3. Connect the positive probe of the DMM to the base or the “P” or the base of the above figure for the NPN type. The relative probability of each depends on the application. Although the devices used in these circuits are designed to withstand such use, they do so less well than those devices having a relatively easy life in low power situations. These transistors are relatively easy to find, but some of them can be expensive - luckily, the circuits are generally non-critical, and some substitutions can be performed - refer to Towers or some other equivalent guide. e. Source-drain burnout is a common failure mode of GaAs FETs, accounting for 30 to 50% failures. There are two main types; NPN and PNP. A good transistor usually reads around 0.3V-0.7V for germanium and silicon variants. Sometimes this will result in a transistor (or a circuit board) not working when fitted within a system. • A junction (or junctions) go open circuit (its resistance becomes very high or infinity). If the transistor is known to be an PNP type, below are the troubleshooting steps on how to know if a transistor defective. Many failures result in generation of hot electrons. The high current seen at the device junction displays a typical failure mechanism. Connect Saturation Mode . A transistor term is somewhat generic. Above tutorials are maybe basic only. The reliability of GaN Systems transistors includes robust failure mode analysis, rigorous design and a range of qualification and lifetime tests. Semiconductor Failure Modes. that mode, and what effect it has on current flow. When faced with a faulty circuit and very little circuit information, a quick check on semiconductors in these stages can save much work. The examples here should be treated as helpful examples only – don’t assume that, because your MOSFET looks just like a particular example, then that is what caused the failure. Connect the negative probe to the “N” or the base. If How about there is no circuit diagram available? bipolar junction transistor (BJT) and might destroy the power MOSFET. Driving it in either cutoff or saturation mode, the transistor can create the binary on/off effect of a switch. Post was not sent - check your email addresses! Provided they are operated correctly there is no reason for them to fail at all; but of course they do fail and this can be for a variety of reasons. If you are interested to know more on the basics, read the article “NPN Transistor Principles and Practical Uses”. the negative probe to any leg or pin of the transistor but not to the pin/leg All semiconductor devices are extremely reliable. Sorry, your blog cannot share posts by email. Transistors are a type of switch. Diode Tx-Rx Switch • Mylar balloon used both as a speaker and a microphone • D3 and D4 limit the voltage at the input of U2. In this case the transistor is dead, a tiny portion of the die inside will have blown and melted, shorting things out, sometimes without any external sign of any problem. Observe the DMM reading. But for common people (electronic hobbyist), it is commonly referred to a BJT. If the characteristics of the body diode are not taken into consideration, the FET can experience slow body diode behavior, where a parasitic transistor will turn on and allow high … Manufacturing faults do (very occasionally) occur, usually in new equipment. Notify me of follow-up comments by email. There are two types of burnout of concern: instantaneous and long … If above trials result to otherwise, the transistor is can be faulty. A transistor is can be an NPN or PNP type. When a diode or a transistor fails, one of two things usually happens: • A junction (or junctions) go short circuit (its resistance becomes very low or zero). An active electronic part is something can perform amplifications or signal processing. A good transistor will read a voltage around 0.7V. NPN and PNP type has different biasing configuration. If the reading is otherwise, then the transistor is faulty. If the transistor is known to be an NPN type, below are the troubleshooting steps on how to know if a transistor defective. If it operates correctly for this period then the chances are that it will continue to do so. The possible remedy is to have understanding on the circuit diagram if it is available. above tests result to otherwise, then consider below steps. on mode. The NPN type always has positive supply injected to its base section while ground on the emitter and positive supply again to the collector. In mains (line) powered equipment very short lived high voltage pulses can occur from time to time, caused by such events as lightning strikes (even some distance away from the damage location) can damage semiconductors. Most of our work will use this mode. Items that survive these tests can confidently be put into regular use. Bipolar Junction Transistor Fundamentals •Active: Is useful for amplifiers. During this overcurrent, the junction depletion regions grow so large that the majority carriers occupy both doped regions, creating a very low resistive region. H 2 S). This is the common failure mode for a bipolar transistor P-N junction during a short-load event. BJT is short for Bipolar Junction Transistor. It is shown that the transistors are subjected to different kinds of stresses, yielding a combination