Thanks for you allHere is the circuit after changing the resistors values and reassembling.
Using 10V supply and 50% duty input signal from function generator at 62.5KHz (the max frequency Arduino would give me for PWM)
And the signal should be squares but due to old scope it does not show perfect squares.
The top wave is coming from the function generator and the bottom one is taking at
VoAt 1Kohm load
At 33ohm load
At 9.4ohm load
At 4.7ohm load
So what do u think , Is it good enough ?side note, the R1 heats up (rated 0.25W), would that be a problem or I just get higher wattage one ?
I will try to get smaller gate charge mosfet later this weak but for now I will work with what is in hand.
And for more information about the project goal, the plan is to run the system from 36V solar panel and the battery to be charged would be 24V and charged at 1.5A.
The charging will be in constant current mode maintained by changing PWM from Arduino.
So if you have any suggestion or things to be consider I will be very glad to hear it.And now about the replies
My MOSFET switches at 10MHz, at, ugh, 30A current .
You do need a gate driver to drive a power MOSFET to anywhere above 1kHz.
That is too much current, can you maintain good switching at very small load like 50mA ?
That's not the same totem pole. How you drive the transistors matters. In that example they're being driven directly by the output of an opamp, in yours they're being driven by a weak little 3k pull-up. You need to drive them better, a start would be reducing the value of R1 significantly. The values proposed by bktemp would be a good start, but you may want to go even lower on R1.
I did try that but it will heat up, I am now on 470ohm but I tried 220ohm , it is faster but consumes power and make heat.
And about R2, is increasing it like bktemp suggested would help ?
From what I understand , the smaller it is the faster the mosfet closing.
These might help -
http://www.irf.com/technical-info/appnotes/an-937.pdf
http://www.st.com/web/en/resource/technical/document/application_note/CD00003900.pdf
https://www.fairchildsemi.com/application-notes/AN/AN-6069.pdf
Regards, Dana.
Very good reading (actually fast scanning), I understood many new things , for sure it is helping.
Max Vgs is usually 20V, many of your drivers will blow the gate oxide at higher supply voltage.
Would not that kill the mosfet ?
And getting higher supply will need voltage doubler, I think that would complicate the work.
At that frequency, you need to slam that Mosfet open and closed. A pull up resistor will not cut it.
I use a MIC4452ZT
http://datasheetz.com/data/Integrated%20Circuits%20%28ICs%29/MOSFET,%20IGBT%20Drivers/576-1212-datasheetz.html
The IN connects to your micro controller, the OUT goes to the Mosfet, and give it 5V and it will switch that Mosfet up to 2Mz. All in a 4 piin TO-220 package. Simple and works.
Unfortunately I looked in the market but there were no drivers available.
I think you just don't get it.
Input capacitance of IRF9540 is 1300pF.
R1 is 3k.
Effectively, these two make an RC-filter. It's cutoff frequency is Fc = 1 / (2 * Pi * R *C) = 40kHz. So grossly it will pass all the signals below 40kHz and block the signals above it. And this is almost exactly what you experience.
So, what you need to do is to change Fc.
Simply, try to change R1 to 300 Ohm.
Generally it's not a good practice because R1 will dissipate some additional power while Q1 is open, but is should work.
Now that is an other way of looking at it I never thought about.
I made R1=470ohm and I will get IRF9630 later this weak which has capacitance = 700pF which is half.
These changes would make me in better position if I understand you correctly.
I think you just don't get it.
Input capacitance of IRF9540 is 1300pF.
The static capacitance may only be 1300pF but the capacitance at the instant the gate voltage exceeds the threshold and the MOSFET starts to turn on will be higher, thanks to the Miller effect.
But making it half (700) the original (1400) would help for sure.
You don't really need a totem pole output, you just need to improve turn-off, your IRL520 already shorts the gate to ground for fast turn-on. When you try to switch at higher kHz like what you are doing propagation and transtion times add up. You should use a small low gate charge fet instead of the irl520 and try just a bjt or n-fet to improve turn-on time. I don't really think its worth it if you want 250kHz just get a driver like the fan3100 they are only about 50 cents and you will never be able to match its performance.
I can not say anything now, I will need to study your circuit and try it.
But thanks for your work.
Plenty of good circuits have been powered in the following thread: https://www.eevblog.com/forum/beginners/bjt-totem-pole-questions/msg888381/#msg888381
Thanks, I will take a look and see what I can do.
Thanks