3 in parellel and 3 in series = 3V, attached to a step up circuit from 3V to 12V which then connected to 6 X K2
3W Leds input current 4.5V - 5V each 3in parellel and 3 in series.

 

[rho-bot]

Parallel configuration of two LED chains ist problematic due to the deviation of the LED forward voltages, which will result in one chain taking all the current while the other chain is off.
I would recommend to use series connection for both, batteries and LEDs. Therefore, a boost converter 6V to 30V is needed.
What kind of boost converter are you using? The LED current has to be limited, this cannot be done with a standard voltage booster. Therefore, there are special LED drivers for LED applications which will boost the voltage and regulate the output current.
For example, LT3591 is a very cheap and easy converter IC for your circuit...

 

[ngwanhoe]

Parallel configuration of two LED chains ist problematic due to the deviation of the LED forward voltages, which will result in one chain taking all the current while the other chain is off.
I would recommend to use series connection for both, batteries and LEDs. Therefore, a boost converter 6V to 30V is needed.
What kind of boost converter are you using? The LED current has to be limited, this cannot be done with a standard voltage booster. Therefore, there are special LED drivers for LED applications which will boost the voltage and regulate the output current.
For example, LT3591 is a very cheap and easy converter IC for your circuit...

Thanks

Booster LM2577

I have actually wire the LEDs 3 parellel and 3 series but use direct 10x 1.5v battery = 15v DC and it works but the Leds is very hot even with heat sinker

 

[rho-bot]

LM2577 is a booster with fixed output voltage.
LT3591 is a booster with fixed output current. This is a current source espacially designed for LED applications.

Assuming yor LEDs have a Vf (ForwardVoltage) of 4.5V each, the LED chain needs 13.5V. Your battery provides 15V, which will result in a huge current, which is only limited by the inner resistance of the battery. This is VERY BAD!
The LED current has to be adjusted/limited, otherwise it gets very hot by overcurrent or/and gets damaged. With fixed voltage, this is usually done by a series resistor.
What LED are you using? What is the maximum allowed current for this LED?

 

[ngwanhoe]

LM2577 is a booster with fixed output voltage.
LT3591 is a booster with fixed output current. This is a current source espacially designed for LED applications.

Assuming yor LEDs have a Vf (ForwardVoltage) of 4.5V each, the LED chain needs 13.5V. Your battery provides 15V, which will result in a huge current, which is only limited by the inner resistance of the battery. This is VERY BAD!
The LED current has to be adjusted/limited, otherwise it gets very hot by overcurrent or/and gets damaged. With fixed voltage, this is usually done by a series resistor.
What LED are you using? What is the maximum allowed current for this LED?

The Leds is K2 3W made in Taiwan. No data but I think same as Luxeon K2 which can hold up to 1500Ma.

The 15V I did just for testing the series Leds for 2mins.

This is the stepup circuit that I will be using

 

[rho-bot]

If you will use this LM2587 booster, then i recommend to put the batteries in one chain so Vin is 6V.
Put the LEDs also in one chain, and add a 0R2 series resistor. Adjust the output voltage of the booster so 0.3V will drop at the resistor (=1.5A LED current). This is not the best solution, as the power dissipation at the resistor will be ~0.5W and the resistor will not fully compensate the thermal Vf drift of the LEDs.

As already said, the best way is to use a dedicated LED (boost) driver as a current source:
very accurate current regulation, simple design and very efficient compared to the solution above.

 

[enjunear]

If you are using four AA batteries to power the K2's, your battery life is going to be very short. I'd probably lean toward a simple 12V sealed lead-acid battery (Powersonic, etc) for a supply.

Also, you need a current-limiting device in your circuit. This can either be a simple series resistor, a constant-current bias circuit like this, or a constant-current self-limiting supply. You'll want a current-controlling device on each series set of LEDs, this will help balance the LEDs due to variations in the V/I curves between parts.