Datasheet help

Discussion in 'General Electronics Chat' started by matty204359, Apr 6, 2011.

  1. matty204359

    Thread Starter Member

    Apr 6, 2011
    105
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    First of all, hello everybody, I'm new to this forum and new to the world of electronics. I could use some help with a specific IC CD4050 Hex Buffer/Converter (non-inverting type) More specifically TC4050BP. I was able to track down the DATASHEET
    for this IC. I need to know how much current this IC can source on its output pins.


    Details below, question above^^^

    ***Originally I bought the IC for a digital clock project in case I needed to switch from CMOS to TTL signals however, I've not needed it for that use and probably never will. I'm currently working on a LED matrix which I hastily purchased some 74HC595 shift registers for but, having examined their data sheets I have come to realize that it cannot source enough current for my LEDs should all 8 need to be turned on at one time. So I was thinking maybe the Buffer might be able to source enough current for this application. I'm strictly a hobbyist and have no formal education so please try not to confuse me too much :p ***
     
  2. BillB3857

    Senior Member

    Feb 28, 2009
    2,400
    348
    See page 3 of the datasheet you linked.
     
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  3. matty204359

    Thread Starter Member

    Apr 6, 2011
    105
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    :confused: I read the data sheet a few times already but, unfortunately I'm not quite sure what many of its specifications mean. Should I be looking at the Output high current or Output low current? What I don't understand is how can the numbers be negative. does this IC also sink current? Perhaps a more direct question would be more helpful. Can this IC be used to power LEDs? I also have some 2n3904 npn transistors would that be a better solution?
     
    Last edited: Apr 6, 2011
  4. BillB3857

    Senior Member

    Feb 28, 2009
    2,400
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    If you look at the equivalent circuit, you will see two Field Effect Transistors in series. The upper FET will tend to pull the output voltage toward Vdd for a Hi output and the lower FET will tend to pull the output toward ground for a Lo output. The current ratings indicate the safe level that these individual FETs can handle for a given Vdd.. From the datasheet, with a Vdd of 15v, you should be able to drive a series string of LEDs (with a current limit resistor sized properly) with ease, if you use the Lo output mode. The datasheet says at 25 degrees C, which is about room temperature, the Minimum current capability is 24ma and the Typical capability is 48ma. Obviously, if your Vdd is less than 15v, you would need to use the appropriate line on the chart to see what currents the device can handle.

    Since you are talking about driving LEDs, do you know how to determine the resistor value needed?
     
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  5. matty204359

    Thread Starter Member

    Apr 6, 2011
    105
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    Thanks for the reply Bill, as a matter of fact I don't know the formula for led resistor ratings, It would appear I still have much to learn. The smell of burnt out transistors, LEDs and IC's is no stranger to me. I'm more of the hands on learning type.


    Based off of a resistor calculator I found on Google I bought some 470 ohm resistors for my green LEDS

    (1.9 V forward voltage 7.5 mA forward current)

    but, I just recently bought some red LEDs for my led matrix which according to the suppliers web site the specifications are (no datasheet is available):

    Forward Voltage: 1.8~2.6V
    Current Rating: 20mA

    I've been using my Arduino (micro-controller platform) 5 volt supply with the 470 ohm resistors on the red leds.

    My LED matrix is going to be 8 columns common-anode controlled by 74HC595 by 6 rows common-cathode controlled by a CD4017 ring counter.

    Would you like me to draw up a schematic to better visualize the situation? I would rather not burn out my Arduino...or my computers usb port :eek:
     
  6. Audioguru

    New Member

    Dec 20, 2007
    9,411
    896
    Don't look at a Japanese datasheet for an American IC.
    Instead look at the CD4050 Texas Instruments datasheet that has a lot more details (because they don't need to translate it).
    They show graphs of the typical output current when sinking or sourcing with supply voltages of 5V, 10V and 15V and with any amount of output voltage from zero to the supply voltage.

    With a 10V supply, it can power a 3.5V blue LED without a current-limiting resistor and produce a current of typically 27mA. It will be pretty warm powering six LEDs.
     
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  7. Maged A. Mohamed

    Member

    Apr 6, 2011
    18
    1
    Most CMOS chips can source and sink current, the current value may differ, unlike TTL family which is current sinking.
     
  8. Audioguru

    New Member

    Dec 20, 2007
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    The graph I posted for the output sourcing current of the CD4050 IC is when its output is high. The negative numbers are the output voltage and current down from the positive supply voltage.

    The datasheet has another graph showing its output sinking current which is much higher than the amount of sourcing current. It shows positive numbers that are the output voltage and current up from ground.
     
  9. matty204359

    Thread Starter Member

    Apr 6, 2011
    105
    3
    I just thought the manufacture would have the most relevant data. Would the Toshiba be a drop-in replacement for a Texas Instruments CD4050?
     
  10. Audioguru

    New Member

    Dec 20, 2007
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    American CD4050 ICs made by many manufacturers even European ones are registered to all have exactly the same spec's. Toshiba changed the part number and their Engrish is not very good so I doubt that it has the same spec's.
    Compare the datasheets yourself.
     
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