Timeline for Simple power amplifier with feedback - designing procedure
Current License: CC BY-SA 4.0
9 events
| when toggle format | what | by | license | comment | |
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| Dec 17, 2020 at 13:58 | comment | added | Bimpelrekkie | Hmm, your amplifier has a gain of roughly: \$gm_{T1}\$ * R3 = 40 * 7.2 mA * 1.5kohm = 430, should be enough. | |
| Dec 17, 2020 at 13:53 | comment | added | Dawid W | I am aware of the capacitors values - they're just for simluation conveniency (I set the steady state with one click anyway). DC voltages and currents are correct (the schematic I posted in an original post shows the quiescent state with input unplugged, You can take a look). Perhaps it's because the open loop gain is low and the \$R1/R2\$ is some kind of simplification only applied to a large open-loop gains? | |
| Dec 17, 2020 at 13:34 | comment | added | Bimpelrekkie | I see you are using VERY large capacitor values. The 1 mF at the input with 8.9 kohms gives a time constant of 9 seconds. So more than 9 seconds are needed to properly charge that 1 mF capacitor and for the complete amplifier to bias properly! I changed it to 10 uF. I suggest that you set the input signal to a very small value ( 1 mV) and then check if all DC voltages and currents are as expected. | |
| Dec 17, 2020 at 13:28 | comment | added | Dawid W | same story... tinyurl.com/y8cwzer9 | |
| Dec 17, 2020 at 13:27 | comment | added | Bimpelrekkie | If your amplifier can handle the 8 ohm load then this should not happen. I suggest that you "scale down" the load, make it 800 ohms. Do you now get the expected voltage gain? | |
| Dec 17, 2020 at 13:26 | comment | added | Dawid W | tinyurl.com/y84tw7jl Give it a go... | |
| Dec 17, 2020 at 13:22 | comment | added | Dawid W | Thank You for Your interest! However, I did some reading on the matter and I am familiar with the basic concepts (my amp is an inverting one and I am trying to apply a negative feedback to it) as well as the formula You posted (\$R2/R1\$) and it does not work here. After applying 8.9k resistor, the output voltage dropped significantly and the maximum swing is +/-\$3.85V\$ instead of the previous +-\$9V\$ . That's why I posted this question in a first place - I seemingly missing something important. The correct value of \$R2\$ is something like 3.5k-3.7k (picked experimentally) | |
| Dec 17, 2020 at 13:09 | history | edited | Bimpelrekkie | CC BY-SA 4.0 | added 206 characters in body |
| Dec 17, 2020 at 13:03 | history | answered | Bimpelrekkie | CC BY-SA 4.0 |