[sci.electronics] switching problem

jime@tekig3.LEN.TEK.COM (James W. Edwards) (06/16/89)

I have a problem for you electronics wizards.  I would like to control
the DC power being supplied to two loads as shown in the following diagram:

  +--[Load 1]-------------[CP1]-------------+-------+
  |                                         |       |
  |                                         |       DC
  +--[Load 2]-------------[CP2]-------------+      POWER
  |                                                 |
  |                                                 |
  |                                                 |
  +-------------------------------------------------+
						    |
       					           GND

CP1/2 = Control Points 1/2

I would like to be able to turn on/off the power to either of
the loads through CP1/CP2.  CP1/CP2 are simply whatever electrical
component(s) that you feel would be necessary to achieve this objective.
The switching action of CP1/2 must be controllable through a digital
signal.  CP1/2 must each be able to switch 15A @ 12/24 V to their loads.
The switching action is actually more complicated than just switching
on/off:  In the off position, the associated load must still
recieve some power (say 10%), and in the on position it will 
recieve full power.  Furthermore, when switching from off to on or
from on to off, the rise or fall in current/voltage to a load must 
be controlled (for example, it could rise/fall exponentially to the
final voltage/current).  The intended circuit must be very
reliable and operate in a harsh environment (-70F to 150F and
high, non-condensing humidity).  If it matters, the power source
is regulated, but probably fairly noisy due to the surrounding
environment.  Finally, it is very desirable that the most 
likely failure mode will result in both loads recieving full 
power (i.e. CP1/2 switched on).  Thanks in advance!

Jim Edwards