Or you could just choose a mosfet with the parameters you need. You can get mosfets that Are fully on at 4 V, why are you not using them?

Bob

 

He is not using a "logic level" Mosfet because his output voltage is at least 220V.
Also, the thing must switch at the very high frequency of 100kHz so the gate drive current must be high enough to quickly charge and discharge the high gate capacitance of the Mosfet.

 

He is not using a "logic level" Mosfet because his output voltage is at least 220V.

I must be missing something? What does gate voltage have to do with the Vds? Logic level to my simple knowledge only means the gate voltage.

 

well the first transistor will be this one https://pdf.direnc.net/upload/rtr040n03tl-4a-30v-n-kanal-mosfet-sot23-datasheet.pdf i think we can make very low current boost converter for only driving the gate of second transistor

You can use a small bipolar for the gate drive boost converter, or use a tapped inductor and bootstrap the date drive.

 

You can use a small bipolar for the gate drive boost converter, or use a tapped inductor and bootstrap the date drive.

can you give me a example schematics

 

I must be missing something? What does gate voltage have to do with the Vds? Logic level to my simple knowledge only means the gate voltage.

He wanted to use an IRF740 which has a max Vds of 400V and can pass 6A for a moment when its gate-source is 10V. Lookup an IRL741, it does not exist.

 

He wanted to use an IRF740 which has a max Vds of 400V and can pass 6A for a moment when its gate-source is 10V. Lookup an IRL741, it does not exist.

That isn't what you said in the quote I was responding to.

He is not using a "logic level" Mosfet because his output voltage is at least 220V.

My question had nothing to do with a mosfet that doesn't exist. It was your statement about logic level mosfets not working to pass 220V that I was questioning.

 

can you give me a example schematics

This kind of circuit works well.
Instead of the LED use a fast diode, capacitor, and some minimum resistance to keep the voltage from going too high.
The NPN transistor can be almost any small NPN like the 2N2222 or similar.
You can try different value inductors also.
Be sure to simulate first. Keep an eye on the BE junction reverse voltage peak on Q1.

There is a single transistor version but you have to wind your own tapped inductor, Search "Joule Thief".

 

my boost converter will just charge a capacitor no load. i want to charge the cap up to 220 V i think its will be slow but its okay

Compare prices:

MOSFET IXFX90N30 Vds=300V, Rds ON=33mOhm.
US $20.19


DC-DC Converter Boost High Voltage 3-5V Step-up to 200...1200V, adjustable.
US $8.99 free shipping

===================================================


ADDED:
DIY converter 4V to 12V:

 

Do you at least know how to setup the experiment to measure it?

 

This kind of circuit works well.
Instead of the LED use a fast diode, capacitor, and some minimum resistance to keep the voltage from going too high.
The NPN transistor can be almost any small NPN like the 2N2222 or similar.
You can try different value inductors also.
Be sure to simulate first. Keep an eye on the BE junction reverse voltage peak on Q1.

There is a single transistor version but you have to wind your own tapped inductor, Search "Joule Thief".

View attachment 207524View attachment 207527

thank you