IRS20957 based selfoscilating class D

[ionutzxpo]

Hi guys ,I have two problems

1- the amp does not start without a load connected at the output
2-the amp starts with a 10R rezistor connected to output and has 190mV DC offset at output

now a few details about the configuration

LT1016 comparator -> IRS20957 driver -> ZXGD 10A buffers -> IRFB4227

dead time set to minimum -> oscilating at 400kHz no heating at the mosfets and the driver

 

[29285]

You should check R42 first!

 

[nigelwright7557]

The irs2092 also doesn't always start without a load.
Sometimes the output sits at +17VDC.

Be careful running a class d without a load on it. The output filter will ring badly with high volts and can sometimes blow up the output filter capacitor.

 

[ionutzxpo]

Hi Nigel,without a load the am struggles to start oscilation but nothing bad hapens even if I let it 10 hours the moment that I connect a load smaller than 50R the amp starts immediately to oscilate.
And yes if I take the load and power off I get about 20V dc at the output

 

[Mops1337]

Did you find the solution? I am struggeling with the same problem...

 

[ledsscp7]

Hi guys ,I have two problems
1- the amp does not start without a load connected at the output
2-the amp starts with a 10R rezistor connected to output and has 190mV DC offset at output

1 Is no problem this very good IMHO, add 47-75k resistor from output to negative rail - to resolve this "problem"
2 add integrator...

 

[Mops1337]

Wherefore do i need the integrator? I just want to put the PWM Signal straight to the "In" Pin, no feedback, no integrator, just like the reference design http://media.digikey.com/photos/rdl/iraudamp6_schematic_4_full.png

 

[ledsscp7]

UcD principle amp? Scheme show please.

 

[ionutzxpo]

@ledsscp7 Scheme is aprox. 99% like yours! just simple integrator to non inverting input of comparator to lower THD 10 times...and I get about 0.005% at 80% power and 0.5% at full power 5V to clipping .