Hi there,
I tried to design a negative version of the 21st century Maida regulator using a LT3090. It works, after a fashion, but whatever I try I can only generate a regulated voltage that is significantly smaller than the input. In the example here, the supply is -200V and the regulated output is -114V, so the dropout is huge. Any attempt to increase R5 or reduce R4 then causes the output to become unregulated because the LT3090 doesn't have the required voltage across it.
Is there something fundamental to the LT3090 that is causing this? Many thanks!
I tried to design a negative version of the 21st century Maida regulator using a LT3090. It works, after a fashion, but whatever I try I can only generate a regulated voltage that is significantly smaller than the input. In the example here, the supply is -200V and the regulated output is -114V, so the dropout is huge. Any attempt to increase R5 or reduce R4 then causes the output to become unregulated because the LT3090 doesn't have the required voltage across it.
Is there something fundamental to the LT3090 that is causing this? Many thanks!
Isn't the problem in the IRFP9240 circuit? It has most of the voltage across it. Maybe you need a different mosfet.
Does the 10V Zener D6 have enough current in it to regulate (less than 1mA)?
The LT3090 dropout voltage is only 300mV, so it's still in regulation, but just barely.
It needs more input voltage to work with, and to accommodate the circuit tolerances.
Does the 10V Zener D6 have enough current in it to regulate (less than 1mA)?
The LT3090 dropout voltage is only 300mV, so it's still in regulation, but just barely.
It needs more input voltage to work with, and to accommodate the circuit tolerances.
Last edited:
I was wondering that, but then why does this problem not affect the MOSFET in the positive regulator below?
It's a different mosfet. So that must be the problem, since it's the only real difference.
The purpose of the mosfet circuit is to absorb most of the excess input voltage,
leaving only 10V or 15V across the regulator.
Not having built this, I suspect a smaller Zener value for D6 will fix the problem.
But you might also need a smaller value for R8 to keep the Zener conducting,
although the sim may ignore that.
The purpose of the mosfet circuit is to absorb most of the excess input voltage,
leaving only 10V or 15V across the regulator.
Not having built this, I suspect a smaller Zener value for D6 will fix the problem.
But you might also need a smaller value for R8 to keep the Zener conducting,
although the sim may ignore that.
Last edited:
rayma - many thanks for the suggestion. I guess the only things that could make a difference are a different zener or the value of R8. I'll give those a try.
Actually the problem is with the mosfet, but a different Zener may allow you to compensate for it.
What happens with a 8.2V or 6.8V Zener for D6? Of course, the real mosfet will vary from the model.
What happens with a 8.2V or 6.8V Zener for D6? Of course, the real mosfet will vary from the model.
Last edited:
Hello,
Why not put two of these positive regulators in series as you would two batteries, ground the center connection.
The top positive output is positive.
The center point where the two regulators connect is ground.
the negative rail of the bottom regulator is the negative output.
Positive output.
Ground.
Negative output.
If you have only one regulator ground the positive output. the negative rail is the negative output.
Thanks DT
Why not put two of these positive regulators in series as you would two batteries, ground the center connection.
The top positive output is positive.
The center point where the two regulators connect is ground.
the negative rail of the bottom regulator is the negative output.
Positive output.
Ground.
Negative output.
If you have only one regulator ground the positive output. the negative rail is the negative output.
Thanks DT
yes.
It has been awhile, I have done this several times.
Not too long ago I put two Mean Well switching supplies in series.
As drawn the mosfet will conduct through the parallel body diode. my guess is you need a P-channel device for the job.
I think you're trying to use the 3090 upside down. It needs a postive voltage between input and output. In you intended circuit, it would be the other way around. There's something inside the chip that protects it and therefor it doesn't work.
This cannot be made to work with this chip, and I don't know any which would.
I think you're out of luck.
Jan
This cannot be made to work with this chip, and I don't know any which would.
I think you're out of luck.
Jan
I should stop posting at 6AM. But im pretty sure your 100K Rload is not meeting some sort of minimum output current requirement
Could work with LM337 however, i dont understand the fad with LT3080 based maida's. Yes, it has 1mA minimum load current as opposed to LM317(3.5mA TYP), and can run a way higher resistance divider owing to its 10uA internal current source. However its 100Hz noise rejection ratio isnt much better than TL783.
Jan, thanks for your note.
The circuit does seem to regulate in principle - is your point that the LT3090 contains a protection circuit, not modeled by the LTSpice model, which makes the concept impossible in practice?
The circuit does seem to regulate in principle - is your point that the LT3090 contains a protection circuit, not modeled by the LTSpice model, which makes the concept impossible in practice?