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Inside the new Korad KA3305P linear PSU
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Gall:
Hi,
I wonder how the series mode work. I'd like to use it for an opamp dual supply. Does it work just as two independent power supplies of the same voltage connected in series, or do their voltages follow each other in case of overloading (going to the CC mode) just one of them?
torch:
I did not know, nor had I thought to check. So I just did a quick experiment.

Series mode, 3vdc per channel, (6vdc total ch.1+ to ch.2 -), current limit to 1.1 amp per channel,

metering  ch. 1 + to ch. 1 -,
shorting ch. 2 + to ch. 2 - :
ch. 1 continues to supply 3vdc, ch. 2 switches to CC mode @1.1A

metering ch. 2 + to ch.2 -,
shorting ch. 1 + to ch. 1 - :
ch. 2 continues to supply 3vdc, ch. 1 switches to CC mode @1.1A

metering ch. 1 + to ch.2 -,
shorting ch. 1 + to ch. 2 - :
both channels drop to 0vdc, both channels switch to CC mode @1.1A each

So I would say it behaves like 2 independent supplies in the case of overload.

(as noted earlier, in both series and parallel modes, ch.2 is the master. ie: the set points of ch.1 are changed to mirror the existing set points of ch.2 when entering either mode. changing ch.2 set points changes ch.1, and ch.1 controls are no longer available)


--- Quote from: Gall on February 29, 2016, 08:43:10 am ---Hi,
I wonder how the series mode work. I'd like to use it for an opamp dual supply. Does it work just as two independent power supplies of the same voltage connected in series, or do their voltages follow each other in case of overloading (going to the CC mode) just one of them?

--- End quote ---
Gall:
Thank you. That means, a dual-supply circuit will become an asymmetric power in case of overload. I wonder how hard it would be to fix that...
Aeternam:
I have one of these and I've been very happy with it.

I've recently hooked it to my scope to see how it was behaving, and I've noticed some strange ripples when I turn it off when the output is set to OFF (see attachments). Is this something I should be worried about? I'd hate to have to disconnect the leads when I turn it off to go watch some telly...

Also, it makes a quite audible GONG sound when I turn it on. (Not always though.) Is this designed so that you're awake when you start using it?  ;D
mos6502:

--- Quote from: Aeternam on March 06, 2016, 02:01:47 pm ---I have one of these and I've been very happy with it.

I've recently hooked it to my scope to see how it was behaving, and I've noticed some strange ripples when I turn it off when the output is set to OFF (see attachments). Is this something I should be worried about? I'd hate to have to disconnect the leads when I turn it off to go watch some telly...

Also, it makes a quite audible GONG sound when I turn it on. (Not always though.) Is this designed so that you're awake when you start using it?  ;D

--- End quote ---

When the output is off, it's high impedance. You're just picking up random noise with your scope. To test this, just hook up a 1k resistor at the output.

As for the *boink* sound: say when you turn the supply off, the switch opens exactly at the top of the positive half wave. The transformer core will remain magnetized in that direction. Then when you turn it on again, you might turn it on at the top of the negative half wave. The winding will create a magnetic field that is opposite to the already existing field of the core. So you get an instantaneous mechanical force of the winding pushing against the core. It's kinda like the transformer is being hit with a hammer.
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