Component choice for class AB amplifier.

Thread Starter

glyndavidson

Joined Jul 26, 2020
12
Hold down the ctrl key and left click on the graph title ["I(Speaker)"]. It will show you the current.
Ahhh, I spent ages trying to find that. Thank you!

So, with a 0.1uF capacitor at C1, I got nearly 6 hours out of the battery! That's amazing! Far better than any of the IC amplifiers I tried. Compared to the 1 hour and 40 minutes I got from my original circuit at the start of this thread that is a huge saving.

It's not as loud as what I had originally, and it sounds "tinny" but looking at the waveform and current consumption suggests that I can modify the value of C1 to find a good compromise between sound quality and battery life.

Edit - Reading back through the thread this is exactly what @Ylli said in the first post, I just didn't understand it at the time. Also, I misread the comment regarding polarised caps. Re-reading the post I realised I could use non-polarised caps and I have a bunch of these on the bench. To get close to my original sound, I need to use a 1uF capacitor. According to the Spice simulation, with a 1uF capacitor, on average, the current at the speaker is still nearly half of what it was originally.

So this was a great success. Not only have I achieved a solution to my original question but I also learnt (a little) about how to do Spice simulations along the way. Thank you so much for your help.

Now, it works, but I'd really like to understand how/why it works... How does the capacitor and diode form a differentiator and how does it clip the signal? I feel like I really need to go back to basics on this one and look at how electrons move around a circuit.
 

Thread Starter

glyndavidson

Joined Jul 26, 2020
12
Sorry folks, another question if you don't mind. Am I right in thinking that with the differentitator circuit I still need a snubber diode across the buzzer for back EMF (D2 in schematic below)?
Annotation 2020-07-28 105042.png
 

Papabravo

Joined Feb 24, 2006
17,318
I don't think so because your pulse will have a fast rise time, but a relatively slow decay. The relatively slow turnoff will prevent the occurrence of an inductive kick.
 

MisterBill2

Joined Jan 23, 2018
9,908
What is so complicated about using an LM386? And there is a connection that provides a 100x gain option.
But it will also work to use a capacitor as a differentiator, which a differentiated square wave is a spike wave. That is calculus 1, week 2. That will produce your noise with far less current draw.
 
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