PI Temperature Control Amplifier for Thermoelectric Cooler (TEC) Driver

This is a simple Proportional, Integral (PI) temperature control amplifier. A complete thermoelectric cooler (TEC) controller can be created using this PI amplifier and OPA569 Power Op-Amp or other output amplifiers such as DRV591, DRV592 and DRV593. Proportional-integrator compensation is simpler to adjust and often provides an adequate thermal transient response to the TEC driver amplifiers. The project consists INA330 chip and OPA2340 OPAMP.  The INA330 provides thermistor excitation and generates an output voltage proportional to the difference in resistances applied to the inputs. OPA2340 is used to create the PI closed Loop.

U1 LM385-1.2V generates the reference voltage 1.23V, and REF3012 SOT23-2 U4 chip can be used as an alternative to U1. PI loop compensation can be optimized for loop stability and best response to thermal transients by adjusting R4, R11, C8, and C9. To facilitate the optimization of loop dynamics, the value of these components is important and will depend on the Thermal behavior of the TEC.

Features

• Supply 5V DC
• NTC Temperature Sensor
• Compact Design
• Precision Temperature Sensor Amplifier
• On Board 1.23V Reference
• On Board Power LED
• PCB Dimensions 31.75 x 18.42 mm

INA330 uses only one precision resistor R2 plus the thermistor RT1, thus providing an alternative to the traditional bridge circuit. The circuit maintains excellent accuracy for temperature control applications. An excitation voltage is applied to the thermistor (R_THERM) RT1 and precision resistor (RSET) R2, creating currents I1 and I2. The current conveyor circuit produces an output current, I0, equal to I1 – I2, which flows through the external gain-setting resistor. A buffered voltage output proportional to I0 is also provided. The loop controls temperature to an adjustable set-point of 22.5°C to 27.5°C. The nominal 10kΩ at 25°C thermistor ranges from approximately 11.4kΩ to 8.7kΩ over this range. A 1.23V excitation voltage is applied to V1 and V2, producing a nominal 100µA current in the 10kΩ RSET resistor. The thermistor current is approximately 100µA at 25°C, but will vary above or below this value over the ±2.5°C set-point temperature range. The difference of these two currents flows in the gain-set resistor, RG. This produces a voltage output of approximately 0.9V/°C. The set-point temperature is adjusted with V_ADJ. Thus, the voltage at VO is the sum of (IO)(RG) + VADJ. VADJ can be manually adjusted or set with a Digital-to-Analog (D/A) converter. Optionally, Thus, the feedback loop will drive the heating or cooling of the TEC to force VO to equal VBIAS. V_ADJ = 2.5V will produce a set-point temperature of 25°C. V_ADJ = 2.5V + 0.9V will change the set-point by 1°C. A 0V to 5V D/A converter will provide approximately ±2.5°C adjustment range. A 12-bit D/A converter will allow for approximately 0.001°C resolution on the set-point temperature. For best temperature stability, the set-point temperature voltage should be derived ratiometrically from VBIAS. A D/A converter used to derive the set-point voltage should share the same reference voltage source as V_BIAS. Likewise.

Connections and Other Information

• CN1: Pin 1 = 5V DC, Pin 2 = Output, Pin 3 = GND, Pin 4 = GND, Pin 5 = V-ADJ 0 to 5V from DA Converter
• CN2: For High Accuracy Omit R12 and R13 and Feed 2.5V External Reference Voltage to Pin 1 , Pin = GND
• J1: No Use
• J2: Disable
• J3: Enable (Solder Jumper)
• U1: Reference Voltage Generator, Use Alternate U4 REF3012 SOT23-3
• D1: Power LED
• R2: 10K 0.1% SMD Resistor Size 0805
• RT1: NTC 10K 1%

Schematic

Parts List

Connections

Application Diagram

Gerber View

Photos

Video

INA330 Datasheet

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