High Current Versions of 74HC595

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Hello Guys

Is there any other high current versions of 74HC595?

There are some alternatives like TPIC6C595 but it cannot source current only sink is involved with them. I need a sourcing chip to add to my LED signboards.I do a row scan.Ex:16 Rows & 128 columns.

Is there any cheaper way of doing this?

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I love these questions.

Why not specify the current that you actually want to source?

You also might like to look at your 'design'. Would it not be easier if you 'sink' current?
Most multiplexed designs end up enabling a column and and displaying the 'dots' on the rows. This means you have a higher current on the column drivers than the row drivers.
So you will always need high current chips for the columns. Common-anodes to column sources, and cathodes to current sinks.

It all depends on your actual requirements. An outside display takes massive currents.

David.

Last Edited: Tue. Nov 2, 2010 - 09:00 AM
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74AC595?

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:D

Most lazy code writers do column scan & even in schools professors tend to teach children because of easiness. when you hit on google you get bunch of poor column scan matrix designs.

For all of my matrix designs I do row scan.My each LED needs 20mA/2V.

From my previous designs 4mA average current make my LED's light up brighter.

When it goes to 16 rows 2mA current is not enough that's where I got stucked.

Now how the values came 4mA & 2mA ??

595 can source 30-35mA maximum so for 7 rows 30/7 = 4.2mA,For 16 rows 30/16 = 1.875mA :(

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Ti tpic6595 and the other variations. Basically a uln2803 and a '595 in one package

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Kartman wrote:
Ti tpic6595 and the other variations. Basically a uln2803 and a '595 in one package

Nop that package is good for the fellows who is doing column scan.But not for the fellows who is doing row scans :)

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Allegro is producing a number of shift registers + driver,
I've been designing an A6282 into a project recently.

Jörg Wunsch

Please don't send me PMs, use email if you want to approach me personally.

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@ millwood

You mean adding some emitter followers to the outputs of the 595??

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Hi Jörg Wunsch most chips that allegro introduces available in some Europe countries & doesn't available in rest of the world.

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Quote:
Most lazy code writers do column scan

Whether you do row scans or column scans is up to you. You still end up with a limit on the currents. e.g. if you are multiplexing by 16, each dot is only getting an average of 2.18mA (35/16).
The common-ed pin is going to pass 280mA (35x8) for each '595.

I would guess that multiplexing by 16 is pushing it a bit. I would split into smaller groups. You may find it as easy to have a '595 for each group of 8.

At the end of the day, 16 columns x 16 rows is much the same as 16 rows x 16 columns. 80 columns x 16 rows is going to be easier to do one way rather than the other.

It is a design choice.

David.

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> most chips that allegro introduces available in some Europe
> countries & doesn't available in rest of the world.

Then you should probably add some hint about your location to your
profile... How would I have known you are *not* located in Europe?

Despite, the A6282 is listed at Digikey. I assumed they are also
selling outside Europe. ;-)

Jörg Wunsch

Please don't send me PMs, use email if you want to approach me personally.

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Be VERY careful with Allegro's parts. They seem to be obsoleting some parts lately and don't intend to provide a replacement. Yes I do use Allegro parts.

John Samperi

Ampertronics Pty. Ltd.

www.ampertronics.com.au

* Electronic Design * Custom Products * Contract Assembly

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Thanks for all of your comments guys.

I have created a schematic of adding some PNP’s to the output of the 74HC595.

My plan is to do a 1/16 scan rate.4mA average current makes LED’s more brighter so I need 4 X16 = 64mA source from 74HC595 side to the anodes of the LED’s.

The LED current limiting resisters ( Rl X 8 ) is a must.
But adding the base resisters ( Rb X 8 ) the pcb gets messy.Is there any transistor package with base resister inbuilt which can drive from direct logic levels??

Please suggest parts which is commonly available & cheap :D

Is this a good concept any modifications?

Attachment(s): 

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In a similar design I use Darlington transistors and a good old 74HC138 to drive the rows so all I need is 7 transistors and lots of current sinking, constant current, column driver.

