This article is part 3 of "Some limitations of power supplies"----What Can Happen When working Temperature Exceed a Power Supply's Working Temperature Range?
Part 1:What Can Happen When Input Voltage Exceed a Power Supply's Range?
Part 2: What Can Happen When Output current Exceed a Power Supply's Range?
Based on living condition,normally we set the power supplies working circumstance temperature with 0-40℃,but under some extrem conditions,the temperature can be out of this range.We will discuss what will happen if the circumstance temperature beyond this range.
Performance problems occur if power supplies continue to work outside of their temperature limits. The electrical performance of most components are affected by the temperature conditions they work in, so temperature limits are defined to keep components work in a suitable range where their performance can come out completely.If outside of this range, the components' behavior cann't be guaranteed any more and the performace of efficiency level,ripple&noisy, regulation and even EMI shall have problems.
Power supplies' components include positive temperature coefficient (PTC) type and negative temperature coefficient (NTC) type.PTC type components value of their loss change at the same direction as the temperature and NTC components' are just on the opposite.
PTC components such as MOSFETs losses increase as the temperature increases.NTC components such as the diodes losses decrease as the temperature increases. As the loading and temperature change either the PTC or NTC components may result in efficiency change of power supplies in one direction or the other.
Other components which do not deliver much current will not affect the power loss,however, their values can affect the power supplies output and limits.For example, the output voltage changes with voltage divider resistors value change,and OCP resistors value changes also affect the OCP point.
Power supplies work below the min. temperature limits also has many of the same problems as working above the maximum limits.One problem in cold temperatures is that electrolytic capacitors capacitance will reduce.The reduction of electrolytic capacitors capacitance can cause increased ripple&noise even failed start up sometimes.
If the temperature is too low,NTC components such as the thermistor which is used to limit inrush value will increase much and reduce efficiency or prohibit power supplies start up.
In addition to some obviously seen performance problems,hidden problems like increased electromagnetic emissions (EMI) can happed.If power supplies work outside of the range,EMI filters will be affected by the temperatures and will not effectively restrain the emissions,then the system cann't comply with EMI regulations.
Many components' reliability and life span of a power supply are related to working temperature in some degree,especially the electrolytic capacitors.
The increased working temperature will reduce the electrolytic capacitors and other components life span,which will certainly reduce the power supply's.
On the other hand,working at low temperatures can cause reliability reduction due to solder joints, ceramic capacitors, SMT components crack.
Many power supplies do not have over-temperature protection,even the components have margin of temperature,but it can be narrower and cause components failures if working exceeding the working temperature.
The working temperature affects every component of power supplies.Working beyond the temperature limits can cause performance problems,reduction of life span,components failures etc.If you need special working temperature power supplies please Contact Top Power Sales Team.
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