MOSFET as a variable resistor
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- เผยแพร่เมื่อ 21 เม.ย. 2020
- MOSFET as a variable resistor
In this video we use a power MOSFET(IRFZ34N) as a variable resistor.
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RDS(on) stands for “drain-source on resistance,” or the total resistance between the drain and source in a Metal Oxide Field Effect Transistor,
explaining how th MOSFET works and a simple circuit that even I can build is why I enjoy this channel. Thanks Paul.
The 'classic circuits you should know' and Basic Components Explained are my favorite vids on this channel. They have been very helpful and my go-to source for information. Many Thanks!
I have some RV 12V LED puck lights that use an LM117 clone in constant current mode. The current set resistor is 4.7 Ohms, so a trim pot is out of the question because it dissipates about 1/3 Watt. The best solution is to build a PWM dimmer, but the MOSFET method is so much simpler. I can put the MOSFET in series with the current set resistor and set it with a trim pot, similar to your example. When the MOSFET is fully ON, the LM117 still limits the current to the maximum brightness. Thanks for the video!
„Kugelschreiber“ Great. Love it. Greetings from Hamburg, Germany.
Yes. Such a German word. I wonder if he speaks any German?
I thought he said googolscriber.
Brilliant video!! Best videos to watch during lockdown. I really appreciate them..
Love the straight up circuit episodes
Very useful simple circuit. Thank you for the measurements as well.
Great video as always. I would recommend to explain that a Mosfet which is not switch completely on the Mosfet consumes a lot of power and gets hot. I find Mostes mainly helpful to switch power completely on or off to benefit from the low resistance.
Regards from Germany.
I was looking for such solution since 2 days.
Thanks for the video !
lighting the way thru dark days of confinement. good job.
Excellent cirquit! Thank you.
Nice video Paul! Thank you!
Neat, simple and useful! Well done!
Another great simple circuit explained. Use another one of your circuits to time off the laser on my chop saw. Retired electrian taking up electronics as a hobby in the winter because it to cold to in my garage workshop thanks for your ideas this maybe good for small motors
Really enjoy these circuit building videos. I don't have any MOSFETs but I will try it with a BJT and see what happens. Thanks
This is, at least on the older, Dewalt battery drills how their trigger circuit worked.
Thank you very much! Very helpful.
Awesome! Thanks again Paul 👍
Helpful video. I liked it
Very informative video
This is the kind of video I like!
Great! Nice an simple.
I missed your favorate IC in this circuit to dim the light 😋 But in these Times it won't be long before you launch that other excellent video 😊
Keep up The good work Paul 👍
Hope you stay healthy! I want to know if the pocket scope that you reviewed (Daniu ADS5012H 100mhz) it's a good choice for the first scope and if it's worth it.
Best Regards.
That's cool, thanks man
A little error at the begining when you mention a Rdson =10V ??
Rdson is the resistance between drain and source in Ohms. According to the datasheet it is 0.05 Ohms specified at Vgs = 10V (here are the 10V).
Except that, thanks for your excellent videos.
Thanks for the correction.
Thanks dude 👊
very usefull
This is one of the reasons I love this channel different uses for various components and how they work. Thanks Paul.
Simple yet powerful potential circuit. Would like to see you add this to a larger design circuit, perhaps with Arduino involved.
Yep as others pointed out Rds on is a resistance (usually in the neighborhood of 0.1 ohms or less) - I've seen designs with power MOSFETs in parallel to decrease Rds on or increase current capacity (heck 30A is more than the current capacity of a typical household circuit). These things are great for switching large loads or power amplification. You can also pulse the MOSFET with PWM for DC motor speed control as well as lamp brightness. An H-bridge motor circuit with 555 PWM would be a great simple demo - sorry if I did not see that if you did do one already. Nice job always enjoy your "back to basics" videos.
New to your channel, very glad I found it. Awesome content, very helpful 🙂
Quick question - I'm trying to control the speed of a 12v compressor (QDZH35G) I purchased which can be done by modulating the resistance. The technical documentation states that...
0 ohm @ 0.87~1.02 mA = 2000 RPM (minimum speed)
1523 ohm @ 3.15~3.61 mA = 3500 RPM (maximum speed)
Is the MOSFET the right component for the job? Or should I go with JFET?
MOSFET or IGBT if the current is high
Nice! Thank you! So with 12V and 265mA passing, the MOSFET is around 45ohms? What is it's usable resistance range when used as voltage-controlled resistor? 1M..45R? 100k..45R?
looks like you could make a very simple class A audio amp useing just an output transformer and a few resistors and one cap.
Another good video. I've just been working with a MOSFET on an ESP32 MCU. needed to drive a 3.3VDC buzzer @25mA. the ESP32 is only capable of around 12mA from its GPIO so I needed to use the MOSFET to get the extra current. MOSFETS are strictly for DC loads and ALL the grounds need connected together. I also had to use a Logic Level MOSFET that would turn on at 3.3VDC. Not many fit that need.
Watch out logic level for fets is 5V, you need to check the datasheet for the Vgs(th) voltage to be less the 3.3V. So many logic level fets where its >4V
Awesome!
How would this hold up in a regulated radio power supply vs a LM319 driving 2955's or 3055's?
Hi Paul. Nice video. Your German skills are also amazing. You know „Kugelschreiber“? LOL Keep up your good work. Thanks
👌👍
Well, now I guess I'll have to make some LED strip dimmer circuits to go with the Wifi Teensy/RPi audio system, that you've inspired me to make, but is at the end of the queue.🥴
💡 Sound to light disco system! See what you do to ppl?
