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Registered Member #162
Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3141
Before you put the psu into service 'scope the output with resistive, capacitive and inductive loads, using constant voltage and constant current control. The 470 pF capacitor is the main loop response component, but unexpected things can happen under certain load conditions. My bench psu has a 'slow' option which makes it less responsive to sudden changes but more stable with some loads.
If you're using a micro then a power sequencing option may prove very useful.
I've scoped the supply during the construction phase and there was indeed problem with oscilations. Had to tweak the 470p capacitor (I am using 1.5nF now and the responce is good and no more problems with oscilations - tested it on quite a few different loads). The noise on the output is about 1mV but think it is caused by the probe of the scope as it is a cheap one (even when i short the probe there is still some noise on the scope).
The constant current mode is a different matter though - under hevy loads (3A+) there is about 10mV p-p "sine" at about 110khz on the output. Clearly caused by the 741. It is "good" for me as I rarelly run supplys in constant current. But if you have suggestions I will be gratefull if you share them.
Ruben - those cases are standartised around here (came in two different hights - this one is the taller) and were used for almost everything (from measuring equipments to power supplies). This one came from an old zener tester (for teaching purposes). It was donated by a teacher of mine. I just replaced the front panel.
Registered Member #3610
Joined: Thu Jan 13 2011, 03:29AM
Location: Seattle, WA
Posts: 506
Beautifully done. I need to find a case like that for the linear supply I'm building. I wound a custom 750VA 5 secondary iron toroid power transformer myself last year but have not finished building the rest of the supply yet.
non of the above - I am using the PIC's ADCs to sample the voltage and current and to drive the seven segments. The bug is that the indication is never really off - if there is zero voltage and current then the 7 segments are off (soo the channel is off). And I have set the reuqired limits (for current and voltage) really low - so sometimes the ADC pick up noise and indication tunrs on for 0.2secs till it is turned off again - but it happens rarelly and not worth to take the front pannel down and add a few lines of code.
I have been programing PICs for quite a lot of time now and someting like this takes about 20 min to program (I just take parts from previous programs and "stick" them together). For me wiring 2 ICL7107 for each channel is too much work (and too much space) hee hee
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Linear power supply
