Alex's Linear Power Supply Build Log


#42

Hey all,

Had to put the power supply to the side for a bit while i was away on work and waiting for parts to arrive. I got the boards back from JLC PCB and the quality is pretty good. I don’t have time yet to get the whole board assembled but I thought I would get the new power section up and running so I could do some load tests on the 5 volt rail.

The voltage is pretty solid throughout a wide input range as expected
5.11 volts with just the LED loading down the output at 2 mA or so. This drops to 4.99 Volts at the rated 500 mA and the switcher IC gets a bit on the warm side, but the diode I’m using is not exactly the correct one as per recommended in the data sheet so I think there is some loss there. I am still waiting on the correct diode as well as some of the digital components


#43

another note, here is a scope view of the transient turn on response of the output voltage. currently just running from a 12V input voltage. about 1.53 milliseconds rise time when power is applied.


#44

I’m sure it’s cooler than the previous linear regulator, but I wouldn’t expect it to be too warm at 500 ma. I have a switcher bucking 24V down to 3V3 at close to 1 A and it barely gets warmer than ambient.

Care to post the schematic for your new board?


#45

Sure, schematic is here.

Lab Bench Power SupplyV3.0.pdf (234.4 KB)


#46

I see you have an input filter on your DC-DC converter. If that isn’t designed correctly it can do more harm than good. It might be interesting to put a scope on it and see how it is performing. A poorly designed input filter can cause the converter to be less efficient.

Also, I would use the output of the current control section (Q4) to instead drop VSET instead of pulling down the output of the voltage control section. As it is it might not be very stable at the current threshold as the voltage control section would continue to try to control the voltage.


#47

I did some more looking into the board and aside from the budget wire you saw in the photo for the feedback wire, I think I was also using a blown catch diode. Checked it out with a meter and it looks pretty dead both ways. I re did the assembly with a nex converter as it seems I also killed it during the process. It looks pretty good now, almost no heat buildup at the converter and the as expected 2MHz switching frequency at the catch diode. The output voltage seems to collapse though as I go up above 400mA, down to 4.38V from the nominal 5.03V. I’m thinking its partly my layout not having large enough traces for the current path? I tried to use big copper pours for all of the converter layout though.



#48

Uploaded one of the wrong photos.


#49

As I mentioned above, check you input filter.


#50

Looking at the input to the switcher and prior to the filter on the scope, I don’t see any oscillations or noise getting into or through the filter at those loads. I did however lower the inductor value from the 470uH i originally designed to a 100uH. I have populated the rest of the board and have started testing the rest of the digital components as well.


#51

I see now that converter is only rated for 500ma, but still it shouldn’t be dropping so much at 400 ma. In the photo above D3 appears to be installed backwards, could be how it got damaged and why things ran warm. Most of the parts don’t match what is on the schematic. It was recommended you use the TI WebBench for the DC-DC converter but you ended up using the minimal example from the datasheet of an Infineon part.