Good day folks. Long time no see. It's been a while since I've tinkered with any new projects, despite one thinking this would be the perfect time, with the pandemic and the quarantine, people tend to stay indoors....it's not my case anyway: I go to work like normal, but it's here where I'm bored out of my mind with nothing to do, so here's something.
A while back, I got myself this adjustable load kit form off Ali. I put it together and it works. It's powered by an AC or DC input and I've been running it off a 12v wall adapter on the bench. What good is such a device if it doesn't have a built-in voltmeter/ammeter to display the status of the DUT ? So I also got myself one of those, with intent of building a case for the whole thing. This is where I ran into a bit of a problem which I didn't foresee: the panel meter requires a separate power supply, since otherwise the GND of the meter would be common to the DUT and I'm not sure how good that is (there must be a reason why the manufacturer specifies this on the back of the meter !). Instead of having two wall adapters, I was thinking of using a dual output transformer. I dug through a box of junk at work and found one. It's unnecessarily large, the size of a cube measuring around 5cm all around. There's a bit of an issue though: it outputs 9v on one set of windings, which is OK, but 32v on the other one ! This is way too high, especially since it jumps to 43v when I add a cap to it...how can I step this down to 12v ? An off the shelf buck converter doesn't go any higher than 30v. I was thinking of a zener+transistor regulator, which would be highly inefficient but doable I think....we're talking a drop of around 30v after all ! At a current draw of 1a, that's already 30w of wasted power if my theory is correct ! ! (though the load most certainly doesn't come close to that). I don't know the current draw of the adjustable load unfortunately (the circuit itself, not the DUT).
Still, one other thought that crossed my mind was to feed the 43v into the input of a wall-powered SMPS and modify that to work with a low input voltage like this....what is the limiting factor here ? I see most wall adapters taking anywhere from 90 to 240v and above, so what's stopping them from going lower ? There's probably something complicated involved with the transformer itself, like saturation or other factors which go a bit over my head. I know the output can be hacked to modify the output voltage (done it before successfully on my own), but what about the input voltage ? I couldn't find anything about this. I know there DO exist SMPSs which take lower input voltages DC or AC (I've seen them for sale), but those are specifically engineered for this purpose. I was thinking a regular-old power brick or phone charger or something readily available. One thing I know for sure from TV sets is that the control IC on the primary of some has a brown-out protection and actually senses the if the input voltage is withing range, so those would require a lot more hacking. The switching frequency would also probably need tuning to cater for the much lower input voltage. Cheers guys. Thank you.
A while back, I got myself this adjustable load kit form off Ali. I put it together and it works. It's powered by an AC or DC input and I've been running it off a 12v wall adapter on the bench. What good is such a device if it doesn't have a built-in voltmeter/ammeter to display the status of the DUT ? So I also got myself one of those, with intent of building a case for the whole thing. This is where I ran into a bit of a problem which I didn't foresee: the panel meter requires a separate power supply, since otherwise the GND of the meter would be common to the DUT and I'm not sure how good that is (there must be a reason why the manufacturer specifies this on the back of the meter !). Instead of having two wall adapters, I was thinking of using a dual output transformer. I dug through a box of junk at work and found one. It's unnecessarily large, the size of a cube measuring around 5cm all around. There's a bit of an issue though: it outputs 9v on one set of windings, which is OK, but 32v on the other one ! This is way too high, especially since it jumps to 43v when I add a cap to it...how can I step this down to 12v ? An off the shelf buck converter doesn't go any higher than 30v. I was thinking of a zener+transistor regulator, which would be highly inefficient but doable I think....we're talking a drop of around 30v after all ! At a current draw of 1a, that's already 30w of wasted power if my theory is correct ! ! (though the load most certainly doesn't come close to that). I don't know the current draw of the adjustable load unfortunately (the circuit itself, not the DUT).
Still, one other thought that crossed my mind was to feed the 43v into the input of a wall-powered SMPS and modify that to work with a low input voltage like this....what is the limiting factor here ? I see most wall adapters taking anywhere from 90 to 240v and above, so what's stopping them from going lower ? There's probably something complicated involved with the transformer itself, like saturation or other factors which go a bit over my head. I know the output can be hacked to modify the output voltage (done it before successfully on my own), but what about the input voltage ? I couldn't find anything about this. I know there DO exist SMPSs which take lower input voltages DC or AC (I've seen them for sale), but those are specifically engineered for this purpose. I was thinking a regular-old power brick or phone charger or something readily available. One thing I know for sure from TV sets is that the control IC on the primary of some has a brown-out protection and actually senses the if the input voltage is withing range, so those would require a lot more hacking. The switching frequency would also probably need tuning to cater for the much lower input voltage. Cheers guys. Thank you.
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