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  1. Two transistors gives double the area used to transfer the heat.
  2. Great, we are on to something! If R10 in liquibytes schematic is shorted, this would happen. Can you measure it's resistance? R10 is the 1k resistor which sets the 5mA current for the reference zener.
  3. Whats the voltage drop over your 0.46 ohm sense resistor? It is past bedtime here, can think more tomorrow. But I think it could be current limit. When you remove the voltage trim pot you get really high gain, which means that the input voltage at the rightmost op amp can be low (caused by current limit) and still provide a high output voltage. If the 100k current limit trimpot is connected wrong it will always be 100k. This will mess up the current limit op amp. So I hope the solution is to put a bridge/jumper/short between pin 1 and 2 on the 100k trim pot.
  4. Hi! I have bought the same board from the same man :-) but not built it yet. Ive done lots of simulations though. I guess this is unloaded? Repairman told me about the 100k trimpot, you need to short pin 1-2 there, did you do that?
  5. Oh. Ok. I thought your fix was for the peak that occurs when you are in current limit mode and turn the supply off (since the current limit function collapses faster than the output is pulled down. Then it's ok. Turn on transients shouldn't be as tricky. 0.2 volt on the base of a 2n4401 shouldn't open it, so it should be ok.
  6. I tried simulating this. Works beautifully. I think I had to switch the inputs U1 though. I have the simulation at work. But in this design, Q1 is pointless though. So I will either remove it or modify the negative supply to work with Q1 only. I think I'll go with the latter. Don't need a good neg supply since it's only purpose is to die at shutoff :-) I love getting rid of the neg supply in current limiting mode though. Otherwise I would feel the need to improve it. I will also move most ground connections to go after the current sense resistor. As it is now the 6mA going from the reference zener to ground (and also other small currents) goes through the current sense resistor which I don't like. Thanks for the idea! :-) Do you still have this pic audioguru? I'd love to see it and the link doesn't work for me.
  7. I could add that when I was looking for a suitable amplifier I didn't know electronics-lab even existed. So I just browsed for the most suitable class d chip and went on from there :-) It was when I gave up on the 14V PSU idea because of a stronger need for a lab PSU that I found this design and this place!
  8. Yeah but it's a lot cheaper to use a regulator rather than quality caps to get rid of the 100 hz ripple :-) Plus I could make sure it runs on 14 V regardless of load (volume, usb charger etc) and temperature! The two amplifiers I had in mind were 45W and 50W into two channels, with losses and other functionality I estimated 6A.
  9. Hi Liquibyte, I have bought two of your PCBs from repairman2be (rev. 8.), awaiting them any day now. I have studied the schematic pretty thoroughly and tried to read up on the threads. Very interesting, and good to have something educating to do with my time :-). So far I have one question that I can't find a comment on in the forums. First, let me introduce myself. I'm a Swedish 30 year old mmWave/μWave/RF engineer (read: allergic to noise) and I just had a second son so I had to find something to do all the nights I stay up taking care of him. Designing a PSU seems like a good choice! It started with me realizing that I today financially can handle some of the ideas I had when I was 20, now time is more of an issue instead. But hey, it doesn't matter if it takes time to reach the finish line. I always wanted to build a boombox. I thought a good place to start was to design a PSU (to not waste battery when a socket is available) and a relay-circuit. I read up a lot on audio PSUs and actually designed a linear 10-18V, 10A supply, and hand drew the breadboard and everything. When I saw the end-price I reconsidered. This PSU is kinda useless for anything but the amplifer, it's better to have a 0-30V supply I can use for lots of things. Especially considering I have no use for or place to store a boombox. The reason I'm saying this is that I might be tainted by audiophiles in my way of thinking :-). That I'm tainted by my RF-world at work I don't see as a problem, RF is probably what I'm going to use it for. Then I found this design and got interested. But I still wanted it to be able to run the amplifier I had in mind for the boombox, which is something like 14V/6A. I considered paralleling two of these or use a LM723 regulator. I ended up with the idea of two 0-15V LM723 PSUs which I can parallel connect for 0-15V/0-10A or series connect for 0-30V/0-5A. I was pretty happy with this idea and started designing. However, I couldn't get the current limit to work as nicely as I desired for a bench PSU. Then I came back to this design, and here I am now. I'll start with building your 3A design pretty much identical to yours. To be able to do some measurements and see how it behaves before I try to improve it :-). After that I will start designing my own board. I'll probably stick to 3A or 5A for a while, if I need an amplifier PSU I'll design it for that purpose. My ideas for improvements is to reduce the voltage drop a little, have a look at the negative supply (it hurts my eyes that it doesn't load both lines symmetrically). If I reduce the voltage drop and feel that I can't find an optimal transformer I might reduce the output voltage a little. I feel 30VAC is a little too high and 24VAC apparently is not enough so there is some unused power wasted there. We will see how it goes. For later I might also take up the idea of LT1236 as reference. We will see. First I believe I have some startup transients to deal with! So, now to my question: Your R9 (original R17), is 68 Ohm. The original design says 33 Ohm but you changed it to 68 Ohm. Why did you change that? Have you found some issues with stability if it is too small? The reason I'm asking is that if I lower the current sense resistor I might want to increase this. Maybe I'm doing this wrong. I calculate the original design to give a minimum current limit of 10mA (while it says 2mA in the description), and your gives 20 mA. Edit: I found the change, it was just to get the voltage divider to give the correct minimum voltage. However I'm still confused, but this can probably anyone answer. It should be simple. I don't get the formula for the current limit. If we have a minimum of 5mV at the non inverting U3 input, that should allow for a 5mV drop over the current sense resistor right? That's 10 mA... Not 2.. Edit2: LTSpice seem to agree with me... I might have more questions but I'll search and think a little more before I speak :-) Best Regards Björn Ps. Thanks for the pdf with QA and other useful info. Would have saved me some time if I read that before I started study the circuit. But imI might learn it better by figuring things out on my own.
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