Part 4: How To Test Diodes And Transistors - A Simplified Explanation
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- Опубликовано: 21 авг 2024
- Part 4 of a series of tutorials on how to test various electronic components with a multimeter. In this episode I'll show you how to test Diodes and Transistors, and give a simplified explanation of what's inside of them.
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#learnelectronics #electronics #components
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I think a couple of things should be added here to a very good basic video:
When using the Diode test mode on a multimeter, what is happening is that the multimeter is sending voltage through the test leads of around 3 volts. When you put those leads on your DUT (Device Under Test), the multimeter is showing the amount of voltage drop across those terminals. A typical voltage drop for a diode is from 0.6 to 0.7V, thus the readings as shown in this video. This is the voltage amount required to "turn on" the diode so that current will flow through it (called the "forward voltage"). If you put 0.3V through a diode when the forward voltage is 0.60v, it won't allow the current to flow, until the 0.6v threshold is reached. Note that you can also use the diode test mode to check if an LED is burned out (or what color the led is) as there's enough current coming out to light one up! Great for surface mount LEDs that all look the same.
For a transistor, I think a better diagram would be with the base in the center, and for an NPN (if you haven't figured it out, that means "Negative-Positive-Negative") the diode arrows would point outward to the C and E. Just a little easier to visualize. Note that you can use the diode drop value to identify the pins on your transistor (assuming the transistor is good). The pin with the larger voltage drop is the emitter, and the other is the collector. e.g. on a 2n2222 transistor I have here, the drop on the B-E is 0.704, and the B-C is 0.702.
While most transistors have their base in the center pin, some do not, and with some deductive reasoning you can determine if your transistor is PNP or NPN, and which pins are the E-B-C (of course, check the datasheet if one is available first!).
Also note, you usually can test diodes in circuit, but often transistors will give you a funky result because of the surrounding circuitry.
Thanks for that Larry 👍There was a couple of things there that I didn't know such as the pin with the larger voltage drop is the emitter. I've used the meter in diode mode to test LEDs before (on the LED disco light I just looked at for instance). Yes I've came across transistors with different pinouts before 🙂
Great 4 part series, it really great learning new things.
Thanks Morten. Hopefully I'll be adding more parts, it's just what I've managed to do over the last couple of days.
Nothing like a refresher course on reading electronic components. My problem is resistors. Although I've been taught Ohms law and resistor codes. I always forget it, so I do what any normal human would do, that cheat with a calculator. lol When my dad taught me the resistor color codes when I was really young, he taught me the adult version of remembering color codes. lol Well it's time for me to go play electrician again today, but I'll have to watch the video on resistors once I get home. Thank you for the video.
Thanks Ron, yes I was too taught an interesting way of remembering the codes which definitely wouldn't be used these days 😂😂😂
What stinks is that some of the new colored resistors are so difficult to discern (for me, mostly the blue resistors), and often it's not even clear which end to start at!
You should do a whole series
I did a 4 part series on testing a few different things. RUclips didn't seem to promote it much apart from 1 video on testing resistors.
Excellent thank you
So nice of you👍
Excellent 👍😊👏
Thanks 🙂👍
Than you. Very useful. 👍
Thanks Matt!
Hi I am just starting out, I tried making a simple FM radio however it did not work. My question is how do you know which way round to solder the component in? Thanking you Roger. Good video by the way.
I can think of a couple of ways. Search the datasheet for the component and it should tell you what pin is what, or use a test meter to determine which pin is which.
When the MM puts out that little bit of current, which probe does it come out of?
Good question. Originally people thought electrons flowed from the positive to negative(conventional flow), but in reality they flow from negative to positive (electron flow), so it would be the negative lead if that's what you mean?
Hi, thanks for your video.
I have question. If my d’iodé not beep’s but shows values in both ways, is it fault ?
It sounds it. If it's just a normal diode you should only get a reading in one direction and not the other.
@@BuyitFixit thanks
My problem that I don’t have schematic. So it’s difficult to know 😞
Hi,
Any chance of a recap on testing N-Channel MOSFETs.
It's briefly in one of your videos but having trouble finding it.
I'm diagnosing a non-working brushed hitachi SDS drill.
On continuity I'm getting readings between drain and source. Nothing between Gate and the other pins so probably OK.
If it's not shorted its probably fine. They read a bit odd at times as the meter can make them trigger or that's what it seems. If it's not short or totally blown open circuit its probably ok. Another alternative would be to get one of those component testers off Amazon. The one I got was £18.99 blue with a yellow button. LCR-T7 that should tell you if they are working correctly.
@@BuyitFixit turns out my other meter has a selector to choose between continuty (resistance) and diode (applies voltage) but still get results. Seems to pass more voltsge one way than the other between Drain and Source pins.
Turns out I should have checked both brushes rather than just one. Will fit new brushes and try to fire it up.
@@ianhelsbyservices From the readings you were getting they sound ok. Like I said they normally short circuit when they blow unless they have extremely high current driving them which can cause them to blow apart inside (after shorting) and makes them fail open circuit.
Hi, im fairly new, im working on a juke box board (for the mother) iv got 2 Y1 transistors next to each other, on both im getting 685 on multi meter when positive is on B and negitive between C & E, but im also getting a value of 1.066 when i switch B to the negative and use the positive on E on one of them wouldcthis be considered short? Also if i use positive on E and negative on C on both of the boards im drawing a value of 1.078 is this normal? (Noob sorry) 😂
Are the transistors still in the circuit? You will get odd readings from other components in the circuit if they are. Normally (but not always) when transistors fail they usually go short circuit so you would see something like 000 or 001
Thanka for the reply, yeah they are still in circuit im going to remove them after work and ill test them again, was just confusing that i was only getting the odd reading on one of them, cheers