Any Suggestions On Input Soft Start For A Linear Power Supply.

[KeepItSimpleStupid]

Anyway, my "soft-start" circuit did require an independent supply. I did a network of optocouplers and zener diodes that basically gave me a signal that all of the supplies (4) were up to about 2/3 their value. When they reached the 2/3 mark, a flame-proof resistor in the AC line was shorted out and the audio was unmuted (actually ramped up exponentially) with another optocoupler and the speakers connected. The "timing" was the RC time constant of the power supply and the approximate on value in the opto circuit set by a zenier diodes and a resistor.

Since there is no set-timing or no certain off-time the flame proof resistor ends up being the fuse. The added benefit is that each (2 x +-50) supply is fused, so if a fuse pops, the resistor will pop too and the amp never operates on one supply.

 

[ronv]

See if this looks like yours and mark it up with the right diodes - Or does you wall wort put out DC?

 

[Brevor]

It sounds like you have a wall wort, bridge, 3300uF and a linear regulator, if that is the case I'm with the group that says you don't need a soft start. If it makes you feel better put a 10Ω PTC in there. There are millions of power supplies just like yours all over the world running at this moment, very few have soft starts.

 

[Honduras]

Perhaps you should ask for a refund?



So almost all electronic equipment prove it's not relevant - but you still imagine it is?.



Perhaps you could mention what this 'experience' is and what 'research' has shown?, certainly any facts disagree with you.

Thus is getting ugly. Let's just drop the conversation.

 

[Honduras]

See if this looks like yours and mark it up with the right diodes - Or does you wall wort put out DC?

That is exactly it. The wall wart puts out AC. I bought it specifically for a test between a wall wart with an AC output and one it with DC output. Both are supposed to produce 12 volts at 1 amp.

As to diodes, the Bridge is a W02M. The protection diodes are 1N4007s.

 

[Honduras]

It sounds like you have a wall wort, bridge, 3300uF and a linear regulator, if that is the case I'm with the group that says you don't need a soft start. If it makes you feel better put a 10Ω PTC in there. There are millions of power supplies just like yours all over the world running at this moment, very few have soft starts.

I'm paranoid. I wear a hard hat whenever outdoors in case of a meteor strike.

 

[Honduras]

Honduras:

Note the option: "Upload a file" at the bottom right of the text box. It's NEXT to "Post Reply" "More Options" allows you to preview, for instance.

TYVM

 

[ronv]

Maybe some bad news.
If it is a 12 volt AC transformer you should have 16.8 volts AC out . (1.41 X 12) and that should be at load.
If it is rated at 1 amp and you want 1 amp out at 12 volts it may get a bit to hot. With a full wave bridge you need to de-rate it.
http://www.hammondmfg.com/pdf/5c007.pdf
Your kind of on the edge trying to get 12 volts out. With 3300 Ufd. the ripple will go as low as maybe 13.4 volts because of the diode drops and the voltage needed by the 317 to regulate. You can help this with better diodes and/or more capacitance.
So if you are looking for 12 volts at about a half amp you are probably ok if you can recheck the transformer voltage.
Whatca think?

 

[KeepItSimpleStupid]

There ARE XENFORO bbcodes (Bulletin Board Codes) **broken link removed** that can be used to help format text.

Popular ones are the QUOTE tag and the CODE tag.

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[QUOTE=the OP]Hello[/QUOTE]

will produce:

Hello

I used "the OP" to mean the Original Poster.

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x=5
print x

I used a tag that turns off the bbcode processing to show the example.

 

[Honduras]

Maybe some bad news.
If it is a 12 volt AC transformer you should have 16.8 volts AC out . (1.41 X 12) and that should be at load.
If it is rated at 1 amp and you want 1 amp out at 12 volts it may get a bit to hot. With a full wave bridge you need to de-rate it.
http://www.hammondmfg.com/pdf/5c007.pdf
Your kind of on the edge trying to get 12 volts out. With 3300 Ufd. the ripple will go as low as maybe 13.4 volts because of the diode drops and the voltage needed by the 317 to regulate. You can help this with better diodes and/or more capacitance.
So if you are looking for 12 volts at about a half amp you are probably ok if you can recheck the transformer voltage.
Whatca think?

I checked it and it is about 16.8 VAC. I can add more capacitance.

Hmmm. 13.4 volts in. Maybe I should set the power supply for 9 volts out.

 

[ronv]

If I was going to worry, I'd worry about keeping the regulator cool, even though it protects itself from catastrophic damage, by adding a heatsink like this:
https://www.aavid.com/products/standard/504222b00000g
The bridge might pop if the output is shorted, so I get the next size up.
https://www.mouser.com/ds/2/115/ds21226-14120.pdf
The inrush to charge your cap is 20 amps for only 1 cycle so even the little bridge is ok for that at 50 amps, so I wouldn't worry about the inrush limiter.

