Logic gate output current

1. Apr 6, 2016

TheRedDevil18

Hi, I have this logic gate

I am using 5V as my VCC. In the datasheet it says that the output current at 6V is 5.2mA. My question is, Is that the max current that it can output ?

2. Apr 6, 2016

Jony130

For sure not.
http://www.nxp.com/documents/user_manual/HCT_USER_GUIDE.pdf [Broken] (page 34)
You can drawn more current but Voh voltage will drop bellow Vih (High-level input voltage ), so the next gate will not be able to properly recognize the logic state at his input.

Last edited by a moderator: May 7, 2017
3. Apr 6, 2016

TheRedDevil18

Ok, is there any way to know by how much it might drop ?, I am feeding it to the base of a transistor

Last edited by a moderator: May 7, 2017
4. Apr 7, 2016

Jony130

How much base current do you need? Also if you drive a BJT base only then you do not have to worry about VIh any more because the BJT is not a logic circuit so you do not have to meet the logic level regiments. Also we can find in datasheet the info that Io_max = 20mA
https://en.wikipedia.org/wiki/Logic_level#Logic_voltage_levels

5. Apr 7, 2016

TheRedDevil18

Assuming the output voltage from the ic is 5V which I used to calculate my base resistance. The current would be about 5.5mA

6. Apr 7, 2016

Jony130

No worries here the gate will survive this.
As we can see from this characteristic

The voltage drop across the gate output will not be larger than 0.8V and typically it will be around 0.3V.

7. Apr 7, 2016

TheRedDevil18

Thanks, So I can assume the output voltage from the gate and hence the voltage to the base of my transistor will be about 4.7V ?

Also, from the same datasheet, how much current does the ic draw when one of the pins is held high ?, I want to calculate a pull up resistor to ensure that the pin gets close to 5V as possible. I read around and they about 5k to 10k should be fine

8. Apr 7, 2016

Jony130

Yes.
The current consumption will depend on the load resistance. Because CMOS circuit in static do not burned any power. Only the load will consume power from power supply.
Do you really want to put a pull-up resistor at the gate output? Why ?

9. Apr 9, 2016

TheRedDevil18

I wanted to create a NOT gate using a transistor. But I don't need it now because I have an ic for it

10. Apr 9, 2016

CWatters

Can I suggest you post a sketch of this bit of your finished circuit?