IR2085S bus converter not working

[prashkd85]

Hello everyone,
I am woking on a planar transformer desing and am using IR2085S half bridge resonator to generate 500KHz frequency which will then be used to drive the transformer. After going through the datasheet I have made the schematics as given in the datasheet **broken link removed** on page 1 and the only change I made was to replace C1 and C2 with a single resonator capacitor in series between pin Vs and the transformer HI side ( port 2 of the Transformer is grounded) . I applied 12V to the IC and ~18V to the Mosfets without connecting the inductor just for the testing purpose. From what I understand, using Ct as 100pF and Rt as 10K and using the given formula f = 1/2*Ct*Rt , IC should generate pulses at pin HO and at pin LO, synchronised in such a way that they pull the MOsfets Hi and Low to generate an AC signal @500KHz frequency at pin Vs. However, when I tried to test the ckt using oscilloscope, I am getting no pulses or freq. at either pins. The HO pin is constant hi and LO pins is constant LO whereas I should be getting a sine wave at the resonant frequency . Also, at OSC pin I AM getting freq. of about 408KHz [IMG_022].
I would appreciate if any1 who has experience with this IC can share their expertise.
Thanks

 

[prashkd85]

Hmmm.. 40 views n not a single reply!!! Do i need to add some more information abt the problem?

 

[prashkd85]

Hi I needf urgent help with this ckt. can any1 tell what's wrong with it??

 

[mtwieg]

Your schematic looks okay. Try checking just the ir2085 along by disconnecting the half bridge completely, and connecting pin Vs to ground. You should see the gate drive waveforms at the HO and LO pins.

 

[Easyrider83]

Please, attach full schematic. I can't understand what are you talking about.
Where is the current limit resistors in gate supply circuit?
Current sensor input floating in air?

 

[prashkd85]

Sure.. I will try it now and will post the result...

 

[mtwieg]

Yeah, if you're not using the CS pin at the moment you should pull it down to GND with a resistor or something.

 

[prashkd85]

@mtwieg .. Yup that solved the problem... I just connected CS to GND through a 10K.... Thanks a lot for your help guys. I will post the correct schematics here so that others can referrer to it.

 

[FvM]

The dataseheet doesn't mention a pull-down resistor or explicite input current of the CS pin. Thus I think, you should better connect it to COM.

P.S.: I see, you found the solution yourself.