Outdoor cameras play an important role in security applications. Therefore, whether they are in tropical, frigid, or climates with extreme daily temperature differences, it is necessary to ensure that they will not malfunction or malfunction.
Old outdoor cameras can only operate reliably within a certain temperature range. When the temperature is low, the internal resistance of the lithium battery is relatively large, causing the battery capacity to rapidly degrade or even fail. At high temperatures, the camera’s image sensor may produce “hot pixels,” which are bright individual pixels that adversely affect the overall image quality.
Designing an outdoor camera that can withstand a wide range of ambient temperatures from -30°C to +55°C faces two major design challenges. The first challenge is the ability to start at extremely high/low temperature. The second challenge is the need to accurately measure temperature over a wide temperature range, because the operation of the fan or heater installed inside the camera is based on temperature measurements. Accurate temperature results maximize the operating temperature range of the camera and prevent equipment failure.
A design with a temperature switch can help solve these two challenges.
How to achieve efficient operation of fans and heaters
Outdoor cameras, especially high-definition cameras, produce higher energy. When the ambient temperature is high, the fan can reduce the internal temperature to keep the camera running normally. In extreme cold conditions, although the camera will generate a lot of heat, but this heat is still not enough to make it work above the minimum operating temperature. Therefore, when the ambient temperature is low, a heater can be used to increase the internal temperature.
Figure 1 shows the traditional temperature protection design, in which the microcontroller (MCU) or processor starts first and detects the temperature with the help of a sensor. However, if the temperature is too low or too high, the MCU or image sensor may be damaged when trying to start. To avoid this, the outdoor camera design should restore it to the lowest operating temperature before attempting to start the camera.
Figure 1: Traditional temperature protection design
TMP390 dual-channel temperature switch can provide independent high and low temperature detection without using MCU. Because the temperature switch directly controls the fan and heater, it can provide a suitable temperature for the entire system before the MCU starts, thereby preventing the MCU from operating at extremely high or low temperatures. The programmable temperature trip point of the resistor provides flexibility for a variety of applications, and the 5°C or 10°C thermal hysteresis option of resistor programming prevents unnecessary digital output switching.
During the startup process at extremely low temperatures (see Figure 2), after turning on the power, the temperature switch will start first; the MCU or other components will remain off. When the temperature exceeds the safe range, it is in a low-level active state, and at the same time, the heater and fan begin to increase the internal temperature. When the temperature reaches the preset value, the whole system starts to start. Compared with the traditional temperature protection design in Figure 1, the TMP390 temperature switch can adjust the temperature before the system starts, thus solving the challenge of starting at extremely low or extremely high temperatures.
Figure 2: Example circuit of TMP390 with 10°C hysteresis at +60°C and -40°C threshold
The TMP390 temperature switch has 3C accuracy in the range of -55°C to +130°C (±1.5°C from 0°C to +70°C), which provides sufficient accuracy over a wide temperature range. Through accurate temperature measurement, outdoor cameras no longer need to leave room for temperature protection, so that the operating temperature range can be maximized and the equipment in the system can be effectively protected. Because the TMP390 temperature switch can precisely control the fan or heater, it can save unnecessary energy consumption in the outdoor camera.