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Is there any variable DC-DC converter suitable for pre-regulation?
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bloguetronica:
Hi,

I finally had time to simulate the pre-regulator circuit using a buck DC-DC converter with the PNP. I suspect that the model is incomplete, and that is why I probably can't simulate this.

Could anyone check if the circuit is done properly? I will probably use the LM2592HV instead of the TPS62140. It has a lower switching frequency that is easier to filter out and it withstands 24V input voltage. The topology should be similar, save a few pins. The circuitry attached to the FB pin is the one I want to analyze and check for correctness.

Kind regards, Samuel Lourenço
bloguetronica:
Hi,

Doing late hours results in mistakes. The circuit was all wrong. Attached is the correct one, which makes far more sense. Still, I can't run a simulation.

Anyway, how can I set the overhead voltage, that is, the voltage difference between the DC-DC output and the one after the pass element? I want to set this voltage difference to 3 or 4V above.

Kind regards, Samuel Lourenço
prasimix:
If your can't run simulation due to circuit complexity you can try to remove everything except SMPS controller/regulator and PNP tracker and apply voltage source on the PNP tracker as for example in this simulation where Vout_sim is 22 V that give 25 V on the pre-regulator output.
bloguetronica:
Hi prasimix,

I can't simulate your circuit, since it doesn't have a schematic. However, my simulation shows Vout skyrocketing.

On another note, it seems that the datasheet of the DC-DC converter I'll end up using (which is the TPS54233, instead of the LM2592HV or the TPS62140) is very pick about maintaining the top feedback resistor a constant 10K. Is there any way we can do this, and put the transistor below? I think the alternative is to reduce all resistors tenfold, guessing that the problem is a too high impedance on the feedback circuit.

Anyway, how is the voltage difference set? Can I set it to 4V? How can I calculate the resistors?

Kind regards, Samuel Lourenço
prasimix:

--- Quote from: bloguetronica on October 22, 2018, 11:40:32 am ---I can't simulate your circuit, since it doesn't have a schematic. However, my simulation shows Vout skyrocketing.

--- End quote ---

The schematic (in .png format) is included into zip file if you followed mentioned link.
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