LED | PartQuest™ Explore

Copy of LED Dimmer Circuit using 555 Timer - on Thu, 08/06/2020 - 15:40

Designer233699

Member for

5 years 2 months

0

designs

1

groups

Add a bio to your profile to share information about yourself with other SystemVision users.

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 (light-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 (purple waveform) are shown just before and after the duty-cycle transition.

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

http://www.555-timer-circuits.com/led-dimmer.html

That original circuit is actually incorrect, one of the diodes 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

Copy of Joule Thief Transformer Physical Design For LED Lighting - on Thu, 07/30/2020 - 16:46

Designer230465

Member for

5 years 7 months

10

designs

1

groups

Add a bio to your profile to share information about yourself with other SystemVision users.

Description

About text formats

Copy of Joule Thief Transformer Physical Design For LED Lighting - on Tue, 07/21/2020 - 11:25

Designer230091

Member for

5 years 7 months

7

designs

1

groups

Add a bio to your profile to share information about yourself with other SystemVision users.

Description

About text formats

Copy of Joule Thief Transformer Physical Design For LED Lighting - on Thu, 07/16/2020 - 06:08

Designer221446

Member for

6 years 2 months

6

designs

1

groups

Add a bio to your profile to share information about yourself with other SystemVision users.

Description

About text formats

Copy of LED Driver with Auto-Dimming for Thermal Protection - on Fri, 06/19/2020 - 14:27

Designer208121

Member for

6 years 10 months

113

designs

1

groups

Add a bio to your profile to share information about yourself with other SystemVision users.

Description

This LED lighting example demonstrates the value of simulating both the electrical and thermal* aspects of power dissipating circuits together, simultaneously.

In this application example, a Vishay NTCS0603 Thermistor provides feedback of the enclosure temperature. This feedback is used to control PWM dimming of the LEDs, thereby limiting the internal temperature when operating at high external ambient temperature conditions.

This is a "Live" design, the user can change key parameter values and then run new simulations to see the results. These parameters include "r_mirror", the resistance of the current mirror that controls the capacitor charging rate of the 555 timer, and thereby set the PWM frequency. The user can also change "r_offset" that controls the temperature level at which the dimming operation begins. Finally, the user can set "r_iLED_set", to control the ON-state operating current of the LEDs.

----------------

* To reduce the time needed to simulate the transition and settling at 6 different temperature levels, all thermal time constants were reduced by approximately 1000x. The actual thermal response time constant of the NTCS0603 is approximately 3 seconds (depends on mounting), not 3 msec! Also, the enclosure thermal capacitance value would more likely be 3 (J/degC) instead of 3 (mJ/degC), giving a thermal time constant for the enclosure of 10 (degC/Watt) * 3 (J/degC) = 30 seconds. This time scaling does not affect the static relationship between the outside temperature and PWM dimming.

About text formats

Copy of LED Dimmer Circuit using 555 Timer - on Thu, 06/11/2020 - 19:05

Designer230321

Member for

5 years 7 months

56

designs

2

groups

Add a bio to your profile to share information about yourself with other SystemVision users.

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 (light-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 (purple waveform) are shown just before and after the duty-cycle transition.

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

http://www.555-timer-circuits.com/led-dimmer.html

That original circuit is actually incorrect, one of the diodes 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

Copy of LED Dimmer Circuit using 555 Timer - on Wed, 06/03/2020 - 10:53

Designer211531

Member for

6 years 8 months

9

designs

1

groups

Add a bio to your profile to share information about yourself with other SystemVision users.

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 (light-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 (purple waveform) are shown just before and after the duty-cycle transition.

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

http://www.555-timer-circuits.com/led-dimmer.html

That original circuit is actually incorrect, one of the diodes 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

Copy of LED Dimmer Circuit using 555 Timer - on Fri, 05/08/2020 - 17:00

Designer231681

Member for

5 years 5 months

4

designs

1

groups

Add a bio to your profile to share information about yourself with other SystemVision users.

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 (light-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 (purple waveform) are shown just before and after the duty-cycle transition.

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

http://www.555-timer-circuits.com/led-dimmer.html

That original circuit is actually incorrect, one of the diodes 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

Copy of LED Dimmer Circuit using 555 Timer - on Sun, 05/03/2020 - 14:48

Designer229892

Member for

5 years 8 months

8

designs

1

groups

Add a bio to your profile to share information about yourself with other SystemVision users.

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 (light-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 (purple waveform) are shown just before and after the duty-cycle transition.

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

http://www.555-timer-circuits.com/led-dimmer.html

That original circuit is actually incorrect, one of the diodes 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

Copy of LED Dimmer Circuit using 555 Timer - on Thu, 04/23/2020 - 02:06

Designer230378

Member for

5 years 7 months

11

designs

1

groups

Add a bio to your profile to share information about yourself with other SystemVision users.

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 (light-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 (purple waveform) are shown just before and after the duty-cycle transition.

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

http://www.555-timer-circuits.com/led-dimmer.html

That original circuit is actually incorrect, one of the diodes 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

Troubleshooting Terms of Use Cookie Notice Data Privacy Notice