Step Down Converter EVM - Review

Table of contents

RoadTest: Step Down Converter EVM

Author: protasio

Creation date:

Evaluation Type: Power Supplies

Did you receive all parts the manufacturer stated would be included in the package?: True

What other parts do you consider comparable to this product?: null

What were the biggest problems encountered?: There is no easy way to change the value of R8 (R_FBT) to change the output voltage.

Detailed Review:

This RoadTest Review is about the TPS54424EVM-779 that its footprint size and current capability really impressed me. I applied the TPS54424EVM-779 in a research that I conduct on Thermoelectric Generator (TEG), in which can operate either as an electrical generator or as a cooling/heating module, since it is used for conversion between thermal and electrical energy and vice-versa. A TEG consists of an array of p- and n-type semiconductor based thermocouples placed between two ceramic plates, where these thermocouples are electrically connected in series and thermally in parallel, as shown below.

 

The TEG used in the test was the TEC1-12706 (http://peltiermodules.com/peltier.datasheet/TEC1-12706.pdf) and its internal resistance is about 2 Ohms depending on the temperature.

 

In the research, maintain the voltage across each TEG is interesting, since we can get stable temperature gradient from the developed test platform. This test platform is composed of a PC computer, running a LabVIEW-based Virtual Instrument (VI) that runs two PID controllers, and a test platform apparatus. This apparatus is a stack of TEGs, Metal Plates and Fans, as shown below. The TECs (or thermoelectric coolers) are essentially the same TEG, but in the case, they are applied electric current to generate a difference of temperature to be applied to the TEG. The PIDs control the TEC1 and TEC2 independently in order to maintain the temperature of the corresponding TEC considering a user-defined setpoint. The feedback paths to the controllers are performed by two K-type thermocouple TP1 and TP2 which were chosen for their sensitivity and the actuation range. Between the TECs, it was introduced the TEG-Under-Test as well as heat reservoir in order to create a heat storing that allows a soft changing of temperature. The power drives work as an actuator to power the TECs. More detail about the test platform and its applications could be find at https://doi.org/10.1109/I2MTC.2015.7151580.

The main idea correlated with the usage of TPS54424EVM-779 is to use them as power drives or to get Insight to other applications. Well, in this context, I chosen to obtain data concerning the efficiency of the TPS54424 dc/dc converter and use the parallel TEGs as the load. I use two Fluke 287 True RMS multimeters and two MiniTec 26 of EXTECH Instruments multimeters to measure the input and output power.

 

In this order, I measured the power for 1 TEG (2 Ohms), 2 TEGs (1 Ohm), 3 TEGs (0.67 Ohm), 4 TEGs (≈ 0.5 Ohm), and 5 TEGs (≈ 0.4 Ohm). In addition, I measure the temperature on the TPS54424 chip using an Infrared Thermometer LaserGrip 774.

 

 

LoadInputOutputEfficiencyTemperature of the Chip
VinIinPinVoutIoutPoutºFºC
1 TEG9.964.80E-024.78E-011.7891.57E-012.81E-0159%74.123.4
2 TEGs9.966.87E-026.85E-011.7832.65E-014.72E-0169%74.523.6
3 TEGs9.968.50E-028.47E-011.7793.49E-016.21E-0173%74.423.6
4 TEGs9.969.61E-029.57E-011.7764.05E-017.19E-0175%74.223.4
5 TEGs9.971.13E-011.13E+001.7724.89E-018.66E-0177%74.223.4

 

 

The efficiency curve is give below.

As we can see, the efficiency tends toward 80% that is about the value described in the datasheet considering the value of output current and input voltage considering (or achieved) in the test.

 

A point that I highlight as negative, but it is particularly to my intention of to use the TPS54424EVM-779 as a precise power driver, is that there is no easy way to change the value of R8 (R_FBT) to change the output voltage. I suggest a serial jump where we can add up a desired resistor.

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