Voltage Divider Signal Feeding Into an IC

[danner123]

I have an IC (7407) buffer which I operate VCC at 3.3V. I am feeding a 5V signal into a voltage divider (to get the voltage down to 3.3V) and then feeding that into the 7407 buffer IC.

Should my voltage divider make sure that the resistors used create a voltage of 3.3V or less?

Does it matter if the voltage I am feeding in is greater than 3.3V?

Thanks!

 

[barry]

You can't run a 7407 at 3.3V, it's designed to operate at 5V. READ THE DATA SHEET!!!

 

[D.A.(Tony)Stewart]

I think 7407's are obsolete, but you can practice with them. If you understand how low voltage transistors work you will appreciate that the absolute maximum of 5.5 on the input with respect to ground must be respected. So in theory, 5V is acceptable.

You can operate them down to 3.3V but the specs will not apply. The biasing is weaker so the output drive will be reduced and your input noise immunity and output transition speed will be significantly degraded, but useable.

Let's see you have a 5V input signal that you want to scale down to 3.3V logic so you can drive an open collector for high voltage output up to 30V with an open collector. with a non-inverting logic Is that right?

The 7407 was the non inverting OC driver and the 7406 was the inverting driver with an extra transistor.

7406 INV OC

7407 NON-INV OC

What input > output V/I response do you need?