LED Driver Features Two-Stage Over-Temperature Protection
Amperor Inc.’s ANP151 family of LED drivers features an innovative two-stage over-temperature protection (OTP) scheme to maximize light output from fixtures and at the same time protect the LED driver circuitry. Its first OTP trigger point is set at case temperature 93C (200F) which is already an upgrade to the industry norm of 85C. Instead of shutting down the driver, it switches itself to the 50% output mode after triggering. The reduced current ensures the slowdown of the two most-likely heat generating sources, LEDs and the LED driver, in the fixture. In laboratory tests, this has produced a more than 10C (50F) case temperature drop after the activation of the first OTP stage.
Amperor has set a 105C case temperature as the second OTP stage triggering threshold. If, for some reasons, such as the present of the thermal runaway issue or other fault conditions, the case temperature keeps raising after the activation of the first OTP stage, the driver will protect itself by completely cutting off the output. Another benefit of this two-stage OTP setup is the ANP151 can automatically perform the output power de-rating task. Without this auto-mechanism, the lighting fixture designer needs to calculate the possible highest ambient temperature the fixture might see, and load the driver according to the de-rating curve. In other words, the driver won't be utilized to its highest potential under the normal, most common temperature condition. This can force the designer to specify a higher power rating driver and result in the system cost inflation.
An optional system level thermal sensing port can be added to the ANP151. The port consists of two wires from the driver. By connecting the wires to an Amperor suggested thermal switch and have the thermal switch installed at the proper location in the light, ANP151 can monitor the temperature in the system and provide a system level two stage OTP as described above. When the thermal protection port is equipped in the driver, two rules need to be follow to make the driver operate correctly. When the two wires of the port are shorted together, the driver can perform like the port is not installed. When the port is opened without having the thermal switch installed in the system, the driver stays in the off stage.
The optional 12V auxiliary output channel can be used if the lighting fixture design calls for a second power source. For example, one fixture design employing the ANP131 collects the power usage data and presents the data to the utility company to negotiate for a rate drop. The 12Vaux channel is set apart from the main output of the driver and can stay in the on stage when the ac input is applied. It is designed to power that measurement function in the fixture.
Another example is to use the 12Vaux to power a thermal sensing circuitry on the system PCB. By working with the dimming port of the driver, a system level OTP can be constructed. Also, the 12Vaux output can be used to power a DALI or other control interface unit. It can enable the usage of the ANP151 driver in a smart control system.
ANP151 can be built in two shapes: Rectangular shape: 8.07" x 2.54" x 1.5" (205mm x 64.5mm x 38mm) and a square shape: 4.13" x 3.94" x 2.28" (105mm x 100mm x 58mm). The rectangular one fits into most roadway lights, street lights and flood lights. If the length of the driver is an issue, the square shape driver can be used. It fits into most canopy lights, spot lights, and post-top lights. The rectangular shape housing is ready to go for production. The square shape housing is currently going through the UL approval procedure. It will be ready before the end of this year.
