Constant voltage drive
This solution achieves control of the LED lamp by controlling the output voltage of the driver. The overall frame is similar to the constant current drive. The difference is that the solution uses a constant voltage driver and the temperature control system circuit is different.
Figure 7 is a connection diagram of the temperature control of the constant voltage driver. The Trim terminal is used to adjust the output of the power supply. The left dotted line type dotted line box is the control circuit, wherein: PTC is a positive temperature coefficient temperature sensitive resistor; R1, R2, Rx are common resistors, and the PTC temperature sensitive resistor is matched to adjust the driver output voltage; Kt is normally closed type The temperature relay has a disconnection temperature of 60 ° C and an automatic closing temperature of 48%.
The part of the dotted line on the right is the LED module part. Kt and PTC are mounted on the LED module and in close contact with the module. K at room temperature. In the closed state, at this time, the rated output of the driver is controlled in the control circuit, and the rated total voltage of the LED module at normal temperature is 24V. When the relay temperature rises to 60 ° C, K.
Automatically disconnected, the entire control circuit works, thus reducing the output of the constant voltage power supply, when the temperature is reduced to 48 ° C, the temperature relay automatically closes, and the power supply is normally output.
After testing, the driver V is obtained. See Table 2 for the relationship between the total resistance scale connected between the terminal and the Trim terminal and the driver output voltage U. It can be seen that as the resistance increases, the output voltage decreases. When the temperature reaches 60 ° C, Figure 7 controls the temperature relay K in the circuit. Disconnected, at this point, as long as the resistors are properly matched, we can get the set output voltage. The calculation method of each resistance value is the same as above, and no specific calculation is made here.
- Trial drive test results
This research carried out the development of high-power LED street lamps and LED projection lights and drivers. Fig. 8 is an LED street lamp sample lamp and its constant current driver. The lamp body adopts an integrated design, and the AC current of the normal temperature input driver is 270 mA.
- The lamp has a good long-term running condition, and its total luminous flux is 3408 lm. The output current is reduced to 87% of normal temperature. Fig. 9 is an LED projection lamp and its constant voltage driver. The AC current of the input driver at normal temperature is 140 mA, and the total luminous flux is 1011 lm. When the temperature is controlled, the voltage is reduced to 90% of the normal temperature.
In the LED lighting process, the constant voltage driver supplies a constant voltage to the LED lamp, and when the temperature rises, the LED lamp PN junction voltage V will drop at a speed of about -2 mV / ° C, so that the current flowing through the LED lamp is rapid Increased, affecting its service life; the use of constant current drives avoids this phenomenon. Therefore, it is generally recommended to use a constant current driver to drive the LED light.
The above solution in this paper effectively reduces the temperature rise of the high-power LED lamp. Once the temperature rises above the set control temperature, the driver will reduce the output and reduce the luminous flux and work of the LED lamp without affecting the use. Consumption, avoiding LED light decay and shortened service life due to overheating.
- This temperature control scheme has shown many advantages in the research process. It is believed that large-scale practical applications will be obtained in the near future, and LED lighting will be upgraded to a greater extent.