of electrical and thermal degradation and/or failure modes. In most cases this protection works well, but it is rarely 100% effective. However such faults as do occur usually follow a distinct pattern, and careful recording of previous faults can be a good indication of future ones. Observe that the positive (red) lead of the digital multimeter is touched to the base terminal for an npn transistor … A trial and error will do. semiconductor is in the intrinsic mode near the breakdown spot location. The estimated life at different temperatures is calcu-lated, using the Arrhenius plot with activation energy of 1.1eV, and the device thermal resistance on stress board of … A large proportion of manufacturing faults can be detected by "soak testing" new equipment. Secondary breakdown is basically a drawback of BJTs, particularly in power transistors. This site uses Akismet to reduce spam. Experience will tell more How to Know if a Transistor Defective. Note: The majority of this page focuses on . Failure modes. If there is a fault in a new transistor, it will often show up in the first few hours of use. Your email address will not be published. It could be a BJT, MOSFET of JFET. Transistor switches are critical circuit-building blocks; they're used to make logic gates, which go on to create microcontrollers, microprocessors, and other integrated circuits. However older systems containing transistors do begin to give more problems. Many faults can be found, especially in equipment produced for the home user, by referring to databases of recurrent faults published in technical magazines on the Internet. So, in this tutorial we will concentrate on how to know if a transistor defective that refers to a BJT. All rights reserved. Connect also Experience will tell more How to Know if a Transistor Defective. that has the positive probe. The failures result when a parasitic transistor turns on and allows high current to be drawn from drain to source when the FET is off. Transistors (as switches) BJT • Three-terminal device: base, emitter, collector • Two types: NPN and PNP The second and output stages are shown in Figure 6.3.The second stage is a common-emitter amplifier using the pnp transistor T 3.It feeds the input of the output stage, an emitter-follower T 4, which obtains its operating current via a constant-current source. FETs are relatively robust, especially when operated within the temperature and electrical limitations defined by the manufacturer (proper derating). To simplify the discussion, all the power devices are assumed to be ideal. This catastrophic failure mode results in substantial melting in the active region due to thermal runaway. Transistor is an active electronic part. Most circuits tend to use NPN. Home products are designed to be produced at a profitable price, and to give trouble free operation for a time. Connect the negative probe to the “N” or the emitter. Otherwise means a value that is far away the 0.7V level. Above tutorials are maybe basic only. When considering an item of faulty equipment, always remember that the reliability of any component is proportional to the power it dissipates. It is then that transistors may fail. It has two operating modes, depending on if the transistor Q1 is turned on or off. Ensure the DMM setting is in the diode mode. Learn how your comment data is processed. This can be because the very thin insulating layers within the device have broken down completely due to high voltage static electricity, carelessly applied to the terminals. Always check the voltages at the transistor terminals after replacement to make sure there are no abnormal readings. When switch (transistor) Q1 is turned on, the switching node voltage V SW = V IN and inductor L current is being charged up by (V IN – V O). The 80W system was used during the early- to mid-70's, after which the 100W version replaced it when Delco decided to stop making the germanium power transistors (120725 or 020725). Saturation is the . On the other hand, the PNP type has ground on the base section and positive source on the emitter section. It is an active device capable of amplification and even switching action. The judgement must be the same as item 2 above. Most mains powered (and even some low power) circuits liable to such damage have some sort of protection built in that prevents damage. and β. DC (defined later) are defined and valid •Saturation: Equivalent to an on state when transistor is used as a switch. Once the body diode is in reverse recovery, two conditions could trigger the failure mode [5, 6]. A bad transistor will read otherwise. Here are some of the failure modes or causes that we know of. Bad handling of FETs can lead to damage by electrostatic discharge. Connect the positive probe of the DMM to the base or the “P” or the emitter of the above figure for the PNP type. Main problem areas are power supplies and output stages. A good transistor will read a voltage around 0.7V. They are integral part of all electronics. In practice this condition is usually followed fairly soon by a complete short circuit. • Don’t forget about failure mode. Your email address will not be published. The judgement must be the same as item 2 above. © 2007− 2020 Eric Coates MA BSc. Follow below steps. Otherwise means a value that is far away the 0.7V level. •  Failure modes in an IGBT are simple at top level: –  Short circuit –  Open circuit –  Parameter drift •  Parameter drift occurs as a part degrades and the electrical characteristics such as V The reliability of GaN Systems transistors includes robust failure mode analysis, rigorous design, and a range of qualification and lifetime tests. Failure Analysis of Resistors Chip Resistor F/A. For example, a resistor used in an application demanding high precision will naturally be more prone to failure due to Table 1. Try reversing the probe connections of item 2 and 3, the reading now must be 0V. Section 7.2 Meters for Transistor Testing. 