HFAN-08.2.0: Thermoelectric Co

　

概要：tegrated with a TEC and a temperature monitor into a single thermally-engineered module. An added bonus with TECs is the ability to heat, by reversing the current. TEC control requires a reversible power source capable of providing positive and negative voltages. To accomplish this from a single supply, an H-bridge circuit can be used. While linear supplies offer low noise, their poor efficiency requires large components and added thermal insulation to prevent the regulator waste heat from loading the cooler. Alternatively, two synchronous buck

HFAN-08.2.0: Thermoelectric Co,http://www.592dz.com
Abstract: The Thermo-Electric Cooler (TEC) is found in many applications that require precision temperature control. The small size of the TEC allows precision thermal control of individual components such as fiber optic laser drivers, precision voltage references, or any other temperature critical device. The temperature-critical components are integrated with a TEC and a temperature monitor into a single thermally-engineered module. An added bonus with TECs is the ability to heat, by reversing the current.

TEC control requires a reversible power source capable of providing positive and negative voltages. To accomplish this from a single supply, an H-bridge circuit can be used. While linear supplies offer low noise, their poor efficiency requires large components and added thermal insulation to prevent the regulator waste heat from loading the cooler. Alternatively, two synchronous buck circuits with complementary drivers provide a higher efficiency supply that can deliver bipolar power from a single positive supply. Forced pulse-width-modulation control of the two output voltages allows current to be sourced and sinked. During current sinking, power is recovered and sent back to the supply line. The MAX1968 is a highly integrated H-bridge PWM switch-mode driver designed for Peltier thermoelectric coolers (TEC) modules.

In 1821, Thomas Seebeck discovered that when two conductors of different materials were joined together in a loop, and a temperature differential was present between the two junctions, a current flowed through the loop. Twelve years later, J. C. Peltier demonstrated the opposite effect -- that by cutting one of the conductors in the loop and forcing a current through the loop, a temperature differential was observed between the two junctions. Due to the materials available at the time, the resistive heat generated by the large currents involved dominated the Peltier effect. Today, with material advances, these junctions have become more practical for use as thermoelectric heat pumps performing the same function as fluorocarbon-based vapor compression refrigeration. While they are still not as efficient as vapor-cycle devices, they have no moving parts or working fluid and can be very small in size.

Because the Peltier effect can be controlled linearly with electricity, the Thermo-Electric Cooler (TEC) has been found in many applications involving precision temperature control. The small size of the TEC has allowed precision thermal control of individual components such as fiber optic laser drivers, precision voltage references or any other temperature critical device. The temperature critical components, a TEC and a temperature monitor are integrated into a single thermally engineered module. An added bonus with TECs is the ability to heat by reversing the current. TEC control requires a reversible power source capable of providing positive and negative voltages. To accomplish this from a single supply an H-bridge circuit can be used. While linear supplies offer low noise, their poor efficiency requires large components and added thermal insulation to prevent the regulator waste heat from loading the cooler. Alternatively, two synchronous buck circuits with complementary drivers provide a higher efficiency supply that can deliver bipolar power from a single positive supply. Forced pulse-width-modulation control of the two output voltages allows current to be sourced and sinked. During current sinking, power is recovered and sent back to the supply line. The MAX1968 is a highly integrated H-bridge PWM switch-mode driver designed for Peltier thermoelectric coolers (TEC) modules.

The MAX1968 is a cost-effective solution for controlling TECs because it integrates the four power switches and the PWM control on a 28 pin thermally enhanced TSSOP-EP package. A metallic slug on the underside of the chip allows the package to dissipate as much as 1.9 Watts and provide bipolar +/-3 Volts at 3 Amps from a single 5 Volts source. Switching is selectable at 500kHz or 1MHz. Independent positive and negative output current limits and a voltage limit are integrated on the chip and can be set using external resistors. An analog control signal precisely sets the TEC current regardless of the TEC voltage. Although the MAX1968 provides a cost and size effective solution for driving a TEC, precision thermal control requires an external control loop.

For precision temperature control, a local monitor inside the TEC module sends temperature information that is compared with a reference, generating an error signal. This error signal is then amplified and sent to the TEC. The TEC then changes the local monitor temperature, completing the loop. Like any control loop, steady state accuracy is related to the DC loop gain. Because of the large thermal mass, it can take tens of seconds for the temperature monitor to respond to TEC changes. Compensation of the TEC and monitor loop can require a slow integrator to avoid oscillations and overshoot. Because the integrator requires large time constants, it can be difficult to find high value capacitors with low enough leakage to achieve high DC gain. Therefore, the smallest size integrator capacitor to achieve stability must be selected.

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