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Damaged IC?

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beakie

New Member
I have an 74LS47 IC.

I connected each of the data pins.
I connected the 7 segment display's +5V and ground.
I then connected the 5V on the IC but hadn't done ground yet.

The 7 segment display lit up.

When I connect the ground and then put 5V into one of the data pins, nothing happens.

Have I screwed it?
 

dknguyen

Well-Known Member
Most Helpful Member
Why wouldn't you connect ground first on both devices before applying power to any of them?

But I'm a bit confused here. Why did the LED have a ground connection? The IC uses open collector drivers and works by connecting and disconnecting the the LED to/from ground. THe only device that should have had a connection to ground was the IC. The LED should have only been connected between +V and the IC, not ground. The "ground" on the 7 segment display is supposed to connect to the drive pins of the IC.
 
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audioguru

Well-Known Member
Most Helpful Member
A 74LS47 is designed to drive a common-anode LED 7-segment display. It will not drive a common-cathode LED display and it will not drive an LCD display.
A common-anode LED display has one pin for +5V and does not have a ground pin. If you connected an LED segment on it to +5V and to ground then the LED got burned out.

The 74LS47 will light all segments of a common-anode LED display when it has all data inputs high or floating.
 

beakie

New Member
A 74LS47 is designed to drive a common-anode LED 7-segment display.
Damn it. Checked the code on the led and Maplin gave me one with the code DC-xxxx and one with the code DA-xxxx. I used the common cathode led, hence the problem. Swapped it with the common diode and it worked fine.

Will check the parts before I leave next time, cheers.
 
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