John Samperi

Ampertronics Pty. Ltd.

www.ampertronics.com.au

* Electronic Design * Custom Products * Contract Assembly

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gsmicro wrote:

The LED current limiting resisters ( Rl X 8 ) is a must.
But adding the base resisters ( Rb X 8 ) the pcb gets messy.Is there any transistor package with base resister inbuilt which can drive from direct logic levels??

Search for "digital transistors" at any distributor. There are many options for less than 10 cents.

Dor

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gsmicro wrote:
Is there any transistor package with base resister inbuilt which can drive from direct logic levels??
UDN2981A?
But why not use a constant current driver as mentioned above? Then you can skip the current limiting resistors too, and even get them in the same package as the shift register.

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Hello john in my 7 rows signboard i use only 7 transistors for the row side & driving led's directly from 595 side.

May be you missed my point.I'm talking about a 16 rows display not a 7 rows one.
For 1/16 scan rate 595s output current (35ma) is not enough.Thats why i'm struggling how to boost current from 595 side.

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:D price of a UDN2981 is more than a price of a uC.

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gsmicro wrote:
:D

Most lazy code writers do column scan & even in schools professors tend to teach children because of easiness. when you hit on google you get bunch of poor column scan matrix designs.


What makes column scan "lazy"? And what differentiates a "poor" column scan design from a (presumably) "good" design?

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Quote:
I'm talking about a 16 rows display not a 7 rows one.
Use 16 transistors and 2 595??

John Samperi

Ampertronics Pty. Ltd.

www.ampertronics.com.au

* Electronic Design * Custom Products * Contract Assembly

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Hi john & millwood now you two have come closer.

Yes I'm using darlington for the row side (16 transistors).

John can you tell me what transistors you using for the column side 74HH595 ??

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I use BD140 in 2 types of displays for the ROWS (7 off). All newer modules use MIC5891/UDN2981 or similar chip for the ROWS.

The columns use constant current driver chips.

John Samperi

Ampertronics Pty. Ltd.

www.ampertronics.com.au

* Electronic Design * Custom Products * Contract Assembly

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js wrote:

The columns use constant current driver chips.

Hi I have never used this before a part number please :)

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Look for something like A6276, TLC5941, TLC59116 etc. lots and lots of them around in many different flavours. Oh yes they cost more than the micro too.. :)

John Samperi

Ampertronics Pty. Ltd.

www.ampertronics.com.au

* Electronic Design * Custom Products * Contract Assembly

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If you don't want to spend money in a constant current driver chip, you can use discrete transistors, resitors and maybe a zener. Check this site: http://www.4qdtec.com/csm.html

I've personally like the number 4 circuit. Circuits 5 to 7 are current mirrors. Don't use them, as they need matched transistors to work well. If you realy want, you can match your own transistors using this technique:

http://www.national.com/rap/Stor...

As the link in the site above is wrong, here is the new one:
http://electronicdesign.com/arti...

Felipe Maimon

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millwood wrote:
depending on what you mean by "well". but typically, with a couple of degen resistors, you can make it work well with unmatched transistors.

But now you are adding one more resistor for each row or column (depending on what gsmicro is using).

In the end, it really depends on what gsmicro wants to do.

Felipe Maimon

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Looks like you cant read... I've never said it cannot work. It just doesn't work well in the configuration displayed in those circuits.

[edit]
BTW, I won't respond to anything else you post

Felipe Maimon

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Quote:
I've personally like the number 4 circuit. Circuits 5 to 7 are current mirrors. Don't use them, as they need matched transistors to work well. If you realy want, you can match your own transistors using this technique:

Mullweed, stop putting your words into other people's mouths. You like to argue, but you should ensure you are correct before opening your mouth. Felipe referred to specific circuits and made his comments regarding these circuits. You suggested adding resistors, in which case the circuits are different and then asserted Felipe's comments were wrong. Open a can of STFU. How many times do you have to be told?

Tell us about those schottky diodes?

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So this applies here too. :? https://www.avrfreaks.net/index.p...

John Samperi

Ampertronics Pty. Ltd.

www.ampertronics.com.au

* Electronic Design * Custom Products * Contract Assembly