At 08:58 AM 20/04/2011, you wrote:
>On Wed, Apr 20, 2011 at 8:31 PM, Michael Watterson <mike@radioway.org> wro=
te:
> > On 20/04/2011 02:04, V G wrote:
> >> I made a constant current source (for battery drain testing, charging,
> >> pretty much any application).
> >
> > Actually I'd make a constant Power sink to test any batteries that are
> > going to be used on any switching regulator gadget.
> >
> > In such a case the current increases as battery voltage falls.
>
>Any simple real circuit to share to implement a constant power sink?
>Thanks. For SPICE, it is rather easy. :-)

One easy way is to control a constant current sink with a micro
and calculate the required current from the battery voltage
and desired output power (inner control loop/outer control loop).

An analog scheme would involve a multiplier or similar function..
conceptually as below, for example:-




                +--------------------------------------- +-------+
                |                               Battery  |       |
                |                                        -       |
             +--|----------------------------------- +  ---      |
             |  |                                    |   |       |
             |  |     Multiplier                     |           |
             |  |  .-------------.                   |  GND      |
             |  |  |             |                   |           |=20
V->I converter
             |  +--| X           |                   |      .--------.
             |     |             |              |\|  |      |    I+  |
             |     |       X*Y/10| ----------- -|-\  |      |        |
             |     |             |              |  >-+------|Vin     |
             + ----| Y           |        +--- -|+/         |1V =3D 1A |
                   |             |        |     |/|         |        |
                   '-------------'        |                 '--------'
                                          |                      |
                               Vref       |                      |
                                +         |                      |
                                |         |
                                |         |                      GND
                               .-.        |
                               | |<-- --- +
                               | |
                               '-'  Power set (1V =3D 10W)
                                |
                                |
                               =3D=3D=3D
                               GND




>Best regards,

Spehro Pefhany --"it's the network..."            "The Journey is the rewar=
d"
speff@interlog.com             Info for manufacturers: http://www.trexon.co=
m
Embedded software/hardware/analog  Info for designers:  http://www.speff.co=
m



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