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Parallel input/output constant current sink driver
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galvanix:
Hello!
I'm currently working on a 7-segment LED clock and am looking for a constant current LED sink driver, ideally something like a ULN280A with constant current outputs.
The seven segment displays I have are rather large (HDSP-C2L1) and have a max. forward voltage of around 9.2V according to the datasheet, which is why I would prefer constant current control over adding series resistors for every segment.
The main feature of this clock is that it doesn't have a microcontroller, it's just a bunch of 74HC390s and 74HC08s for the counting stage.
This is also the reason I don't want to use the usual culprits from TI because those all require a digital interface.
The output of the counters is fed into 74HC4511s for BCD-to-7-segment decoding.
The display brightness control uses a 74HC393 with an R-2R-DAC and a comparator to generate a PWM signal. The other half of the 74HC393 is used together with a 3-to-8 line decoder for multiplexing the displays by enabling them sequentially.
The clock source is the 50 Hz mains frequency from a AC/AC wall-wart adapter.
Because of the way that I want the finished product to look I don't want to deal with 230VAC on the board itself.
TL;DR: Looking for a ULN2803A replacement with constant current sink outputs.
Any ideas?
Thanks!
Benta:
Check Toshiba. They have a broad portfolio of constant-current LED drivers.
galvanix:
--- Quote from: Benta on June 03, 2020, 07:34:50 pm ---Check Toshiba. They have a broad portfolio of constant-current LED drivers.
--- End quote ---
Thanks for the suggestion, alas all of the stuff I can find are serial input devices (shift registers with constant current outputs).
Edit:
Okay so I've been thinking about this all day but haven't made any progress. Say I wanted to use something like an ST STP08DP05, how would I get the data from the 74HC5411 into that one?
I've been playing around with the idea of using a 74HC165 parallel input serial output shift register to convert to serial and then use a ripple counter to count the 8 clock cycles it takes for a single transfer and then stop it based on that.
How would I trigger the start of a transfer after one of my other counters in the counter chain rolls over?
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