MOSFET implementation in TL494 Circuit

[nickbrown_500]

Im using the TL494 app circuit which is in the datasheet,

**broken link removed**

Where the TIP 32A is im looking at changing this for a P-channel MOSFET, IRF9520NPbF.
I understand I will need to change the two resistors around the transistor the 150 ohm and 47 ohm resistor.

Can anyone tell me how to calculate the new values for these resistors??

 

[FvM]

I don't have an application circuit in my present TL494 datasheet (SLVS074E, TI 2005). But I guess, I know which circuit you're referring to.

There are several point involved:
- You have to keep th eMOSFET maximum Vgs absolutely, but should provide a sufficient Vgs to switch the transistor fully on
- Resistor dimensioning is a compromise between switching speed and power consumtion. Everything goes, you have to decide yourself.
- TL494 output is known to switch rather slow, you would want to speed it up to achieve lower switching losses. I remember, that I used a cascode output stage with TL494 many years before, even with moderately fast bipolar transistors.

P.S.: I couldn't see the circuit in your post before. Obviously, the resistor ratio has to be adjusted to the supply voltage, according to what I already said. "10 - 40 V" won't work. Or a Z-diode voltage limiter is required.

 

[nickbrown_500]

Sorry forgot to mention the input voltage will be 17V,