Keep up the good work and stay safe, 'behind your wall'.😎
Thank you! Love the Floyd reference.
Worth noting for a dimmer that the 30A rating is when the FET is fully on (ie Vgs = 10V) and reduces as Vgs reduces. Safe region graph in the data sheet has details
Also worth noting that it's almost impossible to drive a fet at its max current limit as specified as you can't fit a heatsink that big.
Hey man, thanks for the video.
I’m a bit confused about something tho..so basically a mosfet acts like a switch..that switches another circuit..okay...but then..can we replace the mosfet with a relay and use a relay instead? What are the benefits of using a mosfet instead of a relay?
You had a saying about the source and drain, how did it go?
Thanks for todays lesson.
Drain from, source to
il feel funny i think i might lat down. nice video Paul.
STELLAR !! (+1) wow.. is it my birthday? released 2 months ago. Well done.
yeah MOSFET handles high current but better not to do so on breadboard without proper heat sink :) your videos are awesome :)
Can you explain what is going on with that hum and vibration you have at the start of your videos? Love your videos!
Sound effects
@@learnelectronics Hahaha, yeah but it happens for real also.
@@learnelectronics I really like your intro sequence. Switch, buzz, roll up deflecting text... Surely not just me that finds it so satisfying?
i see the rotary resistor does not move much to make the light dim or turn brighter. i want to power a 12 volr dc motor with a rotary pot and only have 60 degrees of rotation from off to on and back to off. so it looks like the higher the pot the less movement of the pot! so would it have to move more with a lets say 500k you used a 1 meg variable resistor and it looked like it did not move much at all! is there any way i can contat you faster than on you tube?
arduino0169@gmail.com
HOW WOULD YOU BUILD THIS IF YOU HAVE TO USE SEVERAL HUNDRED VOLTS TO POWER THE CIRCUIT UP?
Can it be used to do a cheapo dummy load with a heatsink, eg 5V ?
Yes it could
0.260A / 0.0000065A = 40,000 times. The gate current is 40,000 smaller.
Damn, did not know a "Micro Amp" was a thing! I've heard that the Micro verse is scary... Well that is according to Ant Man anyway... Lol
I never have used Mosfets for any projects other than in repairs on radios. I'm not that big of a designer of circuits, I do like to make simple stuff to see how they work like Dark or Daylight circuits and the like.
Like most Hobbyist I know a lot to be Really Dangerous... Lol
Thanks for the video! :-D
LLAP
Try this with a higher load, like with 12V 100W lamp, that'll get some amps in there at like 50% and I'll bet the MOSFET will turn hot enuf for you not to touch it.
For me MOSFETs are only for switching, they are as good or bad as BJTs
Love your vids tho :D
I thought that this would be a perfect application for a J-FET operating in the ohmic region?
By your voice its clear that you need to do strict weight loss diet
Are my calculations wrong at 8:30 or does it show a GAIN of 400:1 ???
more like 40000:1 with my maths !
@@eastcoastandy2905 , You're right. I didn't feed enough 0's into my calculater for the microamps. I used -10000 instead of -1000000.
Thank you.
40000
👍👍
VCC? for a mosfet? I thought it was VDD? Collector =VCC, Drain = VDD.
VCC and VDD both imply voltage or circuit power. VSS is Ground. No reference to a drain or collector.
They used to apply to type of transistor used as you mention with Vcc and Vdd, you will also find Vee and Vss in old datasheets. Nowadays as FETs have become the norm people stick to Vdd and Vss or GND. However, older technicians may still use the older Vcc and Vee as they 'grew up' with those terms, even though technically they are inaccurate today depending on what you are using. Similar to how some in Europe still use imperial even though most are working in metric.
I NOTICED THAT TO
It has a drain not a collector. so VDD it should be. "Make it so"
You will not be able to reach Vgs at 10V with 3 x 1 Meg Ohms resistors in that configuration. So you won't be able to get full saturation of that thing. Best you can get out of that circuit will be 2/3 of 12 V, so 8 Volts. Interesting video though.
'Mosfets' and 'fun' hmmmm .... trying to associate! 😉😆
To better understand the circuit I think it would have been helpful to show how the voltage divider and the pot affect the voltage at the gate of the mosfet.
Measuring the current at the pot with the multimeter but not showing the voltage seemed like a missed opportunity, because if I understand the circuitry right, the important part seems to be the voltage at the gate, the current through the pot not so much.
Yes, since MOSFETS have a huge input impedance, the voltage at the gate is critical.
You will find the difference between on and off is very small. As FET heats up a little current will change. A resistor in the source will give much better results.
YOU TUBE robotizado con cd 4017 , ne 555 pilotos Andre
40,923?
huh?
@@learnelectronics
The current gain.
Really with the slope characteristics of a mosfet wired in this manner you will have nothing as you advance the pot ...and nothing... and nothing ....and then everything, may as well put a switch there - Or a four position switch - Off, one at the knee, one half way up the slope and full on. A bipolar transistor is much better here, or maybe drive it with the inverse of the slope via an op-amp and another fet in the feedback.
Martin D A this demonstrates clearly how to use extremely low current to control 1/4 an amp. resistor divider is the lesson here. And slope characteristics of mosfets vary greatly. your idea of all mosfets being the same is humorous lol 😂
1st Thumbs up...lol
This is just wrong in so many ways.
Oh? In which ways? Please list them along with your reasoning...
Also, notice how the current slowly drops as the filament warms up and becomes more resistive ;)