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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Then [you connected 3. What does “put a led on the 3 output pin” mean?

This circuit will help: And when I connect the Vcc pin, without 19 and 17, my led is on, where I expected this to be off. I’m trying to understand how the 74LS works.

Unless you know exactly what you are doing and its consequences, do not apply voltages to the other pins of an IC, without the correct power supply voltage s also being supplied to its specified power pins i.

Understanding how a tristate buffer works 74LS Ask Question. SE topics where powering devices via other pins, instead of the power pins, caused unexpected behaviour: 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.

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

Sign up or log in Sign up using Google. So here is what I did: I would have guessed the current gain was more than 0. I have the feeling that I have understood the schematic, but the fact is this is not working. JvO 2 Note the invertor symbol tiny o ring at the control gate connected to pin 1; you must pull pin 19 high to activate, and pin 1 low to activate. Sign up using Email and Password. Home Questions Tags Users Unanswered.


I don’t know that I’d actually seen a chip manufacturer document the behavior, but I’ve observed it and understood enough about silicon to understand that two P regions joined by an N region form a transistor.

For some reason, this isn’t working on my circuit. Then i wired the 19 and 17 pin with 3. Texas Instruments discusses some of these results of reduced voltage power supply voltages to ICs, in this short ” Designing With Logic ” document.

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. From what I read, if two input are high on a buffer, then the output will be high.


I didn’t put any resistors on the input. If you pull pin 19 down, the output will float and both LEDs datzsheet glow dimly because current is passing through both of them. Pins 1 and 19 of the LS control this state for the buffers inside the chip. But my led at pin 18 just glow dimly and never change state, no matter if pin 2 is high or not connected.

By using our site, you acknowledge that you have read and understand our Cookie PolicyFatasheet Policyand our Terms of Service. And we still don’t know how you have your LED connected????

Note that you may not enable both G inputs e. Without it, the outputs float.

So your first tests were done without any power connected to the Vcc pin! Do you understand what a buffer is and why we use it? This is not unexpected, since you didn’t power the IC via its power pins for this test. I have tried other gate 19 with 15, 13, 11 and I have the same behavior. 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.


Which I have interpreted as being: These ‘G’ inputs must be activated in order to have the buffers connected to them pull 74,s241 outputs low or high, depeding on their input. Do you understand WHY we have tri-state outputs? I have put a led on the 3 output pin, in order to test the output. It is likely that the output remained in a high-impedance state, so the LED did not light.

Email Required, but never shown. So I clearly don’t understand at all. And when I connect the Vcc pin [ 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.

Therefore any results you get using a power supply of datashfet. Mr Bonjour 1 2 Your explanation “two 74,s241 are high” sounds more like the definition of an AND gate. I was wondering if I didn’t have broke my chip because I don’t have protected the input gate, but it wasn’t asked in the schema. When you connected [3. Post as a guest Name. Please show the schematic diagram. In the first two instances the output is actively pulled low or high using a transistor; in the disconnected state, neither transistor is activated.

Which I have interpreted as: It is not guaranteed to operate at 3. Sign up using Facebook.