LED Analog Incandescent Slow Opening and Closing Circuit Design

Posted by: enthusiast  • Information section:Home appliance

LED lighting has many advantages over traditional incandescent bulbs, including energy efficiency and power output. However, the LED will turn on immediately. For those who want to retrofit the LED, this circuit will let the LED slowly turn on and slowly turn off, all in the analog circuit !

summary

LED Analog Incandescent Slow Opening and Closing Circuit Design

How to run

The circuit consists of three main sub-circuits: a triangular oscillator , a PWM generator and a capacitor charge/discharge circuit. The first sub-circuit, the triangular oscillator, consists of operational amplifiers U1A and U1B, where U1B configures the semiconductor as an integrator and U1A is configured as a Schmitt trigger. The output of the integrator is connected to the input of the Schmitt trigger, which results in four conditions:

If the output voltage of the integrator exceeds the upper threshold, the Schmitt trigger output switch is low

If the output voltage of the integrator exceeds the lower threshold, the Schmitt trigger output switch is high

If the output of the Schmitt trigger is high, the output voltage of the integrator increases steadily

If the output of the Schmitt trigger is low, the output voltage of the integrator drops steadily

The result of these four conditions is the continuous triangular waveform at the U1B output. Incidentally, this oscillator also produces a square wave that can be found at the output of U1A. This circuit is especially useful for square waves that want to be in phase with a triangular wave. But why do we equip this LED driver circuit with an oscillator? The answer lies in PWM, pulse width modulation.

When incandescent bulbs are turned on and off, they do not do so immediately. Instead of ICs, they take time to turn them on and off, something that modern LED lights can't do. Therefore, in order to simulate this effect with LEDs, we need a circuit to effectively control the brightness. One of the most common ways to use LEDs is to use a PWM generator. In our circuit, we use the triangular waveform generated by U1A and U1B and feed it into comparator U2B. The PWM output generated by U2B is related to the negative input pin, so a higher voltage on this pin will cause the PWM waveform to have a lower duty cycle (ie, greater than on). The lower the voltage on the negative input pin, the higher the duty cycle (ie, the more times it is turned on). Since the LED is connected to the transistor switch (Q1) controlled by U2B ,

Now that we have a LED that can be controlled by voltage, we need to generate a voltage signal that is very similar to an old incandescent bulb. For this circuit, we use a simple RC circuit that takes about 2 seconds to fully charge/discharge. Therefore, when the input (ON / OFF) of the circuit is connected to GND, the LED starts to conduct, and when the input is connected to VCC, the LED is gradually turned off.

construction

The project can be built using many different circuit construction techniques, including breadboards, strips, matrix boards, and even pcbs. Initially, I designed a PCB for this project, but this board failed for unknown reasons. The goal is to turn this circuit into a small module that can be fitted with a conversion LED, so all surface mount components are used. I successfully made the PCB, but when turned on, one of the LM358s produced all the magical smoke! Therefore, the breadboard version is shown here.



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read ()  •  Sep 19, 2019  •  Edit


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