How to get through the problem related to MOSFET Switching?

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FvM,
For Floating Supply capacitor used are as follows,
1)Capacitor For High Side : 2.2uF/63V & 0.1uF
2)Capacitor For Low Side : 8000uF/25V , 10uF/63V & 0.1uF
Also find the attached file for floating supply,is this design fine for floating.
Vgs =12V ,Qg =65nC ,Cg =1700pF ,Rg =9.5ohm ,Fsw =10KHz


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Presently for Half Bridge Topology i am using RC Snubber across each MOSFET, Snubber = 22ohm(47ohm parallel 47ohm)MFR , 10nF/1KV Ceramic Capacitor.
Test Conditions are as follows,
Drain to Source Voltage =800Vmax
Drain to Source Current =30A
Power = 10KVA
But can MFR sustain high voltage & do i need to connect snubber across both MOSFET or only across lower MOSFET because in one of the PDF i found they recommend to use across lower MOSFET.

Also can we use only capacitor as an Snubber

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As previously i was using RC snubber across each MOSFET in Half Bridge Topology which were R =22ohm/250mW(47 ohm parallel 47 ohm) & C =10nF/1KV.
Presently i replaced the snubber by a single capacitor 0.1uF/1KV,connected between Drain of upper MOSFET & Source of Lower MOSFET(across capacitor bank)
Single capacitor can act as an snubber?
Also i tested SCT30N120 MOSFET with 4.8ohm & 15.8ohm Gate Resistor,images for which as attached.
Scope Channels are as follows,
Channel 1 :High Side Gate Waveform(Yellow)
Channel 2 :Low Side Gate Waveform(Blue)
Channel 3 WM Waveform(Purpel)
Channel 4 :Trigger Waveform(Green)



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Presently i replaced the snubber by a single capacitor 0.1uF/1KV,connected between Drain of upper MOSFET & Source of Lower MOSFET(across capacitor bank)
Click to expand...
Single capacitor can act as an snubber?
Click to expand...

That's a kind of disambiguation problem. Sometimes bus capacitors are called snubbers, when they are connected near the power transistors. But primarly the term designates lossy elements connected to the switching nodes. The topic has been discussed in the previously linked thread and I don't have much to add, presently.

Regarding your measurements:
- what it's wrong with the waveforms in your opinion

- how do you measure e.g. gate voltages, with differential probes? Did you verify that the probes don't mostly pick up interferences, e.g. by measuring high-side source against high-side source, should be zero

- to understand problems that might show up in the oscilloscope waveforms, we need to see it in higher time resolution
 

FvM,
can scope probe create noise effect?
While testing Scope Probe found picking noise,


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Dear All,
As i carried out re-layout in circuit like now the circuit PCB is of two sided.But,while switching ON the Gate to Source Signal ,without applying Drain to Source i can hear an sound.
So i am confused whether that sound is originated due to switching or some loose connection of MOSFET & Heat Sink?


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Gate signals couple to drain, even without bus voltage. Also the bus may charge up to the gate driver voltage in a bootstrap circuit.

I presume that the sound is emitted from inductor cores, ceramic capcitors are another popular sound source.
 

FvM,
Yes Ceramic Capacitor was the source for creating sound at 10KHz,so shall i go with tantulum or radial?
Also i checked different values of ceramic at 3.3VDC/10KHz i found sound increases as capacitor value in farad increases.
Can this sound will create an problem,so that primarily neglecting the sound further testng can be done?
Currently using AVX Capacitor,but frequency response plot is not given in datasheet
Our Switching freuency is 10KHz


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A certain piezoelectriceffect is normal for high Er ceramic dielectrica like X5R or X7R. They shouldn't be used above 50 % of it's voltage rating to avoid voltage dependant capacitance reduction. I guess, this also reduces piezoelectric effects. And of course there are differences between manufacturers.

If your design also includes inductors, their sound emission will be usually stronger than that of capacitors.
 

FvM,
Also i found sound is been generated by AC Capacitor of LC Filter.
Can this AC capacitor damages Switch?
Do i need to increase the value currently it is 25uF?

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FvM,
Currently using cylindrical 25uF/450VAC EPCOS Capacitor will it works for LC Low Pass Filter.
As i found on net,most of the LC Filter used at Output of Inverter uses BOX Type Capacitor.
So do i need to use Box Type of same value?
What should be the type, X2 or MKP?
But MKP & X2 are same or different as i found it is same.

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Capacitor specification differ a lot regarding ESR and permited AC current. Box type or zylindrical is just a form factor that doesn't say anything about these parameters.

The voltage accross the low-pass filter capacitor will be almost pure 50 Hz fundamental, so the AC current is rather low and should be handled by any 450 VAC capacitor. DC bus capacitors are more critical because they carry large peak currents.

You didn't tell how you designed the low-pass filter.
 

FvM,
Low Pass Filter Specification is as follows,
Inductance(L) =650uH
Capacitor = 25uF/440VAC
Single order Low Pass Filter,
Why in general people suggest to go with Box Type Capacitor,is there any reason or orthodox belief ?


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Hi,
System Design : Inverter
Topology : Half Bridge MOSFET
I am confused with LC filter as capacitor starts generating sound as drain to source Voltage goes on increasing at No Load,
LC Filter Specification are as follows,
L =650UH
C=25uF
Switching Frequency =10KHz
Output Frequency =50Hz

Tried different capacitor as follows,
C=25uF/440VAC (Cylindrical EPCOS) Single
C=16uF/300VAC(BOX Type Capacitor)(4.4uF x 4,2.8uF x 1 )
C=22.6uF/440VAC(BOX Type Capacitor,with wires at output)(7.2uF x 3)

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Dear All,
What shall be the criteria while selecting the DC Bus Link Capacitor for Half Bridge Topology Based Inverter?
Bus Voltage = 800VDC max(Total)
Power =10KVA

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Do we need to use an external diode across drain to source of an MOSFET?
Which diode to select for Anti-parallel connection across gate resistor?
Switching Frequency =10KHz.

RC Snubber connected across each MOSFET Drain & Source in Half Bridge Topology?

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Dear All,
a)Inverter Runned upto 2KW.

b)The only concerned is when inductor reaches to saturation level will it clip AC signal in both direction ?


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Dear All,
Inverter tested up to 5KW with resistive load which works fine.
Now i want to do inductive & capacitive load test,so is there any precaution or extra circuit we need to add.

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1)How to protect MOSFET'S in Half Bridge Configuration at the time of short circuit or cross conduction condition?

2)If Sense resistor in source path and Op-Amp used to pulled down PWM signal to respective ground at the time of short circuit or cross conduction,then what will be the reaction time?

3)Time to pull down PWM depend more upon Op-Amp,what will be Op-Amp propagation time?
As to save MOSFET from blowing during Short Circuit,the action time must be very fast.

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