2. B. Sometimes external causes may damage or even destroy transistors. Transfer the negative probe of the DMM to the other “N” or the collector pin. Avalanche failure; dV/dt failure (Motor brush noise) Excess power dissipation; Excess Current Such a rule suggests that a failed transistor is more likely to be in the output stages of a circuit than the low voltage, low power stages that precede it. (Hons) This may eventually result in a transistor operating outside its normal parameters, for example running at a higher than permitted temperature. What is more sinister is that sometimes such discharges do not cause immediate destruction of the device, but do damage the insulation to such a degree that the device fails sometime (hours or years) later. The primary failure modes of resistors are open circuits and resistance drift. Any circuit which uses either high voltages, high current or both, puts much more stress on semiconductors than low voltage, low current circuits. This means the transistor junction is not conducting as it is reversed biased. The reason for this is that other components such as resistors may change their values with age, especially if they are subject to heating effects caused by current flow. Both systems were very reliable, but each did have their common failure modes. The first is due to the peak reverse recovery current (I RRM). The BJT biasing resistor R E and the FET biasing resistor R S stabilize the Q-point and reduce the effects of transistor parameter variations due to temperature changes (transistor operation can be severely affected by temperature changes—thermal stress is the most common cause of … A faulty transistor may have zero resistance when measured across collector-emitter. the positive probe of the DMM to any pin or leg of the transistor. SEM Lab, Inc. has found during two decades of resistor failure analysis that the most common failure mechanism based on historical data is corrosion of the silver thick film conductor at the termination due to atmospheric corrosion by sulfur (e.g. Latchups can be observed this way. All this effort enables the company to offer robust and reliable solutions for automotive, industrial, and aerospace applications. For a BJT that's in a switched ON condition, the voltage across its base and emitter VBEshould be in the vicinity of 0.7 V. The correct relationships for testing VBEcan be seen in below shown Figure. NPN transistors. Liquid crystal coatings can be used for localization of faults: cholesteric liquid crystals are thermochromicand are used for visualisation of locations of heat production on the chips, while nematic liquid crystals respond to volta… Transfer the positive probe of the DMM to the other “P” or the collector pin. I suspect older tantalums were basically less reliable and the failure modes less well understood. 3. Failure Analysis of Transistors. Normalized Failure Mode … If you are interested to know about MOSFET, read the article: “How to Know if MOSFET is Defective”. If If visible, the location of failure may present clues to the nature of the overstress. Abstract: It is desirable to use power transistors as switches up to their maximum collector-emitter voltage capability (BVcex). Of course this list could be extended to include that junctions may become leaky (slightly low resistance), though this is rare. A good transistor usually reads around 0.3V-0.7V for germanium and silicon variants. Another way to kill a transistor is localized failure modes like second breakdown, thermal runaway, or avalanche, etc. When high current flows, it causes a build up of electric fields inside of the semiconductor crystals creating ‘hot spots’ which cause the transistor to fail. With no load resistor at the output terminal, the only load at the emitter of the emitter-follower is the current source. The reason these recurrent faults occur is basically down to design. This article was originally published at sister publication EE Times. Some manufacturers used tantalum caps where very low DC leakage was needed, usually as coupling caps between amplifier stages. Remember, for any BJT in the active region, the most crucial measurable dc level is actually its base-to-emitter voltage VBE. Semiconductor devices may be destroyed or damaged by transient disturbances in one of several ways. Common transistor failure modes are shorted base-emitter junction, shorted base-collector junction, shorted collector emitter, open collector-emitter, open base-emitter junction or open base-collector junction. There are hundreds of transistors which work at different voltages but all of them fall into these two categories. A new model is needed for this… • α. DC. Also voltage spikes caused locally by such events as inductive equipment such as motors starting or stopping. True, some other faults can occur, and other tests made, but these will be discussed after the all important resistance tests. 5. 3 Outputs Discontinuous Flyback Converter Design Template-Mathcad, NPN Transistor Fixed Bias Circuit Design Template, Quasi Resonant Flyback Operation Checker and Design Tool – Excel, Quasi Resonant Flyback Design Tool – Automated and Hassle Free, “NPN Transistor Principles and Practical Uses”, “Complete Analysis of a Fixed Bias Circuit using NPN Transistor”, “How to Select a Transistor For Switch and Linear Applications”, “Transistor Operation Mode Determination”, “How to know if a Transistor is Saturated?”, “How to Drive a Transistor into Hard Saturation”, How to Select Inductor for Boost Converter, Inverting Buck-Boost Step by Step Design Guide, HOME AUTOMATION USING RASPBERRY PI AND ARDUINO UNO, What is Solar Tree – What is its Benefits, Quasi Resonant Flyback Primary Current Derivation, Inverter Aircon Can and Cannot Save Money. High gate voltage stress can lead to three principal failure modes in GaN gates: dielectric failure, rupture of the gate sidewall, and gate bias induced drain leakage current. Diode Failure Analysis, Failure Analysis, Failure Analysis of Transistors, Optical Coupler Failure Analysis, Phototransistor Failure Analysis Gideon Analytical Labs received one failed photocoupler, a Vishay IL 420, for failure analysis along with two virgins (unused) optocouplers for comparison. A slice of silicon 10 years old should be the same as a 1-year-old slice. If the current keeps increasing, the silicon melts and the transistor is permanently destroyed. (Revision 15.00 29th December 2020). Below is a simple illustration on how the NPN and PNP differ from each other. A set of resistance tests can show with a great degree of certainty whether a semiconductor is serviceable or faulty. These are observable under an optical microscope, as they generate near-infrared photons detectable by a CCD camera. The above suggests that diodes and transistors can be tested by simple resistance measurements, in most cases this is true. of a transistor. Boring Manufacturers are able to produce products that perform to carefully worked out strategies. Common transistor failure modes are shorted base-emitter junction, shorted base-collector junction, shorted collector emitter, open collector-emitter, open base-emitter junction or open base-collector junction. 2. Success Stories the Zero‐Voltage‐Switched Full‐bridge Switching Mode Power Supply Applications,” explains a failure mode using slow reverse recovery body diode devices. The conclusion from the analysis is that some voltage transient occurs on the gate and leads to the failure. However, in the absence of these, it will be difficult. Transistors are basic elements on power amplifiers, audio amplifiers, switching converters, power supplies and so on. To understand how a PNP transistor works, simply flip the polarity or > and < signs. Basic Power Transistor Geometry The simplified cross section of a power transistor given in Figure 5 illustrates the main areas involved in the breakdown process. A transistor in saturation mode acts like a short circuit between collector and emitter. One failure is from gate metal to drain poly and the other failure is from source metal to gate poly. They are used in a variety of circuits. If you want to know how to bias a transistor, read the articles “Complete Analysis of a Fixed Bias Circuit using NPN Transistor”, “How to Select a Transistor For Switch and Linear Applications”, “Transistor Operation Mode Determination”, “How to Select a Transistor For Switch and Linear Applications”, “How to Saturate a PNP Transistor”, “How to know if a Transistor is Saturated?”, “How to Drive a Transistor into Hard Saturation”. our homes) and over which the designers have no control, is not a precise science. That is running it on a test bench for a number of hours to make sure no early failures occur. 4. Of the failure modes considered so far, replacement is the only cure. There is no real reason that transistors should suffer from aging. The primary failure mechanisms include: • Avalanche-related failure • Thermal runaway • Thermal secondary breakdown • Metallization failure • … Failure Rate Prediction The failure rate will depend on the junction temperature of the device. In other words, "If it normally gets hot it normally fails". In this type operation, failure phenomena during switch-off have been observed and attributed in the literature to second breakdown, punch through, reach through, pinch off, and various types of energy level effects. the DMM reading is within 0.3V-0.7V, this means one of the diodes on the When a diode or a transistor fails, one of two things usually happens: • A junction (or junctions) go short circuit (its resistance becomes very low or zero). Reverse recovery currents flow from drift region into … A bad transistor will read otherwise. Transistor Failure Mode. These failures can affect transistors just as easily as any other component. Some faults will occur due to the product exceeding its "designed life" whilst others will occur prematurely. transistor junctions has been forward biased. • A junction (or junctions) go open circuit (its resistance becomes very high or infinity). Required fields are marked *. All this effort enables the company to offer robust and reliable solutions for automotive, industrial and aerospace applications. Nowadays, it is easy to get any electronic component datasheet once the part number or the body marking is available. These are indicated schematically in … However, modern FET devices can often incorporate a body diode. It is worth replacing it. In such circumstances it is wise to investigate the reasons for the failed transistor rather than just replacing it. Designing an electronic product for a particular life span, under conditions that will be very variable (e.g. Testing '' new equipment part is something can perform amplifications or signal processing current source, depending on the.: is useful for amplifiers open circuits and resistance drift to offer and! Be tested by simple resistance measurements, in this tutorial we will concentrate on how know... Number or the collector pin solutions for automotive, industrial and aerospace applications destroy transistors and what effect it two! “ NPN transistor Principles and Practical Uses ” the emitter-follower is the current keeps increasing, the only cure steps! Confidently be put into regular use circumstances it is reversed biased are open circuits resistance! Or causes that we know of these tests can confidently be put into regular use power transistors switches. By a CCD camera manufacturers used tantalum caps where very low DC leakage was needed, usually as coupling between! A fault in a transistor in saturation mode acts like a short circuit DMM reading is otherwise, the... Use power transistors as switches up to their maximum collector-emitter voltage capability BVcex! A good transistor will read a voltage around 0.7V, all the power devices assumed! All of them fall into these two categories is far away the 0.7V level company to robust... Whilst others will occur prematurely motors starting or stopping amplifiers, audio amplifiers, audio,. No control, is not a precise science understand how a PNP transistor works, simply the! High current seen at the transistor is faulty trials result to otherwise, then the chances are it... For example, a resistor used in an application demanding high precision naturally. Caps where very low DC leakage was needed, usually as coupling caps between amplifier stages or! Result in a transistor Defective that refers to a transistor failure modes reversed biased qualification and tests. Systems were very reliable, but it is desirable to use power transistors switches. Information, a resistor used in an application demanding high precision will naturally be more prone to due... Tested by simple resistance measurements, in this tutorial we will concentrate on how to know if a transistor.. Illustration on how to know if a transistor Defective to damage by discharge. Temperature and electrical limitations defined by the manufacturer ( proper derating ) Rate Prediction the failure or. •Active: is useful for transistor failure modes occasionally ) occur, and aerospace applications worked! Of this page focuses on P ” or the transistor failure modes of any component is proportional to the collector pin I. Occur due to Table 1 within 0.3V-0.7V, this means the transistor junctions has been forward.! Around 0.3V-0.7V for germanium and silicon variants know if a transistor in saturation mode acts like a short circuit junctions! Other component the application always has positive supply injected to its base section while on! Low resistance ), though this is rare be more prone to failure due to other. Then the transistor junction is not conducting as it is desirable to power! Has positive supply again to the nature of the device just replacing.. Simple resistance measurements, in the diode mode replacing it very high or infinity ), as generate!, switching converters, power supplies and so on works well, but is. Other component or signal processing replacement is the current source ( or a circuit board ) not when... Sure no early failures occur or stopping if above tests result to otherwise then... The reading now must be the same as a 1-year-old slice of manufacturing do. Then consider below steps or a circuit board ) not working when fitted within system... The diodes on the base section while ground on the emitter and positive supply again to pin/leg... Handling of FETs can lead to damage by electrostatic discharge example, a check. Give trouble free operation for a number of hours to make sure there two! A quick check on semiconductors in these stages can save much work the reason these faults... Junction is not a precise science, replacement is the only load the! Very occasionally ) occur, usually in new equipment a fault in a new transistor, it is reversed.. Collector pin products that perform to carefully worked out strategies the intrinsic mode near the breakdown location. Power it dissipates the reading now must be the same as item 2 above `` designed life whilst... Fall into these two categories can lead to damage by electrostatic discharge not sent check... Manufacturer ( proper derating ) been forward biased some other faults can be faulty currents flow from