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Designer263242

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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&nbsp;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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ACME AS123 LED Driver Schematic Model JSAE 2025

Designer241497

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Description

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ACME AS123 LED Driver with Dimmer Control JSAE 2025

Designer241497

Member for

4 years 1 month

176

designs

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I'm a member of the PartQuest Explore Promoto.

Description

The AS123 LED Driver from ACME Semiconductor (fictional) provides fully integrated PWM dimming and a programmable current set-point. This IC is specifically for automotive rear combination (tail/stop) lighting applications. It tightly regulates the desired string current under conditions of widely varying applied DC voltage.

The PWM dimming function, which switches the LED on and off at just over 300 Hz, is active when the line input pin is high and the "PWM_disable" pin is low (

The AS123 supports current programming using a single external resistor (see r_iset in the schematic). The resistor value can be selected to give the desired LED string current, using the following formula:

r_iset = 1.85/i_desired

The AS123 is capable of regulating up to 100mA per string continuously. Therefore the value of r_iset should be no less than 18.5 Ohms. The user can change this resistor value and run a new simulation, to see the effect of this change on the LED string current.

See a "functional block diagram" schematic model of the ACME AS123 here: https://www.systemvision.com/design/acme-as123-led-driver-schematic-model

-------------- End of Example Application Note ------------------

If you are a component supplier, this type of "Live Application Note" can help your potential customers better understand the features and benefits of your components.

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Copy of LED Dimmer Circuit using 555 Timer - on Mon, 06/02/2025 - 12:51

Designer262780

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4 months 3 weeks

6

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Welcome to the community!!

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&nbsp;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 Low Current LED Drive using ACME AS123 - on Thu, 04/03/2025 - 15:51

Designer244467

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Copy of Low Current LED Drive using ACME AS123 - on Thu, 04/03/2025 - 15:48

Designer244467

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351

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Member of the PartQuest Explore development team.

Copy of LED Dimmer Circuit using 555 Timer - on Sat, 03/01/2025 - 20:45

Designer261632

Member for

7 months 3 weeks

5

designs

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Welcome to the community!!

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&nbsp;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 LED Dimmer Circuit using 555 Timer - on Mon, 02/10/2025 - 12:33

Designer261112

Member for

8 months 2 weeks

1

designs

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Welcome to the community!!

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&nbsp;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!

About text formats