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74LS245 faulty?

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mstechca

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I just made a PCB for my new programmer, chedked the IC's pinouts, and according to logical thinking, the circuit works.

When I tested it with 5V, the 74LS245 was heating up, and the remaining chips did not heat up at all. This makes me think that there is something wrong with the 74LS245.

I make a ridiculously simple circuit (on a breadboard) with the 74LS245 using these connections:

Pin 19 to ground
Pin 10 to ground
Pin 20 to +5VDC
Pin 11 to +5VDC
Pin 2 to LED, LED to 470 ohm pull-down resistor.

I first connected pin 1 to ground, and then a few minutes later, connected it to +5VDC (ground and +5VDC are not connected together).

The LED indicates that the chip is working, but the chip is hot.

Is it just this particular chip?

I don't have these problems with other 74 series chips.
 
Hi MStechca,
Sure it gets very warm, it is an old TTL logic IC. Just think about how much hotter it would be if it wasn't an "LS" IC.

It shoudn't be hot with your small load, just very warm.
Maybe it is oscillating because it doesn't have a 0.1uF supply bypass cap very close to its supply pins.
Maybe it is oscillating because you didn't ground its unused inputs.

Didn't you see its datasheet? The thingy draws up to 95mA whether it is doing anything or not. That's nearly 1/2W.
 

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I have several 74LS245 chips in a circuit I built, and they DO get hotter than the rest of the chips, but seem to work just fine. I too thought I had a problem with them at first. You might try one of the newer variants HCT or AC-ACT and see if they run cooler.
Dialtone
 
A 74HC245 (and HCT) Cmos IC draws zero supply current at idle, and nearly nothing extra when driving an LED through a 470 ohm resistor. :lol:
 
so I guess I should dump the LS (large sinker?) version and always choose HC or HCT for digital work.
 
:lol: :lol: He, he. The "L" in LS stands for "low power". He, he. :lol: :lol:

You might need the fairly high output current when low, of an LS TTL IC, since the Cmos chips don't have much output current.

Except for Schmitt trigger input logic ICs, HC Cmos logic has a limit of 1us rise/fall time for slowly changing inputs. If inputs change slower, then maybe they oscillate or have a high current from the supply to ground through their totem-pole outputs. :lol:
 
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