Electronics > Projects, Designs, and Technical Stuff
Is there any variable DC-DC converter suitable for pre-regulation?
<< < (14/17) > >>
T3sl4co1l:
An unstable system, initialized to a stable point (this is what the DC analysis does), will not move from that point unless perturbed by noise.  Transient analysis does not include noise unless you add it yourself.  So, simply, it's stable because nothing has pushed it off.

It's like stacked bowling balls, except those can remain upright because they have rough surfaces.

The zero-initial-conditions result is the correct one here.

Tim
bloguetronica:
Hi,

More testing with TINA-TI made me to conclude that the simulator is doing AC analysis to evaluate the transient response. Anyway, didn't make any changes to the circuit, and found out that it doesn't oscillate, no matter how I run the simulation. The drifting was caused by the AC analysis.

Thanks to T3sl4co1l for suggesting a series of measures, such as the degeneration resistor, the voltage divider and the feedback network. The feedback network makes sense, because the op-amp has a gain very close to 1 in AC while acting as a comparator regarding to DC voltages. The transistor has its gain reduced, but the current never falls out of regulation since the op-amp doesn't hit the rails, while still showing a wider variation on its output.

Kind regards, Samuel Lourenço
bloguetronica:
Hi Tim,

Can I exclude R15? I mean, the value is so small in comparison to R16. What is the cost of doing so?

P.S.: It seems to be stable now, even when simulating with zero initial conditions.

Kind regards, Samuel Lourenço
T3sl4co1l:
Yes, that is a correct insight.

However, did you try larger values and smaller C values?

The step response is going to be ass with a cap that big.  (Try putting a pulse current in parallel with the load resistance.)

Tim
bloguetronica:
Hi Tim,

Indeed I find the capacitor too large. The inverting input series resistor (R16) is also a tad large and noise inviting, but still OK.

I think it is better to simulate this on a real simulator, also known as a PCB. TINA-TI is just unrealistic, and is showing abnormal behavior on the CC circuit part, that at least no longer oscillates (not that its feedback loop is closed and there is no chance of having positive feedback locally there). The CC control transistor is working better than ever.

But first, I'll have to implement the pre-regulator. I don't want to have excess dissipation on that pass transistor.

Kind regards, Samuel Lourenço
Navigation
Message Index
Next page
Previous page
There was an error while thanking
Thanking...

Go to full version
Powered by SMFPacks Advanced Attachments Uploader Mod