Based on the ADN8830 Uncooled infrared focal plane temperature control circuit design (1)

Infrared technology as a means to identify, detect and identify the target of the important means in the dual-use technology in a wide range of applications, Uncooled infrared focal plane array technology greatly improves system performance.

Uncooled infrared camera is not need refrigeration heat detector focal plane array, using infrared radiation on the focal plane of the sensitive element, so that the temperature change resistance change to probe the target temperature properties. Therefore, only as much as possible to ensure the focal plane array in the sensitive pixel itself base temperature stability and consistent, we can improve the thermal imager of detection sensitivity, and reduce the system's non-uniformity correction later more difficult, and ultimately to fundamentally improve the thermal imager of detection sensitivity, to improve the thermal imager of imaging performance. At present, in the actual Uncooled infrared focal plane array detector using semiconductor thermoelectric cooler (TEC) to stabilize the base temperature. In this focus on a high-performance based on ADN8830 TEC PID temperature control circuits and the adjustment of compensation network.

1 temperature control circuit design

TEC (Thermo Electric Cooler) is to use two different semiconductor materials (P-type and N type) pn junction, when pn junction in DC by the two materials of electrons and holes in the move process across a pn junction in endothermic or pairing (Peltier effect), the PN demonstrate refrigeration or heating effect, change the current direction for TEC's refrigeration or heating, adjustable current size to control the heating refrigeration capacity output.

Use TEC stable method of target temperature as shown in Figure 1.

Figure 1 in the first part is a temperature sensor.

This sensor is used to measure in TEC-the temperature of the target object. The desired target object temperature set point with a voltage to represent, and the representative of the temperature sensor generates actual target object temperature voltage through high precision operational amplifier, and produce the error voltage. This voltage via the high-gain amplifier, also because the target object in thermal-induced phase delay compensation, then drive H bridge outputs, h-bridge control TEC current orientation and size. When the target object of the temperature is below the set point temperature, h-bridge towards the direction of the TEC and heating in a certain amplitude driving current; when the target object of the temperature is higher than the set point temperature, h-bridge will reduce and even reverse the TEC's current TEC's current direction to lower the temperature of the target object. When the balance of control loops, TEC's current direction and amplitude to adjust the temperature of the target object is equal to the set temperature.

In the design, selection and for the control of the TEC ADI ADN8830 TEC controller.

ADN8830 is by far the best single-chip integration, high output, efficiency and high performance of one of the TEC power drive module, for setting and stable temperature, TEC in typical use, the maximum temperature drift voltage lower than 250 mV, can cause the target temperature error ±0 0.01 ℃. Each add-in voltage ADN8830 input corresponds to a target temperature set point. The appropriate current TEC by TEC will be driven on infrared focal plane heating or refrigeration. Infrared focal plane of the temperature by negative temperature coefficient thermistor to measurement and feedback to ADN8830, used to adjust system circuit and drive TEC.

Here the design realization with ADN8830 Uncooled infrared focal plane temperature control circuit shown in Figure 2.

Figure 2 resistance RTH is non-refrigeration infrared focal plane components included with the thermistor.

Resistors R4 resistance RTH of choice and thermistor temperature characteristics and environment temperature. Thermistor resistance of RTH and not as the temperature decreases linearly, resistors R4 's resistance should follow the style (1) calculation:

Type: RT1 and RT3 represent thermistor in the operating temperature of two upper and lower limit of resistance, thermistor in average RT2 for temperatures resistance.

In practice, desirable working temperature of two limit 5 ° c, 45 ℃, the average temperature is 25 degrees centigrade. Through the inspection of the thermistor temperature curve can be RT1 = 10.735 k Ω, RT2 = 4.700 k Ω, RT3 = 2.250 k Ω to calculate the value of the resistor R4 3.304 k Ω, R4 = 3.300 k Ω.

ADN8830 temperature control circuit control principle is sampling the voltage on the thermistor and Uncooled infrared focal plane normal work setting, thus adjusting the flow through the cooler in the current orientation and size to control the temperature.

ADN8830 4 pins (TEMPSET) set voltage values should touch (2) calculation:

Set temperature = 25 ℃, thermistor RTH = 4.7 k Ω, reference voltage VREF is provided by the chip is 2.47 V, the VSET 1.45 V.

2 PID network tuning and parameter setting

[1] [2]