audio SMPS startup

[subwo1]

Thanks for bringing up the idea of the small flyback converter. I have made a small very low power one for powering the control circuit which is very quiet in terms of interference. Since efficiency is not usually critical for such low power, slew rates can be very low.

[Pierre]

There is another possibility, but only for AC input ones.
I am only throwing the idea here, perhaps someone can get something useful from it:

If control circuit in the primary is allowed and there are no DC operation requirements (as stated by N-Channel), you can feed the control circuit by a "transformerless power supply" (basically a 220-470nF high voltage capacitor with a resistor in series, rectified by a diode and a zener.

Something like this:

http://www.geocities.com/tjacodesign/supply/supply.html

It is ok and space/cost economical for up to around 30-50mA. For example, in my circuit, that consumes around 45mA, you would need something like 680nF (that starts to be a bit large on the other hand)...

I have successfully used one of these to power the relay of a slow-start controller for my big toroids, which short-circuits a big NTC that limits inrush current. It provides around 40mA with a 680nF X2 cap.

Hope this helps.

[N-Channel]

Please don't let my comments discourage or dissuade any of us from trying any of the ideas presented here.

Referring to my previous mention of clocking the "small fly-back" housekeeping (hk) supply to the main switcher, this is possible for many setups. For example, the hk PWM could be a UC3842, and the main could be any of the garden-variety of double-ended PWMs. Most, like the SG3525, MC33025, UC1846, and TL494 have notes on multi-unit synchronization, and with a little experimenting, a clean clock signal can be extracted from the hk PWM to clock the main PWM.

Not like most ATX switchers, which have a quasi-resonant control ckt for the stdby supply and a 36kHz fixed-frequency for the TL494 PWM. I wonder what the beat frequencies would be, if any? Hmmm.......

[MOER]

Dear N-Channel,

yes it is possible to operate from 120-230 with NO selector.

Our houskeeping supply does this and automatically switches the main PSU (either SMPS or linear) to suit the incoming mains voltage

[harp mg]

what about the circuit. shematics. pcb and transformer info. dont u wanna help any other person to have this smps. specialyy me!