The time has come! I 'll ask something in the Homework Help!
I was asked to design a AB class amplifier for a course in the uni this semester. All was well, schematics and parts given and I went down on building it. Surprise! It didn't work. Here's the schematic built in Multisim, right before final push-pull couple:
Some specification info about the amplifier:
At first we got a differential amplifier, getting input from the leftmost capacitor. It is powered by the current source built above it so that each branch will receive 0.5mA. Feedback will be driven later on the right branch of the differential amplifier. For now it is grounded.
The second stage is the driver stage. Q7 and Q8 are supposed to have an Ic current of 10mA and thus we have put Q5 as a constant voltage "module" it is supposed to have 1.5+2*0.6=2.7V at its ends.
But here is the problem. In order for that to happen, its vertical branch must have current, 1mA as it is given from a current source of Q4. Unfortunately, no current to be found.
After some messing with the design, I found out that Q6 doesn't conduct and that's my problem. If I put a resistance of 1kΩ in parallel with it for example everything works fine (except that I don't have an amplifier in my hands anymore).
Is there some design flow with Q6, or am should I look elsewhere? Obviously since it doesn't work in Multisim either it's not a faulty part.
Thanks in advance.
Notes:
There IS a connection to the collector of Q3, the arrow of the probe legend hides it.
The other 4 legends to the correspond the 4 green probe arrows from top to bottom.
I was asked to design a AB class amplifier for a course in the uni this semester. All was well, schematics and parts given and I went down on building it. Surprise! It didn't work. Here's the schematic built in Multisim, right before final push-pull couple:
Some specification info about the amplifier:
At first we got a differential amplifier, getting input from the leftmost capacitor. It is powered by the current source built above it so that each branch will receive 0.5mA. Feedback will be driven later on the right branch of the differential amplifier. For now it is grounded.
The second stage is the driver stage. Q7 and Q8 are supposed to have an Ic current of 10mA and thus we have put Q5 as a constant voltage "module" it is supposed to have 1.5+2*0.6=2.7V at its ends.
But here is the problem. In order for that to happen, its vertical branch must have current, 1mA as it is given from a current source of Q4. Unfortunately, no current to be found.
After some messing with the design, I found out that Q6 doesn't conduct and that's my problem. If I put a resistance of 1kΩ in parallel with it for example everything works fine (except that I don't have an amplifier in my hands anymore).
Is there some design flow with Q6, or am should I look elsewhere? Obviously since it doesn't work in Multisim either it's not a faulty part.
Thanks in advance.
Notes:
There IS a connection to the collector of Q3, the arrow of the probe legend hides it.
The other 4 legends to the correspond the 4 green probe arrows from top to bottom.
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