[introduction]Module of TEC use Peltier will cool object or the accurate temperature control that offer an object, can use at a variety of application. They are refrigeration of laser diode condenser, microprocessor, aggregate enzymatic chain reaction (PCR) system and fault scanning, heart and vessels is become picture, magnetism resonance is become picture (of the ideal of the medical treatment application such as MRI) , radiative cure anthology. A lot of application such as control of laser diode temperature use power to come in 5 W the TEC of small-sized low power comsumption inside 15 W limits. Their driver may use 5 V power supply to course moves and offer 1 A the electric current to 3 A.

The article offerred the pyroelectricity condenser that before designing higher power TEC, must understand (TEC) concept, explained the crucial Peltier that limits pyroelectricity condenser cooling power is characteristic, and say how palpability can be restricted around these develop a design. Partial driver give typical examples says palpability controls the condition that place of higher power TEC requires. Still include a possibility additionally block up has a design to realize the problem that its anticipate cooling power.

Module of TEC use Peltier will cool object or the accurate temperature control that offer an object, can use at a variety of application. They are refrigeration of laser diode condenser, microprocessor, aggregate enzymatic chain reaction (PCR) system and fault scanning, heart and vessels is become picture, magnetism resonance is become picture (of the ideal of the medical treatment application such as MRI) , radiative cure anthology. A lot of application such as control of laser diode temperature use power to come in 5 W the TEC of small-sized low power comsumption inside 15 W limits. Their driver may use 5 V power supply to course moves and offer 1 A the electric current to 3 A.

But how to if we need higher power,do? How should be we done? What and us should we pay close attention to what to choice there is? We look from two angle. The first kind of circumstance is, we had had the TEC of a regular job, but this is insufficient still, need promotes power 10% to 20% . The 2nd kind of circumstance is, begin compose to build the TEC of higher power from the beginning. How many cooling power can we gain from Peltier device? With what should we come drive it?

Before begin, let us understand a few crucial Peltier concepts first.

The biggest absorption of heat is measured

The biggest absorption of heat of Peltier module is measured (Qc) will be listed in data manual, but it applies to Δ T to be the circumstance of 0. Δ T is the difference in temperature between Peltier hot end and Leng Duanzhi. When hot end and Leng Duan temperature are identical, if what Qc general narrates in data manual. However, it can show linear to reduce as the addition of Δ T, till a certain bits of Qc = 0. Also call T of the biggest Δ at this o’clock, change is very big, but the typical cost of only course module may be 70 ° C about. Refer to a graph please 1 medium common give typical examples.

Graph 1. Heat up the relation of uptake and Peltier difference in temperature.

Assume we hope the hot end Peltier maintains in + the room temperature of 22 ° C, and the hope maintains Lengduan in – 5 ° C. The biggest electric current of Peltier is 9 A, accordingly we plan to use 7 A driver. Pursue medium in our give typical examples, the difference in temperature of C of below 7 A electric current 27 ° will provide the capability of 41 W for us. However, all interface have thermal resistance, shed classics radiator to keep abreast of from Peltier when quantity of heat accordingly when indoor environment, will appear temperature gradient. Come so, the hot end of Peltier is in the room temperature of 22 ° C impossibly. Assume the temperature that heat up end is 30 ° C. We get the cold hot difference in temperature of 35 ° C. Consult graph 1, reach point of T of Δ of 35 ° C along 7 A line, the ability discharging heat that this demonstrates us will be controlled for 30 W — although we bought 100 W Peltier!

Initiative heat

Another main Peltier idea is generation of the meeting when module is working is many from heat. Initiative quantity of heat may be the caloric that absorbs from target place double. For example, when the quantity of heat that absorbs 25 W from target place, peltier may produce the quantity of heat of 50 W additionally. Accordingly, the radiator that heat up end must can send out the quantity of heat of 75 W.

Improve existing TEC system

Below the first kind of circumstance, we have off-the-peg TEC, need appreciably to increase cooling power only can, for this we should consider a few issues possibly. The insulation of T of the voltage ripple on device of the thermal resistance of interface of component of the temperature heating up end that a few clear problem fields include TEC, TEC, Peltier, Δ and component.

The proposal checks the temperature of hot end above all, refer to a graph please 2. Write down sincerely please, graph a crucial point of 1 is Peltier the small increment between Lengduan and hot end is crucial. As the addition of difference in temperature, peltier is met from ability of target derive caloric abate.

