Class D audio amp not working

Thread Starter

Arijeet

Joined Dec 27, 2019
78
In the beginning you are talking about bridge amplifier ,Did you mean to say that I need to build full H bridge amplifier circuit using two comparators Lm 393 ,1st will be Non inverted output and second will be inverted output and then I need to use two MOSFETs drivers ir2113 for drive full h bridge using 4 MOSFETs? Is this you are asking?
I just wondered how the video guy had done the same thing ,invert the output of comparator.without doing any grounds to the unused pins of hex inverter.Any solutions ?
 

Audioguru again

Joined Oct 21, 2019
1,928
The inverter in this simple circuit is used as a high frequency power amplifier. The output current of the comparator is only 4mA but the output current of the 74HC04 is 40mA to quickly charge and discharge stray capacitances.

ALL IC class-D amplifiers use bridging to increase the output power and eliminate a dual polarity supply or an output coupling capacitor. There are many class-D amplifier ICs made today. Here is a little one:

PAM8403 amplifier IC.png
 

Thread Starter

Arijeet

Joined Dec 27, 2019
78
The inverter in this simple circuit is used as a high frequency power amplifier. The output current of the comparator is only 4mA but the output current of the 74HC04 is 40mA to quickly charge and discharge stray capacitances.

ALL IC class-D amplifiers use bridging to increase the output power and eliminate a dual polarity supply or an output coupling capacitor. There are many class-D amplifier ICs made today. Here is a little one:

View attachment 211946
But This IC will not work at higher power ratings eg.500 watts.
 

Audioguru again

Joined Oct 21, 2019
1,928
I showed one of hundreds of class-D audio amplifier ICs that are used in The West. The PAM8403 has low power and is used in portable audio products.
Texas Instruments make many audio amplifier ICs and the TPA3255 (look it up) produces an output power of 600W into a 2 ohm speaker at 10% distortion or produces 480W into 2 ohms with 1% distortion.

The amplifier you are making has many errors (the missing output coupling capacitor for example) and will produce very low power with lots of distortion.
 

Thread Starter

Arijeet

Joined Dec 27, 2019
78
I showed one of hundreds of class-D audio amplifier ICs that are used in The West. The PAM8403 has low power and is used in portable audio products.
Texas Instruments make many audio amplifier ICs and the TPA3255 (look it up) produces an output power of 600W into a 2 ohm speaker at 10% distortion or produces 480W into 2 ohms with 1% distortion.

The amplifier you are making has many errors (the missing output coupling capacitor for example) and will produce very low power with lots of distortion.
okay. But I will order another ic which produces more than 500watt power but I need to know my current circuit how it would be work?
 

Audioguru again

Joined Oct 21, 2019
1,928
Your current project is a copy of a poorly designed circuit that barely works. When you fix its errors then it will work better:
1) The missing output coupling capacitor or making a bridged amplifier.
2) The exponential sawtooth waveform from the 555 instead of a linear triangle waveform.
3) The low output current of the comparator causing slow risetimes of the PWM waveform.

The original circuit tried to use the 74HC04 inverter to boost the current of the comparator output but its input still has a slow risetime. Maybe an LM311 comparator will produce a higher output current then the inverter is not needed.

Why do you need an output of 500W? An amplifier IC is cheap but an amplifier that you make will be expensive and its speaker will be much more expensive.

Select an output power of 100W then do the math. 100W into 8 ohms is an output of 28.3V RMS which is 80V p-p. The power supply must be 84VDC/1.4A. The voltage will be less if a 4 ohm speaker is used and the voltage will be much less if a bridged amplifier is used to drive a 4 ohm speaker.
 

Thread Starter

Arijeet

Joined Dec 27, 2019
78
Your current project is a copy of a poorly designed circuit that barely works. When you fix its errors then it will work better:
1) The missing output coupling capacitor or making a bridged amplifier.
2) The exponential sawtooth waveform from the 555 instead of a linear triangle waveform.
3) The low output current of the comparator causing slow risetimes of the PWM waveform.

The original circuit tried to use the 74HC04 inverter to boost the current of the comparator output but its input still has a slow risetime. Maybe an LM311 comparator will produce a higher output current then the inverter is not needed.

Why do you need an output of 500W? An amplifier IC is cheap but an amplifier that you make will be expensive and its speaker will be much more expensive.

