Learn How to Dim an LED Array with a Simple Circuit - No Switch Required!

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Discussion Overview

The discussion revolves around a circuit design for dimming an LED array without the use of a switch, specifically focusing on how to achieve a gradual dimming effect when power is cut off. Participants explore the technical aspects of the circuit, including components and configurations, while seeking solutions to the problem presented.

Discussion Character

  • Technical explanation
  • Debate/contested
  • Exploratory

Main Points Raised

  • One participant describes a circuit where the LED lights up slowly when DC power is applied and turns off immediately when power is cut, seeking a way to remove the switch while maintaining a gradual dimming effect.
  • Another participant requests clarification on the circuit's purpose and whether power remains available to the LEDs after being cut off.
  • Questions are raised about the presence of a coil in series with the LED, which could potentially create a delay in turning off the LED.
  • Several participants ask for more details about the circuit configuration, including whether it uses PWM (pulse width modulation) and the arrangement of the LEDs (series or parallel).
  • One participant suggests that a large capacitor might be sufficient to achieve the desired gradual dimming effect.
  • A participant mentions that the circuit includes a ceramic wrapped resistor in series with the LED, which may influence the dimming behavior.
  • Clarifications are made regarding the power supply, indicating that it is an AC to DC converter providing 12Vdc & 8.5A, and that the LEDs are connected in parallel.
  • The original poster reiterates the need for the LEDs to automatically dim down without manual intervention from the switch.

Areas of Agreement / Disagreement

Participants express varying levels of understanding and propose different approaches to the problem, indicating that there is no consensus on how to achieve the desired effect without the switch. Multiple competing views and suggestions remain unresolved.

Contextual Notes

Participants note the importance of circuit details such as component types and configurations, which are not fully specified. There are also assumptions about the behavior of the circuit that are not clarified, such as the role of the capacitor and resistor in achieving the gradual dimming effect.

waterbottle
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Hi. I've got a LED dimmer circuit. When the dc power turns on, the LED will slowly lights up.
There is a switch in the circuit that if I "open" the switch, the LED will slowly turns off.

The million dollar question is how do I remove the switch and the LED will slowly turns off when the power is cut off.

Thanks!
 
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Hi. I've got a LED dimmer circuit. When the dc power turns on, the LED will slowly lights up.
There is a switch in the circuit that if I "open" the switch, the LED will slowly turns off.

The million dollar question is how do I remove the switch and the LED will slowly turns off when the power is cut off.

I have read this many times and still don't know what you are asking.
Please explain why you are doing this. Is the circuit doing something else or is it just dimming LEDs?
Is the power going to be removed completely or is it still available to light the LEDs?
 
is there a coil in series with the led? This would cause a delay on/off.
 
Josh111 said:
is there a coil in series with the led? This would cause a delay on/off.

Excuse me?
 
This sounds very straight forward, but you need to describe the circuit completely. Is it a PWM (pulse width modulation) dimmer, and what is the circuit (e.g., NE555, etc)? How many LEDs? Series or parallel? I suspect a big capacitor someplace is sufficient.
 
Bob S said:
This sounds very straight forward, but you need to describe the circuit completely. Is it a PWM (pulse width modulation) dimmer, and what is the circuit (e.g., NE555, etc)? How many LEDs? Series or parallel? I suspect a big capacitor someplace is sufficient.
There is no analog dial for the dimmer. The LEDs are connected in parallel. There is a AC to DC power supply. 12Vdc & 8.5A.
Basically it is AC converted to DC. When AC power is supplied, the LEDs will slowly light up. When AC power is cut off, the DC power will be cut off too and the LEDs will go off immediately.
I'm trying to find a way allow the LED to "shut down" slowly. This project is for my fish tank.

http://i160.photobucket.com/albums/t172/waterbottle_23/circuit.jpg

The "switch" is normally closed. If you "open" the switch then, the light will slowly shut off. I would like to have the switch in always closed mode and when the AC power is cut off, the LEDs will shut off slowly. will adding a capacitor across the switch do the trick?
Thanks for all the people who responds to my thread. Really appreciate it!
 
Josh111 said:
is there a coil in series with the led? This would cause a delay on/off.
There's a ceramic wrapped resistor in series with the LED.
 
vk6kro said:
Hi. I've got a LED dimmer circuit. When the dc power turns on, the LED will slowly lights up.
There is a switch in the circuit that if I "open" the switch, the LED will slowly turns off.

The million dollar question is how do I remove the switch and the LED will slowly turns off when the power is cut off.

I have read this many times and still don't know what you are asking.
Please explain why you are doing this. Is the circuit doing something else or is it just dimming LEDs?
Is the power going to be removed completely or is it still available to light the LEDs?
The power is removed completely and the LEDs will also shut off completely. The LEDs will light up slowly to full brightness. The only issue is I want the LEDs to slowly dim down, then fully off. But right now it will only shut off immediately when power is removed. There is a switch in the circuit that if it is opened, the LEDs will slowly dimmed n shut off. However, I want the leds to dim down n shutff "automatically" without me toggling the switch.
 

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