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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Unfortunately your test is invalid because dayasheet to your recent schematic your Vcc supply to the 74LS is only 3. Therefore it is also no surprise that when you did connect pins 17 and 19 to Vcc, the LED stayed lit.
Mr Bonjour 1 2 And we still don’t know how you have your LED connected????
Although it is not “best practice” to do this, unconnected LS TTL satasheet will usually float high, as PeterBennet has already kindly explained. Sign up using Facebook. I don’t use the two G inputs at the same time. Understanding how a tristate buffer works 74LS Ask Question. I would have guessed the current gain was more than 0.
In the first two dataxheet the output is actively pulled low or high using a transistor; in the disconnected state, neither transistor is activated.
I have put a led on the 3 output pin, in order to test the output. 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.
Do you understand what a buffer is and why we use it? Your explanation “two input are high” sounds more like the definition of an AND gate.
But my led at pin 18 just glow dimly and never change state, no matter if pin 2 is high or not connected. Datasueet didn’t put any resistors on the input. Post as a guest Name.
What does “put a led on dxtasheet 3 output pin” mean? And if I’m connecting pin 19 and 17 to be high, I’m expecting that my led will be brighter, but it just glow dimly, no matter if pin 17 is high or not connected. 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. I have the feeling that I have understood the schematic, but the fact is this is not working.
A tristrate output can have 3 different states: Another issue I’ve observed is parts that behave as 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. Sign up using Email and Password. So I clearly don’t understand at all.
Please show the schematic diagram. This will also cause behaviour which is different 47ls241 the behaviour when correct power is connected. Then [you connected 3. If you pull pin 19 down, the output will float and both LEDs will glow dimly because current is passing through both of them.
74LS datasheet, Pinout ,application circuits OCTAL BUFFERS AND LINE DRIVERS WITH 3-STATE OUTPUTS
The LED being lit is not a surprise. I’ve done quite a lot of research since first writing this answer, datashwet with unpowered 74LS devices and an input voltage between 0 V and 5. 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.
For some reason, this isn’t working on my circuit. 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 Datwsheet region form a transistor.
Sign up or log in Sign up using Google. 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.
74LS Datasheet PDF –
This is clearly what I am expecting. These ‘G’ inputs must be activated in order to have the buffers connected to them pull their outputs low or high, depeding on their input. And when I connect the Vcc pin, without 19 and 17, my led is on, where I expected this to be off.
Which I have interpreted as being: Why is my microcontroller passing a current through it when not connected?
Email Required, but never shown. I’m trying to understand how the 74LS works. Note that you may not enable both G inputs e.
(PDF) 74LS241 Datasheet download
SE topics where powering devices via other pins, instead of the power pins, caused unexpected behaviour:. This is not unexpected, datasheet you didn’t power the IC via its power pins for this test. SE topics where powering devices via other pins, instead of the power pins, caused unexpected behaviour: