This article summarizes some common methods of secondary constant current in LED lighting power supply, hoping to help newcomers improve. 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 LEDs require constant current drive to ensure uniform brightness and long-term reliable illumination.
First of all, let's talk about several constant current methods of the popular TL431.
Single TL431 constant current circuit
As shown above, it is a schematic diagram using a single TL431 constant current. The principle of this circuit is very simple, mainly using the 431's 2.495V reference for constant current, and 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 accuracy of the TL431 is high, the 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, so we have improved some defects of the line below.
Single TL431 constant current improved circuit
As shown above, it is an improved schematic diagram using a single TL431 constant current.
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