Using MM5316 to drive LEDs

[padler...@gmail.com]

Hi all,
I’m experiencing a strange timing problem when using an MM5316 clock chip to drive a 7-segment LED display. The clock chip drives non-multiplexed individual segments for each of the four digits for minutes, 10 minutes, hours, and 10 hours, and it is designed to drive VFDs directly. It works fine when I set it up to drive IV-12 VFDs. I’m powering the chip with about 12 vdc. But when I connect a 7-segment LED display to it using 560R voltage dropping resistors to each segment, the minutes digit advances every 30 seconds rather than 60 seconds.

Anyone have any thoughts on what might be causing this to happen?

TIA,
Randy


Sent from my iPhone

[David]

The MM5316 datasheet doesn’t say that this part is capable of driving LEDs. It is too high voltage and too low current capability. Use some other chip for that.

David Forbes, Tucson AZ

> On May 16, 2025, at 6:53 AM, padler...@gmail.com wrote:
>
> Hi all,

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[padler...@gmail.com]

Thanks, David. I used the 560R resistors to drop the supply voltage from 12v to 1.8v but I missed that the MM5316 outputs only 1.5 mA. It provides enough current to drive VFDs but it’s way too low to comfortably drive the LEDs.
Interestingly though, I had only connected the minutes LED to the chip and the LED seemed happy and the chip stayed cool. But evidently (I surmise) l the excessive current draw by the LED segments was messing up the internal timing of the chip.

Randy


> On May 16, 2025, at 12:18 PM, David <nixie...@gmail.com> wrote:
>
> The MM5316 datasheet doesn’t say that this part is capable of driving LEDs. It is too high voltage and too low current capability. Use some other chip for that.

> To view this discussion, visit https://groups.google.com/d/msgid/neonixie-l/81EF9844-5383-487A-A487-14272027B259%40gmail.com.