exxos's Atari, Amiga & retro forum

My Opto board just came.. But the problem is it does not actually work :roll:

And this surprises you? :lol: :roll:

JezC wrote: 04 Oct 2021 20:44 And this surprises you? :lol: :roll:

Nope :)

Hall effect sensor should be here tomorrow. I've started designing my own as that probably won't work either.

exxos wrote: 04 Oct 2021 21:12 Hall effect sensor should be here tomorrow. I've started designing my own as that probably won't work either.

Ah, another chance for bodge wires! Yay... ;)

As nobody guessed the printer it was https://www.bigtree-tech.com/products/biqu-bx.html

Oddly flash forge seem to do the same thing https://www.flashforgeshop.com/product/ ... 3d-printer

So who copied who ?

Biqu was a kick starter thing. The voxlab says its open source, but I don't see anything pointing to github etc.

I think flashforge got a bad reputation a while back for copying some other printer out there.

In other news, the new PSU builds are not going well :( for some reason the 12v rail is not behaving . I've been emailing Texas instruments as they make the chip, but as usual , "work it out yourself! Seems to be the solution, they are not getting much past resoldering the board.. I mean come on..

While the chips are really good, the 5v one seemed to always be inconsistent with the output voltage. Its why on this latest batch I added a trimmer to adjust the 5v manually as they were getting to more like 5.8v on some batches. So I spent ages changing the feedback resistors.

But now something is amiss with the 12v chips. I have changed and fiddled with every value in the circuit and nothing really helps. There is some feedback stuff where a voltage sets the over current on a pin on the ic.if I put my finger on one cap in the circuit, it works fine. So its equates to 27k across it.

I ran some simulations of what all the parts do, and it just seems to change the DC offset of the pin. Ironically , there is a internal 1meg resistor which says its down to open loop gain. The date sheet makes nonsense what its trying to do. But it sounds like as the output current increases, this causes the comp pin to increase in voltage, which turns on the high side MOSFET for longer. So I think the high side MOSFET isn't turning on at all as the output regulation is all over the place :roll: when I add the 27k it seems to limit the gain of the feedback and it all works fine.

I can only assume this last batch of 12v chips is out of spec like the 5v ones always seem to be. I'm going to try and find a spare board from the last batch and put it on a new board to make sure it is the ic to blame. Its not helping because of parts shortages. It was lucky I had bought 100 of them extra on the last batch as nobody has stock of them :roll:

Overall, I'm looking at different manufactures of switch mode chips. While I have always liked Texas instruments parts, something has gone really wrong with their production of chips somehow. While I can expect variation , this is just ridiculous. I'm not getting proper support from Texas so I am done with them now.

So the new batch of PSUs are delayed until I am happy this odd fault is fixed. As if I haven't got enough to do already :roll:

@exxos good choice of printer. Very similar to my Creality one :D

What Ti chips you using? I tried some of their buck converters for 24vdc to 5v and 3.3v. Using their suggested schematics the 5V ones were hopeless, 3.3v worked OK for a bit but was too unreliable.

PhilC wrote: 07 Oct 2021 09:41 What Ti chips you using? I tried some of their buck converters for 24vdc to 5v and 3.3v. Using their suggested schematics the 5V ones were hopeless, 3.3v worked OK for a bit but was too unreliable.

Its the TPS range.

You can read the TI thread if you like https://e2e.ti.com/support/power-manage ... ut/3855699

I did spend a lot of time and money reviewing switchmode chips right at the start and a Texas ones offered the best performance by far. However as mentioned in the thread, I have been having issues with the 5 V being "out" from one batch to another. Which is why I added a trimmer pot on the 5V this time around because it takes a lot longer than you think to change 100 resistors!

I think something is just inherently wrong with their manufacturing process or something. Nothing has changed with the PSU circuit other than very minor edits to some tracks. The last batch of boards is basically identical to the new batch other than the preset on the 5 V anyway. I would expect a little bit of variation, sure, but not by that much. But now with the 12V chips doing odd things as well..


Roea says its about 1meg in the datasheet. Considering the voltage is like below 1volt there, the current on that value resistor is absolutely tiny. In fact even adding 27K the current is still minuscule. However the power supply works perfectly well with that value.

Fair enough, I gave up and used something else in the end as I got fed up of the chips not working with the 24VDC input but working fine at 9VDC input which don't help, even though they were rated at 40V.

I've gone for something like a NCS3S4803SC which is pretty much solder it on and ignore it. Although a bit expensive it suits my needs perfectly.

PhilC wrote: 07 Oct 2021 10:17 I've gone for something like a NCS3S4803SC which is pretty much solder it on and ignore it. Although a bit expensive it suits my needs perfectly.

Yeah those fully integrated things are pretty cool.

I am looking at these https://www.monolithicpower.com/en/mp2355.html Trying to find something where I don't have to totally redesign the whole board again :roll:

@exxos good luck, the spec looks pretty good on that chip at 3A.