SMPS for tube pedals

[printer2]

Finally got back to it. Frequency 72.5 kHz, 300V 79 mA. Flattened out a couple of pennies (make sure they are copper kiddies) and did some fancy soldering as well as painted them and the original heatsink flat black, still bare copper in the picture.

I did not get a lot of time on it but the heatsinks felt a little warm to the touch.

Very cool.

I'll try to match something with your numbers.   I'm assuming oscilloscope waveform is the output ripple at the first cap?   (As it sure looks like the diode current passing through the output cap ESR.)

It would be good to get the PWM output from the chip.  It's not possible to extract the MOSFET on-time from the diode current waveform.  The diode current waveform is when the switch is off but it is shorter than the total off time.   So we don't know the on-time or the total off-time.

Almost forgot I found this,
https://dalmura.com.au/static/YH11068A.pdf

It quotes 75kHz operating frequency, which is in agreement with you measurement.    I need to look at the datasheet for that chip.  I was assuming it's constant off time and variable off time, which is how the MC34063 works, but it could be different.

Nonetheless I might be able to narrow the times based on the 8V to 32V input and 40V to 390V output.   Your  72.5 kHz, 300V 79 mA (and 12V in?) would then pin things down in the middle of range.

I did not vary the input voltage (12V) or the load on the module. I did step it up from 100V in 50V steps. At 100V it had a time of 59 kHz and from 150V to 300V it was 72 kHz. I need to make a proper jig so I can clip in my probe, as it was I was only able to clip onto the copper heatsink on the output cap side (only one cap, the other is on the input).

I don't know when I can get back to this, I kind of lost three weeks of my life due to health issues and have a big backload of stuff that needs to be done. But sometimes (heck, most of the time) I get fixated on something and waste time on something rather than more important stuff so I may get to it in a timely matter yet.

[Rob Strand]

I did not vary the input voltage (12V) or the load on the module. I did step it up from 100V in 50V steps. At 100V it had a time of 59 kHz and from 150V to 300V it was 72 kHz. I need to make a proper jig so I can clip in my probe, as it was I was only able to clip onto the copper heatsink on the output cap side (only one cap, the other is on the input).

That might be enough to fill in the gaps.   The key thing being the variable frequency.   I'm assuming a resistive load of 300/79mA = 3.8k, so at 100V the load is 100/3.9k = 26mA.

And yes,   it's often easy to do some quick poking around but there comes a point where you have to set-up everything like a scientific experiment - and that wasn't the idea!

I don't know when I can get back to this, I kind of lost three weeks of my life due to health issues and have a big backload of stuff that needs to be done. But sometimes (heck, most of the time) I get fixated on something and waste time on something rather than more important stuff so I may get to it in a timely matter yet.

I hear you there ...   I've be out for 9 months (and no, I wasn't pregnant ).

[printer2]

At 300V as before.

[Rob Strand]

OK cool, I'll give it another shot.

[printer2]

OK cool, I'll give it another shot.

C1 might be 3 nF, R6 1k. I did a rough calibration of my meter's capacitance when it went out but I am ordering some 1% caps. I could not find my camera tripods so I was poking around with my right hand, had my near sight glasses on with a pair of cheaters over them (eyes getting too old for surface mount), SLR in my left hand trying to keep in focus and push the darn button. It was an interesting evening.

[Rob Strand]

C1 might be 3 nF, R6 1k. I did a rough calibration of my meter's capacitance when it went out but I am ordering some 1% caps. I could not find my camera tripods so I was poking around with my right hand, had my near sight glasses on with a pair of cheaters over them (eyes getting too old for surface mount), SLR in my left hand trying to keep in focus and push the darn button. It was an interesting evening

Is that the clock resistor and cap?  There does seem to be a problem on with the clock capacitance.  I'm seeing C8 on the schematic you posted earlier (no idea if the PCB has designators at all, or that the schematic matches them.)

https://www.diystompboxes.com/smfforum/index.php?topic=130852.msg1284850#msg1284850

For my rough simulation I stripped everything back.   I force the switching frequencies to match what you measured.  I don't even have the chip in the simulation.   As drawn, the schematic has no voltage clamps or snubbers so I didn't add any.   I do get quite a bit of ringing at some points in the circuit.

[printer2]

C1 might be 3 nF, R6 1k. I did a rough calibration of my meter's capacitance when it went out but I am ordering some 1% caps. I could not find my camera tripods so I was poking around with my right hand, had my near sight glasses on with a pair of cheaters over them (eyes getting too old for surface mount), SLR in my left hand trying to keep in focus and push the darn button. It was an interesting evening

Is that the clock resistor and cap?  There does seem to be a problem on with the clock capacitance.  I'm seeing C8 on the schematic you posted earlier (no idea if the PCB has designators at all, or that the schematic matches them.)

https://www.diystompboxes.com/smfforum/index.php?topic=130852.msg1284850#msg1284850

For my rough simulation I stripped everything back.   I force the switching frequencies to match what you measured.  I don't even have the chip in the simulation.   As drawn, the schematic has no voltage clamps or snubbers so I didn't add any.   I do get quite a bit of ringing at some points in the circuit.

Oops, wrong schematic of the same board. R25, C10. I got the 1k but might as well ignore the 3 nF value I got(schematic value 0.1 uF). I just spun a trimmer so the display on my meter matched the reading on my meter but with only one point of calibration I would not bet any money on it. Some 1% caps on order to do it properly.



On the ringing, I grabbed this picture earlier on yesterday but if you ask me where I could not be sure now. I think it might have been at 100V out without a load. Thought it might be due to no load, my spaghetti wiring, who knows so I forgot about it.



Since I got those pictures I decided to live dangerously and bumped up the voltage to 390V and 73 mA, 29W. Before I had a chance to scope anything, 'pop'. I felt the copper fins after and they did not seem overly warm. Puts me out of commission until I get my order in. At least now I can clean up the corner of my desk