Please help with power supply design - multiple precision outputs

[kanonka]

Hi,

I need help with design of PS with following specs:
Input - 19.5V (regular laptop PS);
Outputs -
+43V / 0.8A, precision and load regulation within 0.2% or better; load sharply switches from 10mA to 0.8 A;
+36V/ 50mA, precision within 1% or better; load is constant;
+5V / 2A, precision and load regulation within 1% or better; load can vary from 50mA to 2A, sometimes sharply (user inserts USB device; but mostly this is MCU and precision DACs supply);
-0.04V / 1mA, precision within 1% or better; load is constant;
-1.25V/ 50mA, precision within 1% or better; load is constant;

I don't care about PCB space (well, within reasonable limits, of course )
I don't care much about efficiency, as long as total power draw is less than 65W; but I also don't want to have heatsinks, unless absolutely necessary (because this adds cost).
I do care about cost and minimum components possible (well, cost is the main consideration; if there is a solution with more components but overall cheaper, I'm all for it!)

Right now I have straight, dumb design - one buck, one boost and one inverting convertor; 4 LDOs (3 positive, one negative); supply for -0.04V/1mA is just a resistor divider from shunt reference. Simulated this thing successfully in LTSpice, used cheapest components that fit specs.

But, the whole design is ... ugly. For example, to get 0.2% for load regulation on +43V rail, I beefed up output capacitor to 1200uF (!). (It's dumb, but it works). I think that this could be done simpler and more elegant. I don't know, may be some existing 4 or 5-output chip, or something. Or SEPIC with some off-the shelf transformer. I'm not a PS designer at all, so may be someone can give me a hint?

Thanks in advance!

 

[KlausST]

Hi,

add some Cs or LC to filter the 19V. Add bulk capacitor.

+43V: Step up / boost converter. Instead of adding output capacitors you may speed up regulation loop. At first i´d add a capacitor in parallel to the upper resistor of the feedback voltage divider.
Next you may add a active feedback as P-I regulation loop. Further you may add a load current measurement and add the information to the feedback path.
All the circuits/values must be well chosen to avoid oscillation.

+36V: linear regualtor from +43V, Also possible: voltage reference and opamp. Maybe added a current boost transistor.

+5V: step down / buck from 19V. try to find a high quality regulator.

next i´d use a capacitive voltage inverter (like the old 7660) to generate-5V out of +5V. Try to find one that can supply >50mA for the -1.25V

-0.04V: same reference as above and an additional opamp. Powered from -5V

-1.25V: Linear regualtor form -5V; or use the reference above and an additional OPAMP with current boost transistor. P_tot = about 0.2W..no problem.


Klaus

 

[kanonka]

Well, that's exactly what I did, but it's just too many regulators and components. May be there is simpler design?