24v PSU with soft start

[David Gregory]

Drawing up a schematic for a power supply for an amplifier I'm designing, and just wanted someone to give the soft start components a once over for me. Basically this is just the reference circuit for a LM317 based PSU, but the reference circuit is 15v, not 24. I can't see it causing a problem but would R4, C2 and Q1 be OK to soft start this design at 24v?

Thanks

 

[Harald Kapp]

Hi David,
that looks perfectly o.k. The components mentioned are really not critical.
My suggestion is to use a 1N4148 or 1N914 for D2 instead of the bulky 1N4004. You don't need 400 V / 1 A here.
For D1 any 1N400x will work, whatever is available to you. It's good to have the 1A capability here.

 

[David Gregory]

Thanks Harald,

It looked OK to me, but being only an occasional builder when I have a need, it's good to get a more experienced person to give it a once over before committing it to copper.

Thanks

 

[Harald Kapp]

How do you know I'm more experienced?

Just kidding - I may well be. A bit

 

[David Gregory]

How do you know I'm more experienced?

Just kidding - I may well be. A bit

It wouldn't be too difficult to be more experienced than me

Whilst I've got your attention, I was thinking of adding a crowbar circuit to the output.. rough and ready, but enough to protect what comes after the PSU (audio amplifier).

I'm having trouble working out what value of resistor to have in series with the zener diode. I know it's not critical, but I'd like to be in the ballpark. I'm just planning to use what parts I have lying around the radio shack here, so the zener is a 27v one (close enough for my 24v PSU and as there's no sensitive digital components after it, should be close enough); The SCR is a SC07554 Similar to a BT151 (datasheet attached).

The circuit schematic is also attached.

I'm assuming the anti-spike cap is not critical and around 0.1uf ceramic would do?

Sorry for pestering you.

David

 

[Harald Kapp]

You GIF is almost comletely unreadable. Please attach a better image.

 

[David Gregory]

Sorry about that... it's just a generic crowbar diagram off the internet to highlight the resistor in question... wasn't really needed as there's only really one important resistor in a crowbar.

I've attached it again as a JPEG

Thanks for your help Harald.

 

[Harald Kapp]

This resistor should not be critical. The web page you got this image from tells you which value to use. Can you find it?

 

[David Gregory]

Thanks again,

That same image is plastered all over the website... I just pulled it from Google image for reference. I remember from years ago, someone taught me a formula for the resistor, but couldn't remember it. Something along the lines of r= (1-zener voltage/gate current), but when I tried that, the figure I got made no sense.

Appreciated.

David

 

[Harald Kapp]

My link tells you to use 100 Ω