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| Inside the new Korad KA3305P linear PSU |
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| Salas:
--- Quote from: dom0 on September 07, 2015, 09:43:52 am --- --- Quote from: Salas on September 07, 2015, 08:53:49 am ---How a classic linear chip like 78XX, 317 etc. would react when dragged along that file for a load it could bear? That could give some kind of scaled down screenshot comparison. --- End quote --- Not much, as stability is mostly an issue with "discrete" (i.e. op amp based) PSUs, while the integrated emitter-output regulators are very stable (they don't have a lot of loop gain to begin with and their fT is in the region of 500-1000 kHz). So output waveform will mainly depend on the output capacitor. --- End quote --- I would expect them classic chips steadier too. Maybe torch has one around to drag on the rough file. Is such a bench supply relying just on op-amps or an MCU controls the loop more likely? |
| Salas:
--- Quote from: torch on September 07, 2015, 12:28:08 pm --- --- Quote from: Salas on September 07, 2015, 08:53:49 am ---Using the file on a PSU rings a bell but I can't recall exactly. Was it some guru like Bob Pease or Jim Williams who did it first? --- End quote --- I can't say I know of the file test being applied to a PSU. However, it's certainly not original to me: it is an old trick for down-and-dirty testing of automotive ignition coils. Scrape the primary wire along a coarse file and look for a series of sparks jumping a gap tester attached to the secondary. --- End quote --- So that testing has roots in automotive practice. Interesting. I must have read something in the past about it for an electronics PSU torture test also. It could have migrated by some car tampering electronics engineer. |
| torch:
--- Quote from: Salas on September 07, 2015, 02:40:03 pm ---It could have migrated by some car tampering electronics engineer. --- End quote --- Would have to be an old engineer -- someone who was around in the days of points and condensers... |
| dom0:
--- Quote from: Salas on September 07, 2015, 02:32:46 pm --- --- Quote from: dom0 on September 07, 2015, 09:43:52 am --- --- Quote from: Salas on September 07, 2015, 08:53:49 am ---How a classic linear chip like 78XX, 317 etc. would react when dragged along that file for a load it could bear? That could give some kind of scaled down screenshot comparison. --- End quote --- Not much, as stability is mostly an issue with "discrete" (i.e. op amp based) PSUs, while the integrated emitter-output regulators are very stable (they don't have a lot of loop gain to begin with and their fT is in the region of 500-1000 kHz). So output waveform will mainly depend on the output capacitor. --- End quote --- I would expect them classic chips steadier too. Maybe torch has one around to drag on the rough file. Is such a bench supply relying just on op-amps or an MCU controls the loop more likely? --- End quote --- MCU control loop would be insanely slow and unreliable. There are some very high power / special purpose SMPS which use DSPs for the control loop, though. |
| Kleinstein:
The linear regultor is done analog, the µC just gives the setpoint and might give a controled ramp after power on. A µC might be used to controll the relays and the fan. The reaction to this very rough test looks OK, but not very good - there is one spike going noticable higher than normal voltage. The funny spike at the beginning seems to be part of the normal way of switching from CC to CV. So having short pulse of high current might be a problem for this regulator. This might even leed to overheating of the transistors, as the relays are not very effective with such dynamik loads. For stability testing there are usually three critical cases: 1) having a low loss capacitor in the 10 µF range at the output and essentially no load. Internal Load might vanish at vry low voltage, so something like 50 mV might be the most critical volatge. This might give istability at high frequency (e.g. 100 kHz), especially if the output cap is small. 2) same as befor, but at a high current from an more or less ideal current sink. This might be rather difficult to build. 3) having a large low (as low as possible) ESR cap of some 1-10 mF and large load steps, especially down from a high current (but not limiting) to essentially 0 current. Here a manualy opening contact migh be enough, as reaction is likely rather slow in the ms range. |
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