We seek to understand and document all radio transmissions, legal and otherwise, as part of the radio listening hobby. We do not encourage any radio operations contrary to regulations. Always consult with the appropriate authorities if you have questions concerning what is permissable in your locale.

Author Topic: Beginner class D design  (Read 3958 times)

Offline OgreVorbis

  • Jr. Member
  • **
  • Posts: 69
    • View Profile
    • DosaidSoft
    • Email
Re: Beginner class D design
« Reply #75 on: April 15, 2019, 1119 UTC »
See last two posts.

I realized after my design that it looks like the NCP drivers have an inverter built-in. The truth table in the datasheet makes it look like it won't work for this purpose though, but I don't know why else they would have such a feature. Is this to use in a push-pull amplifier with one square wave input? If so, then I don't even need the inverter :P
Radio and Programming Blog: http://dosaidsoft.com/wp/

Offline Transmitter Man

  • Newbie
  • *
  • Posts: 2
    • View Profile
    • Email
Re: Beginner class D design
« Reply #76 on: April 15, 2019, 1605 UTC »
OV,

I missed the fact the previous board only works up to 5Mhz as I would much prefer the higher frequency board :-(

I will wait :-)

Transmitter Man

Offline Stretchyman

  • Sr. Member
  • ****
  • Posts: 373
    • View Profile
Re: Beginner class D design
« Reply #77 on: April 15, 2019, 1726 UTC »
See last two posts.

I realized after my design that it looks like the NCP drivers have an inverter built-in. The truth table in the datasheet makes it look like it won't work for this purpose though, but I don't know why else they would have such a feature. Is this to use in a push-pull amplifier with one square wave input? If so, then I don't even need the inverter :P

To drive a High side and Low side Devices I guess? Or tie them together for single FET. Just use a dual Inverter from the O/P of your Osc. Sine in and square out, inverted and double inverted to drive either side.

Str.
'It's better to give than receive' so why RX when you can TX!

                            Buy one from me, NOW!

Great discounts on ALL my transmitters if purchased via HFUnderground


                                              ;)

Offline OgreVorbis

  • Jr. Member
  • **
  • Posts: 69
    • View Profile
    • DosaidSoft
    • Email
Re: Beginner class D design
« Reply #78 on: April 15, 2019, 1734 UTC »

To drive a High side and Low side Devices I guess? Or tie them together for single FET. Just use a dual Inverter from the O/P of your Osc. Sine in and square out, inverted and double inverted to drive either side.

Str.

Sorry, I don't understand the term "high/low side device". Does this mean the devices on one side of a push-pull amplifier (like what I'm building)? So then I don't need an inverter. Just use the NCPs?
Radio and Programming Blog: http://dosaidsoft.com/wp/

Offline Stretchyman

  • Sr. Member
  • ****
  • Posts: 373
    • View Profile
Re: Beginner class D design
« Reply #79 on: April 15, 2019, 1905 UTC »
Yes! High and low side being terms used for PWM boost voltage conversion.

https://engineering.purdue.edu/Courses/ECE433/exp5_5th~6thweek_.pdf

Similar methods if not slightly higher frequencies in use here!

The design is already there, just build the same one!

http://amfone.net/Amforum/index.php?topic=42262.0


Str.
« Last Edit: April 16, 2019, 1544 UTC by Stretchyman »
'It's better to give than receive' so why RX when you can TX!

                            Buy one from me, NOW!

Great discounts on ALL my transmitters if purchased via HFUnderground


                                              ;)

Offline Monophonia

  • Newbie
  • *
  • Posts: 13
    • View Profile
Re: Beginner class D design
« Reply #80 on: April 20, 2019, 1521 UTC »
Be careful when relying on the gate driver to act as the inverter! If your clock source gets loaded down or slightly shifts duty cycle then your amplifier will be imbalanced.

I ran into this issue at 7Mhz whereupon the gates were being driven 35/65 instead of 50/50.

That breaks things after a while.

My advice, use an external inverter or better yet, a flip-flop driven at 2x frequency, those are good at maintaining an even split. For added protection in case your clock stops, make diode level shifters with decay resistors that prevent the drive signal from remaining high.


See last two posts.

I realized after my design that it looks like the NCP drivers have an inverter built-in. The truth table in the datasheet makes it look like it won't work for this purpose though, but I don't know why else they would have such a feature. Is this to use in a push-pull amplifier with one square wave input? If so, then I don't even need the inverter :P

Offline OgreVorbis

  • Jr. Member
  • **
  • Posts: 69
    • View Profile
    • DosaidSoft
    • Email
Re: Beginner class D design
« Reply #81 on: June 12, 2019, 2122 UTC »
I have resumed work on the project. It is very near completion. I just need a good heatsink for the FETs and I'm searching for one now. I want a cooling aggregate type.

I still don't know what to do to the transformer when I add another pair of FETs.

Do I change nothing?
Do I need to add another winding on the secondary?
Do I need to add more than four cores for eight FETs?
« Last Edit: June 14, 2019, 0024 UTC by OgreVorbis »
Radio and Programming Blog: http://dosaidsoft.com/wp/