Author Topic: Parallel input/output constant current sink driver  (Read 619 times)

0 Members and 1 Guest are viewing this topic.

Offline galvanixTopic starter

  • Contributor
  • Posts: 38
  • Country: de
Parallel input/output constant current sink driver
« on: June 03, 2020, 07:09:52 pm »
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!
 

Offline Benta

  • Super Contributor
  • ***
  • Posts: 6420
  • Country: de
Re: Parallel input/output constant current sink driver
« Reply #1 on: June 03, 2020, 07:34:50 pm »
Check Toshiba. They have a broad portfolio of constant-current LED drivers.

 

Offline galvanixTopic starter

  • Contributor
  • Posts: 38
  • Country: de
Re: Parallel input/output constant current sink driver
« Reply #2 on: June 04, 2020, 06:01:37 am »
Check Toshiba. They have a broad portfolio of constant-current LED drivers.



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?
« Last Edit: June 04, 2020, 08:14:18 pm by galvanix »
 


Share me

Digg  Facebook  SlashDot  Delicious  Technorati  Twitter  Google  Yahoo
Smf