LED PWM Flicker

[MCU88]

You need to go back and do the test.

My moving message display 245 LED that I engineered back in 2006 does not flicker at 20Hz.

 

[audioguru]

I can shake my hand at only 20Hz. Hear the hum?

 

[ronsimpson]

My moving message display 245 LED that I engineered back in 2006 does not flicker at 20Hz.

Then you need to explain why. Or how.
Do you update the LED at 20hz but leave the LEDs on 100% of the time? It may be like the movies, 20hz update but 60hz flashes.
My advertising sign back in the 80s used multiplex LEDs at 120hz. It there was no multiplexing then 20hz is fine.

 

[MCU88]

Then you need to explain why. Or how.
Do you update the LED at 20hz but leave the LEDs on 100% of the time? It may be like the movies, 20hz update but 60hz flashes.
My advertising sign back in the 80s used multiplex LEDs at 120hz. It there was no multiplexing then 20hz is fine.

Project that I did back in 2006: https://www.picbasic.co.uk/forum/showthread.php?t=6033
I no longer use the BASIC language today I use C. ~2.5% duty cycle. Multiplexed. 8 rows driven from and buffered from MCU. Cascaded decade counters clocked by the MCU to drive the columns. 24LC256 EEPROM to store messages. One character at a time retrieved from EEPROM and shown on display. With all characters loaded the display scrolled from left to right or right to left (user defined option in Windows software to upload messages. All 245 LEDs switched on & off at a rate of about 20Hz with an duty cycle of 2.5% per column. The project worked nicely and was going to be published in an magazine.

 

[Tony Stewart]

Again, unless you specify some application, the degree of flicker is inverse with frequency and with higher sensitivity for rapid lateral peripheral vision.threshold.

With 5 kHz , and certainly at 50 kHz at automotive speeds, you are unlikely to detect any flicker. ( but 500Hz was noticeable in Cadillac Brake LEDs)

https://www.onsemi.com/pub_link/Collateral/CAT4101-D.PDF This chip supports 5kHz down to 1% PWM and 50-KHz down to 10% without an inductor. which is more expensive than the zxld1360.

Your choice.

 

[ronsimpson]

zxld1360

Have used them. There is no flicker. The LED current is continuous.

 

[Tony Stewart]

Have used them. There is no flicker. The LED current is continuous.

If you check again, I don't disagree, but if cost is an issue in volume, the continuous current effects of the choke are offset by the $1.5 additional price tag but for a cheaper chip, it is probably a wash.

But for "continuous" constant current rather than "discontinuous" constant current I agree , zxld1360 from Diodes Inc is a great choice.

Also probably a more reliable solution than have high A peak currents from a smoothing capacitor at some duty cycle to provide 1A continuous with PWM.

 

[Tony Stewart]

My moving message display 245 LED that I engineered back in 2006 does not flicker at 20Hz.

The eye has persistence when the object or eye does not move, so everyone's perception depends on the test conditions & criteria.

There are also longer term effects. Just stare a a bright Yellow LED and watch it change colour, then view the sky for a ghosted complimentary colour dot.

 

[MCU88]

The eye has persistence when the object or eye does not move, so everyone's perception depends on the test conditions & criteria.

There are also longer term effects. Just stare a a bright Yellow LED and watch it change colour, then view the sky for a ghosted complimentary colour dot.

I agree that 20Hz is not the best, but unfortunately with my project there is time taken to read from the serial EEPROM. Usually, however, though -- when I multiplex displays I will scan the columns / digits as fast as possible. Another project I have made which uses multiplexing to deal with 4 digit 7-segment displays runs much faster than 20Hz (I do not know the scan rate but it is probably several KHz: