The article explains a simple 1 amp constant current LED driver circuit using the IC MBI6651 from MACROBLOCK. The IC has been specifically designed for operating high power LEDs safely by providing a constant current output. The circuit includes very few external components and therefore becomes very easy to assemble at home.
About the IC MBI6651
The IC MBI6651 is a high efficiency, step down DC to DC converter chip capable of driving high power LEDs at a safe 1 Amp constant current.
The IC requires just four passive external components for making it functional.
The output current of the IC can be externally set by selecting the appropriate resistor value.
The IC also features a PWM controlled dimming control of the connected LEDs.
Some of the other outstanding features of this IC includes UVLO meaning under voltage lockout, over temperature shut down, LED open circuit protection and LED short circuit protection, all these ensure complete safety to the IC from wrongly configured output loads.
Typical Application Areas of this device are:
Automotive decoration and illumination
LED flood lights using high intensity, high power LED.
The IC also can be used as a constant current source in particular circuit applications.
Setting the output Current
The output current of the IC is fixed through an external resistor Rsen. The output current Iout and the adjustment resistor Rsen has the following relation:
Given Vsen=0.1V
Rsen=(Vsen/Iout)=(0.1V/Iout)
Where Rsen is the value of the external resistor. This resistor is connected across the pin outs SEN and Vsen of the IC.
The optimum current with Rsen 0.1 Ohms is 1000 mA or 1 Amp.
Optimizing External Component Selection
Inductor: Two issues specify the inductor type, the switching frequency and the ripple current. The involved calculation can be written as:
L1>{Vin - Vout - Vsen - (Rds(on) * Iout)} * D/fsw * delta.IL
where, Rds(on) is the on-resistance of the IC's internal MOSFET. The value is typically around 0.45 at 12V
D is the duty cycle of the IC, given as D = Vout/Vin
fsw is the switching frequency of the IC
While designing the inductor for the given circuit, along with the inductance the saturation current must also be taken into account,because these are two basic factors which typically affects the overall performance of the circuit.
The rule of thumb, the saturation current of the inductor should be selected 1.5 times greater than the LED current.
Moreover, selecting high values for the inductance provides better line and load regulation.
Selecting the Schottky diode
The diode D1 shown in the circuit diagram basically acts as the flywheel diode for nullifying the inductor back emf during the periods when the LED is switched OFF.
The diode must be selected with the following couple of important characteristics:
It should have a low forward voltage rating and maximum possible reverse voltage tolerance.
Selecting the capacitor
The general rule is always to select a capacitor value with a voltage tolerance 1.5 times higher than the supply voltage.
Preferably, a tantalum capacitor should be selected because these have high capacitance and low ESR characteristics.
The proposed circuit of 1 Amp constant current LED driver circuit is given below:
The basic operating parameters are given below:
Pin Out Specs:
Courtesy: https://homemade-circuits.com/wp-content/uploads/2012/04/mbi6651.pdf
Ronald Beck says
I’m looking to make a LED device that can be used as photographic flash with a very short duration 0.1 ms or less (ns range would be really cool). I plan to use an arduino uno for the trigger circuit. Could the MBI6651 circuit above be use/modified for this purpose using an appropriate power supply? Thanks for any help you can provide.
Swag says
If you have an easy access to this IC then definitely you can use it, although any simple LM317 CC/CV circuit would do the job as efficiently
Subrata Bera says
Hello Swagatam, you have a really nice and informative blog there. Thanks for sharing all your learning with the world. It really help us a lot.
I need a little suggestion with constant current circuits. Could you please share the details of other such chips in the market which can take universal AC input and gives a constant current (adjustable) for various voltage requirements (Example : LC5226D). The availability of the components should be considered as finding such chips can be a really tedious job.
Thanks & regards,
SB.
Swagatam says
Hello Subrata, thank you very much!
I don't think there are such ICs which might be commonly available in the market, because nowadays SMPS circuits have become an easy alternative for achieving the same, therefore all today depend on SMPS designs which are plentifully available in the market. I too have posted many SMPS design which could be easily built at home.
Regards.
Unknown says
Hi
Can you post a circuit which takes input from user and keeps the current constant as per input? Range is 1 micro amp to 15 micro amp. Volt 10 to 30.
svarbanu
Swagatam says
In uamps it could be difficult….not sure.
Som Nath Roy says
CAn you design a driver with MB16651 for driving a single 10 watt LED with 12Volts input?
Swagatam says
I'll try to do it if it's feasible, and post it soon.
Anonymous says
Will the formulas for the base resistor and the emitter resistor remain the same after changing the transistor to the above mentioned?
Jay
Swagatam says
yes the formulas will remain the same even if the transistors are modified.
Anonymous says
Thank you sir 🙂
Anonymous says
I want to drive more than 50 LEDs. If I put two in series, there will be 25 parallel branches.
Each branch has to get 20 mA for LEDs. So I need 25*20mA = 500mA.
Sir, I checked datasheet of BC547 it says collector current is 100mA, I don't think this is enough for many LEDs.
Will it be good to us MMBT489 (rated for 1A) instead? Will there be any other problem using MMBT489?
I am not confident reading datasheet. Can you say sir?
BC547 : www.datasheetcatalog.org/datasheets/150/128424_DS.pdf
MMBT489 : elcodis.com/parts/6027208/MMBT489.html#datasheet
Could I use MMBT489 with 5 or 6V supply?
Thanks sir,
Jay
Swagatam says
yes BC547 will not work, you may use the referred transistor.
you can also try other transistors like 188, 2n2907, or 8050
Swagatam says
sorry 2907 is pnp, it should be 2n2222
Anonymous says
Thank you very much sir! 🙂
Jay
Anonymous says
Thank you sir. And is the formula for the emitter resistance the same? Can I use this circuit for high value of current like 3A if I want to power many LEDs?
Swagatam says
emitter resistance formula is given in the diagram.
You can use it with high current also.
Swagatam says
for high currents the transistors will need to be charged appropriately.
Anonymous says
Yes, for driving LEDs, by using transistors.
If I have 6V DC battery, and I want a constant current source from this, how will I make one? I found this simple design:
www.hqew.net/circuit-diagram/Constant-Current-Source-LED-Drive_12421.html
But they don't explain why the 4.7k-ohm is used and also they use Vcc as 12V. What modifications I can make for it to be good sir? If the circuit in link is not good, then I can also use LM317 as you suggested. Can you say how good the circuit in link is?
Thank you sir.:-)
Jay
Swagatam says
The circuit is OK.
input resistance value will depend on the connected load current.
You may use the following formula to find it.
R = (U – 0.6)hFe/I, where U is the supply voltage, I is the load current.
Regards.
Anonymous says
Do you have a post on how to design a constant current source depending on what person is looking for, without ICs (but only transistors)?
Jay
Swagatam says
For driving LEDs??
It can be made using a LM317 or LM338 IC, there are plenty of options of making one using this IC.