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| Checking Darlington Transistor |
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| AngraMelo:
Hey guys, I received 3 different orders from 3 different sellers from 3 different countries. They all had 5 pairs of Darlington Transistors. The MP1620 and the MN2488 The reason why I bought them is to replace some blown up transistor on a old receiver. Now, after checking those 3 batches I realized that whenever I checked the Emitter to Collector junction, I always get a diode drop reading from my DMM. All of them. 100% of them show this diode drop which is something that a regular npn or pnp transistor do not show. Is there something I dont know? or am I the unluckiest customer of all times and got 3 batches of blown up darlingtons? |
| drussell:
You do know what a Darlington transistor is, right? It is a compound pair, actually composed of two transistors with one feeding the other to get increased current amplification. This means that you will see some aspects change from a regular "standard" transistor because it is two transistors, so things like voltage drop across the compound pair will be higher than a single transistor, must be biased to two diode drops to begin to conduct in an amplifier situation, etc. That being said, what exactly are you measuring, and how? ... and compared to what? You shouldn't be seeing significantly different behavior across only the C-E junction on a Darlington... Are you sure you're measuring correctly for the pin-out? |
| AngraMelo:
--- Quote from: drussell on June 18, 2018, 04:12:46 am ---You do know what a Darlington transistor is, right? It is a compound pair, actually composed of two transistors with one feeding the other to get increased current amplification. This means that you will see some aspects change from a regular "standard" transistor because it is two transistors, so things like voltage drop across the compound pair will be higher than a single transistor, must be biased to two diode drops to begin to conduct in an amplifier situation, etc. That being said, what exactly are you measuring, and how? ... and compared to what? You shouldn't be seeing significantly different behavior across only the C-E junction on a Darlington... Are you sure you're measuring correctly for the pin-out? --- End quote --- I do know that darlingtons are different from regular BJT transistor. Im using a DMM on the diode mode and checking to see if there is any shorted junctions. That is the point of me measuring them. Im not concerned (yet) about the value of the drop. When I measure the C-E junction on a regular BJT transistor, I get an OL on my DMM, but when I measured those darlington ones I get a diode drop. When I get a reading on the DMM while measuring the C-E of a BJT I assume the transistor is bad because all my good, brand new transistor do not show any readings on the C-E junction. And yes, I do know the pinout and Im aware of how to measure pnp/npn transistors |
| MK14:
I suspect it might be a parasitic (PN) diode, between the Collector and Emitter, because of the way some Darling transistors are made. --- Quote ---Collector-Emitter Diodes In the most popular high voltage Darlington transistors, there is a diode between the collector and emitter terminals. Most often, this diode is a parasitic element. The parasitic nature of the C-E diode can cause --- End quote --- Source: http://www.onsemi.cn/pub/Collateral/AN875-D.PDF I.e. The darlington transistors are probably fine. |
| exe:
Uhm, I thought it's a protection diode... But looking at TIP120 datasheets (e.g. [1]) it's not mentioned it is for protection. So, should be parasitic. [1] https://www.mouser.com/ds/2/149/TIP120-890130.pdf |
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