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Sourcing 15vdc using an IC array

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johncouture

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THE QUESTION:

Is there an inexpensive (<$2) DIP IC similar
to the ULN2803 that will allow me to SOURCE
15VDC on the top side, and switch that 15vdc
between four LED banks using a 5vdc pin from
a MCU?

PROBLEM:
I am trying to light up a 4" high, four digit,
7 segment common anode display using a
microcontroller (i.e. a PIC).

The BCEF segments have 5 LED's each
and the ADG segments have 4 LED's each.
Thus, they take more than the typical 5VDC.

SUCCESSFUL TEST:
I am currently successful with a ULN2803 for
the cathode segments but I have to use eight
transistors on the anode side to source the
15vdc to select the digits using a pin
from a MCU (max 5vdc, 20mA) pin.

What I am looking for is an IC that is an
array of transistors configured so that I
can SOURCE the 15vdc.

Schematic attached.
 

Attachments

  • 4inchLEDdisplay.pdf
    13.1 KB · Views: 116
Udn2981 is a high side driver.
Why are you driving both sides of the LEDs?
 
Last edited:
Sounds like you are looking for a "high side driver array". An MIC2981 or MIC2982 will source up to 50V at 500ma, so should do the job nicely. You want to have some sort of current limiting resistor on the series LED chain. What you have now could send ANY amount of current through the leds.
 
Last edited:
> 4pyros

Thank you for the info. That looks like it will do the trick. The reason for switching both sides of the LEDs is that the display is wired such that you have to put neg on a specific pin for a specific segment. To select the digit, you have to put pos on another specific pin. The display does not have any intelligence in it (of course you could say I don't either for not finding a solution!) and thus I was trying to figure out a way to control the string of LEDs in each segment. In my searching I found lots of chips that could handle a normal 5vdc but none that could handle anything like 14v. Thanks again for the info, I'll order some from Jameco and test them out.
 
> duffy

Thank you. Yea you are right. I actually had a limiting resistor in there but forgot to include it in the schematic. The MIC2981 looks promising also although Jameco apparently does not stock them. The internal structure almost looks identical to the udn2981 and Jameco has some of those so I think I'll try that first.

I ended up getting a couple of the 4" displays for a reasonable price and am itching to do something useful with them like make a big clock or something!

Thanks again guys for helping me out.
 
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