The Gate is directly connected to one digital pin (for example pin 13). The Source and Drain pins are used as a switch. There are 2.5 volts connected. But that voltage can be change If the Gate is High, voltage and current should flow, so the "switch" is closed. Otherwise if the Gate is Low, the "switch" should be open. It works but not as fine. There is every time some voltage between the Source and Drain pin.That should not be. There should only be voltage when the Gate is High, else if the Gate is Low no voltage should flow. How can I solve this probleme? I hope you guys can help me
The IRLZ44N and IRLB8721 are common, cheap and easily available options. I have used both for LED strip PWM dimming with 3.3V ESP8266.
BTW, I always wondered how practically relevant the resistor is. I mean, I totally see that in theory, high currents flow, but on the other hand, it only happens for a very short time and in many other cases, no resistors are used when small caps are involved. Even Adafruit does not use any here: Usage | RGB LED Strips | Adafruit Learning System
ElCaron:
BTW, I always wondered how practically relevant the resistor is. I mean, I totally see that in theory, high currents flow, but on the other hand, it only happens for a very short time and in many other cases, no resistors are used when small caps are involved. Even Adafruit does not use any here: Usage | RGB LED Strips | Adafruit Learning System
It's more a matter of good practice than anything, although the potential is there to damage the chip.
And I wouldn't necessarily take adafruit examples as the epitomy of good practice.
OldSteve:
It's more a matter of good practice than anything, although the potential is there to damage the chip.
Unnecessary. I designed IC off chip drivers for high fanout FET memory cards. It was not an issue for mainframe computers. It is not an issue for hobby projects.
charliesixpack:
Unnecessary. I designed IC off chip drivers for high fanout FET memory cards. It was not an issue for mainframe computers. It is not an issue for hobby projects.
I've seen a great many things work without that series resistor, but that doesn't mean it's not good practice to include one, to keep the pin current within spec for the chip. I did say potential for damage, not that it would happen.
I stand by what I said earlier.
OldSteve:
I've seen a great many things work without that series resistor, but that doesn't mean it's not good practice to include one, to keep the pin current within spec for the chip. I did say potential for damage, not that it would happen.
I stand by what I said earlier.
It is equally good practice to put your project in a waterproof enclosure. Not that it will be dropped in a puddle. There is the potential to be dropped in a puddle.
My understanding is that the resistor is used in high switching frequency motor driver applications where the rapid on/off times result in high gate currents due to gate capacitance charge/discharge current at high frequencies.
ElCaron:
The IRLZ44N and IRLB8721 are common, cheap and easily available options. I have used both for LED strip PWM dimming with 3.3V ESP8266.
BTW, I always wondered how practically relevant the resistor is. I mean, I totally see that in theory, high currents flow, but on the other hand, it only happens for a very short time and in many other cases, no resistors are used when small caps are involved. Even Adafruit does not use any here: Usage | RGB LED Strips | Adafruit Learning System
If you use PWM the high current flows for a non-negligible proportion of the time - most MOSFET gates act
like a few ohms in series with the gate capacitance, so they are essentially capacitors. Also the resistor
helps protect the Arduino from the MOSFET gate back-driving it (which happens due to the
capacitive coupling between drain and gate, and the drain circuit is typically very low impedance).
Ideally, as always with MOSFETs, using a gate driver chip is the best practice.
You should not be driving a capacitive load from a logic signal, its bad practice, whoever does it. There are
special line-driver chips for handling heavy loads like that. Most logic chips would be rated for a few 100 pF if
its specified, and this can be both to protect the output drivers for damage and also to guarantee correct logic
function if that signal goes to another logic input. Ultimately limiting the load on output pins may also
serve to prevent any risk of CMOS latch-up - fortunately modern devices are better at resisting this than
early CMOS. Latch-up - Wikipedia
Thanks for putting it in even better terms, Mark. You're right about using drivers suited to the purpose, but it is very common to drive MOSFETs directly from an Arduino pin, especially for one-off switching but also for PWM, and the resistor helps avoid potential problems.
(I learned all of my digital basics using CMOS4000 series chips, so I'm more than familiar with 'latch-up'. )
That's because OldSteve is younger than I.
I learned my digital basics with TTL 7400 series and Don Lancaster's TTL COOKBOOK. ( but I had his CMOS Cookbook too).
If LarryD is watching I know what you're thinking: "EVERYONE is younger than you")
raschemmel:
That's because OldSteve is younger than I.
I learned my digital basics with TTL 7400 series and Don Lancaster's TTL COOKBOOK. ( but I had his CMOS Cookbook too).
If LarryD is watching I know what you're thinking: "EVERYONE is younger than I")
Ha. I still have my "CMOS Cookbook". (And the "Active Filter" and "IC Op-amp" cookbooks.)
They were great learning references. I haven't looked at any of those for years. I'd actually forgotten that I had them, and had to check the bookcase.
I've even got almost every "paper" Motorola datasheet book. I do still occasionally refer to those.
If the Gate is High, voltage and current should flow, so the "switch" is closed. Otherwise if the Gate is Low, the "switch" should be open. It works but not as fine. There is every time some voltage between the Source and Drain pin.That should not be. There should only be voltage when the Gate is High, else if the Gate is Low no voltage should flow. How can I solve this probleme? I hope you guys can help me
