SN54/74LS • SN54/74LS • SN54/74LS DC CHARACTERISTICS OVER OPERATING TEMPERATURE RANGE (unless otherwise specified). S. b l. P. 74LS Octal Buffers AND LINE Drivers WITH 3-state Outputs SN74S, SN74S OCTAL BUFFERS Details, datasheet, quote on part number: 74LS Texas Instruments 74LS Buffers & Line Drivers are available at Mouser Electronics. Mouser offers inventory, pricing, & datasheets for Texas Instruments .

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Your explanation “two input are high” sounds more adtasheet the definition of an AND gate. I’ve done quite a lot of research since first writing this answer, and with unpowered 74LS devices and an input voltage between 0 V and 5. But I thought gate like those didn’t need to be protected. This is clearly what I am expecting.

SE topics where powering devices via other pins, instead of the power pins, caused unexpected behaviour: Therefore it is also no surprise that when you did connect datashert 17 and 19 to Vcc, the LED stayed lit. So your first tests were done without any power connected to the Vcc pin!

From what I read, if two input are high on a buffer, then the output will be high. This will also cause behaviour which is different from the behaviour when correct power is connected.

(PDF) 74LS241 Datasheet download

Pull pin 19 high, and the output will follow the input 17 and either the green or the red LED will glow brightly; the other one will be off. Pins 1 and 19 of the LS control this state for the buffers inside the chip. I have put a led on the 3 output pin, in order to test the output.


So here is what I did: Home Questions Tags Users Unanswered. Although it is not “best practice” to do this, unconnected LS TTL inputs will usually float high, as PeterBennet has already kindly explained.

Another issue I’ve observed is parts that behave datzsheet though pairs of pins are connected via PNP transistor, such that excessive voltage on one will cause the device to source current into the adjacent pin.

I don’t use the two G inputs at the same time. I have the feeling that I have understood the schematic, but the fact is this is not working.

74LS 데이터시트(PDF) – Motorola, Inc

A tristrate output can have 3 different states: Dxtasheet 74LS or any 74LS family part will normally see an unconnected input as a High – you need to connect inputs directly to Ground to input a Low. Sign up or log in Sign up using Google. By clicking “Post Your Answer”, you acknowledge that you have read our updated terms of serviceprivacy policy and cookie policyand eatasheet your continued use of the website is subject to these policies. So I clearly don’t understand at all. I didn’t put any resistors on the input.

Therefore any results you get using a power supply of 3.

JvO 2 And when I connect the Vcc pin, without 19 and 17, my led is on, where I expected this to be datqsheet. MrBonjour Try another gate then. Texas Instruments discusses some of these results of reduced voltage power supply voltages to ICs, in this short ” Designing With Logic ” document. The LED being lit is not a surprise.


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Sign up using Facebook. It is likely that the output remained in 74ks241 high-impedance state, so the LED did not light. If you use a 5V power supply, and make sure this is always connected to the device Vcc and Gnd pins see belowthen you should see expected behaviour.

74LS datasheet, Pinout ,application circuits OCTAL BUFFERS AND LINE DRIVERS WITH 3-STATE OUTPUTS

When you connected [3. This circuit will help: I would have guessed the current gain was more than 0. I was expecting that my led will be off with pin 17 not connected but pin 19 still high, and the led on with 17 and 19 high, but this is not happening.

By using our site, you acknowledge that you have read and understand our Cookie PolicyPrivacy Policyand our Terms of Service. Without it, the outputs float. For some reason, this isn’t working on my circuit. Which I have interpreted as: SE topics where powering devices via other pins, instead of the power pins, caused unexpected behaviour:.