Measurements are made of temperature in the significant points of the SMPS. Both the power consumed from the electricity network and that being supplied to an electrical dummy load are measured, in order to verify the electric efficiency of the SMPS and its dependence on the thermal and electric parameters. The cooling system is placed in an experimental tool where it is possible to measure and control the flow of the cooling liquid. A detailed analysis of the thermal behaviour of this cooling system is given. Finally, the practical significance of the problem is discussed.
2. Experiment
The experiment consists of a hydraulic testing circuit where we can insert a test section, in this case the cold plate holding the SMPS to be tested. In Figure 2, it is reported a sketch of the hydraulic loop with a cold-plate as the test section.
The tested SMPS supplies a variable voltage from +25 V to +50 V. It uses a mix of surface mount and tradi- tional technology to reduce the space occupied as far as possible. The SMPS disposes of thermal (70˚C on the transformer) and current (100 A) protections. It was originally designed for air cooling; we modified the SMPS to install it in the cooling system discussed in Par. 1. The modifications were particularly simple, because the active components (MOSFETs) were originally placed on the finned vertical sides of the SMPS. We dismounted the fins and placed the MOSFETs in direct connection with the cold-plate (Figure 3 and Figure 4).
To simulate real operating conditions, a dummy load was connected to the power supply output. To identify the components thermally stressed, twenty-five thermocouples were placed in the most significant points of the apparatus. To qualify the performance, both the power exchanged with the cooling water and the efficiency, given by the ratio of the power dissipated in the dummy load to that taken from the grid, was measured.
2.1. Test Section
The test section consists of a cold-plate with the PCB of the SMPS, where the active and passive electronic components are positioned. A view of the cold plate with the PCB is shown in Figure 3.
In a SMPS both the active components and the passive ones generate significantly heat, which must be dissi- pated to control their temperature. In this SMPS the main active components are 12 MOSFETs. They come out from the long sides of the PCB, 5 on one side and 7 on the other one, so as to be cooled directly on the “cold plate”. Among the passive components, the most significant are: a transformer, three coils and two large elec- trolytic capacitors. These components, placed on the PCB and characterized by a significant three-dimensional space occupation, cannot be directly cooled on the cold plate. For this reason they are cooled by forced convec- tion by means of a suitable air flow, generated by a pair of fans.
The “press-fit” cold plate consists in an aluminium plate (thickness 10 mm) where a cooling circuits is manu- factured with a copper pipe (external diameter 6 mm) pressed in a channel machined on the surface of the plate. The pipe runs longitudinally along the sides of the plate. The active components (MOSFETs) are placed on the copper pipe to facilitate their cooling. The cold plate is used as the base of a closed enclosure where a flow of air is maintained. Sides and cover of the enclosure are in transparent polycarbonate. This forced flow is used to cool the passive components.
A view of the cold plate is shown in Figure 4. Inlet and outlet of the pipe are on the same side. On the oppo- site side, the pipe is bended to form a coil. Over the coil is placed a finned heat sink. A thin thermal interface Bergquist Sil Pad 900 S (thickness 0.229 mm, thermal conductivity 1.6 W∙m−1∙K−1) is placed between the heat sink and the cold plate. In front of the finned heat sink (Figure 5) we placed two fans Ebm Papst 500 F (external sides 50 × 50 mm). These fans collect warm air from the passive components of the PCB and push it into the finned cooling surface. The finned heat sink is made of aluminium (base 151 × 157 mm); the fins (31) are 30 mm high, 135 mm long, 1 mm thick and are separated by a 3 mm throat. 开关电源水冷却系统英文文献和中文翻译(2):http://www.youerw.com/fanyi/lunwen_205073.html