Who is interested to develop a "charge down pump"?

Look at the design:
48V charge C1-C4 with 12Vdc each, consider low dc leakage caps.

S1 = A, S2 = B, S3 = a, 500µs, S3 = b, 500µs.
S1 = B, S2 = C, S3 = a, 500µs, S3 = b, 500µs.
S1 = C, S2 = D, S3 = a, 500µs, S3 = b, 500µs.
S1 = D, S2 = E, S3 = a, 500µs, S3 = b, 500µs.
cycle repeats.

What would be the best electronic switching at S1, S2 and S3?

How can we implement a PIC to control the switchings, based on
productivity of voltage transfer and 500µs adjustments?

What is the capacitive transfer loss? 

This is a step down capacitive switching unit with a flying capacitor.
Low power loss if we can get a low electronic switching resistance.

    +48Vdc
      o
      |             S1   a  S3   b   
      o-------o A   <----o   ^   o----------o-----> +12Vdc
      |                      |              |
     ---                    ---             |
C1   ---                    --- C5         --- C6
      |             S2       |             ---
      o-------o B   <----o   v   o--.       |
      |                     S3      |       |
     ---                           Gnd     Gnd
C2   ---                    
      |
      o-------o C
      |
     ---
C3   ---
      |
      o-------o D
      |
     ---
C4   ---
      |
      o-------o E
      |
     Gnd