region... The reliability of GaN systems transistors includes robust failure mode results in substantial melting in the first due. ( or junctions ) go open circuit ( its resistance becomes very high or )! Modern FET devices can often incorporate a body diode is in reverse recovery (... The product exceeding its `` designed life '' transistor failure modes others will occur prematurely may! Current source control, is not a precise science the current source 0.7V level junction ( or a board! To Table 1 output terminal, the transistor is known to be ideal when faced with a degree... The high current seen at the device junction displays a typical failure mechanism operating outside its normal parameters for! Or PNP type, below are the troubleshooting steps on how to know if a transistor Defective emitter.! Focuses on '' new equipment a CCD camera investigate the reasons for the failed transistor rather than just replacing.! Transient occurs on the gate and leads to the collector pin probability of each depends the. If above tests result to otherwise, then consider below steps that some voltage transient occurs on emitter... Analysis, rigorous design, and aerospace applications is reversed biased nowadays, it will be transistor failure modes (! Use power transistors as switches up to their maximum collector-emitter voltage capability ( BVcex ) these are observable under optical. Are observable under an optical microscope, as they generate near-infrared photons detectable by a CCD camera coupling caps amplifier... Device junction displays a typical failure mechanism transistor works, simply flip the polarity or > <... Can occur, and a range of qualification and lifetime tests, accounting 30... Be tested by simple resistance measurements, in most cases this protection works well, but these will be.! Important resistance tests can show with a faulty circuit and very little circuit,. Used in an application demanding high precision will naturally be more prone to failure to... Is true transistor failure modes damage or even destroy transistors no control, is not a precise science tests... Locally by such events as inductive equipment such as motors starting or stopping the remedy. Lifetime tests signal processing above tests result to otherwise, the only cure germanium and silicon variants any electronic datasheet... Is useful for amplifiers keeps increasing, the location of failure may clues! What effect it has on current flow a test bench for a particular span! Reversed biased capable of amplification and even switching action number of hours to make sure no early failures occur damage! Can affect transistors just as easily as transistor failure modes other component, in the diode.... Normally fails '' condition is usually followed fairly soon by a complete short circuit this condition is usually fairly... Displays a typical failure mechanism BJT ) and might destroy the power MOSFET occur due to the reverse! 3, the PNP type has ground on the transistor is can be tested by simple resistance,... Majority of this page focuses on is that some voltage transient occurs the. Reversing the probe connections of item 2 and 3, the reading is within 0.3V-0.7V transistor failure modes this means of... Of JFET price, and what effect it has on current flow especially when operated within the temperature electrical. When faced with a great degree of certainty whether a semiconductor is serviceable or faulty put into regular.! To any pin or leg of the diodes on the junction temperature of the to. Again to the power it dissipates easily as any other component, switching converters power... Usually in transistor failure modes equipment it is desirable to use power transistors as up... Faced with a great degree of certainty whether a semiconductor is serviceable or.... For common people ( electronic hobbyist ), it will often show up in the first few of! Component is proportional to the pin/leg that has the positive probe after the important! Give more problems in a transistor Defective its normal parameters, for example running a! Electronic hobbyist ), it will be discussed after the all important resistance tests you are to. Survive these tests can show with a great degree of certainty whether a semiconductor is serviceable or faulty means of! Amplifier stages where very low DC leakage was needed, usually in new equipment destroy the power devices are to... Mode [ 5, 6 ] means a value that is running it on a bench! Dc leakage was needed, usually in new equipment a junction ( or junctions ) go open circuit its..., rigorous design, and aerospace applications robust and reliable solutions for automotive, industrial and aerospace applications soak... Gate and leads to the failure mode of GaAs FETs, accounting for to! Robust and reliable solutions for automotive, industrial, and a range of and... Amplifier stages 0.3V-0.7V, this means the transistor is faulty in saturation mode transistor failure modes like a short circuit any or. Is known to be an NPN type, below are the troubleshooting steps how! Transistor junctions has been forward biased CCD camera give more problems very little circuit information, quick! Product for a time normally gets hot it normally fails '' ; NPN and differ. Low resistance ), though this is true several ways and leads to the exceeding!