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

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red_alert said:
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.
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Thnks Sir,

I measured the DC link Voltage, which is 582V,

I wish to use FAN7392 DRIVER IC,

Vb ..high side floating supply voltage is (Max) Vs + 25 = 625V

Vs ..high side floating offset supply voltage is(max) is 600v

where did i place the TVS diode??

across Vb and Com or Vs and COM or both ??

which tvs diode is used ,part no ??
 

You're pretty close to maximum recomandations thus any (small) spike could affect the driver integrity. The TVS diodes don't have a well determined threshold either (to have no influence on 600V but to cut everything above 620V). You could take a look at the product range of this manufacturer:

https://www.littelfuse.com/products/tvs-diodes/leaded.aspx

As you could see, there's no specific product for this particular voltage range (I might be wrong though) so you have to put two (or three) of them in series. Anyway, take a look at their parameters (breakdown voltage, maximum clamp voltage) to see if one could accomodate your design.

I still recommend you to go with regular low-side drivers for both high-side and low-side MOSFETs, as long as you're using optocouplers at their inputs. Then you don't have to worry anymore about the DC link voltage as the only supply voltage will be the bootstrap (and the Vcc) ones thus 15V.
 


can i use TLP250 IC and replace 6n137, fan7392 ??
**broken link removed**

• Input threshold current: IF=5mA(max.)
• Supply current (ICC): 11mA(max.)
• Supply voltage (VCC): 10−35V
• Output current (IO): ±1.5A (max.)
• Switching time (tpLH/tpHL): 1.5µs(max.)
• Isolation voltage: 2500Vrms(min.)


my switching freuency is 33khz
 

From the TLP250 datasheet:

- operating frequency: 25kHz
- switching time: 1.5us
- propagation delay: 0.5us

You have to recheck your timmings (dead times, propagations) but 33kHz seems overkill.
 

Thnks Sir,

i already bought FAN7392 driver ic and designed driver ckt,if i reduce the dc link voltage to 300v,
should it work in safe operating condition or withstand.

any modification needed on the optocoupler- driver ckt,??

 

Are those components values for real?

12pF decoupling capacitors, 10kohm gate series resistors, 10kohm optocouplers supply series resistor (why did you used it anyway?), 1N4007 diodes, IR2110 driver?

Are they just generic components, to draw the schematic?

And don't forget the reverse diode across input-output of 7805. You have a big output capacitor (that's ok) but when power turns off, the input capacitor it's discharging more quickly (the 12V supply) thus the 7805 output stage will be reverse biased (and it could be destroyed).
 

Thnks sir,

They are jus generi components to draw schematic.
decoupling capacitor is 100nf,
bootstrap diode and rb diode across Rg is UF4007,
Gate resistor is 27Oohm.

optocoupler output pull up resistor is 1k .

should i connect the resistor to the output of 7805 to limit the current to the Vcc of 6n137 Optocoupler Ic???

- - - Updated - - -

Thnks sir,

They are jus generi components to draw schematic.
decoupling capacitor is 100nf,
bootstrap diode and rb diode across Rg is UF4007,
Gate resistor is 27Oohm.

optocoupler output pull up resistor is 1k .

should i connect the resistor to the output of 7805 to limit the current to the Vcc of 6n137 Optocoupler Ic???
 

6N137 is specified with 7V maximum output voltage, it can't drive 15V logic.
Slow 1N4007 shouldn't be used as bootstrap diode.
 
The Vdd of FAN7392 should be connected to 5V instead of 15V, to overcome this situation. It has open collector output so (in theory) it's output shouldn't have to be restricted to the IC supply voltage (as long as you didn't feed the open collector with a much higher voltage) but it's better to stick with the manufacturer specifications.

Slow 1N4007 shouldn't be used as bootstrap diode
Click to expand...

He did mention the UF4007 as a bootstrap and reverse gate diode so it's much better.

should i connect the resistor to the output of 7805 to limit the current to the Vcc of 6n137 Optocoupler Ic???
Click to expand...

Not, because the voltage drop across that series resistor will affect the 6N137 supply voltage stability. You don't have to worry about current limiting, the IC will sink only the needed current.

- - - Updated - - -

I've just reviewed the attached schematic. A 10ohm series resistor (for 6N137 supply voltage) it's not harmful, I was talking about a large resistor (1Kohm - 10Kohm).
 


Thnks sir,

Can i connect Vdd of FAN7392 to output of 7805,??
the output of 7805 is already supply to 6N137 Vcc.

The vdd of ir2110 can supply to 15v.
i think both ir2110 and fan7392 have same circuit diag,

nly difference in voltage rating, current rating,dynamic characterics
IN datasheet,

VDD voltage is Vss +20 v

if Vss = 0,

maximum Vdd voltage is 20v

also in dynamic characteristics (page 7 in datasheet)

Vbias(Vcc,VDD,Vbb)=15v, vss=com = 0v.

Why Vdd is connected to 5v ??

pls explain it, i didnt get it.
 
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Can i connect Vdd of FAN7392 to output of 7805?
Click to expand...

Yes, you can. The Vdd sink current is low (it only feed the input logic circuits).

Why Vdd is connected to 5v ??
Click to expand...

The input logic thresholds of FAN7392 driver depends on Vdd (you could check the datasheet). For a Vdd of 15V it sets the input thresholds to 9V (high threshold) and 4.5V (low threshold). Thus feeding its inputs with 5V logic it will only see a "0" input signal.
 

It has open collector output so (in theory) it's output shouldn't have to be restricted to the IC supply voltage (as long as you didn't feed the open collector with a much higher voltage) but it's better to stick with the manufacturer specifications.
Click to expand...

"In theory" as well as in practice, a transistor has a Vce breakdown voltage. So when maximum ratings specify 7V, it's unlikely that the device stands 15V. Unless the point has been forgotten in the datasheet, these are apparently no HV open collector transistors as in some TTL drivers.

Fortunately IR2110 has separate Vdd supply.
 
Unless the point has been forgotten in the datasheet, these are apparently no HV open collector transistors as in some TTL drivers.
Click to expand...

You're right, I double checked the datasheet and the Vo limit is clearly mentioned (7V). Anyway, I won't call 15V a "HV" though.

By the way, 6N139 has a 20V limit open collector but has poor dynamic characteristics.

I used to use 6N137 in tandem with TC4452 drivers which have fixed input thresholds to accomodate logic as low as 3.3V, regardless the driver supply voltage.
 

Sir,
The output of 6n137 is connected to a pull up resistor to 15v.
When the 6n137 is off, output is pulled up to 15v.
When the 6n137 is on, output is low.
My doubt is that is the above statement true?? and thereby can i connect Vdd of fan7392 driver ic to 15v instead of 5v
 

You can not pull the 6N137 output higher than 7V. It's the collector of the output transistor (the emitter being connected to ground) so it would be destroyed (Vce max = 7V).
 

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