1. LS is a low-power Schottky, and HC is a high-speed COMS. The LS is slightly faster than the HC. HCT input and output are compatible with LS, but low power consumption; F is a high-speed Schottky circuit.
2. LS is TTL level, HC is COMS level.
3. LS input open circuit is high level, HC input is not allowed to open circuit, HC generally requires a pull-up and pull-down resistor to determine the level when the input terminal is invalid. LS does not have this requirement.
4. The LS output pull-down is strong and the pull-up is weak, and the HC pull-up and pull-down are the same.
5. The working voltage is different, LS can only use 5V, and HC is generally 2V to 6V; while the working voltage of HCT is generally 4.5V~5.5V.
6.The level is different. LS is TTL level, its low level and high level are 0.8V and 2.4V respectively, while CMOS is 0.3V and 3.6V respectively when the operating voltage is 5V, so CMOS can drive TTL, but not vice versa.
8. CMOS devices have poor anti-static ability and are prone to latching problems, so the input pins of CMOS cannot be directly connected to the power supply.
In recent years, the 74 series of high-speed CMOS circuits has also appeared, which can be divided into three categories:
- HC is COMS working level
- HCT is TTL working level, can be used interchangeably with 74LS series
- HCU is suitable for unbuffered stage CMOS circuits
These 9 kinds of 74 series products, as long as the labels behind are the same, their logic functions and pin arrangements are the same. Different types of 74 series products can be selected according to different conditions and requirements. For example, if the power supply voltage of the circuit is 3V, 74HC series products should be selected.
Series Level Typical Propagation Delay ns Maximum Drive Current (-loh/Lol)mA
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