Soft start circuit design and other psu issues

[hcpower]

Or this one, with a Schmitt trigger to provide the instant contact in the relay. The LED-diode is only for chassis mount or to show power-on, it's really not needed...
Delay is approx 200ms and the relay is activated dead on in nano-sec!
The 50ohm/50watt load-res is only an example I started with, and so far altered with two inrush current limiters in series connection.

 

[Mark Johnson]

You'd better measure the DC voltage between relay pins 2 and 5. When D2 is near the bottom end of its tolerance band, relay pin 2 voltage is about 22.8V and relay pin 5 voltage is (Vfwd_D4 + Vbe_Q3 + Vcesat_Q4 + Icoil*R7) which is about 0.60 + 0.62 + 0.15 + 0.52 = 1.89 volts. So the coil of the 24V relay sees 22.8 - 1.89 = 20.9 volts. Ouch.

 

[TonyTecson]

look at how GAS Ampzilla implemeted their soft start switch, no needless complications...

 

[hcpower]

You'd better measure the DC voltage between relay pins 2 and 5. When D2 is near the bottom end of its tolerance band, relay pin 2 voltage is about 22.8V and relay pin 5 voltage is (Vfwd_D4 + Vbe_Q3 + Vcesat_Q4 + Icoil*R7) which is about 0.60 + 0.62 + 0.15 + 0.52 = 1.89 volts. So the coil of the 24V relay sees 22.8 - 1.89 = 20.9 volts. Ouch.

Wow.. my sim says +10/-6.4v at pin 2/5....
It's a simple mobile version, haven't really got into better simulators yet, sorry

 

[steveguo]

pin1 = com
pin4 = NC
pin3 = NO

 

[DaveFred]

Hi AJT,
1. Ok ... got it... If I use a RT424024 TE Connectivity / Schrack | Mouser relay (1.44 kOhms 16.7 mA), I should be able to use 20mA rated leds🙂.

2. yes, the mains is 230 nominal, will use 630V rated.
3. I am not sure when you say LED but the D6 as per schema (1N5819) is https://www.fairchildsemi.com/datasheets/1N/1N5818.pdf , Which I dont think I will be able get hold of. 1N4007 is universal🙂.
4.Also could the zener be of 1-2w rated (as absolute min)?

what I am trying to do here is to use most commonly and locally available parts.

Hello Prasi,

Was there ever a final update on this soft start circuit?

 

[prasi]

Yes, i have been using it in some of my projects thanks to guidance from SGK.
i also sold a few here locally to diy guys.
regards
prasi

 

[DaveFred]

@prasi

Was the final version something you publicly shared, or was it personal use?

 

[prasi]

I dont think so, so here they are.
it was along time ago, so dont remember much abt project.