An alternative Transistor for this?

Thread Starter

Miracletech

Joined Nov 15, 2019
89
Ok. This sounds kind of weird but, I wanted to make a smps buck-boost converter using two transistors(or FET's) , I want to use a MOSFet but unfortunately, there are no logic level FET's. Its a 3.3v power supply from an audrino and then a 3.7v power supply from a 18650 cell. Since there are no LOGIC LEVEL MOSFETS, Should I use a BJT? Load current is 1AMP but maybe 2AMP will be recommended. So what's your take? (T0220 casing because of power handing). Is there any IRF series for that?
 

Papabravo

Joined Feb 24, 2006
12,770
Ok. This sounds kind of weird but, I wanted to make a smps buck-boost converter using two transistors(or FET's) , I want to use a MOSFet but unfortunately, there are no logic level FET's. Its a 3.3v power supply from an audrino and then a 3.7v power supply from a 18650 cell. Since there are no LOGIC LEVEL MOSFETS, Should I use a BJT? Load current is 1AMP but maybe 2AMP will be recommended. So what's your take? (T0220 casing because of power handing). Is there any IRF series for that?
There is no substitute for the right parts. I don't think an smps buck-boost converter can be made with just two transistors. Why do the MOSFETS have to be LOGIC LEVEL? You haven't mentioned what your requirements are and that is the 1st step in any design project, especially one where feasiblility is in doubt.
 

Thread Starter

Miracletech

Joined Nov 15, 2019
89
In where I live, I have searched all over my area and I didn't find any one, that's why I am asking.... or I use a bjt? I can easily buy an IRF Series Mosfet everywhere but they are not working well..... So is there any Standard mosfet that can give 2 AMPS from 3.3v or maybe 3.7v? Please help..
 

SamR

Joined Mar 19, 2019
1,639
I'll throw this in with a huge Caveat Emptor. AliExpress has lots of "generic" chinese/malasia/vietnam/korea/russia made parts extremely cheap. I buy them for my own "amusement" and would strongly advise against using them commercially. Some are considered obsolete parts by the original manufacturers but are still being made in Asia.
www.aliexpress.com
10PCS TIP33C TIP33 T0220
US $1.50 / lot
10 pieces / lot
Shipping: US $0.74
 
Last edited:

Papabravo

Joined Feb 24, 2006
12,770
You didn't mention in your original post that you wanted a 40V output. Didn't you think that was a relevant piece of information? How much current does the input take and how much does the load require in the device you want to make?
 

Thread Starter

Miracletech

Joined Nov 15, 2019
89
Its as simle as that, but voltage output will be much more lesser than that. That's why I need A MOSFET. By the way, if I use IRFZ44N or IRF3205 or IRF540N, how many amps will I get if output voltage is let's say about 9 volts? How do I calculate it? Any formula?
 

Thread Starter

Miracletech

Joined Nov 15, 2019
89
That means as it stands now, there are two roads:
A. Order a MOSFET(May not be possible) or still try looking
B. Use a BJT.
But where I am getting some mixup is most SMPS circuits either say IRF3205, IRFZ44N or IRF540N, BUT THEY ARE NOT LOGIC LEVEL which is where I am kind of lost...
 
An ordinary IRFxxxx needs a gate-source voltage of 10V to turn on well.
But an IRLxxxx Mosfet needs a gate-source voltage of only 5V to turn on well.

Maybe a product manufacturer buys ordinary IRFxxxx Mosfets and tests them all, then uses only the few that work well (if there are any) with a Vgs of only 5V. Or maybe the product manufacturer uses ordinary IRFxxxx Mosfets which switch poorly with the low Vgs, then the manufacturer uses a large heatsink. Or maybe the product manufacturer uses ordinary IRFxxxx Mosfets which get too hot and some burn out soon.

Your circuit uses a very slow 50Hz or 60Hz 1N4007 rectifier instead of a fast switching diode.
 

Thread Starter

Miracletech

Joined Nov 15, 2019
89
OK. From the various points of views from replies and explanations, It has come to a point where I just have to use a BJT then. OH well. BJT's aren't bad afterall :) . I am going to use MJE13005A instead of the IRFZ44N, and as for the diode, I am going to use SR260. But will these changes improve or reduce performance?
 
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