Hi and welcome to the first installment of Teddy’s Tips. I’m Teddy and I will be
talking to you about CV and CC mode. More commonly known as constant voltage and constant
current mode of a power supply. This can be found in most of our power supplies and I
will be discussing with you how to reach the CV or CC mode, what it is and how it
affects your system.
So, as I said before, I will be explaining CV and CC mode, or more commonly known as
constant voltage and constant current mode of a power supply. In CV mode, the power supply
tries to keep the voltage at a constant value, and in constant current mode, the power supply
try to keeps the current at a constant value. So, let me begin this by drawing this graph.
So when we program the power supply, the voltage limit and the current limit, let’s say we
set it at 50 volts and 100 milliamps. That forms a graph like this where this region
is CC mode. And that region is CV mode, but how do you get the CC or CV mode?
Well, the important concept to take away from this is that there is no setting of the power
supply that said, oh, I want to be in CV or CC mode. No, the way you go into either CV
mode or CC mode is through Ohms law, through the load that you connect to the power supply.
So, if we look at Ohms law here, I=V/R and you have these two limits of 50 volts and
100 milliamps. We see that our critical resistance is 500 ohms. This is called the critical resistance
because if you attach a load that is greater than 500 ohms, let’s say we have 600 ohms,
and we have 50 volts, 600 ohms, by Ohms law, the current that it will be trying to
pull is about 0.083 amps. Meaning that it will be in the CV mode since you’re not slamming
into this 100 milliamp limit. Now, if you have less resistance than this critical resistance,
and you have 400 ohms. The current of the load will try to pull about
0.125 amps forcing the power supply in the CC mode because it will slam into this current
limit of 100 milliamps and the power supply will put on the brakes and say, no, I’m
not going to let you go past this 100 milliamps and regulate it at 100 milliamps.
But this will break the laws of physics if we have 100 milliamps, 50 volts and 400 ohms, because
you will be at only 100 milliamps, but it will be wanting to pull 0.125 amps.
So, since it pulls you into CC mode, the voltage will need to drop down. So at this point you
will see that the power supply, through Ohms law, so 100 milliamps times 400 ohms
will equal about 40 volts. So, as you can see, it’s the resistance
or the load that you put on the power supply that determines if you are in constant voltage
or constant current mode.
And we look at first the voltage in determining the constant voltage or constant current mode.
Because the power supplies are optimized to operate as constant voltage power supplies.
So that’s why we first look at the voltage and look at the load that we connect to it
and determine if the current is reaching the current limit or not. So we will demonstrate
these properties in our next segment on an actual power supply and an actual electronic load.
So, I hope that this clears up any doubt that you might have had about this and hope
you enjoy our next segment.