Problem with IRS2092 Deadtime

Status
This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.
Hi all,
I'm working on a 300W Class-D amp with IRS2092 and IRFB4227.
Should deliver up to 300W stereo. The FETs where driven by a BJT totem pole and the amp sounds fairly good.
Theres just one problem: The MOSFETs getting hotter than they should in idle mode.
The Pics show more:

(1) CH1 Low Side Gate Signal CH2 Drain Low Side Rising Edge
(2) CH1 Low Side Gate Signal CH2 Drain Low Side Falling Edge
(3) CH1 High Side Gate Signal CH2 Low Side Gate Signal Rising Edge
(4) CH1 High Side Gate CH2 Low Side Gate Falling Edge
(5) PWM Output Signal Idle (250kHz)
All referenced to -B

In (4) the High Side Gate have enought dead time but in (3) the it isn't enought and causes shoot through.
It seem's the DT isn't symmetrical on High and Low side of the IRS, I dont know what to do because already using max setting(105ns)

Supply is +-40V

thank you for help
 

Attachments

  • DSC01663.JPG
    DSC01663.JPG
    130.4 KB · Views: 724
  • schaltung_1.jpg
    schaltung_1.jpg
    172.9 KB · Views: 787
  • TEK0000_1.JPG
    TEK0000_1.JPG
    38.8 KB · Views: 653
  • TEK0001_2.JPG
    TEK0001_2.JPG
    50.2 KB · Views: 586
  • TEK0002_3.JPG
    TEK0002_3.JPG
    38.3 KB · Views: 580
  • TEK0004_4.JPG
    TEK0004_4.JPG
    38.8 KB · Views: 116
  • TEK0005_5.JPG
    TEK0005_5.JPG
    38.8 KB · Views: 134
Hi all,
I'm working on a 300W Class-D amp with IRS2092 and IRFB4227.
Should deliver up to 300W stereo. The FETs where driven by a BJT totem pole and the amp sounds fairly good.
Theres just one problem: The MOSFETs getting hotter than they should in idle mode.
The Pics show more:

(1) CH1 Low Side Gate Signal CH2 Drain Low Side Rising Edge
(2) CH1 Low Side Gate Signal CH2 Drain Low Side Falling Edge
(3) CH1 High Side Gate Signal CH2 Low Side Gate Signal Rising Edge
(4) CH1 High Side Gate CH2 Low Side Gate Falling Edge
(5) PWM Output Signal Idle (250kHz)
All referenced to -B

In (4) the High Side Gate have enought dead time but in (3) the it isn't enought and causes shoot through.
It seem's the DT isn't symmetrical on High and Low side of the IRS, I dont know what to do because already using max setting(105ns)

Supply is +-40V

thank you for help

Hi,

I would make a different gatedrive circuit, you have some nice drivertransistors and then you add 4R7 in series with both turn on and off.

Why not try and make you gatedrive a little different, start maybe with a 1N4148 in parallel with 4R7 to make turn off faster than turn on?

A base resistor in you gatedrive transistors might also be worth it ;-)

Best regards
\\\Jens
 
Last edited:
The gate drive buffers need base resistors to control reverse behavior of the NPN/PNP when di/dt spikes show up at the gate (through Ld) and drive it temporarily outside the gate drive rails. Also, some resistive drive impedance is needed at high frequencies to damp potential layout resonances (MOS based gate driver outputs are resistive but always have capacitance and body diodes to the rails).

Speed up turn off with diodes and optional resistors as recommended, turn off di/dt must always be higher than turn-on di/dt to avoid "regenerative" cross-conduction during any overlap condition in switching. Don't make it faster than needed, gate drive "commands" EMI production. EDIT: IRFB4227 has 2.2 ohm of built in gate resistance, with a good layout it may not need more, just the diode.

(1) and (2) show cross-conduction further helped by the 20ns/50Mhz resonance. This resonance should be damped with RC(L) for optimum performance and minimum interference between channels. It's d-s capacitance of the MOSFET that is turned off (240pf typ. for IRFB4227) resonating with all the parasitic inductances that close the loop (TO-220 leads typ 12nH d-s, PCB tracks, supply capacitors typ 1nH per mm of lead spacing).
 
