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| My Very first fully custom PCB looking for Schematic Input and maybe any errors. |
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| SirAlucard:
Ok right now I'm trying to solve my power supply, looking at trying to use LM2675M-12/NOPB for my 12v rail and LM2675MX-5.0/NOPB for my 5v rail. Right now I've wired up a quick circuit using the 12v switching regulator to see how it works and on load it drops to 6v, input voltage is @15.7v. It's wired up like it is in the attached schematic. Photo TEK0000.jpg is the output without a load with Ch2 being before the inductor/capacitor and ch1 being after the inductor/capacitor. TEK0002.jpg is with a load supplied. What am I missing here? It should be noted, I've tried tying ON/OFF to ground, with a voltage divider to supply 3v, and tying it to vcc, all of which made no difference. Also to answer someone that asked earlier, its a small 12v motor that draws 200mA at full load. I think this is it. https://www.jameco.com/z/FK-180SH-18130-R-Nichibo-Taiwan-12V-Volt-DC-Motor-11806-RPM_2258523.html but actual measurements show only 200mA at 12v |
| Buriedcode:
--- Quote from: SirAlucard on May 26, 2020, 04:53:36 pm ---Ok right now I'm trying to solve my power supply, looking at trying to use LM2675M-12/NOPB for my 12v rail and LM2675MX-5.0/NOPB for my 5v rail. Right now I've wired up a quick circuit using the 12v switching regulator to see how it works and on load it drops to 6v, input voltage is @15.7v. It's wired up like it is in the attached schematic. Photo TEK0000.jpg is the output without a load with Ch2 being before the inductor/capacitor and ch1 being after the inductor/capacitor. TEK0002.jpg is with a load supplied. What am I missing here? It should be noted, I've tried tying ON/OFF to ground, with a voltage divider to supply 3v, and tying it to vcc, all of which made no difference. Also to answer someone that asked earlier, its a small 12v motor that draws 200mA at full load. I think this is it. https://www.jameco.com/z/FK-180SH-18130-R-Nichibo-Taiwan-12V-Volt-DC-Motor-11806-RPM_2258523.html but actual measurements show only 200mA at 12v --- End quote --- Its been a while since you first posted, but I think we need to take a step back, or I've missed something. You originally posted a schematic that included linear regulators, but with components connected to them designed for a switching (buck) regulator. You then said you made a PCB from this schematic, but we still haven't seen this PCB - design files or photos. We/I can't tell if your schematic is incorrect, whether you used linear regulators and didn't include the inductor/diode, or whether you used a switching regulator, and kept these components. This could be cleared up with the part numbers you populated on the PCB, or a photo of the PCB itself. Preferably both. Now you've prototyped a switching/buck regulator (LM2675M-12/NOPB) and it isn't functioning as it is meant to. There can be many reasons for this: inductor value/Isat/DCR, prototype method, wrong connections, diode selection, input/output capacitance etc.. The bottom waveform shows its switching, so it's at least getting power and "doing something" but the low output could be many things. So even though you have included switching waveforms, it's pretty hard to know why it isn't working as intended without the following: - A schematic of your prototype/test board. Not a schematic you found on the web, the actual schematic of what you've done. Preferably with... - The parts used. The LM2675M has few external components, but the inductor's inductance, its Isat, and DCr are important parameters. As well as the diode used, and the capacitance of the IO caps. - How you prototyped it. A solderless breadboard is handy, but pretty unreliable for switchers, soldered prototype board is better, but if you have long wires between parts it can cause all manner of issues in a switching regulator. Dead-bug can work rather well, but is pretty messy. - A photo might be able to show all of the above. That is a photo of both your original board and the LM2675M test board/setup I realize this sounds like I'm being pedantic, but often with posts about trying to debug things, more information is better. With sparse info, like a couple of waveforms and "its output is too low", we have to make a LOT of assumptions, any of which could be completely wrong, and can end up turning the thread into a mess of random suggestions that could keep you busy for days. This isn't a criticism of your post, rather a way to move forward, and to prevent you getting 50 different suggestions. |
| SirAlucard:
--- Quote from: Buriedcode on May 26, 2020, 06:10:39 pm --- --- Quote from: SirAlucard on May 26, 2020, 04:53:36 pm ---Ok right now I'm trying to solve my power supply, looking at trying to use LM2675M-12/NOPB for my 12v rail and LM2675MX-5.0/NOPB for my 5v rail. Right now I've wired up a quick circuit using the 12v switching regulator to see how it works and on load it drops to 6v, input voltage is @15.7v. It's wired up like it is in the attached schematic. Photo TEK0000.jpg is the output without a load with Ch2 being before the inductor/capacitor and ch1 being after the inductor/capacitor. TEK0002.jpg is with a load supplied. What am I missing here? It should be noted, I've tried tying ON/OFF to ground, with a voltage divider to supply 3v, and tying it to vcc, all of which made no difference. Also to answer someone that asked earlier, its a small 12v motor that draws 200mA at full load. I think this is it. https://www.jameco.com/z/FK-180SH-18130-R-Nichibo-Taiwan-12V-Volt-DC-Motor-11806-RPM_2258523.html but actual measurements show only 200mA at 12v --- End quote --- Its been a while since you first posted, but I think we need to take a step back, or I've missed something. You originally posted a schematic that included linear regulators, but with components connected to them designed for a switching (buck) regulator. You then said you made a PCB from this schematic, but we still haven't seen this PCB - design files or photos. We/I can't tell if your schematic is incorrect, whether you used linear regulators and didn't include the inductor/diode, or whether you used a switching regulator, and kept these components. This could be cleared up with the part numbers you populated on the PCB, or a photo of the PCB itself. Preferably both. Now