# Constant voltage AND constant current?

Hi, smart people of the internet :)
Is there a power supply or a converter that can be set on a specific voltage and current, and keep both constant at the same time?

I looked at ebay converters like B3606, DPS5015, BST400 and the like. They all have constant voltage (CV) and constant current (CC) settings, but they can't do both at the same time. If for example the current being drawn is too high, the unit switches from CV to CC and drops the voltage as much as needed to keep the current constant.

Is a simultaneous CC CV power supply even a thing?

Thanks!

21 days ago

Well, you are sort of ignoring the character of the load. The load is the thing to which the power supply, supplies power.

At the top of the Wikipedia article titled, "Current-voltage characteristic", there are some graphs of some easy, idealized, I-V curves for some real physical things you really could attach to a power supply.

https://en.wikipedia.org/wiki/Current%E2%80%93volt...

The titles of these graphs are the names of these physical things, loads, are "large resistance", "small resistance", "diode", and "battery".

Also I want to mention some loads that are even easier to imagine:

An open circuit has the line I=0 as its I-V curve.

A short circuit has the line V=0 as its I-V curve.

The actual current through, and voltage across, a load when it is powered, is a point somewhere on that curve.

If I imagine that curve is like a stiff piece of wire, with a bead on it, I can slide the bead along the wire, but I cannot move the bead to a place that is not on the wire.

Attaching a load to power supply with CC and CV limits, is kind of like drawing two lines on the same graph for the load's I-V curve. The current limit is a horizontal line, I = llimit. The voltage limit is a vertical line, V=Vlimit.

Unpowered, a passive load (like a resistor or diode) has V=0 and I=0.

When I connect that load to a CC CV power supply, it is sort of sliding the bead up the wire, starting from V=0 and I=0, until it bumps into one of those limits, the line V=Vlimit, or I=Ilimit.

If the bead is bumping against the line V=Vlimit, then the power supply is in constant voltage mode.

If the bead is bumping against the line I-Ilimit, then the power supply is in constant current mode.

iceng21 days ago

There are plenty of low cost lab supplies that can be set to deliver a voltage and set a maximum not to exceed current.

You all ready understand that the load determines the voltage and current by Ohms Law..

Where ; If you set a voltage the current is I=V/R_load..

And ; If you set a current the voltage is V=IxR_load..

NO simultaneously CC and CV cannot exist.. Because it would violate a physical Law !!

rickharris21 days ago

YES / NO.

For any given resistive load then the voltage and current are dependent on each other. V=I xR Ohms law. The current drawn for any given load is governed by what the load draws for a given voltage.

However what you do get are power supplies that can set the voltage and limit the current to a maximum. This will be variable according to your needs.

If that helps.