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DC / DC power module failure causes high temperature

In Electronic Infomation Category: D | on April 20,2011

Abstract: In order to get a military-level module for the reasons led to high temperature failures, through the heating element inside the module test, electrical parameters observed changes in modules, and LTC1334ISW datasheet and the overall heating and LTC1334ISW price and electrical parameters module compare the results. The output of the module are the most important electrical parameters of components, while the device characterization, failure to obtain components with the principle of temperature change. Obtaining the output voltage with the measured temperature rise, while the slow decline of the main reasons for the temperature characteristics from the optocoupler. Ambient temperature reaches about 150 , the module transformer core temperature will reach near the Curie point, the module output voltage is almost zero.

0 Introduction

DC / DC power module (hereinafter referred to as module), is a power semiconductor switching device used to achieve DC / DC power conversion in switching power supply.

It is widely used in remote and LTC1334ISW suppliers and data communications, computers, office automation equipment, industrial instrumentation, military, aerospace and other fields, related to the national economy sectors, and the field of digital communications in remote and has broad application prospects. With the rapid development of electronic technology, switching power supply applications more widely, the work environment is worsening, statistics show that the temperature is increased by electronic components 2 , reliability, decreased by 10%, temperature rise is 50 , the life expectancy is only 25 , the temperature rise of 1 / 6. This power module is studied forty CLP Group is widely used in military industry developed by a high performance DC / DC power modules. With Interpoints MHF2815S + compared with the output of high efficiency, low heat, anti-surge capacity advantages.

In the DC / DC power module power structure of the main components are:

Pulse width modulator (control efficiency), optical coupler (input and output isolation, to avoid interference before and after class, and pass information to the sampling PWM, to maintain a stable output voltage), VDMOS (power conversion components, the use of its good improve the switching characteristics of conversion efficiency) and Schottky diode (rectifier and filter, is the power output of the main components).

1 power module output voltage and operating temperature relationship

To find out the power supply module electrical parameters with temperature variations, the first heat of the whole power supply module, test the input current, output current, output voltage (Vout) electrical parameters, test conditions: 28 V input voltage to maintain , output load 15, the output current of 1 A; test input current and output voltage with temperature changes. Found in the modules output voltage has been significantly decreased, the input current, output current trends are not obvious, the trend is accompanied by temperature, power supply module voltage decreases, and the trend is clear, from Figure 1 can be seen, the heating temperature of 50 , V out is 14. 98 V; when the temperature is 142 , Vout reduced to 14. 90 V. In addition, because the module efficiency is an important indicator of performance, when the efficiency drops to a certain value, the module will fail because of excessive heat. , For calculating the efficiency of the module under test conditions of temperature, can be seen from Figure 2, the efficiency of the module, as the temperature rises, more obvious trend started more slowly, gradually increasing temperature accelerated show Boltzmann exponential distribution. In the test found that when the temperature rose to 150 , the module output voltage is zero.

To find the output voltage causes the power supply module significantly decreased with increasing temperature the main components, according to the module circuit, select the appropriate components to build the circuit, the circuit has been tested all the features of the module can be completed, and because non-integrated technology, its components can be tested separately to avoid the integration of components due to size too small for the test conditions. Here the power module separate heating elements important to test the electrical parameters of temperature, while the test circuit V ou t of the change.

Figure 1 Power Module Vout and the temperature T of the relationship.

Figure 2 power module efficiency and temperature T of the relationship.

2 component temperature performance characteristics of the module temperature

2. 1 Transformer

Transformer can transmit not only energy, but also played the role of electrical isolation, the transformer primary and secondary winding turns ratio of the boost or buck can reach different role. In the module state, because the core of the eddy current effect, the transformer will produce a lot of heat, as the main source of heat generation module. First, the experiment tested the transformer primary and secondary inductance of the coil changes with temperature, shown in Figure 3 can be seen from Figure 3 as the temperature rises, the coil inductance increases first, and then declined slightly, and then slight rise in the ambient temperature of 220 ago, a copy of the transformer primary side inductance and the overall trend is increasing, when the temperature reaches 220 , the core temperature reaches the Curie point, the coil inductance rapidly to zero. Transformer core material for different points of its Curie temperature is different for these transformers, we can see near the Curie temperature of 220 . When the temperature near the Curie point of the transformer, the transformer inductance rapidly decreases, will cause the output voltage decreased rapidly.

Experiment also tested the circuits of other input and output inductance of the inductor with temperature changes. In the heating stage, the other components of the inductance with temperature is very small, compared with the change in transformer inductance can be ignored. But also in the decline stage of the transformer inductance, inductance of the inductor of other changes are still small.

Order to correct for ambient temperature and module temperature from rising heat, choose a module, the module shell perforation, and thermal line into the hole inside the transformer, testing the temperature of the transformer, through the test data processing, transformer temperature and ambient temperature by the relationship between the function: y = 1. 18x +13. Shows the temperature of the transformer is much higher than the working temperature of power module.

When the ambient temperature is 150 , the results of the test line temperature of about 190 , the temperature line is that the transformer test the air inside the hole, not the transformer core temperature, so temperature measurement than the actual line the temperature of the transformer is much lower, which can determine the transformers core temperature will be close to the Curie point, so when the module when the ambient temperature exceeds 150 , the temperature of the transformer module transformer core will reach the Curie point temperature, At this time the modules output voltage is almost zero.

