SN74ls14: Desired Output Voltage not achieved

PeiChen Lin

Prodigy 20 points

Part Number: SN74LS14
Other Parts Discussed in Thread: SN74LVC14A

Hi,

I encountered a problem when I was trying to make an square wave oscillator using SN74LS14N.

From the technical document, it shows that the output voltage (VOH) is 3.4V.

However, I only got the output voltage around 2V when using Vcc as 5V.

Did anyone have the same problem?

Thanks!

PeiChen

over 7 years ago

0 Clemens Ladisch over 7 years ago

Guru 308170 points

That V_OH value is specified for a current of 0.4 mA.

How much current is there in your circuit (which you have kept a secret)?

0 Michael J Schultis over 7 years ago in reply to Clemens Ladisch

TI__Mastermind 24915 points

Hello PeiChen,

Yes, the output voltage will be dependent upon the load current, so it will drop as the load current increases.

You may also want to look at using a newer logic family that has limited dropout. For example SN74LVC14A.

Best,
Michael

0 PeiChen Lin over 7 years ago in reply to Michael J Schultis

Prodigy 20 points

Thanks to both of you!
I'll try to measure the output voltage with additional resistor and see if it works.
If I find other problems, I would come and ask for help again.

0 Michael J Schultis over 7 years ago in reply to PeiChen Lin

TI__Mastermind 24915 points

Happy to help!

Best,
Michael

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SN74ls14: Desired Output Voltage not achieved