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Oscillations! Linear variable PSU

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xavier60:
If it will always be outputting 45V at up to 6A, one paralleled set of transistors will do, assuming an input of about 60V.
If the output needs to be set to much lower voltages, then it will be difficult to deal with unless the input voltage can be reduced also.

ogden:

--- Quote from: xavier60 on May 17, 2020, 01:11:56 pm ---If the output needs to be set to much lower voltages, then it will be difficult to deal with unless the input voltage can be reduced also.

--- End quote ---
Good point. Introduce either mains transformer with multiple output taps (oldskool approach) or switching preregulator + LC  filter.

Datguy123:

--- Quote from: xavier60 on May 17, 2020, 01:11:56 pm ---If it will always be outputting 45V at up to 6A, one paralleled set of transistors will do, assuming an input of about 60V.
If the output needs to be set to much lower voltages, then it will be difficult to deal with unless the input voltage can be reduced also.

--- End quote ---

Unfortunately, the supply I'm planning to build have the full output range of 0-45V. As u mentioned earlier, parallelling transistors would definitely not be a practical solution here.


--- Quote from: ogden on May 17, 2020, 01:18:24 pm ---
--- Quote from: xavier60 on May 17, 2020, 01:11:56 pm ---If the output needs to be set to much lower voltages, then it will be difficult to deal with unless the input voltage can be reduced also.

--- End quote ---
Good point. Introduce either mains transformer with multiple output taps (oldskool approach) or switching preregulator + LC  filter.

--- End quote ---

The aim of building this power supply is to utilize the parts I have available to me. The transformer I'm using comes from a power amplifier and does not have lower voltage taps on the main secondary winding. I wouldn't want to rewind the transformer because my lab doesn't have the capabilities to do so.

I also wouldn't want to introduce a switching regulator as I want the suppy to be as linear as possible and it might introduce more complexity to the overall circuit.

I know the design I created completely negates efficiency, simplicity, and practicality, but it wouldn't hurt to try out a new method. I envision using this as a learning point, and since I have came a long way from a blank piece of paper to a partially working circuit, I would like to cling on to any hope that the circuit could be mended to work. This might be foolish of me to you more senior engineers but I don't want to give up this circuit just yet. I hope you can understand my point of view and aid me in completing this project.

xavier60:

--- Quote from: Datguy123 on May 18, 2020, 07:18:35 am ---
--- Quote from: xavier60 on May 17, 2020, 01:11:56 pm ---If it will always be outputting 45V at up to 6A, one paralleled set of transistors will do, assuming an input of about 60V.
If the output needs to be set to much lower voltages, then it will be difficult to deal with unless the input voltage can be reduced also.

--- End quote ---

Unfortunately, the supply I'm planning to build have the full output range of 0-45V. As u mentioned earlier, parallelling transistors would definitely not be a practical solution here.


--- Quote from: ogden on May 17, 2020, 01:18:24 pm ---
--- Quote from: xavier60 on May 17, 2020, 01:11:56 pm ---If the output needs to be set to much lower voltages, then it will be difficult to deal with unless the input voltage can be reduced also.

--- End quote ---
Good point. Introduce either mains transformer with multiple output taps (oldskool approach) or switching preregulator + LC  filter.

--- End quote ---

The aim of building this power supply is to utilize the parts I have available to me. The transformer I'm using comes from a power amplifier and does not have lower voltage taps on the main secondary winding. I wouldn't want to rewind the transformer because my lab doesn't have the capabilities to do so.

I also wouldn't want to introduce a switching regulator as I want the suppy to be as linear as possible and it might introduce more complexity to the overall circuit.

I know the design I created completely negates efficiency, simplicity, and practicality, but it wouldn't hurt to try out a new method. I envision using this as a learning point, and since I have came a long way from a blank piece of paper to a partially working circuit, I would like to cling on to any hope that the circuit could be mended to work. This might be foolish of me to you more senior engineers but I don't want to give up this circuit just yet. I hope you can understand my point of view and aid me in completing this project.

--- End quote ---
You are rectifying the secondary into split rails? What are the voltages.
Some amplifier transformers have  lower voltage taps in the secondary so that the rail voltages can be reduced when the speaker impedance switch is set to low.

Datguy123:

--- Quote from: xavier60 on May 18, 2020, 10:16:23 am ---You are rectifying the secondary into split rails? What are the voltages.
Some amplifier transformers have  lower voltage taps in the secondary so that the rail voltages can be reduced when the speaker impedance switch is set to low.

--- End quote ---

The amplifier is a conventional class AB type. Wouldn't want to tear apart a fancier class G that has split rails. Anyways, the transformer has 4 secondaries, 2 secondaries to supply the low powered electronics, and 2 center-tapped secondaries for the power amplifiers. They are of similar voltage (+/- 54Vpk unloaded wrt to the center tap), and I am going to parallel them to increase the output current. 

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