General > General Technical Chat

What is an idea behind OVP in Korad PSU?

(1/7) > >>

firehacker:
Just became an owner of Korad KA3010D lab PSU. For a few decades I was using pure analog coarse/fine linear lab power supplies and got tired of ringing/bouncing wipers of potentiometers leading to unstable voltage/current control.

Well, this Korad PSUs have OVP and OCP features.

An idea behind OCP is absolutely clear: when actual current reaches (for whatever reason) a set point, instead of just limiting the current by lowering output voltage the device will completely switch its output off. Indeed, in some cases if you know your load will not draw more current under constant voltage than some known value, if it eventually start to draw, it DEFINITELY means something went wrong in your circuitrarty and immediate shutdown will indeed PROTECT something in your load.

OVP is different story. I can't get an idea behind this feature. If your load is always sinking current/energy, then UNDER NO CIRCUMSTANCES voltage on the output terminal may become higher than what you set on you Korad PSU. And thus OVP is just useless since in never happens to have OV condition. But if your load can sometimes become a source of electromotive force itself and start producing power, then, yes, voltage on output terminals may become higher than what you just set. An example of this may be a DC motor which, if spinned by some external force, may become a voltage generator rather than consumer.

Okay. But! Turning off series pass transistor of the PSU in such condition does not make any difference. If you set your PSU to output 15V and your load started to produce 20V on it's terminals, switching off PSU will not cancel this 20V to be present on output/input terminals.

So what does this overvoltage protection really protect? What it intended to protect? If it is intended to protect the load from overvoltage condition, then it is useless since the load itself generate this overvoltage condition and it will keep producing it despite of PSU series-pass transistor state. If it is intended to protect the PSU itself (rather than "load"), then, again, it doesn help at all since voltage produced by load will be still present on internal circuitrary of the PSU (unless there is a relay which physically disconnects PSU's output terminals from PSU internal circuitrary).

On the other hand, if an idea behind OCP is "instead of current-limiting just immediately prevent any current from flowing out of PSU", OVP must (by analogy) work as follows "instead of voltage-regulating just immediately prevent any voltage to be present on PSU terminals". To achieve this PSU must short its terminals when OVP is triggered. However, even if such such OVP is not turned on, "voltage-regulating" ability of the PSU has to include sinking current from extenal device to keep voltage on predefined level, not just sourcing current.

At this point we come to something what is called four-quadrant power supply.

An ideal voltage source is four-quadrant: it can produce positive voltage and source current, positive voltage and sink current, negative voltage and sink current and negative voltage and source current. I believe (even though I didn't look though schematic or revese-engineer it) Korad PSU is not even a two-quadrant PSU — as it is true for almost every lab bench PSU of this class and price. It can only produce positive voltage and it can only SOURCE current (but not sink).

So, if it has single-quadrant operation by design, then having OVP which shorts PSU's terminal is inconsequent. If only it was, it would be reasonable if without OVP the PSU tries to keep voltage at defined value even by sinking current from the "load" (in quote-marks, because the "load" itself produce a voltage) literally pulling down "V+" rail to "V-" and with OVP switched instead of clamping voltage by sinking current it shorts its terminal to completely remove any voltage from the terminals (like in case with OCP it completely "removes" a current from the output).

So, I am almost sure Korad is single-quadrant operation. And if so, it is likely not going to short its terminals on OV-condition. And just switching off series-pass transistor does protect neither the PSU nor a "load" from overvoltage.

So, what's the point and how it is intended to work?

ataradov:
I think the idea is to just disconnect the power supply when something unexpected happened to not make things worse potentially. It may not be a constant thing, but if something in the powered circuit periodically starts to be a source, then it makes sense to turn the power off as soon as possible and not subject the circuit to over-voltage condition longer than necessary.

thm_w:
If I'm working with a sensitive 3V device, I can set OVP to 3.5V and prevent accidentally sending excess voltage to the device.
Yeah?

https://www.reddit.com/r/AskElectronics/comments/48ujfe/please_help_me_understand_the_over_voltage/
https://www.us.lambda.tdk.com/resources/blogs/20231025.html

ataradov:
I guess it also helps against wrong user input too. If you get too happy with a knob, it will prevent damage. Although more useful version of the feature would be a user limit where PSU itself does not generate more than some set limit. And may be turn off the output if it sees that it can't regulate the output.

firehacker:

--- Quote from: thm_w on January 14, 2025, 01:11:19 am ---If I'm working with a sensitive 3V device, I can set OVP to 3.5V and prevent accidentally sending excess voltage to the device.
Yeah?

--- End quote ---

No, you can't. There is no two different voltage settings in Korad PSU: normal output voltage and overvoltage threshold. There's only one voltage setting: output voltage. That's it.

And if you are working with sensitive 3V device, you are going to set 3.00V as output voltage. And even without OVP functionality any decent PSU will not go higher than what you set, so the PSU itself can't cause overvoltage. The device-under-power actually can cause overvoltage if it contains switchable caps or inductors or other source of EMF such are thermo- or photovoltonic cells, motors and so on. But in this case the device overvoltages itself, not the PSU. I mean PSU can't protect device from creating overvoltage on device's power rails.


--- Quote ---I guess it also helps against wrong user input too. If you get too happy with a knob, it will prevent damage.
--- End quote ---
You are confusing LOCK button functionality with OVP functionality. If you mean unintentional rotation of the know leading to overvoltage.

If you mean the other thing: trimming upper boundary of the range in which user can change voltage by rotating know, this is not the case for KAxxxx PSUs since there are no such thing as adjustable upper boundary of accessible voltages range.

For KA3010D full available voltages range is 0V to 31V. If you mean that one want to limit himself say for being able to adjust voltage (by turning a knob) only in range from 0V to 5V — no, that isn't how OVP works on Korad. You can't set OVP to 5V and then go anywhere from 0V to 5V by careless rotating knob being sure that PSU won't let you above 5V.
a) You can't set OVP threshold to arbitrary voltage, there's no such settings. There's only one voltage setting: the output voltage
b) There is no setting that limits the range of voltage adjustment.


Navigation

[0] Message Index

[#] Next page

There was an error while thanking
Thanking...
Go to full version
Powered by SMFPacks Advanced Attachments Uploader Mod