How to simply add specific delta V to my changing voltage?

Hi,

Need your help. Few questions:
How to simply add specific delta V to my changing voltage Vin?
I have another 5V DC signal. How to trigger this voltage addition (dV) to my Vin by the appearance of this 5V signal?
The addition of dV to my Vin, should not rise above 4.5V. Thus, I need to add dV to my Vin but up to Vout=4.5V. And then, I need it to stay at 4.5V even that my Vin is still rising. How do I do that?

Thanks a lot!!

Hi Leo,

I wonder of what is the application of this case, but I think this is some kind related to instrumentation. Dealing with the basics, if you don't want to rise voltage above a certain level then add a voltage regulator then so can now simply add the two voltages without worrying that it will rise above 4.5V etc.. For some technical control system they simply connect in parallel and consider other parameters like current which in Control System it is 4-20mA....

It is good to provide also a specific application with this case.

Good Luck.

Best,
Neil