Well , TL494 has internally dead time matching . see page 8 of datasheet . with two resistor . by the way , do you know the aim of another IGBT that used as diode ? you can use a low power IGBT , and then use a high power diode in parallel with it's collector emitter to decrease the cost . it used to provide a path to charge the boot strap capacitor . so it won't has high current . the diode that is in parallel should be able to tolerate high currents . ( minus voltage ) .
BTW : you'd better to increase the value of boot strap capacitor . but it depends on the frequency of operation . how much is the frequency ?
I think the value of your out put capacitor is low too . how you designed them ? randomly ?
Good luck
Goldsmith
That diode , has two purpose , in this circuit :1. remove the diode (when the circuit is still running). the diode seem to not be playing any role right?
Our eyes , can't understand , the frequencies , above 50 HZ . use an oscilloscope . ( smart eye of each engineer !! )2. remove the diode + inductor + capacitor. the LED still lit up. but of course, if with the cap, the LED lit brighter.
the design initially was suppose to carry out 240Vac and be rectified to the buck converter. but i have to scrap that when the sync buck wasn't working. (but it was perfectly fine the first week of testing, i wonder what happened). i guess that IGBT was appropriate for that.why , IGBT ? why not mosfet ?
i am familiar a bit with the basic buck theoretically. but i might understand it wrong. if it's okay maybe you describing it might clarify certain things i have doubts on.Are you familiar with basic of a buck converter , really ? if , no , i can describe it for you .
Anywhere , even you can use a simple bjt , in parallel with a fast diode , instead of , 2nd switch .
yes, i did saw the AC square wave at the inductor when i tried the normal buck converter. i'm carrying out the experiment again tomorrow, i'll capture some waveforms of the 2 cases i tried (with and without the diode)That diode , has two purpose , in this circuit :
1st one is , to keep the switch from minus and high voltage . the cause of this high voltage in minus polarity is lenz law .
If you see the voltage across the inductor , it will be an AC square wave .
2nd : to recharge the capacitor when the switch is off .
Our eyes , can't understand , the frequencies , above 50 HZ . use an oscilloscope . ( smart eye of each engineer !! )
input voltage = 30 - 100VAnd about the LC filter at he out put , give me the value of your input voltage and maximum and minimum output voltage and current
Hi again
And about IGBT : it can handle your aim , but not as well as possible . you can change it with better one , or you can use a mosfet , for instance , IRF740 . the VDSS of that is around 400 volts and ID= around 10 amperes and rdson is about 0.5 ohms ( approx ) .
Well , i wrote 3 pages for you , read them and then if you have any problem , ask me again , please :
In addition to Goldsmith's recommendations...
You might like to look at my video on Youtube which portrays switched-coil converters in simulated animation. It includes the buck type.
www.youtube.com/watch?v=FT_sLF5Etm4
Is it possible the system deteriorated in operation (even though it worked properly at the beginning), because the IGBT characteristics were altered by repeated kicks from the coil?
i think that's probably it. that's why i think i'm gonna go get the mosfet goldsmith suggested me.
i'm pretty bumped out because it works perfectly in the beginning. now that it's near submission, it decides to fail me
anyway, have you ever tried them practically?
Remember to use precautions for static charge around a mosfet.
You may not need a heatsink. You're using it as a switch for under an amp of current. Nevertheless it's a good idea to check whether it overheats. Did you check as to whether your present device is running hot or cool?
sorry for asking, but why need the precaution?
ok..Hi again
At first , about the values that i told , those are the best values for a buck converter with your specifications .
And about the attached waveform , i can see a little overlap , and it means that you have to increase dead time .
Also if your coil is 2mH, then consider running it at a lower frequency. Say 2 to 10 kHz. Try observing what it does at various frequencies, because a given henry value responds according to its time constant, as determined by resistance of the charge/discharge path.
Your coil will need time to charge through the mosfet. It takes about 5 time constants before it reaches maximum current. Say overall resistance is 2 ohms. Then it will need 5 x .002 / 2, or .005 second to charge up to maximum.
what about the 100uF? i've been using 1uF, is that not large enough, would that be better if i get a larger one than 100uF?
if i increase the inductance, the frequency could go higher?
the bootstrap capacitor i'm using now is 100uF. it seems to be ok1uF is probably too low. It exhibits large voltage swings, and is liable to encourage ringing (parasitic) oscillations.
You mentioned 22uF at some point. That should be good for a light load. But there's nothing wrong with using 100uF.
i tried with 800uH at 5kHz, the response this time is good. but like the above, without the capacitor, the waveforms seems to be ok.Higher henry value goes with a lower frequency.
You mentioned 50 kHz. This frequency goes with a henry value in the tens of uH (maybe a few hundreds of uH). This is an estimate based on simulations I've done, from observing that the transistor needs to be on for a long enough time, until the coil is passing sufficient current so that the load will continue to receive power through the transistor 'off' time.
Are you trying to select randomly ?? with events ??? it isn't design . you should learn , how to design . this way isn't correct and your value isn't correct too .i tried with 800uH at 5kHz, the response this time is good. b
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