please help regarding volatage and current requirement for 25 shift register

Good day to all,

I am working on a personal project to control high power led in my garden, which require 200 high power led. I working in phase manner. I successes in controlling the 8 LEDs using sn74hc595 and uln2803alg ic and later I wired 5 sn74hc595 and uln2803alg that too I succeed,

now I want to add 25 sn74hc595 on one circuit board and 25 uln2803alg one on other and connect using individual connectors. (This to reduce distance between shift register to minimise noise add on)

So as mentioned above I want some guidance regarding powering 25 shift register voltage and current. I have decoupling 0.1 uf for each shift register.

Can I drive all shift register using 5v 800mA dc power. This only to power shift register 25 unit board only. Please help

Thanking you

Hi, See This Page and scroll to 74HC595

Download the data sheet and you'll see the Max supply current is 70 mA.

So 25 * .07 = 1.75 Amps max. In practice it MIGHT be less. But you'd need to measure it on your existing examples.

There are some nice one-chip shift registers with high output current and that might be a good solution...

The shift registers themselves require very little current to operate. The question really is: How many LEDs per shift register will be turned on at one time, and how much current will each of them require? 595's can source/sink a good deal per pin, but the total current the device can source/sink is far less than 8x the per-pin maximum. You should spend some time with the 595 datasheet and make sure you're operating with its constraints.

Getting some idea thanks

but I have two boards one with shift register and other with uln2803 chips, I want to have a clean noise free shifting. I will use external power to uln chips to drive LEDs.

So as per terry King can I use 3 volt 1.5 amp to drive my shift register board.

Thanks again

"high power led " Please explain more. High power LEDs usually need a current controlled driver per LED to keep the LEDs from getting too hot and going into thermal runaway, drawing even more current, and burning up.

You can use TPIC6A595, TPIC6B595, TPIC6C595 with 350mA, 150mA, and 100ma output sink capability per output for LEDs that don't need current limiting beyond a series resistor. Control them just like 74HC595, and you don't need the ULN buffers after the chip. I also offer a board with 4 shift registers and 32 AOI514 open drain, high current MOSFETs. Might be what you need. http://www.crossroadsfencing.com/BobuinoRev17/ |500x453

So as per terry King can I use 3 volt 1.5 amp to drive my shift register board.

3V? Do you mean 5V?? 1.5 Amps is less than the "Max" the data sheet shows (1.75A) but it's probably fine.

There are many 5V 2A supplies around for $2 or so...

Thanks Crossroad,

I brought 30 shift register and uln chips, the mosfet boards great but I haved plan to use shift register to avoid noise problem and voltage drop in signal when i connect 25 of shift register together and individual connector to connect the uln chips on the other board.

I want to use it as a multipurpose controller. In future I may connect relays, instead of LEDs

I will replace the uln chip with. MOSFET later but I am more concerned about shift register board. I will be using buffer non inverting ic cd4050 in between 10 shift register.

Why I am concerned is that I am planning a circuit board using expresspcb and make a PCb and I don't want to make a mistake.

Should I use current limiting diode or resistor to pair of shift register for input current.

What voltage and current should I use, please provide a calculation of voltage and current so in future if I need to add another 25 I many do so.

Thanks terry king

I have another board with 9 of TPIC6B595, and have daisy chained 5 together for 45 shift registers total. Clocked data in at 8MHz using SPI with clock divisor at 2. Need a good ground plane, top & bottom, to handle the current coming back.

Here's another board I offer with up to 12 TPIC6B595, I've daisy chained two together to run a large display, video clip below, and others have daisy chained 3-4. Bring power out to the LEDs separately, just run the cathode from the strips back thru the board. |500x455 http://www.crossroadsfencing.com/BobuinoRev17/Prototype_in_action.MOV Movie clip

Do you have a link to the LEDs yet? ExpressPCB is terrible for laying out cards. Poor rubberbanding, mechanical footprints need to be manually linked to schematic symbols. I did one design like that for a board, then switched to Eagle. It's good for capturing a schematic and then laying out a board you plan you plan to wirewrap up.

Thanks for the product, that's what I was thinking about.

The reason I am using 595 is that I have bunch of them with me and also locally available at cheap price.

My concern is about frying the board of 595 if I power all 25 shift register with 5 volt 2 amp power supply. Do I need to add resistor or diode to limit current at each or bunch of shift register to protect from current supplied. Please advice