Simple LED Driver Circuit using IC 555

This circuit uses a special chip 555 IC, normally used for timing things, in a surprising way.

Here, it acts like a conductor controlling the flow of electricity to your LEDs.

The chip creates a special pulsing signal square wave that gets sent through a transistor which acts like a gatekeeper for the electricity.

This way, the circuit efficiently powers your LEDs and keeps them shining bright.

Circuit Working:

Parts List:

This basic LED driver circuit enables the operation of up to seven LEDs using a single AAA cell.

By pulsing the 220uH inductor the circuit generates voltage pulses at a much higher level than the input supply voltage.

A high Q Q>90 power inductor is essential for this setup.

When the input is 1.25V and the LEDs are connected the voltage pulse level reaches 23V.

The LED driver employs a 7555 suitable for low voltage operations and can function for approximately 190 hours with a single NiMH battery cell rated at 2000 mAh.

The 7555 timer drives the transistor at a rate of 222 kHz.

The seven LED groups can be connected in parallel if their forward voltages match.

However, if the forward voltage values differ the LED group with the lowest value will dim the other groups.

This parallel connection does not impact the total current drawn from the battery but does reduce the brightness of the LEDs.

When powered by a single 1.25V cell, the seven LED group draws about 8mA from the battery.

Increasing the input value to 2.5V raises the total drawn current to 20mA.

Formulas:

The following basic formulas is applied to the circuits construction and analysis using 555 Astable Mode

555 Astable Mode

Frequency (f):

f = 1.44 / ((R1 + 2*R2) * C)

where:

• R1 and R2 are resistors connected to the IC 555
• C is the capacitor connected to the IC 555

Duty Cycle (D):

D = R2 / (R1 + 2*R2)

Boost Converter

Output Voltage (Vo):

Vo = Vin / (1 – D)

where:

• V_in is the input voltage
• D is the duty cycle

Inductor Value (L):

L = (V_in * D * t_on) / (Δ_IL)

where:

• t_on is the on time of the MOSFET
• Δ_IL is the desired inductor current ripple

Note:

In order to enhance performance, repeated calculations, simulations and experimental changes are frequently used in practical boost converter design.

How to Build:

To build a Simple LED Driver Circuit using IC 7555 you need to follow the below mentioned assembling steps:

• Connect the positive terminal of the AAA cell to pin 8 of the 7555 IC.
• Connect pin 1 of the IC 7555 to the negative supply of the cell.
• Connect pin 4 of the IC 7555 timer to the positive supply.
• Connect pins 2 and 6 of the 555 timer together and connect them to pin 7 through a resistor 10k and 1k resistor to the positive supply.
• Connect pin 5 of the IC 7555 timer to ground with capacitor 0.01µF.
• Connect pin 3 of the IC 7555 timer to the base of the NPN transistor 2N2222 through a resistor 1k.
• Connect the emitter of the transistor 2N2222 to the ground.
• Connect the collector of the transistor to one end of the 220uH coil inductor.
• Connect the other end of the inductor to the anode of the 7 LEDs.
• Connect the cathode of the LEDs to the ground.

Parallel LED Groups:

• If using multiple LED groups, connect them in parallel ensuring their forward voltages match to avoid dimming issues.

Powering and Testing:

• Power the circuit using the AAA cell.
• Verify that the LEDs light up and are not dimmed by mismatched forward voltages.

Adjustments:

• Fine-tune resistor values to achieve desired LED brightness and efficiency.

Note:

Please note that building electronic circuits requires basic knowledge of electronics and safety precautions.

If you are not familiar with these, consider seeking assistance from someone experienced or consulting a professional.

Conclusion:

The LED driver circuit using the IC 7555 provides a simple and efficient way to drive one or more LEDs.

By configuring the IC 7555 as an astable multivibrator, a square wave output is generated to switch the LEDs on and off at a controlled frequency.

This circuit is easy to build and can be customized for various LED lighting applications.

However, it is important to select the appropriate resistor and capacitor values for the IC 7555 to achieve the desired frequency and duty cycle for driving the LEDs.

Overall, the LED driver circuit using the IC 7555 is a cost effective and reliable solution for driving LEDs in lighting projects.

References:

Driving 72 leds with 555 timer

Datasheet IC 7555