LED Driver Circuit Working and Applications

LED Driver Circuit

LED i.e., Light Emitting Diode is a special kind of diode that emits energy in the visible band of the electromagnetic spectrum. However, it conducts in forward bias the same as the p-n junction diode. It is used as an optoelectronic device. 

Now let me ask you a simple question. At our home we get 230 volts AC supply, can we give this directly to an LED? The answer should be Of course not. This is because an LED needs a constant current input. Thus to serve this purpose, we need a driver circuit. 

In this particular article, we will be learning about the design of a 230 volts LED driver Circuit. Generally, an approach of using a transformer for AC to DC power supply is widely used. But just think will it be a good option for driving a load like an LED? Not at all. So let us try it out the other way.

Principle of LED Driver Circuit

I hope after the above discussion you are very clear with the aim of the article. Yes, we have to design a transformerless LED driver circuit (which can be used at home especially.)

The driver circuit design contains AC capacitors that are designed for high voltage and are connected line to line. The basic function of the capacitor is to limit the current of the supply. As the capacitor only reduces the current, high voltage is delt (rectification and regulation) in the later part of the circuit.

Components of a LED driver circuit

• Electrolytic capacitor (non-polarized 2.2μF)
• Four resistors (1KΩ,10KΩ, 22KΩ, 390KΩ)
• Bridge rectifier
• Zener diode (4.7V)
• An LED (Bright white LED)
• And, a polarized capacitor (47μF)

LED Driver Circuit Design

• To the main supply, an AC capacitor is connected in a line with the mains supply.
• Then, a resistor of 390 Kohm is connected in parallel with this capacitor. This is to discharge the capacitor in the absence of supply. One more resistor of 10Ω is connected between the mains supply and the rectifier which can be called fuse here.
• To make the incoming AC voltage as DC, we use the Full-wave Bridge rectifier. Its capability is 1.5A for current.
• Now, bridge rectifier output is filtered using a capacitor (C filter) of 4.7μF.
• Zener diode is used next for regulating the output of the full-wave bridge rectifier. Keeping in mind the current that goes to Zener, we have connected a resistor of 22 KΩ in series. The value of the Zener voltage is 4.7 volts.
• Once more the Zener output is filtered with a capacitor of 47 μF, and finally given to the LED (load).

Working of LED Driver Circuit

The X-rated capacitor is the most vital component here as we are designing a transformerless driver. Let us calculate the capacitive reactance as below:

Capacitive Reactance X_c = 1/2πFC

therefore, Xc = 1/(2π*50*2.2*10^(-6)) 

we have C = 2.2 µF

=1447.59

Therefore, from Ohm’s Law the capacitor current, I = V/R

putting values of V & Xc , I = 158 mA

Now, this current enters the rectifier. Also, the input to the bridge circuit is 230 V RMS. So Vmax = 230*√2 = 325.26 V. Thus, the capacitor filter must be rated for 400 V. After rectifier, the voltage will be around 305 V which further needs to be brought down to use it as an LED input.

Zener diode serves the purpose. Also, its power rating should be kept in mind along with a series resistor and its power rating. Let us first calculate the suitable value of series resistance.

R_s = (V_in – V_z )/( I_L + I_z) 

where Iz = 10 mA, IL = 5 mA

Vin = 305 V , Vz = 4.7 V

Therefore, Rs = 20020 KΩ

Now the power rating of this resistor needs to be calculated, as it determines the amount of power it can dissipate.

Ps = (V_in – V_z)² /R_s

putting all the values, we get

Ps = 4.5 W

Lastly, the power rating of Zener Diode = Vz*(Vin – Vz)^2/Rs = 0.07 W

So the rectified regulated voltage along with the limited current is given to the LED load.

Also, watch Half wave Rectifier

Advantages of Driver Circuit

• It is simple and cost-effective as transformerless.
• Small size and have very weight.

Limitations of LED Driver Circuit

• The application here suits best for domestic use and single-phase supply.
• The capacitor used here may produce spikes with the fluctuations of mains.

Applications of LED driver circuit

• It is used for lightening and decorative purposes at home.
• It is also used in car, bikes and various other automobiles as an indicator.
• This circuit is also used in the combination with the doorbell to provide the indication.
• It is used in various domestic applications like commercial and residential lighting.

I hope you have gained some ideas about designing the driver circuit. I would love to see any new creative ideas on the same in the comment section below. Also, give your feedback on the article (design) above, so as we can keep on improving on the quality for you.

Also, watch Solar Battery Charger Circuit Explained in Detail