If you drive the MOSFETS at 50.5%/49.5% (not symmetrical) there will be DC current. You could look for this DC current and adjust the drive. Or you can add a capacitor.The problem is that a little DC component (about 100mA) put transformer into saturation and the output waveform has a distorsion as in figure
I'm thinking of a transzorb protection across the capacitor. Is it a good idea?If you drive the MOSFETS at 50.5%/49.5% (not symmetrical) there will be DC current. You could look for this DC current and adjust the drive. Or you can add a capacitor.
If things go wrong you could get 70V across the cap. Look for a high current cap. Most caps will burn up at high current.
AG - regarding the above, I think that the diagram is intended to be conceptual rather than a complete schematic. You're right, of course, but I suspect that the OP knows how to drive FETs.Don't you see that the lower Mosfets have a good gate voltage much higher than the grounded source pin but the upper Mosfets are source-followers and need a gate voltage 10V higher than the supply voltage for them to properly turn on??
I don't know if that applies here? If I'm reading the schematic correctly than the OP is using a ferrite core.power inverters based on low frequency iron core transformers
I don't know if that applies here? If I'm reading the schematic correctly than the OP is using a ferrite core.
Hi,
i'm testing an inverter with these features:
Fswitching=220KHz
Fout=3KHz-10Khz
Vout=150Vac
Pout=150W
Current feedback.
Sinusoidal output is obtained with transformer leakage inductor+output capacitor.
In the figure below there is the schematic.
View attachment 105292
The problem is that a little DC component (about 100mA) put transformer into saturation and the output waveform has a distorsion as in figure
View attachment 105293
I don't understand from where it can come this DC component. Could you help me?
A capacitor could solve my problem? what features should have this capacitor? Ceramic or film cap? I had thought of 47uF@25volt as the voltage across it should never be too high.
Let me know.
One way to get rid of it is to integrate the primary voltage and use that as feedback. Your capacitor might work though, i have never had to do it that way. The cap has to be able to handle the RMS current.
Doh! I apologise - I'd been thinking about this in the wrong way (which is why TCM's comments didn't make sense to me initially).
I had been thinking of the transformer working at the switching frequency of 220kHz - the transformer (and any capacitor in series with the primary) is actually seeing the output frequency, which could be as low as 3kHz. Of course!
Ok for the RMS current, but what about voltage? Can i use a low voltage capacitor? I calculate an impedance of about 1 Ohm @ 3KHz with a 47uF capacitor. The voltage drop shouldn't be higher than 3Vrms with 3Arms output current. Is it correct?
Core saturation from unbalanced current happens in a voltage mode PWM. (Where you drive duty cycle with out watching current)
In a current mode PWM each cycle terminates when the current reaches a set point. If the core heads into saturation the duty cycle change automatically to compensate.
A voltage mode full bridge can slip into saturation if things are not perfect.but before that there was no current monitoring.
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