Electronics > Projects, Designs, and Technical Stuff
Simple DIY Linear PSU
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panoss:

--- Quote from: xavier60 on March 07, 2020, 08:47:54 am ---I would also expect the op-amps to be allowing Q1's Base voltage to go up much closer to 9V. Check this.
Without knowing the current gain of the output transistors, I can't work out the expected maximum output current.
You can try lower values for R10 as a temporary fix.
Watch for stability problems.

--- End quote ---
With R10=1k:
RL=5 Ohm, Q1: Vb=7.60V
RL=10 Ohm, Q1: Vb=7.15V

With R10=300 Ohm:
RL=5 Ohm, Q1: Vb=6.43V
RL=10 Ohm, Q1: Vb=6.13V

With R10=300 Ohm it seems to work a lot better (it can give more current and voltage remains stable).

For knowing the current gain of the output transistors I should simulate my first design? (the kakopa design from my first post?)
panoss:

--- Quote from: kallek on March 07, 2020, 09:15:16 am ---Next measure Q2 current to check if pass transistors get enough base current.

--- End quote ---
With RL=5 Ohms and R10=300 Ohms:
Q2 Ie=0.147A
Q3 Ib=0.0691A
Q4 Ib=0.0691A
xavier60:

--- Quote from: panoss on March 07, 2020, 09:33:40 am ---
--- Quote from: kallek on March 07, 2020, 09:15:16 am ---Next measure Q2 current to check if pass transistors get enough base current.

--- End quote ---
With RL=5 Ohms and R10=300 Ohms:
Q2 Ie=0.147A
Q3 Ib=0.0691A
Q4 Ib=0.0691A

--- End quote ---
That works out to 20 for the output transistors. The simulator must be using the minimum spec from the data sheet.
xavier60:
150 for the driver transistor which is reasonable.
A suitable value for R10 can be chosen after the design is built with real parts.
panoss:
So you 're saying the circuit is ok?
I should built it and after this experiment with the value of R10?
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