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halisimon
Joined: 11 Sep 2006
Posts: 7
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 11 Sep 2006 9:06 Distortion issue on drive signal of IRFS4610 MOSFET |
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Hi All.
I was trying to develop a two stage inverter (DC-AC) with a half bridge on the primary side of the flyback transformer.
As shown in the figure 1, each switch on the upper and lower rail operates half cycle which is defined at the line frequency(60Hz). Moreover, the switch at each half cycle will turn on and off at 40Khz which is modulated by PWM signal, on the other hand, the other switch will stay OFF during the whole period until the other half cycle comes.
I hooked up the drive circuit and measured the output signal on the LO (since the lower output return is defined as the common ground and high output return haven't been connected yet), the output drive signal is perfect with the amplitude 15V.
However, when I connected the low and high output to the Gates of the MOSFET as shown in thr schematic diagram. The gate-source voltage which is supposed to be the real drive signal presents a serious distortion as shown in the fig 2.
Apparently, the distortion shows some charging and discharging phenomenon of the capacitor, I am not sure is this because of the Miller effect in the MOSFET or the outside capacitor which is connected between the VB and VS.
The IR2110 is designed to drive the MOSFET directly and MOSFET is 'voltage control' device, I really don't think something wrong with the Gate current. or issue on the drive capability
Anyone met this kinds of problem before? I need a solution to get rid of the distorton.
Thanks alot, everybody.
Hali-Simon
Fig for distortion 2
Last edited by halisimon on 13 Sep 2006 1:06; edited 1 time in total |
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IanP
Joined: 05 Oct 2004
Posts: 6361
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Location: West Coast
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| 11 Sep 2006 9:20 Re: Distortion issue on drive signal of IRFS4610 MOSFET |
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With 3.3kΩ resistors in the MOSFETs' gates you will have exactly what you have recorded - ramp up and ramp down ..
Keep in mind that MOSFET have quite substancial capacitance in its gate ..
Change the 3.3kΩ resistors to something like <10Ω ..
Regards,
IanP
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halisimon
Joined: 11 Sep 2006
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| 11 Sep 2006 9:34 Distortion issue on drive signal of IRFS4610 MOSFET |
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thanks  IanP, actually, the resistor i use is 1K, still too big, isn't it? I will try to hook it up with smaller one as you mentioned tomorrow.
another question is that: the boostrap diode should be the fast recovery diode or normal shockey diode to make floating power supply>15V which is on the VB.
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IanP
Joined: 05 Oct 2004
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Location: West Coast
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halisimon
Joined: 11 Sep 2006
Posts: 7
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| 13 Sep 2006 1:04 Distortion issue on drive signal of IRFS4610 MOSFET |
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Hi IanP
Thanks alot for your help.
I tried the smaller resistor to hook up the IGBT drive, say 20Ω. Basically I built a simply half-bridge, as I stated in the previous poster. However I use simple pure resistor to simplify the question just to check if the IR2110 can work properly or not.
As U can see from the bottom fig, the high side drive has a serious distortion, but the low side drive signal looks all right except a little bit overshooting at the raising edge.
I measured the high side drive signal from HO and VS which means the Vge.
Cos in the first half cycle, the lower switch is OFF all the time, the VS is influenced by the load voltage whcih is pure resistor( up and down from 12V-0V), so the process of charging and discharging happen all the time. Based on that, I surmise, the capacitor connect between VB and VS may effect alot.
In my case, I follow the application sheet value which is 0.47 UF, I guess the value probably is too small. I haven't tried other value yet.
I probably need some input, what do U think.
Thanks again.
Halisimon
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