Select an output power of 100W then do the math. 100W into 8 ohms is an output of 28.3V RMS which is 80V p-p. The power supply must be 84VDC/1.4A. The voltage will be less if a 4 ohm speaker is used and the voltage will be much less if a bridged amplifier is used to drive a 4 ohm speaker.
Thank you for briefing everything and giving your valuable time. I want to tell you that my class d amplifier application will be used in Exciting an Electromagnetic Actuator(Single pole copper wire wounded) which will produce force. I am not going to use the speaker for that, right now I am using this load as a speaker, later if it is built, I will put an Electromagnetic Actuator. Now come to the second question of yours was "
The original circuit tried to use the 74HC04 inverter to boost the current of the comparator output but its input still has a slow rise time. Maybe an LM311 comparator will produce a higher output current then the inverter is not needed." can I use the LM393 comparator instead of using Hex inverter? my 3rd question is " The missing output coupling capacitor or making a bridged amplifier." ,in the schematic a coupling capacitor is placed already as a value of 1.1 uf.which coupling capacitor I need to put ?
 

Audioguru again

Joined Oct 21, 2019
1,928
The output current of the LM393 comparator is too low to quickly charge and discharge stray capacitances at 200kHz. The inverter does not help and is not needed.
The 1.1uF output capacitor to ground is part of the LC high frequency filter, not a series coupling capacitor. This simple amplifier has an average DC output voltage of half the supply voltage that will produce a high DC current in a speaker load. A series output coupling capacitor blocks the DC but passes the AC audio to the speaker.
Won't your Electromagnetic Acuator simply vibrate at the audio input frequency without producing any force?
 

Thread Starter

Arijeet

Joined Dec 27, 2019
78
The output current of the LM393 comparator is too low to quickly charge and discharge stray capacitances at 200kHz. The inverter does not help and is not needed.
The 1.1uF output capacitor to ground is part of the LC high-frequency filter, not a series coupling capacitor. This simple amplifier has an average DC output voltage of half the supply voltage that will produce a high DC current in a speaker load. A series of output coupling capacitor blocks the DC but passes the AC audio to the speaker.
Won't your Electromagnetic Actuator simply vibrate at the audio input frequency without producing any force?
I have a Max 913ESA comparator which has a dual output (Q & compliment Q), I haven't tried yet. can I use this comparator if you have knowledge regarding this . What would be the value of coupling capacitor (0.1 to 10 uf )? the last one, My electromagnetic Actuator Won't simply vibrate at an input frequency, it needs a current amplifier.
 

Audioguru again

Joined Oct 21, 2019
1,928
Didn't you read its datasheet? The Max913 comparator has almost the same low output current as the LM393. An LM311 has almost 10 times more output current.

Coupling capacitors are calculated for a -3dB cutoff frequency. A 1000uF output coupling capacitor produces a -3dB cutoff frequency into a 4 ohm speaker of 40Hz. -3dB is half the output power that sounds only a little less than full output power.

What will your Electromagnetic Actuator be used to vibrate? What frequencies? Since it might not be used for audio frequencies then the 555 can have its frequency reduced. Then the weak LM393 or Max913 will work fine.
 

Thread Starter

Arijeet

Joined Dec 27, 2019
78
Didn't you read its datasheet? The Max913 comparator has almost the same low output current as the LM393. An LM311 has almost 10 times more output current.

Coupling capacitors are calculated for a -3dB cutoff frequency. A 1000uF output coupling capacitor produces a -3dB cutoff frequency into a 4 ohm speaker of 40Hz. -3dB is half the output power that sounds only a little less than full output power.

What will your Electromagnetic Actuator be used to vibrate? What frequencies? Since it might not be used for audio frequencies than the 555 can have its frequency reduced. Then the weak LM393 or Max913 will work fine.
okay Lm311, I will check it.so I can use the Lm311 comparator for getting the PWM signal and another one Lm311 will invert the signal. My electromagnetic Actuator will be used for the vibration of rotating tools. a milling machine which has a spindle which will rotate a circular saw or disc, do I need An electromagnetic actuator to force or vibrate the circular saw.circular saw will rotate at high speed, my actuator will produce a force in the saw. when saw will feel vibrations, it will change its dynamics structure, you can say frequency response. a good example is when Aeroplane is manufactured, it's parts are checked by actuator because m, when the airplane will in the sky, it will feel high pressure on their body, so we need to damp the actual force from the actuation principles,, yes this application test on ground level before final manufactures of airplanes. I am just working in a small part. yes in last part you asked which frequency I need to work, it would be (500Watt, 20hz- 1khz ).
 
Top