Hi tried to post a reply as in ronsimpson's post, but had some difficulty doing so. Here is my thoughts.
What I am sayings is if you want the power supply to supply a continuous 3A then the transformer needs to be rated at 3/.566. This figure came from two sources, 1 Triad Transformer Co. and 2 from a transformer manufacture friend of mine. As you know the peak voltage of the transformer is 1.414 times the rms. The filter capacitor will charge to near this value. Since the average load curreuld be 3A then the peak charge current is close the double that or 3/.566 so if the transformer is not rated at near 6A rms load current the winding supplying the current will heat up.
I am on a short vacation so I am away from home and don't have my notes with me so when I say the average value of a brute force filter capacitor is 3000uf per amp. I know there is a formula that has ripple voltage frequency and load current to calculate the exact value of capacitor required. I have built a great number of linear power supplies and have been real successful with the 3000uF/amp. I once built a high current linear power supply and the transformer was getting hot, so a did some research on max current.
Yes, I have a laptop computer I take with me. In the way of history, I have been in electronics about 60 years. I started out in about the 6th grade before transistors, circuit boards and a lot of other things. I made a living in repair, engineering and project management. I will have my 72nd birthday in about 6 months.Thanks you so much, really. You even replied when you are on a vacation. =)
Remind me of the minimum and maximum voltage drop accross the regulator. I reread all the threads and I had some difficulty determining those two voltages.
Yes, I have a laptop computer I take with me. In the way of history, I have been in electronics about 60 years. I started out in about the 6th grade before transistors, circuit boards and a lot of other things. I made a living in repair, engineering and project management. I will have my 72nd birthday in about 6 months.
Yes, I have a laptop computer I take with me. In the way of history, I have been in electronics about 60 years. I started out in about the 6th grade before transistors, circuit boards and a lot of other things. I made a living in repair, engineering and project management. I will have my 72nd birthday in about 6 months.
If I were doing this, I'd ditch Q2and Q4, keep in R2 and R5 for current balancing, and put in a classical over-current limiting circuit using a resistor straight after the rectifier to short out R2 in the event of over-current, possibly with some hysteresis built in - that way you don't have to deal with current balancing to use the 317's own protection, and you know the transformer and rectifier are protected. I'd put a fuse in too. It's a more primitive circuit than what you have, but is tried, tested and robust.
Excuse my ignorance but what is D5 for?
Is R3 a dummy load? Only it seems rather small for a bleeder resistor.
You could implement a "soft start" circuit where the current is drawn through a resistor for the first second, or few milliseconds, whatever, then the resistor is shorted out for normal operation. It's easy to do using a relay, though a low Rds(on) mosfet would do the same job - I'm not too familiar with mosfets though.
Ok here's a diagram (based on your first one) to illustrate what I meant in the first place, with the soft start added in. The over-current protection will only limit the output to the 317's lowest voltage which is about 1.2volts? but that should be adequate for most things most of the time - any more severe conditions and the 317's own protection will cut in anyway. I'll leave it to you to calculate R91 and R92.
If you had 2 sets of contacts on the relay, the other set could ensure the output from the circuit is connected only when the surge current is finished. I'm thinking you could possibly build this into your over-current protection too - but you would need a latch/reset mechanism so it starts getting complicated again.
Am I correct in thinking that the relay you are talking about is a mechanical relay that *clicks* whenever turned on? Is RLA the energizer coil of the relay?
If that is so, wouldn't that short the rectifier?
Also, isn't the rectifier 0V the same as ground (in the picture)?
If I put R92 there, wouldn't it cause voltage fluctuations (which is what I'm trying to avoid in the first place).
Can you please tell me what is the purpose of the Q91 and R92? Sorry if I'm slow, I just can't seem to get it.
wakoko79;1054865I said:also found a somewhat useful webpage: http://chemelec.com/Projects/Diodes-in-Parallel.htm
I think it's similar to what you are suggesting, albeit minus the relays.
You seem to reference the old circuit, I'll update the first post so that there wouldn't be mix ups. =)
The 1N4007's are to small for your application anyway. The surge won't be as high as the simulation because the transformer can't supply it. But use something like this anyway.
https://www.electro-tech-online.com/custompdfs/2012/04/GBPC1510.pdf
All that said, the bridge rectifiers ronv suggests or similarly rated diodes would make the whole problem irrelevant anyway. Wish I'd thought of that...
Given that you want to be able to supply 6A with this supply, you should probably be looking for diodes capable of handling more than that though. Use a fuse - cheaper to replace than rectifiers!
Out of curiosity, it would be interesting to know what the real world surge current actually is for this circuit.
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