Nowadays, the volume of switching power supply module is smaller and smaller, the power is higher and higher, and the office environment of control module is more extreme. The high and low temperature test design scheme, thermal design scheme and in-situ stress problem gradually cause the attention of all technical engineers. What is the secret of reliability design of power supply module?
For a power supply module, the I / O characteristics such as working voltage range, maximum power, protection breakdown voltage, high efficiency, Ripple & noise, etc. should be considered first. After that, the main parameter that you technical engineers are most concerned about is its high and low temperature test characteristics.
1. High and low temperature test
Generally, the operating temperature range of switching power supply module is different in different application industries
The high and low temperature test is used to determine the adaptability and integrity of commodities under the two extreme natural environment standards of ultra-low temperature and high temperature. Due to the characteristics of electronic devices, they can produce the necessary changes under the ultra-low temperature and high temperature standards, and the technical parameters have the characteristics of temperature drift.
Therefore, many power supply modules have no problem under normal temperature standard, but when the high and low temperature test is achieved, the natural environment detection will find that the work is abnormal or the technical parameters are significantly reduced.
The following problems often occur in the ultra-low and high temperature operation of power supply module:
(1) During the operation, the output voltage ripple and noise increase, the frequency changes, and even the output voltage jumps, the control module noise.
(2) Poor start-up, such as start-up output voltage rise wave has significant ditch, output voltage is not stable, and even the control module completely start invalid.
(3) The working ability with capacitive load becomes weak, so it is impossible to start with larger capacitive load（ 4) The overshoot strength of starting output working voltage increases and exceeds the required scope.
(5) When the load is light or full, the output voltage drops sharply（ 6) High temperature embrittlement damage, control module has no output.
2. Thermal design scheme
The thermal design scheme of power supply module is simple, that is to say: according to the thermal design scheme, under the premise of considering the specified characteristics, minimize the heat generated inside the control module, reduce the heat transfer coefficient, and select an effective water cooling method.
We should try our best to make the distribution of the electronic devices for scalding reasonable. When designing PCB, the current carrying capacity of the printed line should be ensured, and the total width of the printed line must be suitable for the transmission of electric flow.
For power chip mounted electronic devices, large-scale copper foil can be used to increase the total heat dissipation area of PCB heat pipe. The temperature of the electronic components in the control module can be reduced by adding thermal conductive silica gel and epoxy resin into the power module.
For the power module with large volume, it can use the radiator to carry out heat pipe cooling, improve the area of heat convection and radiation source, and greatly improve the actual heat pipe cooling effect of electronic components.
3. Adjustment design scheme
The design scheme of adjustment is to make the applied ground stress of parts less than its rated value. In order to make the in-situ stress of electronic components moderately less than the required rated current, the electronic devices are applied to adjust the rating.
4. In situ stress design scheme
According to the in-situ stress design scheme of power supply module, the most important concern is MOSFET, diode, transformer, power inductor, electrolytic capacitor, current limiting resistance, etc. Ensure that the full range of operating voltage, steady-state, transient, short-circuit fault and other limit standards can have sufficient adjustment, to ensure the credibility of the goods.
