Doing a class D Amp project using TL494

[ledmania]

my wifi connection is kaput?
try again

 

[circuitcity]

Thanks mate.. I'll use your schematic as my reference.

Though can you please explain to me what error amplifier 1 or Pin 1 and 2 are doing though? I don't understand what they do.

Also what happened to the feedback network you had in your other schematics. A half-bridge topology requires a feedback from the Output mosfets (before filtering) being sent back to the input error amplifier to minimize errors.
You've taken it out on this one, but used the FB pin (pin3) as your feedback.

You had a control circuit for SD control in your other schematics. Can i just pull this to ground initially?

I've already ordered and received the IR2110. So i'll use them for now, using the schmitt trigger to get my complimentary pair of pulses to feed into the gate driver. But I'll look into the IR2010 and the IRS20124.

 

[circuitcity]

Oops forgot to ask. What are you using as your music source? A standard Mp3 player and your taking the output from the Mp3 player from the earphone out?

 

[ledmania]

from my old schematic I use error amp on pin 1 and 2 as logic 0 shut down pin only and does not interfere with the output of other error amp.

yes you can pull down sd pin to grd or to vcc to enable or disable the
IR fet driver.
the feedback network in my old schematic has a basic flaw that it
took bias voltage from half VCC to grd which will affect the duty cycle when the power supply varies, and this is bad.
so the best choice for FB is to get it from pin 3 while the plus pin 16 should be tied to 10k pot to adjust the duty to 50.
This pot can also be used as output offset voltage eliminator to your speaker as well.
I have a bad feeling that the source of leading or trailing voltage spikes from tekko's project is the lacking of dead time in between, so IRS20124 is a good choice.

 

[ledmania]

Yes I use MP3 player to drive the input of tl494.

 

[circuitcity]

Ok thanks, so in that schematic you posted, you just got a 2K resistor pulled to ground, connecting to Pin 1.
Since your not feeding your shut-down control like in your old schematic.

Although it looks like there's another line connecting to R19 (2K resistor) in the one you just posted.

I'll try it with the MP3 method as well..

 

[circuitcity]

Allright i'll pull up SD to Vcc to enable the IR gate driver then.

 

[ledmania]

Correct, pulling down pin 1 means I disable that error comp so as not to interfere with error comp 2. Or you can parallel those pins to act as one comp such as pin 1 tied to pin 16 and pin 2 tied to pin 15 but I’m not sure the resulting sound though. Try to explore anything that will satisfy your curiosity. It’s your own universe dude.

 

[ledmania]

If you pull down SD pin to grnd you enable it.

 

[Pafi]

Or you can parallel those pins to act as one comp such as pin 1 tied to pin 16 and pin 2 tied to pin 15

It's not comparator. It's OPA.

Paralelling OPAs (or comparators) is not a good idea. (At least this way.)

 

[circuitcity]

Alright thanks guys. I'll wire this up and post some results in the next day or two.

Big thanks goes to you guys for helping me with this project (Led, Pafi and Eva).

 

[ledmania]

It's not comparator. It's OPA.

Paralelling OPAs (or comparators) is not a good idea. (At least this way.)

Thanks for correcting me Pafi. I wonder why I call it comparator while
in my old thread I usually call it OPA too. Perhaps I seldom post and I
have less practice in posting. LOL! Oh well

 

[circuitcity]

Ok i went and wired just the TL494 section and the schmitt trigger part and I ended up getting this.

http://img35.imageshack.us/i/tek0006.jpg/

The yellow is my sine wave from a function generator. Blue is the sawtooth created and the complimentary PWM is from the schmitt trigger.
Looks ok to me.. But I'll inspect it further to see if this is right or wrong.

Some modification to your circuit i did was, I didn't use the 10K pot but rather just used two 10K resistors and made a voltage divider and feeded that into Pin 16. But I'll be modifying this circuit tomorrow and try it with the 10K pot.


But i encountered a problem today. I didn't hear anything in my earphone across the output from Pin 11. This is my graph across Pin 11.

http://img33.imageshack.us/i/tek0007.jpg/


My concern is, am i implementing music correctly? Because what i did today was took some cheap earphones and snipped out the actual part that you put in your ear.

Here's some pics:

http://img268.imageshack.us/i/dsc00018wlw.jpg/

I connected that to the C7 capacitor today (10uF), but nothing.

Also I used the earphone sockets into the PC input and plugged the copper wire at the other end into C8 (3.3uF).

I tried playing some music off Youtube to see if i could hear anything in the earphones, but nothing.

http://img518.imageshack.us/i/dsc00019nxz.jpg/

Did I implement the music wrong?

 

[circuitcity]

forgot to add

I don't wanna move onto the gate driver and output mosfets until I'm 100% certain the PWM control circuit is fully working.

 

[ledmania]

Based on your scope, I noticed that your blue trace (saw tooth) is almost only 4x speed of your sine wave which I assumed its your function generator? Your scope says the yellow trace is about 6khz so it means that the sawtooth is 24khz only. As far as I know, your saw tooth should cover at least more than 30x.. Am I reading your scope correctly?
Your oscillator frequency is too slow to me. If Im correct.
Cheers

 

[ledmania]

When I’m using my CRT scope, one complete cycle sinewave @ 1khz, I cannot count how many sawtooth within it. How much is your oscillator frequency?
Cheers

 

[circuitcity]

Sorry i had Channel 1 triggered. My Oscillator freq is 205KHz while the sine wave is 6KHz.

I'll take a better picture today. I just left channel 1 (yellow sine wave) on triggered, so even the PWM look dodgy come to think of it.

 

[circuitcity]

oops my bad, placed the wrong cap for the oscillator.. Your right ledmania, that graph i posted earlier is 28KHz.

Here's the edited version today..

The oscillator freq is around 200KHz. The sine wave is 100Hz,

This is the PWM from the output off Pin 8.

http://img39.imageshack.us/i/tek0008.jpg/

Does that look satisfactory?

I used the SN74LS14N Schmitt trigger.

Here's what I observed as the two pulses that would go into Hin and Lin of the gate driver.

http://img269.imageshack.us/i/tek0009.jpg/

Here's the datasheet off the schmitt trigger.

http://focus.ti.com/lit/ds/symlink/sn74ls14.pdf

I just pulled pin 11 to Vcc (the other collector output) because for the moment i gave up on the earphone testing. i don't understand how to implement it it until i get some further clarifications on it.

Only annoying effect i saw today was this bouncing/oscillating effect where the green and purple graphs meet up. I don't really understand what's happening there or how to fix it.

 

[ledmania]

Wow! nice teeth! No cavities . This looks good to me. But please
dont put pin 11 direct to Vcc. You have to pull it up with at least 1k resistor. Please check my schema, pin 8 and 11 are tied together then pulled up by 680ohm.
I' excited

 

[circuitcity]

Ledmania the gate driver chip your using comes in SOIC form only
I would like to test my circuit on a Breadboard, so i would like a dip form ideally.

What do you guys think about the IR2111?

Its Ton and Toff times are ridiculously long, but is it enough to be implemented in a class D circuit?

Ton = 750 ns
Toff = 150ns


But everything is inside the chip. I don't need a schmitt trigger to get complimentary pulses, since this chip does it and it already has a typical dead time of 650ns to avoid shoot-through.