LED | PartQuest™ Explore

LED Dimmer Circuit using TLC555 Timer

Mike Donnelly
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Mike Donnelly

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Member of the PartQuest Explore Development Team. Focused on modeling and simulation of analog, mixed-signal and multi-discipline systems covering a broad range of applications, including power electronics, controls and mechatronic systems.

Description

This LED Dimmer Circuit uses a 555 Timer to control the PWM duty cycle of the current drive. Rather than apply proportional but continuous current to the LED for dimming, which can cause color shifts, modulating the duty cycle allows the LED to operate at its nominal current during the “ON” portion of the cycle. Because the frequency response of human vision is limited, using a PWM frequency of 250 Hz avoids the perception of flicker for the observer.

The LED model has an internal monitor for the "perceived" light output (blue waveform), which is a low-pass filtered version of the instantaneous light output. The filter pole frequency is set to 15 Hz to represent the bandwidth of the human eye. The value of the dimmer setting (green waveform) is increased from 10% to 90% at time 100msec. The LED current pulses (red waveform) are shown before and after the duty-cycle transition.

Part of this design is based on a dimmer schematic found on-line:

<a href="http://www.555-timer-circuits.com/led-dimmer.html">http://www.555-timer-circuits.com/led-dimmer.html</a>

That original circuit is actually incorrect, one of the diodes connected to pin 7 on the 555-Timer needs to be reversed. There was a comment from a reader who said he built the circuit as shown and it didn’t work. This is a good example of the value of simulating circuits before building hardware!

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Copy of Transient Stability Testing of Transmission Line Fed LED Driver - on Fri, 08/16/2024 - 16:30

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Copy of Transient Stability Testing of Transmission Line Fed LED Driver - on Tue, 07/30/2024 - 19:58

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Welcome to the community!!

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Copy of Slayer circuit Tesla coil - on Wed, 07/17/2024 - 15:53

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Copy of LED Dimmer Circuit using 555 Timer - on Tue, 07/16/2024 - 22:14

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Description

Este circuito dimmer de LED usa um temporizador 555 para controlar o ciclo de trabalho PWM do acionamento atual. Em vez de aplicar corrente proporcional, mas contínua, ao LED para escurecimento, o que pode causar mudanças de cor, a modulação do ciclo de trabalho permite que o LED opere em sua corrente nominal durante a parte "ON" do ciclo. Como a resposta de frequência da visão humana é limitada, usar uma frequência PWM de 250 Hz evita a percepção de cintilação para o observador.

O modelo LED tem um monitor interno para a saída de luz "percebida" (forma de onda azul), que é uma versão filtrada passa-baixa da saída de luz instantânea. A frequência do polo do filtro é definida como 15 Hz para representar a largura de banda do olho humano. O valor da configuração do dimmer (forma de onda verde) é aumentado de 10% para 90% no tempo 100 mseg. Os pulsos de corrente do LED (forma de onda vermelha) são mostrados antes e depois da transição do ciclo de trabalho.

Parte deste projeto é baseado em um esquema de dimmer encontrado on-line:

<a href="http://www.555-timer-circuits.com/led-dimmer.html">http://www.555-timer-circuits.com/led-dimmer.html</a>

Esse circuito original está realmente incorreto, um dos diodos conectados ao pino 7 no 555-Timer precisa ser invertido. Houve um comentário de um leitor que disse que construiu o circuito como mostrado e não funcionou. Este é um bom exemplo do valor de simular circuitos antes de construir hardware!

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