New to Electronics

[tony3d]

Hi all, I'm new to this hobby, and just in the beginning learning stages. I just purchased the book Make Electronics, a bread board, a Klein mm1000 DMM, and just ordered a Korad power supply. Been having a blast going through the first chapters of the book. Never dealt with these DC power supply's before, and just want to make sure I understand this. If I set the volts to say 6.3, and hook the outputs to a 1K 1 watt resistor, the circuit should pull about 6.3mA's. So I preset the volts to 6.3, the amps to maybe 100mA's, and the circuit will only draw the 6.3 mA's it needs correct? So theoretically I could set amps to 7mA's, and the supply should power the circuit fine right?

[alm]

Yes, the resistor won't draw more current than dictated by Ohm's law. Under these conditions the current setting on the power supply only determines the maximum current. If you would take a 1 ohm resistor, however, according to Ohm's law 6.3 A would flow. The power supply would limit this to for example 100 mA. Does that mean it no longer obeys Ohm's law? No, it will reduce the voltage until the current reaches 100 mA, so the output voltage would be about 0.1 V. You will probably also notice a constant current light / annunciator turn on.

[c4757p]

Another way to think of it is that the power supply will always increase its output until it hits one of the two settings, where both are "limits". It's a constant-current power supply as much as it's a constant-voltage power supply, it just stops at any limit you set. And because whatever you connect will have some defined voltage-vs-current relationship, one will always be reached before the other.

That's usually how the circuit is implemented, too - two amplifiers, one monitoring current and one monitoring voltage, that are both able to restrict the output.

[tony3d]

Ok I see. So what is the best procedure to use when setting the supply? Mine does have an output switch.

[c4757p]

For the vast majority of applications, set it to the voltage you need, and then set it to just above the maximum current you'll ever need in that circuit.

Beware turning it on and off with a circuit connected - a surprising number of newer power supplies give a little unregulated fart at startup, I don't know if the Korad ones are included.

[alm]

In general you would set the voltage to whatever level you need, and then set the current limit to somewhat higher than you expect your circuit to draw. For example if your circuit is supposed to draw 100 mA, you might set it to 150 mA. This limits the current that will flow if something goes wrong. If you have no idea about the current, you might set it to some high value and then lower it based on the current it actually draws (as shown on the power supply).

[smashedProton]

Are you sure that you are a beginner?   You sound a hell of a lot better than most of the people giving advice around here .

[tony3d]

Wow! Thanks for all the advice. I was a hit nervous about playing with this thing, but now I have a much better understanding of how it works. Glad to know I have a solid resource.

[tony3d]

I have one more question. The korad has a feature called over voltage protection, and over amperage protection. The online manual is very vague about how to set it. Can anyone give me some insight. Can't wait to get this thing on Thursday. I just hope it works. After seeing all the bad press, I don't have a lot of faith.

[Electro Fan]

I have one more question. The korad has a feature called over voltage protection, and over amperage protection. The online manual is very vague about how to set it. Can anyone give me some insight. Can't wait to get this thing on Thursday. I just hope it works. After seeing all the bad press, I don't have a lot of faith.

I should know since I have a Korad but I haven't used these features.  I just gave Over Current Protection a try and I "think" this is what it does.  If you set the current to some max and then turn up the voltage to a point where the voltage becomes high enough that the DUT reaches the max current setting the unit will go into Constant Current mode where it will sit at the maximum current setting you specified even if you continue to turn up the voltage.  This is a "normal" behavior.  If you invoke the Over Current Protection and turn up the voltage instead of allowing the PS to supply the current right up to the max you had specified the PS shuts off the output at the max current specified.  I don't know what the Over Voltage Protection does.  Maybe you can tell us when you get your unit.

Let us know what you find out and figure out when you yours arrives.

[tony3d]

I will. Have you had any issues with your unit?

[Paul Price]

OVP is overvoltage protection.

When the output voltage rises above the set voltage due to "unexpected conditions (by connecting power supply output  to a voltage source greater than the output set voltage)", then the power supply cuts out until the voltage becomes equal to the set output voltage.

Copied from the online manual for the KA5000.

[c4757p]

It can also be useful to prevent accidentally setting your output voltage too high. My main power supply can go to 50V total (+/- 25V), and if I'm working on something more sensitive, I'll usually set the OVP threshold much lower than that. This way, it will shut down if I accidentally exceed my own set limit.

[tony3d]

ok, so once you set the voltage and amps you want, you just press the OVP, and OCP buttons, and thats it?

[Electro Fan]

ok, so once you set the voltage and amps you want, you just press the OVP, and OCP buttons, and thats it?

I'm not sure that on the Korad OVP works quite like c4757p describes for his PS - that's a TBD.
For OCP, yes, it's just a simple button push.  (It's a button push for OVP protection too, I just don't understand yet what Korad had in mind overall for OVP.)  Nothing on the Korad is hard, it's just a matter of whether it works 

I'm just kidding you - I think you are suitably balanced on the line between enthusiastic and suspicious 
You are going to be fine EEVblogger 

[tony3d]

I don't know, the more I read, the more I'm getting a bit afraid to even plug the damn thing in the wall! Thats all I need to do is have the thing blowup, and my wife will never let me live it down. Electro Fan, Has your Korad given you any trouble, because being that I'm just starting to learn the basics, I could never fix the thing if it failed?

[smashedProton]

I looked at the korad and it looks well enough designed.  Dont plug the output to the mains or to hv and yoy will probably br fine .  At this point you should be getting a parts surplus.  May I ask, what is your background?   You seem to be able to wright well. An engineer from another field?

[tony3d]

Thanks for the reply. Professionally, I'm a computer 3D modeler/ animator. I ran across this blog, and it inspired to get back into electronics which I left as hobby many years ago. In fact the last thing I ever built was a Heathkit Hero One robot! Now I've given away my age. I have been wanting to get back to electronics for a while now, and finally decided to do it. I attached a rendering I did for a Cary tube power amplifier.