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by tlfong01
Sat Feb 23, 2019 1:55 pm
Forum: Beginners
Topic: Resistors and MOSFETs and fire-prevention, oh my
Replies: 156
Views: 9601

Re: Resistors and MOSFETs and fire-prevention, oh my

Bad IRF540N Still Can Pass 1.7A when Vgs = 5V The cheap 1.2 yuan IRL540N, though not conducting at Vcc = 12V Vgs = 3V, can still pass 1.7A at Vgs = 5V. So it is still usable, with a gate driver such as optocoupler EL817C. ... The good and the bad IRL540Ns The day before yesterday I unhappily found ...
by tlfong01
Sat Feb 23, 2019 9:26 am
Forum: Beginners
Topic: Resistors and MOSFETs and fire-prevention, oh my
Replies: 156
Views: 9601

Re: Resistors and MOSFETs and fire-prevention, oh my

Bad IRF540N Still Can Pass 1.7A when Vgs = 5V The cheap 1.2 yuan IRL540N, though not conducting at Vcc = 12V Vgs = 3V, can still pass 1.7A at Vgs = 5V. So it is still usable, with a gate driver such as optocoupler EL817C. ... 10 Bad IRL540N Guys Testing Results I tested 10 bad guys and found them s...
by tlfong01
Sat Feb 23, 2019 2:08 am
Forum: Beginners
Topic: RPI Zero W multiple sensors
Replies: 27
Views: 2619

Re: RPI Zero W multiple sensors

I also day dream of Starting Up something one day. I am setting up a learning goal. ... to learn enough in 3 years. You might also need 3 years. One thing you need to know is how other guys compete or succeed in startups. Element14 Project Ideas on Motors, Solenoids, and WiFi I said you need to kno...
by tlfong01
Fri Feb 22, 2019 2:36 pm
Forum: Beginners
Topic: Resistors and MOSFETs and fire-prevention, oh my
Replies: 156
Views: 9601

Re: Resistors and MOSFETs and fire-prevention, oh my

tlfong01 wrote:
Fri Feb 22, 2019 1:20 pm

Bad IRF540N Still Can Pass 1.7A when Vgs = 5V

The cheap 1.2 yuan IRL540N, though not conducting at Vcc = 12V Vgs = 3V, can still pass 1.7A at Vgs = 5V. So it is still usable, with a gate driver such as optocoupler EL817C.
...
by tlfong01
Fri Feb 22, 2019 1:20 pm
Forum: Beginners
Topic: Resistors and MOSFETs and fire-prevention, oh my
Replies: 156
Views: 9601

Re: Resistors and MOSFETs and fire-prevention, oh my

IRL540N Test Results Bad Power Electronics Heavy Current Heat Problem I also found the 5R 20W power ceramic cement resistor becomes very hot when passing only 1.8A. Cracks are formed at the base of the resistor. The touching connecting wire's plastic sleeve got burnt to charcoal. I worry that ifI d...
by tlfong01
Fri Feb 22, 2019 12:12 pm
Forum: Beginners
Topic: RPI Zero W multiple sensors
Replies: 27
Views: 2619

Re: RPI Zero W multiple sensors

I also day dream of Starting Up something one day. Now I am setting up a learning goal. But there are too many things I need to learn, so I hope to learn enough in 3 years. You might also need 3 years. Three Year Learning Plan One thing you need to know is how other guys compete or succeed in start...
by tlfong01
Fri Feb 22, 2019 8:35 am
Forum: Beginners
Topic: Resistors and MOSFETs and fire-prevention, oh my
Replies: 156
Views: 9601

Re: Resistors and MOSFETs and fire-prevention, oh my

Your analysis is flawed. the rise time of the digital output is around 1.6ns That's only true for an unloaded GPIO pin. Assuming the GPIO is ideal is nonsense, and leads to nonsense results like it supplying 2.8A to charge the 1350pf to 3.3V in 1.6nS. That just isn't going to happen ! :roll: The GP...
by tlfong01
Fri Feb 22, 2019 4:59 am
Forum: Beginners
Topic: Resistors and MOSFETs and fire-prevention, oh my
Replies: 156
Views: 9601

Re: Resistors and MOSFETs and fire-prevention, oh my

Which Skills are Most Important on the Job and Which Skills are in Short Supply? - M Herk, CED, 2015 https://www.ced.org/blog/entry/which-skills-are-most-important-on-the-job-and-which-skills-are-in-short-su Critical thinking and Problem solving stand out as the skills that are deemed essential to ...
by tlfong01
Fri Feb 22, 2019 1:52 am
Forum: Beginners
Topic: Resistors and MOSFETs and fire-prevention, oh my
Replies: 156
Views: 9601

