I have corrected the SIMSC schematic in

http://groups.yahoo.com/group/beam/files/simSC1.gif

and changed some component values to lower the voltage drop across
the current sensing resistor to give a sharper cutoff at Voc. This is
primarily useful for battery charging. The original simSC components
(10 ohm shunt and 200K series resistor)can also be used to give a
softer cutoff at Voc.

The 78L12 provides the regulated volatge required at the input of the
Solar Cell simulator. It limits the voltage to 12V and the current to
about 100ma. A 15V-24V unregulated voltage is used as the input to
the 78L12. Any other regulated 9V-12V source can be used.

The LM324 is a quad opamp of which only two sections are used. A
LM358 dual opamp (8 pin) can also be used.

One opamp is used as a current source with the 0-60mV Isc reference
voltage as one input and adjusts the opamp output current ("+ out")
until the voltage drop across the 1 ohm resistor (shunt) is equal to
the reference input.

The second opamp uses a 0-6V Voc reference as one input and monitors
the "+ out" voltage on the second input. When the "+ out" voltage is
equal to the reference, the second opamp output applies a positive
voltage to the current source inverting input causing the current
source output to drop while maintaining the "+ out" equal to the Voc
reference voltage.

The net result is a constant charging current up to Voc-Vshunt and
the a rapid tapering off as the "+ out" voltage is limited to Voc.

wilf

--- In beam@yahoogroups.com, "wilf_nv" <wrigter@d...> wrote:
>
>
> Have a look at the Simulated Solar Cell (SIMSC) circuit in the file
> section. Also good for charging small NiCd batteries.
>
> wilf