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tlfong01
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Re: Resistors and MOSFETs and fire-prevention, oh my

Wed Feb 27, 2019 9:27 am

tlfong01 wrote:
Wed Feb 27, 2019 8:02 am
Now I tested a 5 resistor 20W, and found everything OK.

No Ringing Even Rg = 30R or 0R

I decreased Rg fom 1k2 to 0R, but disappointedly did not see any ringing.

What I don't understand is that smaller Rg means longer Cgs charging up time, not sure is because the Miller period is longer.

...
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tlfong01
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Re: Resistors and MOSFETs and fire-prevention, oh my

Wed Feb 27, 2019 9:38 am

tlfong01 wrote:
Wed Feb 27, 2019 9:27 am
No Ringing Even Rg = 30R or 0R (no Rg)
No Cgs Charging or Discharging Problem Even Rg = 0 (Rgs = 4k7)

Testing Vgs 2V ~ 7V 1kHz square wave signal to IRL540N 12V 5Ω

Now I testing 1kHz 2Vpp to 7Vpp signal for IRL540N.
...
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tlfong01
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Re: Resistors and MOSFETs and fire-prevention, oh my

Thu Feb 28, 2019 6:47 am

tlfong01 wrote:
Wed Feb 27, 2019 9:38 am
tlfong01 wrote:
Wed Feb 27, 2019 9:27 am
No Ringing Even Rg = 30R or 0R (no Rg)
No Cgs Charging or Discharging Problem Even Rg = 0 (Rgs = 4k7)
Testing Vgs 2V ~ 7V 1kHz square wave signal to IRL540N 12V 5Ω
Now I testing 1kHz 2Vpp to 7Vpp signal for IRL540N.
...

Vin = 5V
...
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tlfong01
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Location: Hong Kong

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

Thu Feb 28, 2019 6:49 am

tlfong01 wrote:
Thu Feb 28, 2019 6:47 am
Vin = 4V
...
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tlfong01
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Re: Resistors and MOSFETs and fire-prevention, oh my

Thu Feb 28, 2019 6:50 am

tlfong01 wrote:
Thu Feb 28, 2019 6:49 am

Vin = 3V
...
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Re: Resistors and MOSFETs and fire-prevention, oh my

Thu Feb 28, 2019 6:52 am

tlfong01 wrote:
Thu Feb 28, 2019 6:50 am

Vin = 2.5V
...
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tlfong01
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Re: Resistors and MOSFETs and fire-prevention, oh my

Thu Feb 28, 2019 7:04 am

tlfong01 wrote:
Thu Feb 28, 2019 6:52 am

Vin = 2.0V and Conclusion

For power MOSFET IRL540N, the channel seems to almost completely closed at Vin ~= Vgs ~= 2V.

At Vgs = 5V, 12V 5R 1kHz 50% duty cycle, rms current = 850 mA, dropping to about 800mA at Vgs = 4V, 3V.


My quick and dirty conclusion (based on one and only one sample :mrgreen: ) is that IRL540N works with Rpi GPIO 3V if and only if the resistive loading is 800 mA rms.

Since the unofficial spec of Rpi GPIO is Voh > (2.4V ~ 2.8V). It is unreliable to use Rpi GPIO signal directly on IRL540N. A logical level shifter such as EL817C or TSX0102/4/8 to convert 3.3V logic to 5V is more reliable.

I am only using ICL8038 sig gen to simulate Rpi GPIO signal.

Next step is to use the real thing, Rpi to do the testing.

...
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