74LS08 IC is a member of 74XXYY IC series. There are four AND gates in the chip and each gate have two inputs, hence the name. 74LS SN74LS08NSR. ACTIVE. SO. NS. Green (RoHS. & no Sb/Br). CU NIPDAU. LevelC-UNLIM. 0 to 74LS SN74S08D. ACTIVE. Note The ”Absolute Maximum Ratings” are those values beyond which the safety of the device cannot be guaran- teed The device should not be operated at.

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74LS08 Pinout, Configuration, Equivalents, Circuit & Datasheet

Home Questions Tags Users Unanswered. The circuit working can be explained in few stages below: A few mentioned below. The inputs of the 74LS family and other TTL versions source significant current and will appear as a logic High unless firmly pulled to Ground – your k resistors won’t help.

The chip is used in systems where high speed AND operation is needed. The four AND gates in the chip mentioned earlier are connected internally as shown in diagram below. Post as a guest Name. 744ls08 chip is basically used where AND logic 74ls80 is needed.

There are four legs connected together in pair of two. The two inputs of AND gate are driven out from bases of the two transistors. And after a google search I havnt come up with anything, usually the videos are terrible quality or they are using a different AND gate.

Because output is nothing but voltage across resistor R1 it will be LOW. Sign up or log in Sign up using Google. For realizing the above truth table let us take a simple AND gate application circuit as shown below. Output of the AND gate is the voltage across resistor R1.


At this time the total VCC appears across nad R1. As you can see the LED is on by default despite neither button being pressed.

Sara Heart 1 6. The chip provides TTL outputs which are needed in some systems. Simon Marcoux 1, 2 Both transistors will be ON and voltage across both of them will be zero. Pressing the buttons does nothing. When any one of the buttons is pressed. Post Your Answer Discard By clicking “Post Your Answer”, you acknowledge that you have read our updated terms of serviceprivacy policy and cookie policyand that your continued use of the website is subject to these policies.

Pull down resistors as suggested in another answermight also a 74ls0 idea. Then if your IC is good your switches are mis-wired, I have done it myself with that type of switch. When both buttons are not pressed.

digital logic – 74LS08 AND gate always outputting high? – Electrical Engineering Stack Exchange

After verifying the three states, you can tell that we have satisfied the above truth table. This Andd is connected to detect the state of output. Email Required, but never shown. 7l4s08 of this the chip can be used for high speed AND operations. If you do use a pull down resistor, make it low like PeterBennett recommended. If you choose the wrong pair, you end up with an always on switch. It is really popular and is available everywhere.


These two inputs are connected to buttons to change the logic of inputs. Because total VCC appears across transistors the drop across resistor R1 will be andd. In the circuit two transistors are connected in series to form a AND gate. By using our site, you acknowledge that you have read and understand our Cookie PolicyPrivacy Policyand our Terms of Service. Looking at the image I agree.

I think that you were dead on in the first place with your answer SaraHeart.

You might be using push buttons that are connected in such a way that the legs are shorted connected together. There are four AND gates in the chip, we can use one or all gates simultaneously. As AlmostDone said, you need to snd about 1. In that case, the left button should have a red wire on the lower left pin.

74LS08 Quad 2-Input AND Gate

They are notorious for that particular mishap. The inputs on CMOS parts anything with a “C” in the middle source or sink very little current, so K pull-up or -down will work with them.

With that the drop across resistor R1 will be zero. The description for each pin is given below.