Electronics > Projects, Designs, and Technical Stuff

Constant current constant voltage linear supply problems/questions

(1/6) > >>

Sniper1:
So i am trying to include a small constant current constant voltage supply in one of my projects ( active load) and after searching the web i found Dave s design that uses just 1 power element (very important for me since i only have 1 heatsink slot that is not used, the heatsink is recovered from something old and it 2.5x1.5x10cm long i calculated online that it can dissipate 15W with no fan and that would be plenty for me atm) ,
to be more precise i am trying to make something similar to this:   https://eevblog.com/uploads/uSupplyBenchRevA.pdf   

But fists i thought it would be a good idea to simulate a bit in LTSpice and apparently what i have works well with ideal op amps but real ones dont work well ( i am also attempting to replace the NPN with a Pmos with no success.
On paper they should work unless i forgot to account for something ......
As for the specs I am aiming for they would e loosely this:

* 0V out ( i plan to use 2 Si diodes and have the output come from a floating GND that is 1-1.5V higher then true GND
* 0-12V output range but i can settle with less if it makes sense ( i think here i am sort of limited by the transistor and op amp input voltages + max dissipated power by the heat sink)
* low noise ( that i why i want ti to be linear)
* As for output current i want like 1A for 5-6V and under
* Stable , aka no oscillation and the CC limit to work wellNOTE: power supply kill be a 12-24V AC-DC adapter so i get isolated DC and sort of regulated input, or some battery)
I think/hope that my requirements are reasonable ( yea at super low voltages it would be harder to get large currents because of the large dissipation but at that point i will simply use a lower input voltage like 5V USB)
Regarding the DACs for control i plan to use I2C 8 bit ones for now ( there is a 12bit drop in replacement that i can se later or for a V2)
 

coromonadalix:
overdesigned   with an lt3080

you could do it with multi turn pots

and for sur a linear psu will dissipate more than a smps or any switching psu

Sniper1:
well i want to avoid pots and use a DAC since this way i can avoid some mistakes and can also ramp up nice from soft + atm the circuit can accept a pot in the DAC  net labels
Regarding the LT3080 tht seems excessive + not so much in stock ( also like 20$ last time i did check )  + if i use a more common Darlington NPN or Pmos it is easy to replace but wwith the LT3080 i am sort of stuck with only 1 component

PS SMPS preregulator is also added but i am confident there while on the analogue linear side i am not ahtat is why this blcok is designed to work as standalone so that i cn more easily test it / simulate it

Kleinstein:
Going linear with up to some 12 W of power loss this may not work that well with a LT3080. Even if the chips can just handle the heat the temperature rise compromises drift and accuracy.

This is more like something for a seprate regulator and power transistors. This could be an LM723 based circuit (usually pretty poor constant current performance and going down to 0 V need a little care) or a more classical one around OP amps with diode OR. There are a threads around a LM324 "based one" that may work - though I would replace the 324 with at least an MC33174. The plans around are more for 3 or 5 A, but scaling down to 1 A should be pretty easy.

Sniper1:
THX
regarding the op am i agree i will use something with under mV input offset
A and i also found the problem in my simulation it was the CC part and more precisely it was the op amp , it acted as a compactor not as a differential amplifier , i blame the model , the voltage regulation seems to be working well ......
I cant get the circuit to compensate 2 diode drops but that also may be because of the op amp model , ill search a bit on LCSC and see if i have that model in SPICE (or just use a similar model and hope it works....

Is the thread you are reffering to this one: https://www.eevblog.com/forum/projects/bench-cccv-psu-based-on-daves-usupply/?action=dlattach;attach=690201;image  ?

Navigation

[0] Message Index

[#] Next page