Re: Resistors and MOSFETs and fire-prevention, oh my

1. You need a load on the gate. If you touch the gate with the 3.3V. It will turn on. 2. Then you need to discharge the gate. ... simply use a gnd wire and touch the gate. It should turn off. Power MOSFET Preliminary Testing - The Newbie Way 1. Use a current limiting resistor (10K) and super bright...
by tlfong01
Thu Feb 21, 2019 1:41 pm
Forum: Beginners
Topic: Resistors and MOSFETs and fire-prevention, oh my
Replies: 156
Views: 9601

Re: Resistors and MOSFETs and fire-prevention, oh my

Now I have started testing IRL540N. IRL540N Test Results Bad For IRL540N, Vgs = 3V, Ids = 0 (not conducting) :( For CSD18511KCS Vgs = 3V, Ids = 1.77A (saturated) :) I tested one more IRL540N, the results is as bad. Spec says at Vgs = 3V, IDS should be 15A! This reminds me of Warren Beffett saying: ...
by tlfong01
Thu Feb 21, 2019 8:49 am
Forum: Beginners
Topic: Resistors and MOSFETs and fire-prevention, oh my
Replies: 156
Views: 9601

Re: Resistors and MOSFETs and fire-prevention, oh my

Burngate wrote:
Wed Feb 20, 2019 6:17 pm
Just with a quick look, there doesn't seem to be a path to discharge the gate - once it's been switched on via the opto isolator, it'll stay on.

Gate Driver Design V2.0

Ah, many thanks for catching my careless error. So I have updated the schematic to V2.0.
...
by tlfong01
Thu Feb 21, 2019 6:45 am
Forum: Beginners
Topic: Resistors and MOSFETs and fire-prevention, oh my
Replies: 156
Views: 9601

Re: Resistors and MOSFETs and fire-prevention, oh my

... I failed English and so had to do Engineering ... Oh my goodness. I failed English and so could not do engineering Critical Thinking and Problem Solving Skills I often hear that critical thinking and problem solving skills are also important. I am not sure how to develop these skills, perhaps I...
by tlfong01
Thu Feb 21, 2019 4:36 am
Forum: Beginners
Topic: Resistors and MOSFETs and fire-prevention, oh my
Replies: 156
Views: 9601

Re: Resistors and MOSFETs and fire-prevention, oh my

Resettable PPTC Fuse vs Circuit Breakers With Manual Reset Button However the shop there does not sell PPTC, but recommended a black thing with a push button. I have never seen such a thing before, but it is 15 yuan only, worth taking a risk. I bought it and found it a good toy, because is hand pus...
by tlfong01
Thu Feb 21, 2019 3:58 am
Forum: Beginners
Topic: Resistors and MOSFETs and fire-prevention, oh my
Replies: 156
Views: 9601

Re: Resistors and MOSFETs and fire-prevention, oh my

Driving Big Motor Mabuchi RS-540SH 12VDC Motor So now I have become a logic level Power MOSFET expert! In order to build up my reputation, I decided to test the biggest motor in my junk box, the Mabuchi 12V 7,100rpm , 250mA (only! ) motor. I changed the 37GB motor by the big guy and switched on pow...
by tlfong01
Wed Feb 20, 2019 1:46 pm
Forum: Beginners
Topic: Resistors and MOSFETs and fire-prevention, oh my
Replies: 156
Views: 9601

Re: Resistors and MOSFETs and fire-prevention, oh my

1. An optocoupler driving the gate will help. 2. If that Solenoid diode cannot handle the spikes then there will be induced spikes everywhere. 3. Solenoids are not much different than those ignition coils in cars, zap. 4. Try to electrically isolated high voltage/high current stuff from low voltage...
by tlfong01
Wed Feb 20, 2019 12:25 pm
Forum: Beginners
Topic: Resistors and MOSFETs and fire-prevention, oh my
Replies: 156
Views: 9601

Re: Resistors and MOSFETs and fire-prevention, oh my

1. Well first this is the wrong mosfet when you have 3.3V for the gate. 2. I looked at your chart I see that it won't be able to switch the valve. Logic Level Power MOSFET Solves The Problem Yes, IR F 540 replaced by IR L 540 or similar logic level MOSFET solves the problem. https://youtu.be/eXIxTt...
by tlfong01
Wed Feb 20, 2019 10:39 am
Forum: Beginners
Topic: Resistors and MOSFETs and fire-prevention, oh my
Replies: 156
Views: 9601

