Spehro Pefhany wrote:
wrote:
(snip)

If you have several different
supply voltages feeding different loads, and some of the
loads are inductive, you could connect pin 10 to the most
positive voltage, so that none of the diodes can become
forward biased by any of the normal load swings, but can
still provide a path for the inductive current.

Note that there is a possible problem with this. If the inductive load
is switched and the stored energy from the inductance of the relay
coil goes into the power supply for the LEDs (suppose no LEDs are
turned on), then there may be nowhere for the energy to go.

Good point. I guess I didn't consider that the most
positive supply would be driving LEDs.

With a lot of switching (or with a single switching but very light
capacitance on the LED power supply) the voltage could exceed the
voltage rating of the transistors.

If it is a possibility, a relatively large capacitor plus a bleed
resitor if there is no load, or a zener, will provide a simple
solution.

Or you could use external diodes across the inductive loads,
and not connect pin 10 to anything.