EEVBlog #221 power supply build.

[Beamin]

So after watching this video: Why doesn't the load resistor he uses on it get super hot when it's connected up in constant voltage mode? I tried this a while ago and thought I burned up or burned myself on the resistor when I tried this. Can't that part put out an amp (5W) or so? Or does he have his supply CC limited? I shorted mine by accident and the LM part got hot enough to melt plastic before I shut it off. It still works though that's a durable part was shorted for a while before I noticed the smell of burning.

Is it possible to build the LM out of discrete parts or does it contain things like those transistors with multiple legs that you can't simulate or other exotic parts like temp regulated resistors inside?

[Beamin]

How does the LT3080  know you are trying to control current and voltage off the same pin?

[Kleinstein]

The LT3080 like most other voltage regulators normally controls the voltage. It is only if the current exceeds a certain limit (around 1.1 A for the LT3080) that the chip changes to current control. This similar to a lab supply - it is either the voltage or current control active to keep the output at the boundary of the set voltage or current. It is the load that decides which control is needed.


It is possible to build a voltage/current regulator from discrete parts. There are no magic parts inside that are essential. One may not be able to directly copy the circuit because of such odd parts like multi-emitter transistors and some parts like current mirrors don't work as good. However discrete resistors are generally better than on chip ones and one has larger caps available - so discrete circuits usually look different.
Simulation is possible anyway, if one gets the right models.  Essentially all modern analog chips are simulated before making them from silicone.

[Beamin]

The LT3080 like most other voltage regulators normally controls the voltage. It is only if the current exceeds a certain limit (around 1.1 A for the LT3080) that the chip changes to current control. This similar to a lab supply - it is either the voltage or current control active to keep the output at the boundary of the set voltage or current. It is the load that decides which control is needed.


It is possible to build a voltage/current regulator from discrete parts. There are no magic parts inside that are essential. One may not be able to directly copy the circuit because of such odd parts like multi-emitter transistors and some parts like current mirrors don't work as good. However discrete resistors are generally better than on chip ones and one has larger caps available - so discrete circuits usually look different.
Simulation is possible anyway, if one gets the right models.  Essentially all modern analog chips are simulated before making them from silicone.

What I don't understand is he can adjust the current and not just have it max out at 1amp. As far as the part knows it is just seeing a change in voltage at the input pin. Why doesn't the second part just change the voltage fed to it like the first one?


And how do those resistors not get super hot at 10ohms or what ever low value it was?