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On the design of the power module dare

2017-03-31

Module power supply in the work of a certain degree of their own power loss, that is to say there is a conversion efficiency. The conversion efficiency is related to the input voltage, input voltage range, operating temperature, output voltage and output power. The conversion efficiency directly affects the design of the heat dissipation system.

1. Conversion efficiency and calculation of their own loss Our company's product conversion efficiency can be found in the technical manual. Special custom products, can call and sales technical support consulting, the user can also be obtained through the experimental conversion efficiency.

Calculated as follows: ŋ = Pout / Pin ŋ - Conversion efficiency Pout - Output power Pin - Input power Know the efficiency of the module to calculate the power module's own loss. Ie Pd = Pin-Pout = Pout / ŋ-Pout Pd - self-loss

2. Calculation of temperature rise In our company's manual, each product provides the thermal resistance θca of the model power module in ° C / W. Knowing the thermal resistance θca and self-loss Pd can accurately determine the temperature rise ΔT of the power supply module. Calculation method: ΔT = Pd • θca Example: I know our product XX model module, the output parameters: Vin input voltage = 48VDC Vo output voltage = 12VDC lo output current = 4A Po power = 48W N conversion efficiency = 89% According to the design of the product, assuming that the model of θca = 5 ° C / W, into the ΔT = Pd • θca = 6W (see the manual) to find their own loss Pd Pd = Pout / ŋ-Pout = 48 / 0.89-48 ≈ 6W check our company's product manual, • 5 ° C / W = 30 ° C. Thus we can conclude that the temperature of the module during normal operation ΔT = 30 ° C. Temperature rise ΔT is a very important parameter, we know the temperature rise ΔT and ambient temperature Ta can be very easy to calculate the working shell temperature TC. The equation is: Tc = Ta + ΔT Tc - shell temperature Ta - ambient temperature ΔT - temperature rise such as ambient temperature Ta = 20 ° C, then the shell temperature is Tc = 20 ° C + 30 ° C = 50 ° C The conventional technology module Tcmax is set at 85 ° C and the aluminum plate process module Tcmax is 100 ° C, and we calculate the shell temperature Tc = 50 ° C, which is much lower. In this case, In the high allowable value, to meet the Tc << Tcmax, can be used normally. Here users should also pay attention to an important issue: the root hammer reliability calculation method, the lower the temperature when the reliability of the higher reliability, data show that the power module temperature rise 10 ° C, MTBF will drop 20%, according to customers This principle, the temperature of the module at work should be as low as possible. Handbook found in the high temperature Tcmax is the limit, the manufacturer to ensure that the high temperature Tcmax can work properly, but MTBF to reduce, this point the user must pay attention to the temperature down there are many ways to use different methods will Directly affect the size of the thermal resistance θca. Installation on the general installation and installation of radiator installation, installation of radiator should consider different physical area. The size of the radiator affect the size of θca, the parameters of the radiator can refer to the manufacturer of the radiator data, my company's power products are generally equipped with radiators, individual products with different sizes of radiators for users to choose, Where my company's radiator are marked with thermal resistance θca. The air flow rate is meters per second M / s, also available in English units linear feet per minute LFM. Conversion relationship is similar to: 200LFM = 1M / S All my company's supporting radiator are data, the user can be used with the radiator θca resistance into the formula can be calculated when the module work Tc. If the user uses forced air cooling, according to the different wind speed M / S under the θca value into the formula, you can get the wind speed under the temperature rise ΔT. The use of forced air cooling, increased air flow rate will bring significant results, can greatly reduce the physical size of the radiator, or even do not heat sink. But the fan to bring the volume increase and significant wind noise, the fan itself, the reliability of the MTBF will also directly affect the entire power system MTBF, the user should consider the balance. Installation of the radiator should pay attention to the direction of air convection problems.

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