Re: Resistors and MOSFETs and fire-prevention, oh my

1. I notice on one of your picture that the resistor was on the ground instead of the GPIO. 2. Then The Raspberry Pi wasn't really at the same ground level than the rest of your setup . 3. You have a kind of faulty ground there. Setting Rpi Ground and MOSFET Ground Not At the Same Level The followi...
by tlfong01
Wed Feb 20, 2019 10:16 am
Forum: Beginners
Topic: Resistors and MOSFETs and fire-prevention, oh my
Replies: 156
Views: 9601

Re: Resistors and MOSFETs and fire-prevention, oh my

Power MOSFET Gate Capitance and Gate Charge (Ciss) Now I am reading Toshiba's MOSFET tutorial for newbies. Section 1.2.1 has a good picture of gate capitance and gate charge. I don't know what is Miller Period . So I need to google deeper! https://penzu.com/p/39922833 (Toshiba tutorial on gate char...
by tlfong01
Wed Feb 20, 2019 5:33 am
Forum: Beginners
Topic: Resistors and MOSFETs and fire-prevention, oh my
Replies: 156
Views: 9601

Re: Resistors and MOSFETs and fire-prevention, oh my

If the fet is getting hot then it is probably in the analog region. A higher gate voltage turns it on more and so the resistance goes lower and hence heat goes down. Most fets will have a 10 V gate voltage so driving them with 3V3 does not turn them on enough. There are chips called gate drivers de...
by tlfong01
Wed Feb 20, 2019 4:39 am
Forum: Beginners
Topic: Resistors and MOSFETs and fire-prevention, oh my
Replies: 156
Views: 9601

Re: Resistors and MOSFETs and fire-prevention, oh my

1. If we take a look at the datasheet of the SoC, we can see that the rise time of the digital output is around 1.6ns (page 12). 2. Let assume that this Rpi is ideal and the MOSFET only is made out of the input capacitor (Ciss). Then the current can rise to 2.8A to charge the input capacitor! 3. As...
by tlfong01
Wed Feb 20, 2019 4:16 am
Forum: Beginners
Topic: Resistors and MOSFETs and fire-prevention, oh my
Replies: 156
Views: 9601

Re: Resistors and MOSFETs and fire-prevention, oh my

If we take a look at the datasheet of the SoC, we can see that the rise time of the digital output is around 1.6ns (page 12). Let assume that this Rpi is ideal and the MOSFET only is made out of the input capacitor (Ciss). Then the current can rise to 2.8A to charge the input capacitor! As showed i...
by tlfong01
Tue Feb 19, 2019 1:07 pm
Forum: Beginners
Topic: Resistors and MOSFETs and fire-prevention, oh my
Replies: 156
Views: 9601

Re: Resistors and MOSFETs and fire-prevention, oh my

MOSFET Capacitances https://penzu.com/p/39922833 ( Power MOSFET References / Toshiba FAQ ) Toshiba MOSFET Gate Drive Circuit Application Note Now I am reading Toshiba's app note. I found this newbie friendly. :mrgreen: MOSFET Gate Drive Circuit Application Note - Toshiba 2018-07-26 https://toshiba....
by tlfong01
Tue Feb 19, 2019 9:45 am
Forum: Beginners
Topic: Resistors and MOSFETs and fire-prevention, oh my
Replies: 156
Views: 9601

Re: Resistors and MOSFETs and fire-prevention, oh my

MOSFET Capacitances https://penzu.com/p/39922833 ( Power MOSFET References / Toshiba FAQ ) Toshiba MOSFET Gate Drive Circuit Application Note Now I am reading Toshiba's app note. I found this newbie friendly. :mrgreen: MOSFET Gate Drive Circuit Application Note - Toshiba 2018-07-26 https://toshiba....
by tlfong01
Tue Feb 19, 2019 9:37 am
Forum: Beginners
Topic: Resistors and MOSFETs and fire-prevention, oh my
Replies: 156
Views: 9601

Re: Resistors and MOSFETs and fire-prevention, oh my

2.8A is indeed scary. As a MOSFET newbie, I have been experimenting with IRF540 and so far only read the datasheet sections of Rg, Rgs, Ids, Vgs(th), etc. I have not yet read the sections on capacitance and diodes. I need to read them and google further before I can understand what you are discussi...
by tlfong01
Tue Feb 19, 2019 8:32 am
Forum: Beginners
Topic: Resistors and MOSFETs and fire-prevention, oh my
Replies: 156
Views: 9601

Re: Resistors and MOSFETs and fire-prevention, oh my

The only change will be a slightly increased turn-on and turn-off times as the gate capacitance (1350pF from data sheet) will take longer to charge/discharge. Yes, when the MOSFET is in a steady state. The current is very small. But, that is not the case when you turn it on or off. Like I explained...

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