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MOSFET driver

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TKS

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Is there a way to switch on mosfets in PWM mode

by using components instead of a driver?

For example:
Would it work if i tied the gates to Voltage with a 20Ohm resistor and a huge transitor would Pull it down (to switch it off??)

i now it will destroy allot of current but its just the question if it can do that fast enough or not...

I have used a couple of BC373 (darlington arrays) they have high gain...
but looked like the PWM freq was to fast (i only applied 3Khz)

what could be the problem??


Tks
 
Using a resistor anywhere will only slow down the speed that the FET switches at. I think if you Google you will find some discrete drivers that involve some BJTs and MOSFETs working in parallel but I don't quite remember.
 
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mhhh

ius there a way to calc the speed of it??

i saw a design wich uses one NPN and one PNP bases tied together
Collector of NPN to 12volts Emitter to Gate mosfets
Collector of PNP to gates and Emitter to ground..

would this work?

if i simulate this in crocclips i get still current flowing (a bit) and when applied volts to the base it conducts fully (that part works)

EDIT: This seems to be the method! Due to not proper grounding the BASES it stayed on...

Tks

for the rest on google i cant find nothing....
 
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Would this work???

How can i calc a estimate max frequency??

Regards,


Tks
 

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Your circuit is frequently used to switch a Mosfet quickly.
The supply to the Mosfet should have a bypass capacitor.
It is recommended to have a 10 ohms resistor or a ferrite bead in series with the gate of the Mosfet to prevent it from UHF oscillation.
 
what is a bypass capacitor?? i already have on over the battery (if its that)
the resistors are also there 22Ohms..one for each Fet (6 in parallel)
have 4amps NPN and PNP darlington ones..

sow less current is needed to switch it all not??

Tks
 
A bypass capacitor is across the supply voltage at the part that needs it, not "over at the battery" where there is plenty of wiring inductance between them.

22 ohms is good in series with each gate.

Darlingtons? Your circuit doesn't have and doesn't need any darlingtons.
 
audioguru said:
A bypass capacitor is across the supply voltage at the part that needs it, not "over at the battery" where there is plenty of wiring inductance between them.

22 ohms is good in series with each gate.

Darlingtons? Your circuit doesn't have and doesn't need any darlingtons.

Its true that my circuit doesn´t show them!
but i planned to use them! they switch faster as normal transistors do they?

else i only have BC547C and a PNP one... BC556 and those only supply
100ma of current.

The darlingtons supply 3Amps!!

Tks

would it only work with normal ones??
6 fets in parallel is allot of pF wich needs to be charged fast and de charged fast...

what are your thoughts??

Tks
 
A darlington transistor switches very slowly and wastes about 1V when it is turned on. A Mosfet switches extremely quickly if you use a proper driver for it.
 
A complementary pair with a BS250 and 2N7000?
 
Complementary Mosfets will both be turned on when they switch, shorting the supply and blowing the Mosfets. They would need to have a "dead time" circuit so that one switches off before the other one switches on. Too complicated to do with individual parts, a Mosfet driver IC has the circuit built-in.
 
yeah...sow you can do 2 things... limit the current with a high watt resistor
or just use a mosfet and a Transistor... problem is that most driver ic's don't permit bootstrap tech...(have VDD internally connected to VB...

i think it all depends on switching speed doesn't it?

Tks
 
also has to be noted that when partly on the resistance is quet high...

sow the amps flowing are low...also the duration is low...

Tks
 
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