As LED lighting is getting hotter and hotter, as the life pillar of LEDs, LED driver power is getting more and more attention.
We all know that LED power supply is nothing special. It is characterized by constant current limiting, and long-term operation under full load, so the efficiency requirements are relatively high; some power supplies have height requirements due to structural size limitations.
Below I will try to summarize some common methods of secondary constant current for the current small and medium power LED lighting power supply; not necessarily comprehensive, not necessarily deep, but finally some engineers who are new to the line help.
Disclaimer: Not all circuits are original, posted for the convenience of discussion, if it involves infringement, please inform me in time to delete in time.
It is no exaggeration to say that the LED driver power supply will directly determine the reliability and life of the LED lamp; as a power supply engineer, we know that the characteristics of the LED require constant current drive to ensure uniform brightness and long-term reliable illumination.
Let's talk about several constant current methods of the popular TL431.
1, a single TL431 constant current circuit
As shown above, it is a schematic diagram of using a single TL431 constant current.
Principle: This circuit is very simple, using the 431's 2.495V reference for constant current, which also limits the voltage drop across the LED, but the advantages and disadvantages are equally obvious.
advantage:
The circuit is simple, the components are few, and the cost is low. Because the reference voltage precision of TL431 is high, R12 and T13 only need high precision resistors, and the constant current precision is relatively high.
Disadvantages:
Since the TL431 is a 2.5V reference, the loss of the constant current sampling circuit is extremely large, and it is not suitable for a power supply with an excessive output current.
The fatal flaw of this circuit is that it can not be idling, so it is not suitable for external LED power supply.
You can discuss how to improve the defects first, and I will continue to post improved circuits tomorrow.