 

[Honduras]

If I was going to worry, I'd worry about keeping the regulator cool, even though it protects itself from catastrophic damage, by adding a heatsink like this:
https://www.aavid.com/products/standard/504222b00000g
The bridge might pop if the output is shorted, so I get the next size up.
https://www.mouser.com/ds/2/115/ds21226-14120.pdf
The inrush to charge your cap is 20 amps for only 1 cycle so even the little bridge is ok for that at 50 amps, so I wouldn't worry about the inrush limiter.

I bought a pound of heat sinks, too. And I have upgraded to The NTE 53001 rectifier.

Well, the bridge is not the real problem. I'm more concerned about the LM317T. As I understand it, repeated 50 amp spikes degrade the LMs capabilities in a short time.

I want my stuff to last longer than I do. It seems that most electronics hobbyists still have the IC = Kleenex mindset.

 

[audioguru]

See if this looks like yours?

Your schematic has an LM317 but it is using the 240 ohm resistor shown in the datasheet that is used for the more expensive LM117. The LM317 has a maximum minimum load current of 10mA so the resistor should be less than 1.25V/10mA= 125 ohms.
When this resistor value is too high then the output voltage of the regulator rises when it does not have any other load.

 

[Honduras]

Your schematic has an LM317 but it is using the 240 ohm resistor shown in the datasheet that is used for the more expensive LM117. The LM317 has a maximum minimum load current of 10mA so the resistor should be less than 1.25V/10mA= 125 ohms.
When this resistor value is too high then the output voltage of the regulator rises when it does not have any other load.

According to the data sheet, the LM317 can use anything between 100 an 1000 ohms.

This is getting ugly. Let's just agree to drop the comversation,

 

[audioguru]

According to the data sheet, the LM317 can use anything between 100 an 1000 ohms.
This is getting ugly. Let's just agree to drop the comversation,

Nothing is ugly. You need to understand that every circuit in the datasheet shows the more expensive LM117 with a 240 ohm resistor because its maximum minimum load current is 5mA which is half the amount for the LM317.
The datasheet says it is because all the operating current for the IC goes to the output so that the ADJ pin has very low current, and it says the output voltage will rise when there is not enough output current.
When there is no actual load then the 120 ohm resistor for the LM317 has a current of 1.25V/120 ohms= 10.4mA so the minimum required load current is established.

If you use an LM317 to be the power supply for a new Cmos circuit you made and the total load current on the LM317 is less than 10mA (Cmos circuits have a very low supply current) then the output voltage will rise and blow up your Cmos circuit.

But you might be lucky to get an LM317 that performs like an LM117 because some are better than others.

 

[ronv]

I always wondered why the 317 data sheets often use 240 ohms, so I looked a little more. It is dependent on the Vin - Vout differential. So with only 16 volts he should be OK with the 240 ohm and 5 ma.

The 50 amps does not pass thru the 317, only the bridge. Don't worry, be happy.

 

[audioguru]

I always wondered why the 317 data sheets often use 240 ohms, so I looked a little more. It is dependent on the Vin - Vout differential. So with only 16 volts he should be OK with the 240 ohm and 5 ma.

The datasheets use 240 ohms for the more expensive LM117, not for the LM317. They don't even show an LM317.
The graphs on a datasheet are for a "typical" device that you cannot buy. If you get one with a higher maximum minimum load current then IT MIGHT NOT WORK.
Don't you want ALL your circuits to work properly or only some of them? What if the manufacturer had a poor but passable yield so that all of them have the maximum minimum load current? Then ALL of your circuits will not work.

 

[Cicero]

It sounds like you have a wall wort, bridge, 3300uF and a linear regulator, if that is the case I'm with the group that says you don't need a soft start. If it makes you feel better put a 10Ω PTC in there. There are millions of power supplies just like yours all over the world running at this moment, very few have soft starts.

Out of curiosity, I see quite a few people advocating for a PTC instead of an NTC. Isn't an NTC more suited here for inrush?

As I understand it PTC's are more suited to inrush limiting for high wattage devices (few hundred watts), high temperature applications, and they also protect against short circuit conditions. But generally for this kind of low power ICL, the NTC is the general accepted method?

 

[Nigel Goodwin]

The 50 amps does not pass thru the 317, only the bridge. Don't worry, be happy.

It doesn't pass through the bridge either, as it doesn't exist

 

[KeepItSimpleStupid]

Cicero:

I thin the Surge Stopper Devices https://www.google.com/url?sa=t&rct...ZOX1el2UNCPMk2A&bvm=bv.87269000,d.cWc&cad=rja from Linear technology is more appropriate for these low power devices.

PTC's and even NTC's are very finicky to work with.
In a Fire Alarm panel I purchased each Class two output was protected with a PTC. You had a choice of PTC's or fuses.
Because of inrush currents some strobes would not operate., The manufacturer fixed the inrush problem in some devices, I had some of each. Class II supplies are around 100 W.

PTC's for motors work nicely because the overload characteristics are well known.

NTC;s were used in tube televisions. PTC's were used to run the degaussing coils.

In-rush current limiting and surge suppression are not quite the same and I had to use both. A Y-Delta motor starter is sort of a soft start.