# An alternative Transistor for this?

#### 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.

#### peterdeco

Joined Oct 8, 2019
73
Logic Level FETS: IRLZ44N, STP55NF06L. Turn on with as little as 2V.

#### BobTPH

Joined Jun 5, 2013
2,204
there are no logic level FET's
Starting with a false premise makes your project more difficult.

Bob

#### Audioguru again

Joined Oct 21, 2019
694
Logic Level FETS: IRLZ44N, STP55NF06L. Turn on with as little as 2V.
Only a few of the IRLZ44 Mosfets turn on with a Vgs of only 2V. Some of them conduct only 0.25mA which is almost turned off.
All of them turn on well with a Vgs of 5V and when you buy one you do not know if it must use 5V.

#### Papabravo

Joined Feb 24, 2006
12,770
Despite Hurculean efforts, magical thinking persists.

#### 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..

#### bertus

Joined Apr 5, 2008
20,230
Hello,

There are mosfets with low Rds(on) at 2.5 Volts Vgs.
They are in SMD packages.

Bertus

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#### Miracletech

Joined Nov 15, 2019
89

#### Papabravo

Joined Feb 24, 2006
12,770
They will be increasingly hard to find since nobody buys those packages in volume anymore. You can't buy TTL in beam-lead packages either.

#### 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

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#### Miracletech

Joined Nov 15, 2019
89
Hmm. Now , that's a problem...... Or, I use a bjt like mje13005 or mje13007 based on my MOSFET predicament

#### Miracletech

Joined Nov 15, 2019
89
This is NOT (*in a loud voice*) what I want to do, but like a guide to what I want to do.

#### Attachments

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#### 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?

#### Miracletech

Joined Nov 15, 2019
89
This is NOT (*in a loud scary voice*) What I want to do. Voltage output would be lesser than that, between ~12V OR LESS.

#### 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?

#### bertus

Joined Apr 5, 2008
20,230
Hello,

The so called logic gate fets are usualy starting with IRL in the partname.

Bertus

#### 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...

#### Audioguru again

Joined Oct 21, 2019
694
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.