[sdiy] 7-segment LED displays with 4511 driver chip - max current?

Jason Tribbeck jason at tribbeck.com
Sun Aug 9 11:29:33 CEST 2015

Hmm - just realised both NPIC6C595 and 596 are open-drain, so that's
probably why I'm not using it (Sunday mornings, heh?) :)

On Sun, 9 Aug 2015 at 10:18 Jason Tribbeck <jason at tribbeck.com> wrote:

> With the '595 you can shift the values in, and then tell it to transfer
> the shift register to the output register. This means you can pre-shift the
> pattern into the register, change the row, and then shift the pattern to
> the output.
> If you're clever with your design, you could make the row change and the
> output transfer use the same signal - so there would not be much in the way
> of delay. And if you're using SPI, then you could use the CS signal
> connected to the RCLK signal (which does the transfer) - it's a positive
> edge triggered input...
> Although if you are concerned about the power going through GND (or +5V),
> then I would look at the NPIC6C596, which is similar to the '596 (which is
> an open-collector version of the '595) - this is designed for higher
> current LED drives, and is functionally identical to the '596, and doesn't
> cost that much (quick look at Farnell, and the NPIC6C596 price is £0.64;
> 74HC595 is £0.43).
> Unfortunately, it's not pin-compatible (and I prefer the pin layout of the
> '596).
> And I'm using an HC595 and NPIC6C596 together in an LED matrix, so I shift
> 16 bits and then clock both at the same time - the HC595 drives a ULN2981
> for the rows, and the NPIC6C596 drives the columns directly. I will be
> bit-banging the signals, because the PIC I'm using doesn't have SPI (it's
> the smallest one I could find with a UART).
> Although there is the NPIC6C595 which is open-drain, which I've only just
> considered using for driving the rows directly...
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