Explaination required (Audio amplifier Class-AB)

Status
Not open for further replies.
A

ahas1234

New Member
Hi everyone !
I'm new to electronics.

I was trying to design AB-push pull audio amplifier (using Darlington). for load current 1.6A (rms) across 4ohm

My input peak is 9v (peak). but at output, my voltages reduces to 8.66V (peak). Wjile required is 9v peak (6.4V rms)
And power despite of around 20Watt (peak), is around 18Watt peak only.

Can someone please provide me a reason, why does this happen ?
Or any way to fix this out !

 

Attachments

  • circuit.asc
    2.1 KB · Views: 260
Last edited:
To get 1.6A through a 4 Ohm load, you need 4 x 1.6 = 6.4V RMS.

The amp must be capable of providing a peak voltage across the load of at least 1.414 x that, so more than 9.05V positive and negative.
You need a higher input voltage swing.

The transistor base current will reduce and the input moves away from 0V. You could add capacitors from input to base either way (across the diode pairs) or try "bootstrapping", split R1 and R2 into two series resistors each, with capacitors from the amp output to the resistor junctions.
 

Actually, i'm trying to amplify a 200mV (peak) input to 9V (peak) using (non-inverting opamp first ).

I set gain to 45. so output becomes 9V. which goes as input to AB amplifier. (to get theoretical output of 9V peak from AB after amplification).

you mean, i should increase the gain ? to provide more input voltage signal to amplifier?
 
Yes, a bit more gain should give you the 1.6A RMS; the output voltage needs to be at least 9.05 peak.

The other mods are to get nearer 1:1 input to output and probably improve linearity a bit.
 
Like I said on the other website, all audio amplifiers have negative feedback from their output so that the voltage loss and distortion produced by your darlington transistors is eliminated.
 
Status
Not open for further replies.

Similar threads

S
  • Question
Stereo to mono class-d amplifier
2
Replies
26
Views
9K
audioguru
K
  • Question
Non-Inverting Amplifier
Replies
3
Views
1K
Kiddie
K
E
  • Question
2N2222A NPN transistor as Current Amplifier
Replies
9
Views
2K
Tony Stewart
  • Question
Rookie needs help to understand why his A-class amplifier doesnt work (measurements and schematic attached)
2 3
Replies
53
Views
7K
GreenGecko7
  • Question
Successful creation of an oscillator and class A amplifier - Schematics and explanations for rookies.
Replies
1
Views
2K
Tony Stewart
Menu
Log in
Register
Cookies are required to use this site. You must accept them to continue using the site. Learn more…