I am using the LM7805CV voltage regulator to regulate 12 V to 5 V and power a device that requires 5 V/0.8 A. The LM7805CV works flawlessly and I don't want to change it for a buck converter.
The LM7805CV's output, without load, is 4.94 V and I want to increase the output to 5.00-5.10 V.
By adding a 10 Ω resistor (R9), between the regulator's GND and my circuit's GND, I managed to increase the output to 5.05 V, which is great for my needs.
Is this voltage output increase method safe for the LM7805CV and my circuit?
No. The voltage regulation will be very very bad, besides the L7805CV has a voltage tolerance of 2%.
That mean you may buy one that outputs 4.9V and another one that outputs 5.1V and another that is somewhere in between.
Do you really need that extra 6mV for you circuit to work correctly?
I guess you are right.
I am trying to generate PWM pulses, as clean as possible and as close to 5V as possible and I thought that it was a good idea to "boost" my LM87805
Why do you think that increasing the voltage would make the pulses cleaner? How are you defining cleaner and how are you testing the cleanliness of the pulses?
As to getting it as close to 5V as possible, what is the device you are connecting it to that is so fussy?
This is digital electronics and those sorts of precession voltages are not required.
Increasing the voltage will not make the pulses cleaner, it will just make the voltage "stronger".
I am building a PWM driven motor controller and I want to make a 12V to 5.1V stepdown that can eliminate as much as possible any external ripple coming in.
That doesn't make much sense. What ripple, and what effect do you think having ripple on a PWM signal might give you? It will certainly have no effect on a motor's smooth running.
It will not make sense until I have time to explain the whole project to you.
My goal is to to build a 12V to 5.1V stepdown that "eliminates" any external incoming ripple.
I am done with the "eliminate ripple" part and I am looking for a way to make the LM7805CV make 5.1V, or at least 5.05V.
Repeat: My goal is to to build a 12V to 5.1V stepdown that "eliminates" any external incoming ripple.
I am done with the "eliminate ripple" part and I am looking for a way to make the LM7805CV make 5.1V, or at least 5.05V.
Use an adjustable Vreg instead of a 7805 with a resistor at the ground pin can output a higher V but there is a distinct possibility that the 7805's OP may oscillate.
If your goal is to reduce ripple, then you need to look at the regulators PSRR (Power Supply Rejection Ratio). It specifies how well the regulator will reject incomming ripple, the higher the number the better.
How much current will you need to output from the regulator?
Why do you want to eliminate all ripple?
What sort of ripple figure do you want to get down to, don't forget the world is not perfect.
I think you will find the HF ripple of a DC-DC converter is easier to eliminate than the 50/60Hz ripple of a regulated supply.
As I suggested before, experiment, build your project with just the LM7805 and analyse it in the real world.
Do you have a scope to monitor the ripple?
If you want to know how to do what you initially drew properly, refer to a datasheet. For example, TI 7805 Datasheet
See page 15. Use two resistors. The actual regulated voltage of the regulator, in combination with the one resistor, sets the offset current, and the lower resistor defines the voltage elevation achieved by that offset current. Simple, stable, and recommended by the manufacturer.
But, as the others have said, why? What you're trying to do is to say the least, unusual.