you've prototyped a switching/buck regulator (LM2675M-12/NOPB) and it isn't functioning as it is meant to. There can be many reasons for this: inductor value/Isat/DCR, prototype method, wrong connections, diode selection, input/output capacitance etc.. The bottom waveform shows its switching, so it's at least getting power and "doing something" but the low output could be many things. So even though you have included switching waveforms, it's pretty hard to know why it isn't working as intended without the following: - A schematic of your prototype/test board. Not a schematic you found on the web, the actual schematic of what you've done. Preferably with... - The parts used. The LM2675M has few external components, but the inductor's inductance, its Isat, and DCr are important parameters. As well as the diode used, and the capacitance of the IO caps. - How you prototyped it. A solderless breadboard is handy, but pretty unreliable for switchers, soldered prototype board is better, but if you have long wires between parts it can cause all manner of issues in a switching regulator. Dead-bug can work rather well, but is pretty messy. - A photo might be able to show all of the above. That is a photo of both your original board and the LM2675M test board/setup I realize this sounds like I'm being pedantic, but often with posts about trying to debug things, more information is better. With sparse info, like a couple of waveforms and "its output is too low", we have to make a LOT of assumptions, any of which could be completely wrong, and can end up turning the thread into a mess of random suggestions that could keep you busy for days. This isn't a criticism of your post, rather a way to move forward, and to prevent you getting 50 different suggestions. --- End quote --- I did actually end up finding the problem, it was a dumb mistake on my part, I was using a diode that wasn't rated high enough so it kept breaking down the voltage as it drew more power than the diode could handle. After replacing it for better suited ones the power regulation was stable and correct. Laugh at me if you will, but this is how I prototyped the switching regulator hah, had to work with what I had cause I don't have any bare copper boards around. Also I'm a little shy in sharing, as it is my first board I feel a little intimidated in having others critique my work. |
| Buriedcode:
--- Quote from: SirAlucard on May 26, 2020, 09:22:40 pm ---I did actually end up finding the problem, it was a dumb mistake on my part, I was using a diode that wasn't rated high enough so it kept breaking down the voltage as it drew more power than the diode could handle. After replacing it for better suited ones the power regulation was stable and correct. --- End quote --- So, was that for the LM2675M test circuit, or your original design? Glad its working correctly, I would still like to know the part numbers used. --- Quote from: SirAlucard on May 26, 2020, 09:22:40 pm ---Laugh at me if you will, but this is how I prototyped the switching regulator hah, had to work with what I had cause I don't have any bare copper boards around. --- End quote --- I don't think anyone here is going to laugh. I have seen beautifully neat circuits that didn't work at all because they were very poorly designed, and "dead bug" rats nest complete mess of prototypes that worked flawlessly. I've prototyped SOIC devices using stripboard (vero board with copper strips) and it worked well for rough 'n' ready testing. Also your connection looks like it has good thick connections so nothing wrong with it. But I am still curious about the parts used. There are many inductors about, ranging from ratings from mA to tens of Amps, form nano henrys right up to 500mH, something I used to regularly see in the beginners forum is people using small axial "filter" inductors for power switchers - ones that look like resistors. This is why I asked for a photo of the whole test set up, the components, and/or the part numbers used. --- Quote from: SirAlucard on May 26, 2020, 09:22:40 pm ---Also I'm a little shy in sharing, as it is my first board I feel a little intimidated in having others critique my work. --- End quote --- So was I, and I have posted things that were criticized. But rarely were those criticisms unhelpful. Some may be quite rude with how they point out flaws but are still technically correct (engineers get straight to the point generally). But don't worry, if we can see the circuit, and the parts used, others can see what you've done, if you've done anything "incorrectly", and how to proceed to meet your design goals. If anyone posts something that doesn't provide useful information - ignore them. |
| SirAlucard:
--- Quote from: Buriedcode on May 26, 2020, 10:45:21 pm --- --- Quote from: SirAlucard on May 26, 2020, 09:22:40 pm ---I did actually end up finding the problem, it was a dumb mistake on my part, I was using a diode that wasn't rated high enough so it kept breaking down the voltage as it drew more power than the diode could handle. After replacing it for better suited ones the power regulation was stable and correct. --- End quote --- So, was that for the LM2675M test circuit, or your original design? Glad its working correctly, I would still like to know the part numbers used. --- End quote --- Yes, that was for the LM2675M-12/NOPB, I'm also using a LM2675MX-5/NOPB for 5v. --- Quote from: Buriedcode on May 26, 2020, 10:45:21 pm ---But I am still curious about the parts used. There are many inductors about, ranging from ratings from mA to tens of Amps, form nano henrys right up to 500mH, something I used to regularly see in the beginners forum is people using small axial "filter" inductors for power switchers - ones that look like resistors. This is why I asked for a photo of the whole test set up, the components, and/or the part numbers used. --- End quote --- Atm my final parts haven't been chosen, I'm looking at a 68uH inductors to go onto the 12v and 5v rails, I'm mostly following TI's power supply designer WEBENCH atm, it suggests 68uF Electrolytic on the output but is that really enough? I've already got 220uF that I was going to reuse. Also What's the best way to figure out filtering? As I'm noticing my 12v rail is being effected by the 5v switching. That also may be because I'm not using the correct inductors atm. |
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