Class H decreasing dissipation

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Class H decreasing dissipation

Postby yb0djh » Tue Jun 04, 2013 11:44 am

Hi All

Long time no activity i notice in this mirror. hope everything are running well.

I have made a class h modulator from Steve schematic (previous version using MOSFET in High Rail and Low Rail) and try to increase efficiency by reducing zener voltage near 1 volt from 12 volt on schematic. what i found was burning one FET in high rail and one FET low rail.

Why am i reducing the voltage on zener, because i have the transformer that produce only 50 volt in low rail and 106 volt on high rail (loaded) and i try to get 40 volt on the output for carrier. if i put 12 volt zener i only got 30 volt under 6 ohm load. additionally i want to get the voltage closer from low rail voltage to output voltage for carrier, and expecting high efficiency. i got 40 volt actually and after steady burn test for 5 minutes and the FETs shorted (burned). :roll:

what i want to know is why this happen? i already remove high rail to make sure using low zener voltage is good enough.

thank you for your advices..

BR

Agus HY

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Re: Class H decreasing dissipation

Postby steve_qix » Fri Jan 10, 2014 9:40 am

Hi - This post is very old, and I don't know if you are still working with the class H modulator....

Which zener are you modifying? Oh, what class H schematic are you using? I've released at least 4 different class H modulators over the years.

Regards, Steve
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Re: Class H decreasing dissipation

Postby yb0djh » Mon Feb 10, 2014 3:38 am

Hi Steve

Thanks for replying my posting.

I build your old version back in 2004, which was using all IRFP260 in high side and low side.

Now my modulator is running OK. I modified zener diode 12 volt become 5 volt, i believe that circuit is to set the carrier output voltage.

The other thing i want to modify the output carrier voltage to 100 Volt so the high rail will be 200 Volt, what should i do to implement this plan. What i thing is:

- modify the carrier voltage divider
- two resistor 22K Ohm to + and - first floated OPAmp

What else should i do?

My plan is to supply the double H bride class D Amp. Class D amp was tested OK with low voltage (40 volt) this is not satisfying because the transformer output ratio become 1:3 and many ringing i found in waveform.

Thank you for responses.


Best Regards


Agus H. yb0djh.
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