Last edited:
@Eva
OK i will add Base Resistors and Speed Up turn-off diodes, lets see if it improves switching timing.

Where i have to add the damping RC network because of the cross-conduction resonances?
Are the 1n 10R at the PWM Output bad dimensioned?

@luka
The ZXGD3002E6 look very nice, I think i will test it in a new desing later.
 
Hi, I'm back
sorry but a had a lot to do for school last weeks
update:
I don't know why the MOSFETS got so hot but after adding the LPF there was no heating up.
The amp delivers 20W with 0,005% THD 200W with 0,065% THD and around 370W with 0,1% THD
Now I'm playing around with different output inductors. Like in many threads recommended the best results was achived with Amidon 106-2 core.
The only thing that bothers me is that the core needs 40 turns to get 22uH.
I'm using 18AWG (d=1mm) litz wire but in my view the DC resistance of the inductor is too high for my require output power isn't it?
To solve the problem i could use more litzes in paralell but one the core there isn't any space for more windings. What are your experiences with T106-2 or should i use a bigger one?

Thanks

BTW: Power Supply is Connexelectronic SMPS800R +-60V now
 

Attachments

  • DSC01699.JPG
    DSC01699.JPG
    120.4 KB · Views: 364
  • DSC01698.JPG
    DSC01698.JPG
    87.3 KB · Views: 367
Now I'm playing around with different output inductors. Like in many threads recommended the best results was achived with Amidon 106-2 core.
The only thing that bothers me is that the core needs 40 turns to get 22uH.
I'm using 18AWG (d=1mm) litz wire but in my view the DC resistance of the inductor is too high for my require output power isn't it?
To solve the problem i could use more litzes in paralell but one the core there isn't any space for more windings. What are your experiences with T106-2 or should i use a bigger one?

I use the same core for a 750 watt peak amplifier.
I wind on 2 metres of 18swg but go around twice to get the required inductance. The core barely gets warm.
 
I had the same problem,the mosfets was heating so much in idle state,cross-conduction.
The falling time was too big. The way I solved this was adding and 1N4148 diode to speed the discharge,also I increased the DT to 80ns.

Fosc=450KHz
Mosfet = irfb4212
Supply=+-35vdc
DT= Firts attemps 45ns , succes with 80ns and diode.

I just add a diode in parallel to Hi gate resistor.

Ty , nice tips!
 

Attachments

  • dt_xcond.jpg
    dt_xcond.jpg
    24.2 KB · Views: 285
  • dt2.jpg
    dt2.jpg
    20 KB · Views: 265
  • hi_g_com.bmp
    146.3 KB · Views: 92
  • lo_g_com.bmp
    146.3 KB · Views: 61
  • nice_g_signals.jpg
    nice_g_signals.jpg
    28.3 KB · Views: 258
  • dead_time.jpg
    dead_time.jpg
    24.1 KB · Views: 110
Did you end up adding base resistors and, if so, what value did you end up with? Did gate drive waveforms improve?

Thanks!

Hi, I'm back
sorry but a had a lot to do for school last weeks
update:
I don't know why the MOSFETS got so hot but after adding the LPF there was no heating up.
The amp delivers 20W with 0,005% THD 200W with 0,065% THD and around 370W with 0,1% THD
Now I'm playing around with different output inductors. Like in many threads recommended the best results was achived with Amidon 106-2 core.
The only thing that bothers me is that the core needs 40 turns to get 22uH.
I'm using 18AWG (d=1mm) litz wire but in my view the DC resistance of the inductor is too high for my require output power isn't it?
To solve the problem i could use more litzes in paralell but one the core there isn't any space for more windings. What are your experiences with T106-2 or should i use a bigger one?

Thanks

BTW: Power Supply is Connexelectronic SMPS800R +-60V now
 
Status
This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.