Figure 3, the transformer inductance between L and temperature T,

2. 2 pulse width modem (PWM)

PWMs main function is based on output feedback, adjust the pulse duty cycle and drive power devices, resulting in a stable DC output voltage.

In the models of power modules, PWMSG3524s function is to provide two square wave signal to the transistor and VDMOS, and in accordance with the width of the control square wave signal conduction VDMOS and off time. In this trial, the state of the circuit PWMSG3524 separate heating, and test the output square wave signal with temperature, no significant change in the measured waveform; at the same time heating the modules input and output current and voltage were recorded and found With the ambient temperature where the PWM input current and input voltage variations are small; the output voltage and output current change is small, the heating causes PWM module electrical parameters and electrical parameters compared to the overall heating can be ignored. Prove that the temperature characteristics of the module PWMSG3524 little effect.

2. 3 VDMOS

VDMOS (vertical double diffused field-effect transistor) circuit in the module as a switching device, to work in the inductive load, withstand high peak voltage and high current with high switching losses and temperature rise, the switching frequency of up to 130 kHz, at such high frequencies, can cause a variety of degradation mechanisms of internal, resulting in decreased performance of VDMOS, and even failure.

In this experiment on the module VDMOS separate heating, electrical parameter test module changes, obtained by testing the temperature to 180 , the input current with increasing temperature have a more significant increase. The output voltage, output current changed little with increasing temperature. In addition the output efficiency calculation module to determine whether the module is in normal working condition, can be calculated separately for VDMOS heated to 180 , the modules input current is increasing rapidly. When the temperature rose to 220 , the output voltage is almost unchanged at 150 and the module has failed, at which point the heating temperature has reached a separate 180 , the module is much higher than the overall failure of the heating temperature, so the temperature characteristics of VDMOS is not affected output voltage change.

2. 4 diode (SBD)

Diodes used in the module with voltage regulator diode, rectifier diode, rectifier diode voltage conversion which had played an important role. The output of the transformer, the two rectifier diode conduction at different times, so that AC ripple voltage is converted to pulsating DC. In this experiment, the SBD on a separate heating circuit and found that with increasing temperature, the modules output voltage is no more significant changes. Therefore, the work of the module in high temperature environment, SBD module output voltage drop is not caused a major factor.

2. 5 optocoupler

Optocoupler (hereinafter referred to as opto) to the medium of transmission of light signals. Its input and output signals have a good role in isolation. Optocoupler generally 3 parts: the light emission, light reception and signal amplification. Input signal to drive the LED diode (LED), so that given a certain wavelength of light, it was light detector receives light generated current, and then after further amplified output. This completes the electro - optical - electrical conversion, which play input and output isolation effect. As mutual isolation between input and output coupler, with one-way signal transmission characteristics, which has good electrical insulation and anti-jamming capability.

In a module optocoupler as isolated input and output of the important parts, while comparing the output of current amplifier output signal to PWM 9 feet and 9 feet PWM compensation side, its anti-comparator connected to the input, control of 11 feet and the PWM output pulse width of 14 feet. To adjust the modules output voltage stable.

In this experiment, the first test module optocoupler NEC2705 used in the input current and output current scale factor with temperature, the applied input current is 11 mA, the results showed that at 25, the light coupling of the current transfer ratio close to 1: 1, but as the temperature rises, the input current constant, the output current decreases, each increase of about 10, the optocoupler current transfer ratio decreased 4%, the results shown in Figure 4.

Working state then a separate heating module optocoupler (module optocoupler larger wire can be removed separately after heating), the output voltage measurement module, shown in Figure 5. Found that with increasing temperature, the module voltage is gradually decreased, and the overall heating and measured module output voltage decreases with increasing temperature trend is basically consistent. Through analysis shows that, with the ambient temperature, power supply module to increase the power consumption of each component, will result in the modules output voltage drop, this time should be connected through the optocoupler feedback circuit, PWM output pulse width to increase and improve output voltage, but because the transmission efficiency of optical couplers decline can not be transferred to the result of negative feedback PWM. Makes the PWM output pulse width narrower than the actual, reduced ability to adjust the voltage, the output voltage with the ambient temperature rises.

Figure 4 optocoupler current transfer ratio and the temperature T of the relationship.

Figure 5, the output voltage and the optocoupler between the temperature T,

3 Results languages ??

In summary, the module temperature characteristics were as follows: when the temperature is less than 150, the modules output voltage slow decline, due to a decline in the optocoupler current transfer ratio caused; when the temperature is higher than 150, the power module rapid decline in the output voltage, output voltage is almost zero or even, the reason is that this time the module temperature of the transformer core temperature near the Curie point (220). Effects caused by the failure of the transformer. In this case, if the module did not produce other internal injuries, when to stop heating, the module temperature returns to room temperature, re-power the module, the module output voltage is able to return to normal. However, for this experiment to test the module, when the ambient temperature exceeds 150 or so, because the transformer core temperature of the module from the point so that the core temperature, core temperature of the positive feedback will increase rapidly, resulting in more heat, causing damage to other devices inside the module, it is likely to cause permanent damage to the module.

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