[Moved]: how to calculate the gate resistance of Igbt (fg25n120) /Mosfet

[mobinmk]

Re: NEED HELP ,how to calaculate the gate resistance of Igbt (fg25n120) /Mosfet

Thnkz Red_Alert

You might choose to put both 6-pin headers beside every MOSFETS row, passing down the common drain trace with the gate series resistors.

i did 2 no of 6 pin header t block on near to the row of igbt.
pls check the modified layout.

**broken link removed**

any modifications needed??

 

[red_alert]

Re: NEED HELP ,how to calaculate the gate resistance of Igbt (fg25n120) /Mosfet

You still have some sharing current paths (gate current + source current).

You better try something like this:



- - - Updated - - -

Or you could use 2-pin headers for every gate circuit and run (between them) with separate high current traces from every MOSFET source to the 3-pin motor header located bellow.

 

[mobinmk]

Re: NEED HELP ,how to calaculate the gate resistance of Igbt (fg25n120) /Mosfet

Thnks Red Alert

Finally i etched this pcb lay out

 

[mobinmk]

Re: NEED HELP ,how to calaculate the gate resistance of Igbt (fg25n120) /Mosfet

can i use FAN7392 driver ic instead of ir2110

https://www.fairchildsemi.com/datasheets/FA/FAN7392.pdf

i think itz better than ir2110.

bcz it can operate upto 600v,IO+,IO- =2.5A-3A

ir2110 can operate upto 500v,IO+,IO0 =2A.

am using fg25n120antd igbt,

both fg25n120 and Fan7392 Driver ic mfd by farhilid.

 

[red_alert]

Re: NEED HELP ,how to calaculate the gate resistance of Igbt (fg25n120) /Mosfet

Have you forgot the series gate resistor for the bottom-right IGBT? And the reverse diodes across series gate resistors are missing, too?

IR2110 has a slighty better dynamic characteristics but for your switching frequency (~30kHz) FAN7392 it's a good option.

 

[mobinmk]

Re: NEED HELP ,how to calaculate the gate resistance of Igbt (fg25n120) /Mosfet

No sir, i put the Rg,Diode on driver ckt.
in order to make the inverter ckt look simple.

now am designing driver ckt and optocoupler ckt in proteus

 

[mobinmk]

Re: NEED HELP ,how to calaculate the gate resistance of Igbt (fg25n120) /Mosfet

sir,

at last i decided to use FAN7392 driver ic.

https://www.fairchildsemi.com/datasheets/FA/FAN7392.pdf

i converted 415v ,3 phase ac supply into dc.
my dc link voltage is 500v- 580v == 600v

absolute voltage rating of driver ic is 600v.(VS)

Should this driver ic withstand ???

 

[red_alert]

The DC link voltage level is dangerous for your driver (any small spike could destroy it).

You better find another solution to drive the high-side MOSFETs. As you're already using optocouplers between the MCU and drivers, you may choose any regular low-side driver and the bootstrap technique for that.

Another (more expensive) solution is to use separate (isolated) power supplies (15V) for the high-side drivers and use regular low-side drivers, too.

 

[mobinmk]

would you recommend,

how much dc link voltage can give??

to operate driver ic fan7392 in safety condition??

 

[red_alert]

If you think you could guarantee that maximum 625V for your driver, just go for it. Some TVS diodes across VB and COM could help, too.

 

[mobinmk]

my dc link voltage 500v-550v

should i connect ceramic capcitor with electrolytic capcitor 10uf,63v, b/w Vb and Vs,

also Vdd and Vss , Vcc and Com ??

like ir2110 ckt.

in datasheep ,appnotes they didnt recommend low esd ceramic capcitor for decoupling...

 

[red_alert]

Yes, that's a good practice. The capacitor across Vcc and Com should be at least ten times the capacitor across Vb and Vs as it needs to supply the current for the driver IC, for driving the low-side MOSFET and for charging the bootstrap capacitor (Vb to Vs), too.

Low esd ceramic capacitors represents a low impedance path to ground for any parasitic spikes thus limiting their amplitude (and distructive effect).

 

[mobinmk]

thnks sir ...

i have some doubt

my power supply to driver ic is 15v from 7815 regulator ic,

output of 7815 is connected across 100uf ,63v electrolytic capacitor.

then additional capacitor is needed??

output is connected to Vcc AND COM,

in my project 3 driver is used.

shall i take the power supply to 3 driver ic by single 7815 output.??

or design 3 seperate 7815 ic to power 3 driver ic ??

should i use decoupling capacitor ceramic with VCC and COM.

if i use large decoupling capacitance of ceramic , any problem ??

in the data sheet of 6n137 .1uf decoupling capacitior is used.
pls reccomend a good value

 

[red_alert]

my power supply to driver ic is 15v from 7815 regulator ic,

output of 7815 is connected across 100uf ,63v electrolytic capacitor.

then additional capacitor is needed??

Low ESR capacitors are mandatory, regardless the electrolytics size. Only ceramic (or film) capacitors withstand the high current pulses for driving the MOSFET gates. Electrolytic capacitors are just some energy buffers who deliver power to ceramic ones during gate pulse inactivity (take it as a simple terms explanation).

in my project 3 driver is used.

shall i take the power supply to 3 driver ic by single 7815 output.??

or design 3 seperate 7815 ic to power 3 driver ic ??

That depends on your total peak gate currents. LM7815 it's only rated for 1A; a better solution is LM338 (5A, 7A peak):

https://www.ti.com/lit/ds/symlink/lm138.pdf

should i use decoupling capacitor ceramic with VCC and COM.

if i use large decoupling capacitance of ceramic , any problem ??

Surely you need decopling capacitors. The size depends on gate currents and switching frequency. Larger is better, anyway.

in the data sheet of 6n137 .1uf decoupling capacitior is used.
pls reccomend a good value

For the optocouplers, .1uF it's enough (closer to supply pins).

 

[mobinmk]

can u reccommend the decouping capacitor value ???
b/w VCC and Com, and B/w Vb and Vs

 

[red_alert]

Could you (re)post, please, the gate peak currents, the switching frequency and the maximum dutyu cycle? And your converter rated power?

 

[mobinmk]

at present design
gate resistor is 27 ohm

vcc is 15 v

gate current is
15/27 =.6A

But i wish to use 10 ohm resistor bcz nw i use fan 7392 driver.

Ig = 1.5A

switching freq is 33khz.

in v/f , i vary the duty cycle.

maximum value is 100%.

but cant acheive, bcz bootsrap ckt so duty cycle is 97%,i use 10uf,63v electrolytic capacitor as bootsrap capacitor.

and 100uf ,63 v capacitor is used across vcc and com

i wana to drive an motor less than 5 hp,

igbt is fg25n120, it can carRy 25A

 

[red_alert]

The bootstrap and Vcc capacitors look OK (just don't forget the ceramic capacitors).

 

[mobinmk]

thnks sir,

Is 100nf ceramic capacitor is enough for Vb and Vs , also Vcc and Com ??

 

[red_alert]

It's ok.

What about the LM7815? Actually, the gate peak current it's fed by the ceramics capacitors thus LM7815 don't have to withstand 6 x gate peak current but a mean value.

Altough it might be enough, it's better to use LM338 or equivalent.