In the process of design and development of LED power supply, engineers have many factors to consider when designing lighting devices when choosing a driver. Generally speaking, constant current drive and constant voltage drive are the two most important driving choices for LED lighting devices. Choice, in fact, from the perspective of the development status of LED power supplies, these two modes are currently relatively common driving methods on the market. Let us follow the editor of the switching power supply to look at the constant voltage and constant current LED driving power supplies. the difference:
(1) Constant pressure type:
a) When the various parameters in the voltage regulator circuit are determined, the output voltage is fixed, but the output current changes with the increase or decrease of the load;
b) Constant voltage circuit is not afraid of load opening, but it is strictly forbidden to short-circuit the load completely.
c) The LED is driven by a voltage-stabilizing drive circuit, and each string needs to be added with a suitable resistance to make each string of LEDs display an average brightness;
d) The brightness will be affected by the voltage change from the rectification.
(2) Constant current type:
a) The output current of the constant current drive circuit is constant, but the output DC voltage varies within a certain range with the size of the load resistance. The smaller the load resistance, the lower the output voltage. The larger the load resistance, the output The higher the voltage.
b) The constant current circuit is not afraid of the load short circuit, but it is strictly forbidden to open the load completely.
c) Constant current drive circuit to drive LED is more ideal, but relatively speaking, the price is higher.
d) Pay attention to the maximum current and voltage values used, which limit the number of LEDs used.
The difference between a constant current source and a constant voltage source is the constant current part of the circuit.
Constant current part: It is mainly composed of T1, R8, R9, and R5. The turn-on voltage of the triode, 0.7V, is a known quantity. The resistance of R8 is also a known quantity. When the circuit starts to work, as long as the product of R8 and the current flowing through R8 is greater than 0.7V, the transistor starts to work, and the circuit enters constant current operation.
In the design process of the LED power supply, both the constant current drive method and the constant voltage drive method have their own advantages and disadvantages, but in fact the most ideal method is to combine the two methods. Not only relatively constant current, but also proper voltage adjustment. It is necessary to monitor the change state of the load current as well as the load voltage. In terms of the current development direction of LED power supply design, where space permits, intelligent lighting solutions that integrate light source circuits will be the mainstream direction of LED drive power design in the future.
