Push-pull or choke-loaded A can be 50% efficient.
CSS A can be 25% efficient.
Resistor loaded A is at best 6% efficient.
Class B can be 78% efficient.
Invert the question. We need One Watt. How much power does the amplifier suck?
At FULL power:
P-P/choke A - 2 Watts
CSS A -------- 4 Watts
R-load A ----- 16 Watts
Class B ------- 1.6 Watts
But life is not FULL power test tones. At average 10% of max power:
P-P/choke A - 2 Watts
CSS A -------- 4 Watts
R-load A ----- 16 Watts
Class B ------- 0.22 Watts
That is a 72 to 1 difference of battery drain.
At these power levels, if your religion prohibits class B, choke-loading is perfectly practical, actually cleaner than resistor-loaded, and only 10X more hungry than B.
Good day to you, Gents. I am a newbee in the class A game but am keen to try this as my first foray into this. May I confirm my understanding about the circuit in post #1? The input impedance is 48k Ohm, so a film capacitor 2.2uF should serve nicely as input cap? The 10uF as drawn is for when we use electrolytic to allow low distortion, is that correct? If using electrolytics, is there a rule to connect the polarity with the source? Thank you very much.
This is what I came up with, with what I have lying around. Output cap is 1000uF, positive towards the circuit, negative to speaker (+). Hope I got that right. MOSFET is IRFZ44N. Input cap is 47uF/25V. Thanks for the design, inspiration, and wealth of information.
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lemme see ...... gate is at 19V x 47K/(10K+47K)=15.66V
source is at some 4V less , so 11V66
so , current through 8R loading resistor is 11V66/8=1A458
thus , dissipation of entire circuit is 19V x 1A458=27.7W
dissipation across MOsfet is (19V-11V66) x 1A458=10W7
so , two mosfets are burning 21W4 together
for Mighty Moi , that's some heat .... Papa wrote nicely that 8R resistor must be 25W capable thingy
baaaaaad Papa is having cardboxes of these (resistors and mosfets) , same as Ocean nearby , to toss them in and keep them cool even without heatsink
source is at some 4V less , so 11V66
so , current through 8R loading resistor is 11V66/8=1A458
thus , dissipation of entire circuit is 19V x 1A458=27.7W
dissipation across MOsfet is (19V-11V66) x 1A458=10W7
so , two mosfets are burning 21W4 together
for Mighty Moi , that's some heat .... Papa wrote nicely that 8R resistor must be 25W capable thingy
baaaaaad Papa is having cardboxes of these (resistors and mosfets) , same as Ocean nearby , to toss them in and keep them cool even without heatsink
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Thank you for this. I will see what I can do about the heatsink situation and report back.
