[moved] calculation of bootstrap circuit, gate resistance by driver ic ir 23364

[mobinmk]

[moved] calculation of bootstrap circuit ,gate resistance by driver ic ir 23364

Hi,

i wana to make vfd for 3 phase induction motor(415v, 1/4 hp,50hz), in the 3 phase inverter section , i wana to drive mosfets/igbt. by ir2336

data sheet
**broken link removed**

dc link voltage 600v.
recommend me to select mosfet/igbt.

how to calculate bootsrap capacitor,diode ??
also gate resistor??
design tips...!!
circuit diagram


thankz and regards

mobin:shock:

- - - Updated - - -

Hi,

i wana to make vfd for 3 phase induction motor(415v, 1/4 hp,50hz), in the 3 phase inverter section , i wana to drive mosfets/igbt. by ir2336

data sheet
**broken link removed**

dc link voltage 600v.
recommend me to select mosfet/igbt.

how to calculate bootsrap capacitor,diode ??
also gate resistor??
design tips...!!
circuit diagram


thankz and regards

mobin:shock:

carrier freq is 32khz from aurdino uno

 

[Electro nS]

Re: [moved] calculation of bootstrap circuit ,gate resistance by driver ic ir 23364

use double voltage : all capacitors should be 1000v

donot use series capacitors , use parallel thats a better practice .. although in theory is the same .

regards

 

[mobinmk]

Re: [moved] calculation of bootstrap circuit ,gate resistance by driver ic ir 23364

use double voltage : all capacitors should be 1000v

donot use series capacitors , use parallel thats a better practice .. although in theory is the same .

regards

Thnkzz Electro nS,


Finally i selected 1uf/1000v capacitor for bootstrap capacitor.

but the problem facing is

ceramic capacitor , electrolytic capacitor is not available in market.

at last i bought 1uf/1000v capacitor, itz axial type,P O L Y P R O P Y L E N E F I L M - F O I L C A P A C I T O R S

datasheet

**broken link removed**

can i use this capactior as bootstrap capacitor?? can i use decouple capacitor ??? ceramic ??

Precaution (IN DATASHEET)
1. These capacitors are not suitable for ‘across the line’ applications
2. VAC(rated) : Frequency should be less than 1000Hz
3. VDC(rated) : 1.4 x Vrms + VDC should be less than rated VDC


Regards

mobin

 

[Electro nS]

Re: [moved] calculation of bootstrap circuit ,gate resistance by driver ic ir 23364

yes it can be used film and ceramic are good , but it should not be electrolytic .

by the way a friend of me is suggesting that the bootstrap capacitor voltage rating should be above Vcc of the IC by 2x (not V bus x2 ) so 40v 1uF is enough !! i have not tested this so i cannot confirm

so please test the 1000v 1uF , and test any capacitor ceramic 40v 1uF and check the results i might work , maybe i am wrong , sorry !!

good luck

 

[mobinmk]

Re: [moved] calculation of bootstrap circuit ,gate resistance by driver ic ir 23364

Thnks Electro N S

I will test, as earliest,reply back with results

regards

mobin

 

[red_alert]

Re: [moved] calculation of bootstrap circuit ,gate resistance by driver ic ir 23364

The bootstrap voltage is applied to MOSFET gate.. if you think it could be greater than 18V, then your MOSFETs are coming from the future.

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Thnkzz Electro nS,

Finally i selected 1uf/1000v capacitor for bootstrap capacitor.

Now serious.. the bootstrap capacitor is charging through the bootstrap diode from Vcc (driver IC supply voltage), which is usually between 10 and 18V.

Thus the bootstrap capacitor is only charged at Vcc - Vd (18 V - 0.6V = 17.4 V) maximum voltage.

The bootstrap capacitor voltage is referenced to high-side MOSFET source. So whenever the MOSFET source voltage is 0 V (low-side MOSFET in ON state) or 600 V (high-side MOSFET in ON state), the voltage across bootstrap capacitors remains 18 V (maximum).

The only high voltage rated component within the bootstrap circuit is the bootstrap diode, which should accept a reverse voltage greater than DC_BUS (350 V, 600 V.. depending on your application).

 

[Electro nS]

Re: [moved] calculation of bootstrap circuit ,gate resistance by driver ic ir 23364

The bootstrap capacitor voltage is referenced to high-side MOSFET source. So whenever the MOSFET source voltage is 0 V (low-side MOSFET in ON state) or 600 V (high-side MOSFET in ON state), the voltage across bootstrap capacitors remains 18 V (maximum).

The only high voltage rated component within the bootstrap circuit is the bootstrap diode, which should accept a reverse voltage greater than DC_BUS (350 V, 600 V.. depending on your application).

thank u very much for this clearification

now this is what missed up my mind at the first , if the high side mosfet is ON , then the capacitor is seeing (18-600v)=-582v !! or does the bootstrap diode prevent that from happening ??

by how much the bootstrap diode should be above Vbus: X1.2 or X2 or it sees no spikes ???

