How to distinguish between constant current and constant voltage LED switching power supply? First, understand what constant current and constant pressure mean. After the concept is clear, it will be much easier to distinguish. Constant current refers to a constant current, which means that the output current is constant and will not change with changes in the load. Constant voltage means that the output voltage is constant and will not change with changes in the load.
For the LED constant current power supply, when the load is allowed, the output current is constant and does not change with the change of the load.
For the LED constant voltage power supply, when the output power of the power supply allows, the output voltage is constant and does not change with the change of the load.
After understanding the basic concepts, how to distinguish?
1. Directly distinguish from the indicator parameters printed on the LED power supply
If it is a constant voltage source, the output voltage is generally marked with a fixed value, and the output current is marked with the maximum value. As shown in the figure below, the output voltage is marked with a fixed value of 45VDC, and the output current is marked with a maximum value of MAX: 0.5A.
If it is a constant current source, the output voltage is marked with a range, and the output current is marked with a fixed value. As shown in the figure below, the LED constant current source, the output terminal is marked with a voltage range: DC72~125V, and the current standard is a fixed value: 300mA.
2. Connect the load to measure. When the load changes, one voltage remains the same, one current does not change, the voltage does not change is a constant voltage source, and the current does not change is a constant current source. First use a multimeter to measure the no-load output voltage of the LED power supply (if it is a constant voltage source, the voltage is the output voltage, if it is a constant current source, the voltage is the maximum output voltage), and then estimate the appropriate load based on the measured voltage. (Pure resistance can be connected), such as measuring the voltage after connecting 50Ω and 100Ω resistance respectively. If the voltage does not change, it is a constant voltage source, if the voltage changes linearly, it is a constant current source. Note that the connected load should be as close to the power source as possible The output power, but do not exceed the output power of the power supply.
The following figure shows the constant current source drive circuit composed of LM317.
A deeper understanding of LED constant current source: Constant current means that the current does not change. According to U=I*R, since I does not change, the output voltage is proportional to the load. The greater the impedance of the load, the greater the output voltage. For example, if the output voltage is 3V when one LED is connected in series, the output voltage is 6V when two LEDs are connected in series, and the output voltage is 9V when connecting three LEDs in series, and so on, until the maximum load capacity of the constant current source is reached.
Summary: The constant current source means that the output current does not change, and the constant voltage source means that the output voltage does not change. After understanding their differences, it is much easier to distinguish them. LED lights with better quality are generally driven by a constant current source, which has higher stability and longer life.
