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Topic: Which transistors should i use? (Read 2973 times) previous topic - next topic

ted

#30
May 20, 2018, 02:26 am Last Edit: May 20, 2018, 02:27 am by ted
IRF540
Gate-Source Threshold Voltage VGS(th) VDS = VGS, ID = 250 μA 2.0 - 4.0 V

below 2V transistor will not will turn on
Above 4V must turn on
between - it depends on the mood of the transistor.
Logic level or not, 5V is more than 4V

ted

A logic level mosfet must have a threshold voltage <2volt.

Silly advice.
Leo..

I don't care about your opinion,
First learn how to be a polite ........

outsider

#32
May 20, 2018, 02:51 am Last Edit: May 20, 2018, 02:52 am by outsider
@ted:
 VGS(th) is the gate voltage that barely starts conduction (threshold), if it's 4V then at 5V it would conduct but RDS(on) would be pretty high, the IRL's VGS(th) is 1 to 2V so at 4V it would be at full conduction.

ted

#33
May 20, 2018, 03:07 am Last Edit: May 20, 2018, 03:10 am by ted
Being above the maximum (5V), you can be sure that this way, the MOSFET will be turning fully on and off each time it is switched.
@ted:
  it would conduct but RDS(on) would be pretty high,
not sure about that.


Being above the maximum (4V), you can be sure that this way, the MOSFET will be turning fully on and off each time it is switched.



google - Vgs(th) min/max .

Wawa

I don't care about your opinion,
First learn how to be a polite ........
I think Vgt has already been explained to you in previous threads.
It seems you still don't fully understand the concept.
Not a problem, but until you do it's wise to keep advice to yourself.
Leo..

ted

#35
May 20, 2018, 04:30 am Last Edit: May 20, 2018, 03:49 pm by ted
to you in previous threads.
I know what is that and don't need any explanation,
on previous thread you have discussed this for a long  time digging in wrong place, where solution was pointed by me, and magik, all 4 MOSFETS start to work regardless of voltage threshold.



puelon

Alright so specifying my problem here, around my area theres no IRL at all, i have a few IRF, but from the conversation, i should use a 2N2222?

Wawa

I think you were already told in post#3 that a 2N2222 with 220ohm base resistor is ok for a 140mA load.
Leo..

MarkT

MOSFET works similar to NPN (2N2222).
Arduino drives a voltage into the Gate thru 150 ohm resistor, (like R1),
Source connects to Gnd,
Drain connects to the 'bottom' of the motor.

Rds of the MOSFET is very low, so the motor will see almost all of the battery voltage, vs the NPN wasting 0.7V across the Collector-emitter.

A saturated 2N2222 wastes about 0.4V, not 0.7V, that's the Vbe you're thinking of.  Some good modern switching BJTs would have 0.05V saturation voltage for this load in fact.

Note that if using a MOSFET it needs to be a logic level MOSFET, the others need 10V to operate.
[ I will NOT respond to personal messages, I WILL delete them, use the forum please ]

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