 

[red_alert]

Re: [moved] calculation of bootstrap circuit ,gate resistance by driver ic ir 23364

if the high side mosfet is ON , then the capacitor is seeing (18-600v)=-582v !! or does the bootstrap diode prevent that from happening ??

Think about you (1.8m) staying on the top of a mountain (3000m). That won't make you 3001.8m tall, am I right?!

Simillary, the bootstrap capacitor is charged at 18V all the time, but it stays on top of the high-side MOSFET source.

If you measure the voltage across the "top" of the capacitor and ground, you get 618 V, indeed. But if you measure the voltage across the capacitor, you only get 18V. It's like an ant riding an elephant.

The Vcc voltage always stays low (on the ground). When the low-side MOSFET is in ON state, it puts the high-side MOSFET source to ground, too.

At this time, the bootstrap capacitor is connected between ground (GND) and Vcc (through the bootstrap diode) and it's charging from Vcc.

When the low-side MOSFET is switched OFF (and the high-side one is switched ON) the bootstrap capacitor is "lifted" by the source of the MOSFET to 600 V. It is still connected to the bootstrap diode but this time, the diode is reverse biased so it's a "wall" between the capacitor and the "grounded" Vcc. The voltage across the bootstrap diode is the DC_BUS voltage.

by how much the bootstrap diode should be above Vbus: X1.2 or X2 or it sees no spikes ???

Spikes might occur on DC_BUS so a slighty higher reverse voltage rated diode is indicated. x1.2 or x2, there's not a great price difference. The bootstrap capacitor could also be a bit overrated (x1.5 - x2) as there could occur some negative spikes from the high-side MOSFET source, so a 25 V - 40 V rated capacitor should be OK.

 

[mobinmk]

Re: [moved] calculation of bootstrap circuit ,gate resistance by driver ic ir 23364

Thnks Frnds.

Is Ton time depend on capacitence of bootstrap capacitor??

can i increase the capacitence of bootsrap capacitor ?? any problem ??

i think that minum value of bootsrap capacitor should 1uf for 33khz spwm.
if i use 47uf or greater than 1uf , any problem??

regards

mobin

- - - Updated - - -

Thnks Frnds.

Is Ton time depend on capacitence of bootstrap capacitor??

can i increase the capacitence of bootsrap capacitor ?? any problem ??

i think that minum value of bootsrap capacitor should 1uf for 33khz spwm.
if i use 47uf or greater than 1uf , any problem??

regards

mobin

 

[red_alert]

Re: [moved] calculation of bootstrap circuit ,gate resistance by driver ic ir 23364

There will be no problem as long as the bootstrap diode allows a greater charging current.

Also, take into account that the bootstrap capacitor charging current flows through low-side MOSFET and if you're designing a very low power converter, it might overcome the MOSFET current ratings (hardly to believe but you better know it).

A common practice is to put a small resistor in series with the bootstrap diode - that limits the maximum charging current and the voltage spikes across bootstrap capacitor.

 

[mobinmk]

Re: [moved] calculation of bootstrap circuit ,gate resistance by driver ic ir 23364

Thnkz red Alert.

i wana to make 3 phase inverter by using 6 igbt , FG25N120ANTD.

datsheeet

https://www.fairchildsemi.com/datasheets/FG/FGA25N120ANTD.pdf

Ic = 25A,



can i work with 100% duty cycle..??

regards

mobin

 

[red_alert]

Re: [moved] calculation of bootstrap circuit ,gate resistance by driver ic ir 23364

Is Ton time depend on capacitence of bootstrap capacitor??

Ton is mainly dependent of the gate current. Of course, there should be enough energy stored in the bootstrap capacitor to be transfered to the gate.

Anyway, the same energy could be transfered during 10 us (if the gate current is smaller) or 0.1 us (if the gate current is higher). Thus if you need lower Ton, use a higher gate current but the capacitor should be a low ESR one (to sustain the high current pulse).

Ususally, you have to use a small ceramic one and a larger polarized one (aluminium/tantalum) in parallel.

- - - Updated - - -

With a 100% duty cycle (I presume you're using a full bridge topology) there's no possibility to charge the bootstrap capacitor during those full cycles.

Anyway, if the bootstrap capacitor is large enough and you're using sine modulated PWM (I presume) then the stored energy from the previous smaller duty cycles might be enough to keep the bootstrap voltage above the driver's undervoltage lockout threshold (9 V) during those 100% cycles.

 

[mobinmk]

Re: [moved] calculation of bootstrap circuit ,gate resistance by driver ic ir 23364

Thnkz Red Alert....


Can you recommend the bootsrap capactior value??
suggestions??
DRIVER IC is IR2110.
IGBT FG25N120ANTD.
SPWM freq is 33khz
1uf is enough??
my application is variable frequency drive for 3 phase induction motor.

regards

mobin

 

[red_alert]

Re: [moved] calculation of bootstrap circuit ,gate resistance by driver ic ir 23364

1uF might be enough for your switching frequency and IGBT requirements but, like I said, it's better to oversize the capacitor for that 100% duty cycle. You better use a 10uF capacitor but you can go up to 47uF, too (there are more exactly calculations available but even IR recommends in their app notes to at least double the calculated values). Just use a fast recovery diode for quick charging the bootstrap capacitor.

