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CV Constant Voltage source,-1st example on top, is most common, Voltage is fixed, current changes base on how much devices uses all the way up to the maximum the supply can deliver.
CC Constant Current Source- 2nd example, Is where the current supply is fixed, but now the voltage will actually dynamically go up or down to keep the current the same. But as you can see it's supply 2v at 40mA just like the 1st example on top. For all intensive purposes they are the same. The only time you they're different is when you set the current limit below or above what the circuit draws. Set it low, circuit won't get enough voltage, set it high, circuit get's too much voltage.
3d example at the bottom, we see a CV source and it's able to supply the needed 20mA to each LED. 40mA is needed and used for the LEDs to be fully on for the whole circuit.
We see the supply source is a CC source note the symbol how it's different the the typical battery symbol.
In this example we've set the supply to only supply a maximum of 20mA. We can see that the LED's are getting half the power since the supply won't deliver more then 20mA total so each LED has to share the 20mA only getting 10mA each.
The way this is done is that the voltage is decreased note how it's showing 1.93v.
*Note the opposite is true also, if set the current higher then the devices normally uses, the supply will increase the voltage as much as it's capable until either it can't produce more voltage pressure, or the circuit burns up since the voltage and the current have gone above the normal voltage the devices uses, bulbs will glow brighter then ever and burn right out, motors will spin very fast and short out, sensitive components will release their magic blue smoke. You can play with the examples and see what happens with the voltage when you set the current lower then the devices' maximum, or far above it.
I've added to extreme circuits at the bottom so you can see what setting constant current supply too low or high does, check out the values.
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