NTC for LED

Ts output current does not change with changes in input voltage, load and ambient temperature. However, when the ambient temperature of the LED is higher than the safe operating point temperature, the forward current of the LED will exceed the safe area, which will greatly reduce the life of the LED or even damage it. This is the shortcoming of a constant current driver, because maintaining a constant output current will only further increase the temperature of the LED.

A. Dissipate the heat generated by the LED chip in time through a suitable radiator to reduce the junction temperature of the chip. However, this solution is a pre-adopted solution when designing LED lamps, and sufficient margin must be reserved for heat dissipation. In actual work, it is difficult to guarantee an ideal and economical effect.

B. Use the overheating protection circuit inside the LED driver chip to shut off the output of the LED driver, forcing the LED to go out to achieve the purpose of cooling down. This solution is only an overheating protection measure that the LED driver chip is forced to take under extreme circumstances, and cannot guarantee the long-term stable operation of the LED.

C. Adopt constant voltage/constant current (CV/CC) LED driver, which is characterized in that when the output current reaches the specified value, the current control loop keeps it constant. This solution is a passive indirect overheating protection measure, because the constant voltage/constant current control circuit starts the current loop by detecting the output current, which is not directly related to the ambient temperature of the LED, so it cannot be real-time based on the temperature of the LED. to adjust the magnitude of the output current.

D. Specially design a temperature measurement and control system for LED lighting. However, due to the high cost, it is difficult to popularize and apply it in the field of LED lighting.

The analysis shows that adding temperature compensation function to the LED driver is a simple and easy solution. The basic principle of temperature compensation is that once an abnormal situation occurs and the LED temperature is too high, the LED driver can automatically reduce the output current value according to the temperature detected by the thermistor to ensure that the LED works in a safe area, which is fundamental It solves the problem of LED overheating damage or reduced service life, thus greatly improving the reliability and safety of LED lamps; when the temperature drops to a safe area, the output current of the LED-~g actuator can automatically return to the normal value. Obviously, this kind of LED driver chip with temperature compensation function is an "intelligent" chip with automatic real-time control. It not only represents the development direction of high-quality LED drivers, but also has important practical value.

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