| Electronics > Projects, Designs, and Technical Stuff |
| Turning a fixed SMPS into a variable power supply. |
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| Yamin:
Hi, I bought a broken 24V power supply and got it fixed, the model is Meanwell sp-320-24. I would like to turn it into a variable power supply which preferably goes from 5V to 24V. I found a very interesting article which shows how to do it. http://www.imajeenyus.com/electronics/20151028_smps_variable_voltage/index.shtml But it is not similar to the power supply that I have got. The power supply I have has got a AZ431 shunt voltage regulator (same as the TL431). Here is what I have done so far: I have tried changing the values of R74 and R73 no matter what I did the output voltage doesn't seem to go below 16.50V, even when I left R74 open the output was 16.50V . The reference for the regulator is 2.5V. Any idea what I could do?. As it is the voltage could be changed from 18.4V to 27.2V by turning the 1K pot. I have also attached a screenshot of the regulator section from a schematic I found online. There is a full schematic downloadable from elektronaya https://elektrotanya.com/meanwell_sp_320.pdf/download.html Again thanks for the help |
| coromonadalix:
I dont think it will be that easy, you have hacked some feedback for the control smps ic`s, but normally they have some values range in their feedback to add tolerance for the ovp protection if any implemented. The tl431 or any variant is normally used in the feedback loop, not has the main regulator, it drives the feedback optocouplers to the main smps chips you have to search the 4800 ic`s specs and see what can you hack, sometimes disabling the ovp may help, but you`re loosing some protections too, unless you really know what you`re doing, i would not mod this, use a variable linear regulator at the output instead. Your modification link point to an based tl 494 smps ic, theses are more easily modifiable, there is some google projects too, an 0-50vdc variable smps based on it. |
| Yamin:
Thanks, you're right I've been looking for a ML4800 mod. Doesn't give too much results. What do you suggest I do then to vary the output voltage (any suggestion on how to build a variable regulated supply). Do you suggest on using a LM317?. I don't have a specific current requirement but the higher the better hehehe. |
| strawberry:
to regulate output voltage from 0..100%and at full current. and not run ML4800 into UVLO , power that chip from external power source but dont run output voltages too high , othervise MOSFET in your FORWARD topology will overvoltage and blow |
| Yamin:
I got a suggestion from someone - he suggested that I remove ZD4, and link out ZD8 and ZD9. I'm trying to figure out the logic behind it. |
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