Driver to control ground connection like a shift register - Page 1
Forum section: electronics / general

author: FlevasGR
author_rank: Regular Contributor
timestamp: April 21, 2015, 10:07:51 pm
content: Hello,the last few days i'm playing arround with my 74HC595 Shift registers controled by an arduino board. They're very nice and esy to use however the problem with shift registers is that they are the ones who gives the current. Unline common anode led display drivers which only supply the ground connection those need to give the positive connection. So my question is this, like the TIP120 which only closes the circuit is there anything like this which only provides the ground connection instead of giving the power?

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: April 21, 2015, 10:17:04 pm
content: tpic6b595 and tpic6c595 - like 74HC595 but with open-drain power drivers

author: senso
author_rank: Frequent Contributor
timestamp: April 21, 2015, 11:10:54 pm
content: tpic6b595 are what you want, I used a couple of them(16) to make a digital gas station electronic price portal, pretty good back them, still working today after years of hot and cold weather.

author: FlevasGR
author_rank: Regular Contributor
timestamp: April 22, 2015, 02:08:52 am
content: Thanks for the advice. I bought few from eBay

author: Muxr
author_rank: Super Contributor
timestamp: April 22, 2015, 04:21:10 am
content: I would just like to add, this is also often called current sinking. Might help your google searching in the future.

author: David_AVD
author_rank: Super Contributor
timestamp: April 22, 2015, 07:57:39 am
content: Quote from: mikeselectricstuff on April 21, 2015, 10:17:04 pmI take it that they can take the place of a 74HC595 and ULN2803 for example with no code changes?

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: April 22, 2015, 08:47:05 am
content: Quote from: David_AVD on April 22, 2015, 07:57:39 amYes. And it will be better than the ULN as the TPICs have MOSFET outputs, so you don't get the voltage drop of the darlingtons.

author: David_AVD
author_rank: Super Contributor
timestamp: April 22, 2015, 09:07:58 am
content: Thanks for that.The TPIC6C595 looks like an ideal replacement for a 7 segment board I'm revising (converting to SMD) at the moment.Each segment only draws about 10mA with a 24V rail, so well within the ratings.

author: westfw
author_rank: Super Contributor
timestamp: April 22, 2015, 09:58:16 am
content: A 74hc595 has outputs that will both source and sink current. They can't sink ENOUGH current to provide gnd for all 7 segments of a common cathode display, but they're fine for signing current from one segment of a common anode display.The other drivers people have been mentioning are for higher current, but they are sink-only, usually.

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: April 22, 2015, 10:02:35 am
content: Quote from: David_AVD on April 22, 2015, 09:07:58 amYou may also want to look at LED driver chips, typically 16 channels with constant-current outputs, so you don't need resistors.

author: David_AVD
author_rank: Super Contributor
timestamp: April 22, 2015, 11:01:41 am
content: Quote from: mikeselectricstuff on April 22, 2015, 10:02:35 amAre there any with the same '595 type control though? I'd like the new board to be compatible with the existing '595 data stream.

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: April 22, 2015, 12:42:53 pm
content: Quote from: David_AVD on April 22, 2015, 11:01:41 amGenerally yes (usually 16 channels so like two 595's)

author: BloodyCactus
author_rank: Frequent Contributor
timestamp: April 22, 2015, 12:48:31 pm
content: you can use the MBI5026 (5v) and the WS2803 (5v or 3.3v) chips as shift registers, they each are cc led drivers.MBI chip does 5 to 90mA @ 5V supply voltage on each of its 16 pins. ws2803 does 5-20ma at 3.3v or 5-30m at 5v.ws2803 has 18 outputs, and does pwm internally so you need to pump 144 bits to the chip, 8 bits greyscale per LED. from memroy (some time ago since I used the MBI chip), the mbi is just 1 bit per led, on/off only, you need to do your own pwm if you need to.both chips are just clk/data and can daisy chain them like 595's.

author: FlevasGR
author_rank: Regular Contributor
timestamp: April 22, 2015, 02:36:38 pm
content: Quote from: mikeselectricstuff on April 22, 2015, 10:02:35 amI also bought the Maxim MAX drivers

author: Muxr
author_rank: Super Contributor
timestamp: April 22, 2015, 02:42:46 pm
content: Mikeselectricstuff also recommended a MBI5031 in one of his videos:http://radiodetali.com/pdf/macroblock/MBI5031%20Datasheet%20VA.00-English.pdfI ordered some but it's still on a slow boat from China.

author: David_AVD
author_rank: Super Contributor
timestamp: April 22, 2015, 09:22:48 pm
content: The MBI5026 looks interesting although the 5mA min current is right at the limit for some of the LED colours I'll be using. The LEDs are very efficient and I think I'm actually running some at about 3-4mA.I see the limit on output voltage is 17V, so with a 24V LED rail is the LED string Vf enough to keep it happy?Digikey and Mouser don't seem to sell it either, but I assume it's readily available from other sources?I might stick with the TPIC device and resistors as some of the display boards have an indicator (different current on the 8th bit) in addition to the 7 segments.

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: April 22, 2015, 09:36:52 pm
content: Macroblock are chap but hard to find. For non-greyscale applications there are a number of devices, many of which have the same pinout.e.g. TI TLC59282