voltage comparator replacement in class D amp

[Enzy]

Im reading up on class D amplifiers and I found a design that I would want to prototype but I dont have the lm311 chip I have seen where op-amps can be used as voltage comparators also. Would I be able to redraw this using a op-amp say a tl07x series?

 

[FvM]

Although being quite old, LM311 is an active part at major manufacturers TI, OnSemi and ST.

The circuit expects a comparator with open collector output and logic ground. It has to be redesigned to use a comparator with push-pull output.

I don't foresee if the simple self oscillating design would work with TL071 after fixing the comparator to gate driver level conversion. I'm not even sure if it works reliably under all load conditions.

 

[KlausST]

Hi,

I don't think a TL071x can replace the LM311.

Opamps and comparators are designed for different applications:

Usually comparators:
* are designed for switching applications (saturating outputs)
* are faster in response
* have higher rise/fall rate
* have less gain
* don't suffer from phase reversal
* don't suffer from large overdrive recovery time (input stage as well as output stage)

Therefore I recommend to use an Opamp for linear/analog applications and comparators for switching applications.

Klaus

 

[Enzy]

Ok so it seems I will need a comparator. it seems it could probably work as you said but might not work with all loads.

I would test it out just the same though to see how it works, but how would the tl071 be used in place of it?

- - - Updated - - -

Therefore I recommend to use an Opamp for linear/analog applications and comparators for switching applications.

Klaus

Ok then I was looking a work around but ill just order some.

would you recommend any specific comparator for this circuit (something newer).

 

[KlausST]

Hi,

I can't recommend a comparator, especially because of the extra emitter_out.

The TI datasheet of LM311 is revised on March 2017....it seems the device is still in focus.
The device is not that expensive and good available.
I wonder if it really is worth the effort to redesign the circuit.

Klaus

 

[Enzy]

redesign would just e for testing purposes since I now have some free time to read and experiment. If I should order the lm311 it would take 3 weeks to arrive thats the only reason I suggested that so i would just try to use something i currently have available.

 

[FvM]

To use a push-pull comparator or sufficient fast OP in the circuit, you'll connect the 4k7 resistor between comparator output and VT1 emitter, and place a 1N4148 diode between VT1 emitter and base to clamp negative voltages.