Re: Op-amp mystery

From	Jan Panteltje <alien@comet.invalid>
Newsgroups	sci.electronics.design
Subject	Re: Op-amp mystery
Date	2024-09-12 10:12 +0000
Message-ID	<vbueqp$5435$1@solani.org> (permalink)
References	<1qznz5d.1m219rjmrzni6N%liz@poppyrecords.invalid.invalid> <rhm0ejtf032lq1g2q7kkvl20081gsd1v8r@4ax.com> <vbt7de$3r928$2@dont-email.me> <vbu558$4nm1$1@dont-email.me>

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On a sunny day (Thu, 12 Sep 2024 08:27:36 +0100) it happened piglet
<erichpwagner@hotmail.com> wrote in <vbu558$4nm1$1@dont-email.me>:

>On 11/09/2024 23:59, Lasse Langwadt wrote:
>> On 9/10/24 16:47, john larkin wrote:
>>> On Tue, 10 Sep 2024 10:31:37 +0100, liz@poppyrecords.invalid.invalid
>>> (Liz Tuddenham) wrote:
>>>
>>>> It's always the stupid things that cause the most trouble:
>>>>
>>>> I was working on a fairly straightforward experimental audio circuit
>>>> using TL074 op-amps laid out on Veroboard, which is prone to inter-track
>>>> shorts unless you are very careful with your soldering.   The gain of a
>>>> virtual-earth stage was too high, so I altered some resistor values to
>>>> cut it down.
>>>
>>> Show us a pic of your breadboard!
>>>
>>>>
>>>> As this was a stereo system, I experimented with one channel first and
>>>> then switched off and replaced the equivalent resistors in the second
>>>> channel (one of the other op-amps in the same chip).
>>>>
>>>> The input signal was a 6 Kc/s sinwave at about -10 dBu.  After the
>>>> modification, the volume control, which was in a feedback loop, didnt
>>>> seem to make much difference.  Then I realised that applying the signal
>>>> to the left channel gave a distorted version of it in the right channel
>>>> and vice-versa.  Obviously I had shorted two tracks somewhere - but
>>>> where?
>>>>
>>>> Things got even worse when I realised that the input signal was
>>>> appearing on the virtual earth input of each op-amp, this definitely
>>>> can't happen!  I decided it was time to switch off the power supply and
>>>> go and ponder the problem over a cup of tea.
>>>>
>>>> That was the point where I discovered I hadn't switched the power supply
>>>> on in the first place.
>>>
>>> Sometimes people note that a CMOS circuit works properly with no power
>>> supply, because some ESD diodes are rectifying a logic input.
>> 
>> until all the inputs are low, then it only works until the bypass cap is 
>> discharged ;)
>> 
>> seem to remember seeing a boost converter made from just a cmos gate and 
>> an inductor, using the output as input and the supply pins as output via 
>> the ESD diodes, but I can't find it again, but I found this
>> 
>> https://www.edn.com/efficient-voltage-doubler-is-made-from-generic-cmos-inverters/
>> 
>> 
>> 
>
>It is possible you were remembering my posting this in April 2016:
>
><https://www.dropbox.com/scl/fi/8n4fz5o0r79rkmbn05j1a/micropowerBoost.pdf?rlkey=v1w9vm0his1pzd3lwd93dsm3v&st=5x8irpk6&raw=1>
>
>All power flows through the inductor. The ESD diodes are only involved 
>during startup, once oscillator running the output stage n-fet is the 
>boost switch and the p-fet is the synchronous rectifier. A version built 
>using 74HC132 was in a successful product which needed micropower 5V 
>from 2-3V input.
>
>piglet

Interesting!

Classic voltage doubler is the Villard circuit:
 https://josepheoff.github.io/posts/diode-capacitors-volts-pt1

And if you need more low power voltage:
 https://panteltje.online/pub/PMT_regulated_power_supply_diagram_img_3182.jpg
 https://panteltje.nl/pub/PMT_HV_supply_componet_side_img_3180.jpg
 https://panteltje.nl/pub/PMT_HV_generator_size_img_3174.jpg
has been working for decades now...
also all battery powered
 https://panteltje.nl/pub/gamma_spectrometer_plus_probe_plus_geiger_counter_2_IMG_4185.JPG
 https://panteltje.nl/pub/gamma_spectrometer_supply_side_MG_6578.JPG

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Thread

Op-amp mystery liz@poppyrecords.invalid.invalid (Liz Tuddenham) - 2024-09-10 10:31 +0100
  Re: Op-amp mystery Don Y <blockedofcourse@foo.invalid> - 2024-09-10 05:27 -0700
  Re: Op-amp mystery john larkin <jlarkin_highland_tech> - 2024-09-10 07:47 -0700
    Re: Op-amp mystery Jan Panteltje <alien@comet.invalid> - 2024-09-10 15:05 +0000
    Re: Op-amp mystery Lasse Langwadt <llc@fonz.dk> - 2024-09-12 00:59 +0200
      Re: Op-amp mystery Don Y <blockedofcourse@foo.invalid> - 2024-09-11 19:00 -0700
      Re: Op-amp mystery john larkin <JL@gct.com> - 2024-09-11 19:10 -0700
      Re: Op-amp mystery piglet <erichpwagner@hotmail.com> - 2024-09-12 08:27 +0100
        Re: Op-amp mystery Jan Panteltje <alien@comet.invalid> - 2024-09-12 10:12 +0000
    Re: Op-amp mystery liz@poppyrecords.invalid.invalid (Liz Tuddenham) - 2024-09-12 13:21 +0100
      Re: Op-amp mystery piglet <erichpwagner@hotmail.com> - 2024-09-12 14:34 +0000
        Re: Op-amp mystery liz@poppyrecords.invalid.invalid (Liz Tuddenham) - 2024-09-12 18:03 +0100
  Re: Op-amp mystery John Robertson <jrr@flippers.com> - 2024-09-10 12:38 -0700
    Re: Op-amp mystery Don Y <blockedofcourse@foo.invalid> - 2024-09-11 12:15 -0700
      Re: Op-amp mystery liz@poppyrecords.invalid.invalid (Liz Tuddenham) - 2024-09-11 21:35 +0100
        Re: Op-amp mystery Don Y <blockedofcourse@foo.invalid> - 2024-09-11 18:37 -0700
  Re: Op-amp mystery legg <legg@nospam.magma.ca> - 2024-09-11 09:29 -0400

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