Copy pasted from 7400-series integrated circuits - Wikipedia * Bipolar74 – Standard TTL. The 74HCT family is a special version of 74HC with 74LS TTL-compatible inputs so 74HCT can be safely mixed with 74LS in the same system. The 74HC family of logic devices are high speed, low power devices that use CMOS circuitry. Choose one or the other, not both, for your "practical" project builds. Y'mean comparing new 74LS? * 2V to 6V operation * Very high impedance inputs * Can sink and source approx. G. ghall426 New Member. Now people are telling me that the 74HC series might be a better choice. The following is a list of 7400-series digital logic integrated circuits.In the mid-1960s, the original 7400-series integrated circuits were introduced by Texas Instruments with the prefix "SN" to create the name SN74xx. But I need some help figuring this out. Google "74hc vs 74ls" for some informative links.Basically, as @kellys_eye said, they are functionally and logically identical. 74LS is bipolar transistor TTL. 74HCT (74HC + TTL) is compatible (within the limits of the power supply specs). When I started working with ICs, the 74LS series was common. the original logic familyhad no letters between the "74" and the part number. As you can also see, the 74HC can source and sink up to 15mA more than that of the 4000 series, which also means that it (74HC) is better at sourcing and sinking current as compared to the 4000 series. The 74HC consumption is considered to be more than that of the 74LS series, which means it can be used in higher amperage applications. The 74HCT family is a special version of 74HC with 74LS TTL-compatible inputs so 74HCT can be safely mixed with 74LS in the same system. Compare and contrast the 7400 series and 4000 series logic familes with reference to at least 5 characteristics e.g. The HCT output can source and sink 20mA while that of 74LS can only sink 16mA but source 2mA. 20mA * Large fan-out capability Wouldn't think there's a difference... 74HC and HCT are compatible, HCT being fully compatible and HC being HC-output to TTL-input compatible (and TTL-output to HC-input compatible with a pull-up resistor, if you don't mind it being slow; but HCT is better to just drop in). And there is the 74HCT series which is a near replacement for the 74LS series. Working voltage, maximum frequency, threshold voltage for ones and zeros, fan-in, fan-out, power consumption. The high and low logic levels of 74HCT have been tweaked to match TTL where (with Vcc=5V), high is around 2.4V and low is around 0.4V. The 74LSxxx series is low-power Schottky and the 74HSxxx series is high-speed CMOS. 74LS Series of High Speed, TTL Logic Gate Chips including AND, OR, NAND Gates as well as counters, shift registers and multiplexers. The devices are pin compatible with many existing devices such as the 74TTL, 74STTL and 4000 series. However, it is a bit slower than 74LS (25MHz vs 35MHz). 10 ns gate delay, 10 mW dissipation, 4.75–5.25 V, released in 1966. A 74LS output cannot reliably drive a 4000 or 74HC input unless a 'pull-up' resistor of 2.2k is connected between the +5V supply and the input to correct the slightly different logic voltage ranges used. 74LS Series. A circuit which includes 74LS or 74HCT ICs must have a 5V supply. HC and HCT have identical outputs. Note that 74HC inputs cannot be reliably driven by 74LS outputs because the voltage ranges used for logic 0 are not quite compatible, use 74HCT instead. Note that 74HC inputs cannot be reliably driven by 74LS outputs because the voltage ranges used for logic 0 are not quite compatible, use 74HCT instead. Note that a 4000 series output can drive only one 74LS … 74LS vs 74HC vs 74HCT Page history last edited by Wayne Warthen 1 year, 7 months ago. L.Chung. The two types can be mixed in the same circuitry ONLY IF you know what you are doing, which you obviously do not. OK, this probably needs to be moved to somewhere more appropriate. Both works on 5V only but HCT use 1/1000 of the power that 74LS does.