Hi all,
I’m designing an unregulated dual-rail supply to generate ±12 V from a single +9 V source (either battery or regulated DC PSU). The DC-DC stage is based on the LT1054. The topology follows LT1054 datasheet (dual-output voltage doubler/inverter).
Target load current is very low, about 5 mA per rail (10 mA worst-case including margin).
Questions:
1) Capacitor values
Given the light load, is it possible to reduce the 100 µF (input/output) and 10 µF (flying) capacitors from the reference design?
Modern options I am considering:
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Option 1: 100 µF aluminum-polymer, 10 µF aluminum-polymer (very low ESR)
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Option 2: 100 µF aluminum-polymer, 10 µF MLCC (noting MLCC bias-derating)
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Option 3: 100 µF aluminum electrolytic + 10 µF MLCC in parallel (for ESR balance), 3x 10 µF capacitors MLCC
Will the very low ESR (options 1 and 2) increase peak current stress on the rectifier diodes and LT1054 internal switches? Is this a real concern at ~5 mA load?
2) Diode selection
The reference design uses 1N4001 diodes. Since forward-drop wastes headroom in this application, would a Schottky diode be acceptable (or preferable)?
Given the low current, could the diode be scaled down (e.g., SMD 40–60 V, 0.5 A Schottky)? This would reduce losses and help post-regulation margin.
Any practical guidance or experience with reducing capacitor sizes and using modern low-ESR parts with the LT1054 would be greatly appreciated.
Thanks!
