In our daily life, we always use constant voltage power supply, such as accumulator, dry battery and so on. Meanwhile, we use alternating current, which is also a kind of constant voltage power supply. And its output voltage never changes. However, the constant current power supply is different. For example, if constant current sets to 1A, the highest output voltage will be 100 volt. When opening the switch of constant current power supply, we can see the datum being displayed on the voltmeter and ammeter: the output voltage is 100 volt and the current is zero. You may doubt what’s wrong with that. In fact, according to the Ohm’s Law, constant current power supply is just how it is.
Why shall we need constant current power supply when we use lighting? Why not choose constant voltage power supply? There are four points to explain that. Firstly, LED is a kind of non-linear device. The small change of forward voltage leads to large change of forward current. For example, when using 3.5V 20ma LED, we should need three batteries. Though the voltage of new battery we buy from the supermarket is 4.5V, the current is five times higher than the specified valve, which is very easy to damage LED lighting. Secondly, about 1W LED lighting, if the voltage changes, the current will change and the light will darken. Thirdly, LED light output is proportional to forward current. If the forward current is lower, the light output will be lower. Fourthly, LED is semi-conducting lighting emitting diode. The volt-ampere characteristic of LED will change with the temperature changing.
As LED power supply, the goal of constant current power supply is LED glowing. In fact, we need use it in many cases. Such as indoor decorative lamps, stage lamps, advertising boards, advertising signboards, squares, etc. LED power supply is widely applied in our daily life. This, I believe, will be future trend. Because it is not easy to damage LED lighting.