Power On Delay

[Quad]

An ac cycles counter based delay here -

http://www.chinaicmart.com/uploadfile/i ... 255697.gif

The circuit shows it is directly powered from the ac mains, but
you can adapt the general idea and drive it from the
6.3V heater winding to be safe.

[Geek]

Oh hey, I like that

The timing chart is based on 50Hz. For 60Hz, the timing increments will be in 4.25 seconds instead of 5.1

<spam>
If you want to go ultra simple, I have a delay board that could be adapted
</spam>

Cheers!

[kt88pppamp]

Instead of the MCU, I made up this 555 timer circuit to trigger the FET's gate circuit after about 30 seconds. I dicked around with that thing a lot in high school. It was of sorts my favorite component.



- The RC network going to the trigger makes the trigger high after a few milliseconds power is applied. The trigger needs to be low to begin the pulse.

- The RC network going to the threshold and discharge inputs makes the pulse last 30 seconds.

- The 74LS04 inverter inverts the output as the gate circuit of the FET has to be off for 30 seconds and the 555 timer output is high.

What do you all think about this circuit? I do have more experience in the solid state world and making a solid state relay in not that complicated.

[Quad]

You can save a chip by replacing the NOT gate with a simple
transistor.

[kt88pppamp]

Finally, I want to add a fuse to protect the B+ regulator from shorts. A short I heard will take out the regulator quickly but adding a pass resistor protects it. I have a 10 ohm pass resistor in there but to prevent that from overheating I want to add a fuse. What type of fuse should I use? I'd think it would have to be higher voltage than a standard 5x20 or something.

[kt88pppamp]

http://www.digikey.com/product-detail/e ... ND/1973283

For a second power supply revision on my newly completed KT88/KT90 PPP amps I want to include a 20 second B+ delay. The link above is to a part that I plan on using for the 550V B+ switching. The part will be placed after the choke. Do you think it will do the job or has anyone observed surges/anomalies that could fry such a device? The data says it is intended for industrial robots and can work with up to 1000 volts. I think they will be OK, just want to run it by you guys.

[Shannon Parks]

That part looks good to me. I think I might consider still putting a resistor in parallel with it - maybe 10K? Just to lessen surges and pops and things, but actual testing would determine if it was needed (or what value).

Shannon