Hello everyone,
I am realy struggling with using mosfets and transistors in general and I'd like to get a little explanation of why nothing I make works starting with that simple E switch.
Here is the circuit I've made:
Now when I give it power no matter the state of the physical switch it always gets stuck at the on state even when I directly short out the output to ground.
Any idea why?
The mosfet is: IRFS7530
System voltage: 50V
Thanks for helping.
What do you think will happen if you connect 50.4volt to a gate with an absolute max rating of 20volt.
Leo..
What?! So you say that 20V V(gs) at the datasheet means the absolute max? Ithought it was the normal op voltage
Are those dead?
Besides that, where do you give it power?
What do you mean? It is connected in series with the ground and 50.4V
That makes sense, if you had labeled output as "load" with a connection to +Ve it would have been crystal clear. 
Put 390k ( or similar) resistor between "2" and joining point of 39k and 100R.
Both fets are dead.
Maximum VGS = 20V.
ted:
Put 390k ( or similar) resistor between "2" and joining point of 39k and 100R.
That would drop Vgs to a safe value of 4.58volt, but also would make switching of the fets sloooow.
That could still kill the fets of they are switching heavy loads.
Leo..
MikeLemon:
What?! So you say that 20V V(gs) at the datasheet means the absolute max? Ithought it was the normal op voltage
I think the fact that Vgs 20V is in a datasheet table headed "Absolute Maximum Rating" is intended to give you a fairly broad hint.
Steve
Wawa:
That would drop Vgs to a safe value of 4.58volt, but also would make switching of the fets sloooow.
That could still kill the fets of they are switching heavy loads.
Leo..
Ok so from what I understood when the Vgs is low the FET resistance gets high and that's also what I don't want sins these two have to be able to handle a load of 60A with no heatsink...
What would then be the proper way(in terms of reliability and operation) to turn it on and off using that switch(when having the switch as a short the FETS should allow current to pass and when the switch opens it should be close.)
Thanks for helping again!
Google - mosfet opto isolator
opto isolator - Optocoupled MOSFET drive
Found this schematics:
what should R2 be to fit my "High voltage" app?
Also if Vgs is max 20V what is the right voltage to apply at the gate to achieve the 1.2mOhm Rds On resistance?
What kind of load are you switching. Is it seriously 50volt/60Amp (3000Watt).
I wouldn't dream of switching those high gate-charge fets with an opto coupler or (bouncing) switch at that power level.
I think this requires a special gate driver chip (not enough experience there).
Leo..
Hi,
What is your output connected to?
Where is the 50.4V from, what device?
Can you tell us the application of all this?
Thanks.. Tom...
This is for 24V may work for 50V, to be safe increase r3 to 1k and test it.
TomGeorge:
Hi,What is your output connected to?
Where is the 50.4V from, what device?
Can you tell us the application of all this?
Thanks.. Tom...
Well so the voltage comes from a 12S liion battery connected to 2 bldc esc's to drive electric skateboard motors
Hi,
MikeLemon:
Well so the voltage comes from a 12S liion battery connected to 2 bldc esc's to drive electric skateboard motors
So you will be ground switching power to the ESC's, what is controlling the speed of the ESCs?
Because of your load being an ESC with some controlling circuitry attached, you may have to high side switch the ESC On and OFF.
Thanks.. Tom...
TomGeorge:
Hi,So you will be ground switching power to the ESC's, what is controlling the speed of the ESCs?
Because of your load being an ESC with some controlling circuitry attached, you may have to high side switch the ESC On and OFF.
Thanks.. Tom...
No the motors are just general loads, I want to make that e switch to contain the whole system and turn it on and off with a small little switch sins there are not alot of switches that can handle that that much current that are of a reasonabke size.
Did you Google "battery isolation switch".
The ones with the red key are common as dogshit.
Just don't switch them on or off when the motor is running.
Leo..
