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| PSU Constant Current response timing comparison |
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| Peter_O:
Having collected some PSUs with CC capability I’d like to know how quick they are responding to an overcurrent condition. Test setting is like this: PSU is configured to deliver 25V/1A. PSU is connected to a 10 Ohms resistor. This load circuit is switched on/off by a MOSFET-Module, controlled by a function generator. off: No load, PSU idles at 25V/0A on: PSU would deliver I=U/R=2,5A but limits current to 1A by lowering the voltage to 10V. The question was: How quick does this happen? Here are the results: Agilent 6653A see picture above. C1/yellow: Mosfet control C2/magenta: Voltage over R C3/cyan: PSU voltage With the load switched on, the Agilent needs about 20ms to adjust to 1A current. Siglent 3303X(-E) The Siglent is slower with about 30ms. Going down from 25 to 10V it switches the transformator outlet by relay. HP6114A For the HP6114A the test runs with it’s voltage limit of 20V. It needs about 30ms to adjust to 1A too. Interesting to see, that it needs about 300ms to recover back to 20V when idle. Voltcraft PS 303 pro Surprisingly, the low cost Voltcraft is the fastest one: It needs 5ms to adjust to 1A, even with a transformator relay switching, which can been seen in the 2nd shot. To be continued with the next post about the TDK Lambda Geness 50-30 ... |
| Peter_O:
TDK Lambda Genesys 50-30 The Genesys is by far the slowest one: It needs about 400ms to adjust to 1A. With the Genesys, a fold back delay can be configured via the serial interface and would be persistent over a power cycle. I tried to reset any fold back delay, but got an C01 Error (Wrong command) for all fold back related commands. Other commands are fine. So I assume, this PSU might just be that slow. Overall, the Voltcraft and the TDK are the surprises of this short shoot out. |
| switchabl:
--- Quote from: Peter_O on July 30, 2022, 09:12:11 am ---Overall, the Voltcraft and the TDK are the surprises of this short shoot out. --- End quote --- To be fair, they do tell you this in the datasheet. Down-prog response time no-load: 800ms At a current rating of 50A, 2.5A is basically the same as "no-load". That 800ms spec will be 30V to 0V, so 400ms from 25V to 10V is really spot on. Current fold-back is really about overcurrent protection. It will turn off the power supply completely when tripped instead of going into CC mode. So it won't help with response time. In fact, it is probably done in software. |
| maxwell3e10:
Thanks for posting these plots! Always great to see actual data. |
| alm:
Thanks for posting the data, indeed! If you subtract the time it takes to discharge the output cap down to 10V through the resistor, how much time remains that can be attributed to the regulation? The magenta curve in many of the traces looks quite a lot like exponential discharge to me. For example the 6114A has a 490 uF output cap according to the schematics. Discharging a 490 uF cap through a 10 Ohm resistor from 25V to 10V takes: $$10\textrm{V} = 25\textrm{V} e^{\frac{-t}{RC}}$$ $$t = -\ln{\frac{10 \textrm{V}}{25 \textrm{V}}}\cdot 10 \textrm{Ohm}\cdot 490 \textrm{uF} = 2 \textrm{ms}$$ But I imagine the Genesys might have much larger output caps. An active down programmer, which I'm not sure if any of these units have (the 6653A maybe?), would speed up the process of discharging the cap. By how much depends on the current the down programmer draws. |
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