Graph 2. Sky is right of empty TEC component simplify graph.

A kind of method that knows the temperature that heat up end quickly is be close to in TEC most temperature of radiator of the examination when high-power. Need to use thermocouple only, perhaps will measure a result to send to microprocessor, thermal resistor can work effectively. Refer to please ” the temperature testing system that is based on thermal resistor, the 1st part: Design challenge and circuit configure ” and ” the temperature testing system that is based on thermal resistor, the 2nd part: The system is optimized with evaluate ” these two excellent thermal resistor articles. If heat up the temperature that carries radiator room temperature of apparent prep above, need possibly bigger radiator and / or fan.

Regretful is, afore-mentioned fast examination did not tell us to arrive about Peltier any information of radiator interface. This interface may touch harder, because this needs normally,disassemble this device. This interface often uses heat conduction to cream, we want to check it to whether exist in order to decide to disturb the gas acupuncture point that heat conducts possibly. Because air is body of undesirable heat conduction (0.026 W/(mK)) , the action that creams because of this heat conduction is to eliminate gas acupuncture point. But do not use very thick, because come in 0.2 W/(mK) when 0.3 W/(mK) , heat conduction creams also is not good conductor, although metallic type may be inside 4 W/(mK) limits. However, it is 10 times better that this kind creams the function of body still compares air. Compare to it, aluminium is 200 W/(mK) , PCB copper is make an appointment with 380 W/(mK) , PCB FR4 comes to make an appointment with 0.3 W/(mK) 0.8 W/(mK) , water is 0.6 W/(mK) , glass is make an appointment with 1.0 W/(mK) .

Ask an attention, be in likely when achieving a certain a little bit, increase the electricity that carries Peltier meeting generation and expect contrary result, can make Leng Duan calefacient namely! Because Peltier may be close to his,this is T of the biggest Δ , and because come loose,be heated up inadequate, increase electric current to be able to make hot end calefacient so. When hot end is calefacient, meeting general Leng Duan is pushed up.

Additional, check the voltage ripple on TEC how to can reduce the efficiency of Peltier please. Ripple should not exceed 10% , but proposal 5% or lower. The resistance of effective series connection that reduces laden electric capacity (ESR) may be the safest change. However, no matter produce what change, no matter be to increase frequency, increase output electric capacity or increase inductance, the efficiency that needs to notice to prevent to affect switching equipment reachs his to control stability.

New design

To new high power design, the first thing that people may think of is, whether to use Peltier module or Peltier component. Itself of this kind of module is Peltier, place in underlay of pottery and porcelain and hot end namely (+ upright) the tellurium between changes bismuth, solder have two electrical wiring. Below this kind of circumstance, be will design by the client radiator and medicinal powder of hot interface. On the other hand, package is included already joined the Peltier module of radiator. Typical plant may be included two radiator and two fan and derivative the wiring to join port. Radiator cent is different sort, for example wind cold, water-cooling or glycol refrigeration and connect refrigeration continuously, and include some sort that is used at receiving machine ark or other equipment repeatedly possibly still model frame. The client needs to join for fan only a power source, next OK and dedicated design at driver.

No matter be which kinds of means, no matter be,begin from package, if want compose to build high power TEC, have balance and choice with respect to need. For example, to roughly same power, all sorts of Peltier module (TEC module) electric current and voltage are likely difference is vast. Many module are used in application may more advantageous, perhaps can choose multistage module to increase Δ T. For drive the module of higher power, ADI supplied LT8722 and chip of new power of LT8204 complete bridge. Next, we will see these problems carefully.

Choosing what should realize above all when Peltier module is, their electric current / voltage balance is likely difference is vast. For example, come with respect to 95 W the usable module inside 105 W limits, the span of resistor can arrive from 0.34 Ω 4.4 Ω . In addition, the biggest norms of module of the 95 W below 27 ° C is 19 A and 7.7 V, and the biggest norms of module of below 27 ° C another 105 W is 7.6 A and 21.2 V. Although their power is not identical, but the key is balance may exist between electric current and voltage, and this decided you are right again conversely the requirement of driver.

