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Friday, 20 June 2014

What does HC and LS in 74HCxxx and 74LSxxx Indicates ?

by realfinetime  |  in TTL at  00:12

For a long period, after I had started my electronics carreer, I was not aware about the importance of HC and LS in IC names ( Eg : 74HC595  and 74LS595 ). But nowadays I felt some problems in my circuit. I purchased these ICs without specifying the category HC or LS. I think this may be the problem.

Then I searched for the difference between 74HC chips and 74LS chips. Then I found that 74LS chips are made of bipolar transistors ( TTL) and there is a pull up resistor at the input. But 74HC chips are made of CMOS transistors and there is no resistance at the input. In an electronic circuit, all the components must be either LS or HC. Combination of HC and LS in the same circuit will result in Voltage level difference and the circuit will not work properly.


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