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Hi - thanks for your reply.</div>
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I tested with and without loads, and the start-up issue seems to happen more often with loads applied (say, 3-400ma worth of modules) than without.</div>
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<div id="divRplyFwdMsg" dir="ltr"><font style="font-size:11pt" face="Calibri, sans-serif" color="#000000"><b>From:</b> tpuefke <tpuefke@protonmail.com><br>
<b>Sent:</b> Thursday, August 27, 2020 12:32 AM<br>
<b>To:</b> ackolonges fds <ackolonges@hotmail.com>; Synth-Diy mailing list <synth-diy@synth-diy.org><br>
<b>Subject:</b> Re: [sdiy] Power Supply Start-up Issues</font>
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Hi,<br>
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dumb question: a load was always present when this happened?<br>
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i've been using the same design for ages, never had any problems.<br>
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(albeit using 4004 diodes, like the Ray Wilson basic wall wart design)<br>
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however the positive regulator can fail to power up if no load is present at all. <br>
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cheers,<br>
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Tom<br>
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Am Mittwoch, den 26.08.2020, 11:52 +0000 schrieb ackolonges fds:<br>
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<div><span style=""><span>><span> </span></span></span>I believe C7, C8, and C9 in the schematic are meant to represent capacitance on the modules to be<br>
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<div><span style=""><span>><span> </span></span></span>powered - ie. not part of the power supply itself. In my own modules I generally just put<br>
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<div><span style=""><span>><span> </span></span></span>capacitors to the rails from ground, so at the moment there isn't really a "C9", but since it's<br>
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<div><span style=""><span>><span> </span></span></span>for a modular synth, it needs to be able to handle modules that do have it.<br>
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<div style="width:100ch; word-wrap:break-word; word-break:break-word"><span style=""><span>><span> </span></span></span>From: Liam Wall <<a href="mailto:liam.wall@gmail.com" style="color:rgb(45,113,184)">liam.wall@gmail.com</a>><br>
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<div style="width:100ch; word-wrap:break-word; word-break:break-word"><span style=""><span>><span> </span></span></span>Sent: Wednesday, August 26, 2020 11:39 PM<br>
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<div style="width:100ch; word-wrap:break-word; word-break:break-word"><span style=""><span>><span> </span></span></span>To: ackolonges fds <<a href="mailto:ackolonges@hotmail.com" style="color:rgb(45,113,184)">ackolonges@hotmail.com</a>><br>
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<div style="width:100ch; word-wrap:break-word; word-break:break-word"><span style=""><span>><span> </span></span></span>Subject: Re: [sdiy] Power Supply Start-up Issues<br>
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<div><span style=""><span>><span> </span></span></span>From the description there the diodes are not the problem. C9 is the problem, with the diodes<br>
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<div><span style=""><span>><span> </span></span></span>being a (partial) fix.<br>
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<div style="width:100ch; word-wrap:break-word; word-break:break-word"><span style=""><span>><span> </span></span></span>Do you have an equivalent of C9 in your circuit?<br>
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<div style="width:100ch; word-wrap:break-word; word-break:break-word"><span style=""><span>><span> </span></span></span>On Wed, 26 Aug 2020, 12:26 ackolonges fds, <<a href="mailto:ackolonges@hotmail.com" style="color:rgb(45,113,184)">ackolonges@hotmail.com</a>>
wrote:<br>
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<div style="width:100ch; word-wrap:break-word; word-break:break-word"><span style=""><span>><span> </span></span></span>Hi All,<br>
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<div><span style=""><span>><span> </span></span></span>I've been having issues with a very standard +/- 12V power supply design for a modular synth.<br>
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<div><span style=""><span>><span> </span></span></span>Every once in a while when powering up, the positive rail doesn't rise, and it needs to be reset<br>
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<div><span style=""><span>><span> </span></span></span>to work. After some trial and error, and research, I found mention of this issue in Douglas Self's<br>
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<div><span style=""><span>><span> </span></span></span>'Small Signal Audio Design' book, where he shows a circuit almost identical to my power supply. A<br>
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<div><span style=""><span>><span> </span></span></span>screen grab of the related page can be found here:<span> </span><a href="https://pasteboard.co/Jo8PuIu.png" style="color:rgb(45,113,184)">https://pasteboard.co/Jo8PuIu.png</a><br>
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<div style="width:100ch; word-wrap:break-word; word-break:break-word"><span style=""><span>><span> </span></span></span>This paragraph from that page describes the issue I'm having perfectly : <br>
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<div><span style=""><span>><span> </span></span></span>"D2, D4 will prevent damage in this case, but leave the power supply vulnerable to start-up<br>
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<div><span style=""><span>><span> </span></span></span>problems; if its output is being pulled down by the 15 V regulator, the 15 V regulator may refuse<br>
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<div><span style=""><span>><span> </span></span></span>to start. This is actually a very dangerous situation, because it is quite easy to come up with a<br>
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<div><span style=""><span>><span> </span></span></span>circuit where start-up will only fail one time in 20 or more, the incidence being apparently<br>
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<div><span style=""><span>><span> </span></span></span>completely random, but presumably controlled by the exact point in the AC mains cycle where the<br>
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<div><span style=""><span>><span> </span></span></span>supply is switched on, and other variables such as temperature, the residual charge left on the<br>
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<div><span style=""><span>><span> </span></span></span>reservoir capacitors, and the phase of the moon. If even one start-up failure event is overlooked<br>
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<div><span style=""><span>><span> </span></span></span>or dismissed as unimportant. then there is likely to be serious grief further down the line. Every<br>
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<div><span style=""><span>><span> </span></span></span>power supply start-up failure must be taken seriously."<br>
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<div><span style=""><span>><span> </span></span></span>Unfortunately after stressing how important it is to fix such an issue, no solutions are<br>
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<div><span style=""><span>><span> </span></span></span>mentioned... I've tried removing all of the protection diodes, increasing and decreasing the<br>
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<div><span style=""><span>><span> </span></span></span>value of the smoothing caps, tried many different makes of voltage regulators, and also tried an<br>
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<div><span style=""><span>><span> </span></span></span>NTC thermistor to slow the in-rush current, all to no avail. <br>
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<div><span style=""><span>><span> </span></span></span>I'm starting to run out of ideas, so if anyone on the list has come across a fix it would be great<br>
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<div><span style=""><span>><span> </span></span></span>to hear about it. <br>
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