Besides, you also can use many module, but, they must have electric series, because their resistor follows temperature,change. Come so, between shunt-wound device all flowing will be a challenge. Of course, device of use series connection, pressure fall can increase, and can need the drive of taller voltage. However, the Peltier device of electric series connection still will be had medicinal powder hot collateral function. If unavailable taller voltage, but still need two module, criterion every module must by oneself driver drive. But, individual temperature feedback can be used at two module at the same time.

Another kind of choice is use multistage module. These module are included arrive by what manufacturer pile is together 5 module. Those who change character, medicinal powder heat will be series connection, accordingly total Δ T increases, can cool inferior temperature. However, this is not the method of an all-round. Write down sincerely please, the hot end of every module must send out the quantity of heat that absorbs from the target and initiative quantity of heat go out. Accordingly, the initiative quantity of heat that the next joins the Leng Duan of module must want move to come from the first device and target quantity of heat, and the 3rd module in this series connection must want can send out the quantity of heat that comes from a target and the initiative quantity of heat that come from 3 all device go out. This kind of additional temperature capacity is increase in order to be being shown medicinal powder heat is cost. Multistage module looks like a pyramid normally, because be apart from a target,farthermost module need sends out a large number of quantity of heat, must bigger.

15V/4 A driver can achieve higher power

Apparent, want to enhance the power of TEC, need taller driving voltage normally. LT8722 absolutely, its VIN voltage is 15 V, its are compositive the rated electric current of FET is 4 A. The design of this controller considered the temperature control of high accuracy. It uses compositive formula converter of 25 digit model (DAC) from serial peripheral interface (SPI) receives information, so that accurate difference is set on TEC,divide voltage. 9 DAC can install two additional compositive type to losing value of output current limliting.

This framework is transformer of complete bridge DC-DC, a side is wide modulation of arteries and veins (level of PWM) step-down power, another side is linear class, the efficiency of 92.6% is provided below 4 A, 15 VIN and 3 MHz condition. Although among them an output is outputted for linear, also can carry efficiency, because be when tall electric current, switching equipment controls electric current, tall or of linear driver or is low, bring about pressure fall very small. During the changeover with retrorse electric current, linear output will be in its linear area, but electric current is very small. Accordingly, linear driver won’t affect efficiency significantly. Use this kind of framework, can come true not only efficient, and because need an inductance only, size is accordingly smaller. Does this switching equipment still use Silent Switcher? The technology will reduce electromagnetism as far as possible to disturb / electromagnetism compatibility (EMI/EMC) radiate.

SPI interface manages control in the round, include to make can, start, voltage of the peak value electric current, frequency, output that need branch and current limliting value. SPIS_STATUS register offers 6 breakdown and condition of 5 additional position, and AMUX monitoring 13 imitate function. LT8722 is a low noise (only 1 side is switching equipment) , small size (only an inductance) H bridge, its assist a function compositive already in chip. Refer to a graph 3.

Graph 3. LT8722 uses circuit.

The 40 V drive that has exterior FET can achieve higher power

To gain additional cooling power, can use ADI to have the controller of bridge of 40 V LT8204 H of outside power FET. This can help design personnel design voltaic level for any application. LT8204 is muti_function driver. It is an outstanding Peltier driver, but also can use at of all kinds inductance, capacitance or resistor load, for example a powerful person of electric machinery, electromagnetism, batteries charges, power source of automatic test equipment and heat system, namely any application that need half bridge or complete bridge drive. Its control mode can be voltage mode or voltaic mode control, and can control output voltage or output electric current. Control exports electricity to drive TEC module particularly practical.

This controller has SPI interface, control completely by microprocessor. 16 DAC are two compositive type two-piece the bridge or complete bridge configuration offer the accurate port that comes from microprocessor. In addition, compositive type low input is maladjusted voltaic amplifier can offer accurate two-way electric current to detect. Breakdown register provides 16 breakdown instruction, can answer its pass to processor. Actually, simple H bridge controller change is accurate TEC driver wants major job is already compositive in controller. Refer to a graph 4.

Graph 4. LT8204 uses circuit.

Conclusion

No matter be the cooling power that needs to raise existing TEC, still plan to make new higher power design, the program that involves among them is done not have so complex. Originally design what exist possibly to come loose heat or efficiency problem can be solved. New design will need module of the Peltier module of higher power, many series connection, or if ask taller Δ T, need multistage module. Without doubt, driver will need taller voltage and voltaic capability, and had better be have inside of buy accurate control lukewarm function.

Origin: ADI wisdom library

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