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### Topic: how many output voltage 74hc595 ? (Read 2951 times)previous topic - next topic

#### ironheartbj18

##### May 31, 2013, 09:58 pm
if the five voltage input to vcc 74hc595. i looking at it on the datasheet page 5 of 13. i looking at DC SPECIFICATIONS "V OH"

High Level
Output Voltage
(for QA to QH
outputs)                 approximate voltage 4.5.

how many the QA to QH able output mA? i could not find the excalty output each mA.

I am trying to figure it out by using 8x8x8 matrix.

#### ironheartbj18

#1
##### May 31, 2013, 10:01 pm
p.s. data sheet link is http://pdf1.alldatasheet.net/datasheet-pdf/view/23119/STMICROELECTRONICS/M74HC595B1R.html

#### dannable

#2
##### May 31, 2013, 10:26 pm
The link to the data sheet doesn't work for me.

However, I think you are confusing voltage and current. The maximum output on pins QA-QH is ± 35 mA, but the total amount of current per device is ± 70 mA. So you will either need a transistor on each pin or consider using TPIC6B595N.
Beginners guide to using the Seeedstudio SIM900 GPRS/GSM Shield

#3
##### May 31, 2013, 10:26 pm
With a 5V supply, the 74HC595 can output 4mA and maintain ~4.5-4.8V output.  More current than that and the voltage will start dropping.
The whole part is only rated for 70mA max current flow.
A better solution is to use a high current sink shift register such as TPIC6B595 to sink current from the layers, and switch P-channel MOSFETs to provide current to each layer.
Designing & building electrical circuits for over 25 years.  Screw Shield for Mega/Due/Uno,  Bobuino with ATMega1284P, & other '328P & '1284P creations & offerings at  my website.

#### ironheartbj18

#4
##### Jun 01, 2013, 08:52 am
i am starting consider using TPIC6B595N  intead of using transistor it would be too much work on the PCH.  TPIC6B595Ns are cheaper than transistors and 74HC595.  maybe save five dollars not bad. i did not realized that.
thank you so much to dannable and crossroads!

#### fungus

#5
##### Jun 01, 2013, 12:19 pm

However, I think you are confusing voltage and current. The maximum output on pins QA-QH is ± 35 mA, but the total amount of current per device is ± 70 mA. So you will either need a transistor on each pin or consider using TPIC6B595N.

Can the TPIC6B595N ouput 5V with high current? I read the datasheet and it seemed like it could only sink it (even the pins are called "DRAINx".
No, I don't answer questions sent in private messages (but I do accept thank-you notes...)

#6
##### Jun 02, 2013, 05:46 am
TPIC6B595 only sinks current. Use a resistor from 5V to supply current.
Here's an example where the LEDs are wired up as if they were 8 LEDs in a common anode package.
Designing & building electrical circuits for over 25 years.  Screw Shield for Mega/Due/Uno,  Bobuino with ATMega1284P, & other '328P & '1284P creations & offerings at  my website.

#### ironheartbj18

#7
##### Jun 02, 2013, 06:33 am

the layer using the P CHANNEL IRF9Z24N output. once the TPIC6B595N received the sink current at row the current will go into DRAINx called N channel.

I am wondering if the P CHANNEL output with high current on 8x8x8 each layer. the led is 20mA forward voltage so 8x8 = 64 then 64 time 20mA = 1280 mA? will it effect voltage reduce? what is the best use voltage output using the P CHANNEL?

so far i know is green and blue is range 3.5 voltage for 20 mA.

#### ironheartbj18

#8
##### Jun 02, 2013, 06:36 am

TPIC6B595 only sinks current. Use a resistor from 5V to supply current.
Here's an example where the LEDs are wired up as if they were 8 LEDs in a common anode package.

that what i thought

#9
##### Jun 02, 2013, 07:01 am
5V is good for the P-channel to connect to the anodes.
You do indeed need a good power supply, 5V@ 2A would be good.
I have used this one in several projects too. Little overkill, so it will run cool, and a good price.
http://www.mpja.com/5-Volt-DC-Plug-Power-Supply-4A-Regulated/productinfo/18520%20PS/

Designing & building electrical circuits for over 25 years.  Screw Shield for Mega/Due/Uno,  Bobuino with ATMega1284P, & other '328P & '1284P creations & offerings at  my website.

#10
roger that.

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