Re: [CAD_CAM_EDM_DRO] Re: Power supply for Servos - Energy dump and such - UR...

turbulatordude wrote:

>I'm adding an LED for the main AC power and one to show the energy
>dump.
>
>for the dump, I will add a cap to the line so the LED will light,
>then fade. I think it might just flash too fast to see otherwise.
>
>

That's an excellent idea.

>There is an unused output of the comparitor, so the output of the
>comparator can be used when the mosfet is powered to indicate the
>dump without having to make allowancs for the LED.
>
>

I'm not sure I understand what you mean. Even if you're planning on
running the dump LED from the comparator, the power will come from the
+12V rail, so you'll still need to change the 6.8k resistor to allow
more current. Thinking about it, that's a wash anyway, because the
current limiting resistor would have to be 3.9k, 2W (assuming an 80V
supply, ~20mA LED) if the LED were run directly across R7. So just
change the 6.8k to a 1.5k 5W (a 45mA supply, for 2 LEDs @ 20mA + the
comparator), and make sure the zener is at least 1/2 W. (when the load
dump LED is off, 20mA would be going through the "active" LED, a small
amount will be used by the op-amp and associated circuitry, and the
zener will be sinking roughly 25mA at 12V = 300mW, 350 is closest and
500 gives a little safety margin). A lower voltage supply would need a
lower value resistor, but the same zener diode.

>Dave
>
>

- Steve