 

[mobinmk]

Re: [moved] calculation of bootstrap circuit ,gate resistance by driver ic ir 23364

Thnks..

can i use uf4007 diode ??

if i use 47uf,
q=cv
q= 47uf*15
q= 705uc.
i=q/t
t=1s
i=15uA

If avg = 1A,PIV =1KV. from datasheet

 

[red_alert]

Re: [moved] calculation of bootstrap circuit ,gate resistance by driver ic ir 23364

It's perfect!

 

[Electro nS]

Re: [moved] calculation of bootstrap circuit ,gate resistance by driver ic ir 23364

Ton is mainly dependent of the gate current. Of course, there should be enough energy stored in the bootstrap capacitor to be transfered to the gate.

Anyway, the same energy could be transfered during 10 us (if the gate current is smaller) or 0.1 us (if the gate current is higher). Thus if you need lower Ton, use a higher gate current but the capacitor should be a low ESR one (to sustain the high current pulse).

Ususally, you have to use a small ceramic one and a larger polarized one (aluminium/tantalum) in parallel.

- - - Updated - - -

With a 100% duty cycle (I presume you're using a full bridge topology) there's no possibility to charge the bootstrap capacitor during those full cycles.

Anyway, if the bootstrap capacitor is large enough and you're using sine modulated PWM (I presume) then the stored energy from the previous smaller duty cycles might be enough to keep the bootstrap voltage above the driver's undervoltage lockout threshold (9 V) during those 100% cycles.

100% cannot be acheived , you still need to charge to the capacitor through the low side mosfet as red_alert pointed out , so by increasing the bootstrap capacitor you are increasing the maximum duty cycle but stay less than 100%
example : 1uF is good for 95% , 10uF is for 97% , 47uF 99% , but 100% will cause bootstrap failure

if you want 100% you have to use a gate driver with integrated charge pump , which i donot know if exist for this Vbus ,
i know that intrensil have products but limited at 80v example HIP4080 ..etc

 

[red_alert]

Re: [moved] calculation of bootstrap circuit ,gate resistance by driver ic ir 23364

100% cannot be acheived , you still need to charge to the capacitor through the low side mosfet as red_alert pointed out , so by increasing the bootstrap capacitor you are increasing the maximum duty cycle but stay less than 100%
example : 1uF is good for 95% , 10uF is for 97% , 47uF 99% , but 100% will cause bootstrap failure

Very well pointed out, though I was assuming that he's using a sine PWM control signal which only reaches 100% duty cycle during a few waveform periods (at the sinewave peaks).

A steady 100% duty cycle means that the low-side MOSFET is continuously kept in OFF state and the high-side MOSFET is continuously kept in ON state. That's a very uncommon situation for a DC-AC converter (it is mostly encountered in a buck-boost H-bridge topology or other simple ON/OFF switching applications).

 

[mobinmk]

Re: [moved] calculation of bootstrap circuit ,gate resistance by driver ic ir 23364

Thnks frnds,

at last i decided 47uf,63v capacitor used as bootsrap capacitor across Vb and Vs, but the capacitor is electrolytic.

should i parallel a ceramic capacitor with electrolytic?? how much value is good??

also i find some tips in improving decoupling. from irf app notes

Improve local decoupling.
3a. Increase the bootstrap capacitor (CB) value to above 0.47 µF using at least one low-ESR capacitor. This will reduce overcharging from severe VS undershoot.

3b. Use a second low-ESR capacitor from VCC to COM. As this capacitor supports both the low-side output buffer and bootstrap recharge, we recommend a value at least ten times higher than CB.

is second capacitor value is 470uf across VCC to COM ?? its also electrolytic , should i use ceramic capacitor across with vcc to com ?? hw much value ??

regards

mobin

 

[red_alert]

Re: [moved] calculation of bootstrap circuit ,gate resistance by driver ic ir 23364

You should always use a decoupling ceramic capacitor beside the electrolytic one. The electrolytic capacitor is for bulk energy storage and the ceramic one is for high frequency high pulse currents.

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3b. Use a second low-ESR capacitor from VCC to COM. As this capacitor supports both the low-side output buffer and bootstrap recharge, we recommend a value at least ten times higher than CB.

is second capacitor value is 470uf across VCC to COM ?? its also electrolytic , should i use ceramic capacitor across with vcc to com ??

Theoretically, the ten times higher Vcc capacitor relates to calculated VB capacitor (0.1uF - 1uF).

We came to the conclusion of using a much higher VB capacitor just because you're going to have short periods of 100% duty cycles thus the VB capacitor should withstands more than one gate control pulses.

During those periods of 100% duty cycle the VB capacitor it's not charging anyway so a higher Vcc capacitor is useless.