Replacement IC needed

[Steve Harrison]

At 10:46 PM 2/18/99 -0500, Michael Tallent wrote:
>I am pretty sure there is no direct sub for this short lived Motorola
>part.  I would probably use a LM723 with necessary circuit changes and
>use the pass power transistor that is already in the circuit.  A 3
>terminal regulator is probably the simplest but you need to use the
>correct one based on the load current and voltage.

Actually, you can use an adjustable 3-terminal regulator to drive the
existing driver and output pass transistors. The downside is that there is
no way to get feedback into the 3-terminal device to control the voltage
under load. But it would be the simplest way to get the supply working
under some semblance of regulation again.

OTOH, there have been literally dozens of circuits published for the LM723
using "booster" transistors, and the device will also allow external
current limit sensing. With a three-terminal regulator, you would be
relying on the Hfe of the pass transistors remaining constant so that you
could use the internal, preset current limiting of the three-terminal
device. It wouldn't be much fun.

Whatever you use, I highly recommend that you use an oscilloscope when you
first fire up the repaired supply into a dummy load of some type to make
certain that nothing is oscillating.

73, Steve Ko0U/1

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