Circuit drive scheme based on a high-power white light LED module

“The Circuit drives a high-power white light LED (WLED), when the temperature is too high and the thermistor has an open circuit or short circuit fault, the LED will be turned off. If working outside the extreme operating temperature range, the life of any IC will be shortened. When the junction temperature of the chip exceeds a certain value, it will be completely damaged. Philips Lumileds LUXEON high-power LED Modules are manufactured on a thermally enhanced substrate, so they generate less heat. This base material improves thermal performance and allows continuous work under high currents, thereby meeting the requirements of high-brightness lighting.But for applications like camera flash, in order to avoid power consumption during continuous work

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The circuit drives a high-power white light LED (WLED), when the temperature is too high and the thermistor has an open circuit or short circuit fault, the LED will be turned off. If working outside the extreme operating temperature range, the life of any IC will be shortened. When the junction temperature of the chip exceeds a certain value, it will be completely damaged. Philips Lumileds LUXEON high-power LED modules are manufactured on a thermally enhanced substrate, so they generate less heat. This base material improves thermal performance and allows continuous work under high currents, thereby meeting the requirements of high-brightness lighting. However, for applications such as camera flashes, in order to avoid damage to the device due to power consumption during continuous operation, additional thermal protection is required.

The circuit in Figure 1 includes a charge pump regulator (IC1) suitable for camera flash applications. This device can provide regulation current for up to 8 white LEDs (WLEDs). Connecting all 8 channels in parallel can provide a current of up to 480mA for a single 1W, LUXEON Star high-power WLED module. When the open-drain input EN is pulled to ground, IC1 enters shutdown mode.

Figure 1. The circuit drives a high-power WLED. When the temperature is too high and the thermistor has an open circuit or short circuit fault, the LED will be turned off

A thermistor and a dual open-drain comparator (IC2) with internal reference can be used to construct a compact and cost-effective thermal shutdown circuit. When VTHERM drops below the 1.2V internal reference voltage, comparator A pulls EN low to ground. This operation is performed when the thermistor (R2) temperature is high. Comparator B is used to provide open-circuit failure protection, that is, when the thermistor contact is disconnected, EN will be pulled low. When the thermistor has an open-circuit fault, VTHERM is pulled high by R1, so that the comparator B pulls EN low. The resistor divider R3-R4 sets the threshold voltage for open-circuit faults, and the resistor R1 and thermistor R2 sets the thermal shutdown threshold.