Mosfet gate resistor in Oscillator circiut?

[gary350]

I have 16 resistors that are all Red Yellow Brown, my digital meter shows their actual values are 214 ohms to 298 ohms, none are 240 ohms.

Circuit drawing calls for 240 ohms. The closest thing I have is 245 and 249 ohms. The only way I can get exactly 240 ohms is put some higher value resistors in parallel.

R1 and R2=240 ohms.

Di and D2 =1N5818

Mosfets =STP55NF06, 60v, 50a, .016 ohm

Choke= 8uh, 35a

C1=.47 uf x8

Coil= 8T, 1"dia 1.5L

What I would like to know is, what does wrong none matching resistor do to this circuit???

I have learned if I change the resistor from 240 to 200 the mosfets run hotter but I don't know the real ohm value I did not test the 200 ohm resistors with my meter. I also notice every time a mosfet burns out it is always the same mosfet. I am guessing current is higher in the mosfet that fried because of miss matched resistors?

 

[ronv]

What I would like to know is, what does wrong none matching resistor do to this circuit???

If one was 400 ohms and the other 240 it might make a difference - but a few ohms no.

I have learned if I change the resistor from 240 to 200 the mosfets run hotter but I don't know the real ohm value I did not test the 200 ohm resistors with my meter. I also notice every time a mosfet burns out it is always the same mosfet. I am guessing current is higher in the mosfet that fried because of miss matched resistors?

I would have expected them to run a little cooler with the smaller resistor because they would switch a little faster.


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[gary350]

I tested both resistors I had in the gate circuit, both red yellow brown, 214 and 262 ohms. I changed the resistors to 245 and 249.

 

[chemelec]

Are your resistors Red, Yellow, Brown, SILVER
10% Tol.

Or Are your resistors Red, Yellow, Brown, GOLD
5% Tol.

Or Are your resistors Red, Yellow, Brown, with No last Color
20% Tol.

Personally I would recommend Lower Value Resistors.
Of 100 Ohms.

 

[ronsimpson]

I think R1, R2 have little to do with turning on the gates. I think there is a path from gate through diode to the other end of the transformer that is the turn on path.
As the transformer "flips" one end is driven hard to ground and the other end jumps to 30 volts. The two gates see this 0V and (30-Zener) voltage. Once the oscillator starts there is little reason for the two resistors.

 

[chemelec]

YES Ron, Sorry I was interpreting the circuit incorrectly.

If the Gate voltage is Really HIGH from the Zeners, that could damage the Mosfet.
I think Especially T1.

 

[ChrisP58]

100% of the turn ON current for T1 comes from R1, and the same for T2 and R2.

Diodes D1 and D2 are turn OFF components. They have no part in the turn ON process as they are reverse biased when turn ON occurs.

As for resistor values, a 240 Ohm 5% component could have an actual value from low of 228 ohms to a high of 252 ohms If you're seeing values from 214 to 298, it sounds like they may be 10% parts. If you want them to match more closely just use 1%, or even 0.1%, resistors.

 

[ronsimpson]

Diodes D1 and D2 are turn OFF components. They have no part in the turn ON process as they are reverse biased when turn ON occurs.

Yes you are right. I thought they are Zener.