How much of a variance is allowable in the rails of my SMPS psu? I have just finished my prototype (on a solderless breadboard) but I am not sure if it is ok or not. Input is 12V (from a unregulated DC power supply) and my output are +31V, -28V (should be +/- 31V)with no load at all¡K however even with a small load (such as a 1000ohm resistor) the rails go to 22.5 and 22.7 is this ok? I am not concerned with the voltage drop as my input supply is really weak and it is dropping itself, I am only concerned with the difference in the rails. None of the FET¡¦s are getting hot at all, and none of the diodes are hot at all.
I will be using this PSU for a Tripath based AMP1 Module (http://www.41hz.com/) , should it be ok?
The whole thing is running at 45,000Hz and the transformer is a hand wound Toroidal FT-140-77, 4+4 turns on the primary (bifiller), and 11+11 turns on the secondary (bifiller).
P.S.
I have attached my schematic.
I will be using this PSU for a Tripath based AMP1 Module (http://www.41hz.com/) , should it be ok?
The whole thing is running at 45,000Hz and the transformer is a hand wound Toroidal FT-140-77, 4+4 turns on the primary (bifiller), and 11+11 turns on the secondary (bifiller).
P.S.
I have attached my schematic.
Attachments
The output voltage is proportional to the input voltage. The difference between the outputs at no load should not be of concern. However, in order to determine if things are ok, you need an input supply with a reasonable current capability. 22 volts with a 1k load is not very meaningful. It just means your input supply is too weak.
I have a old computer PSU here I am now using as the power source, it is not the best PSU but it is rated for +12V @ 13A, now the problem remains that the voltage drops even with a 1000ohm load... playing around with the circuit some i see removing the output inductor stops this problem (of course there is a larger ripple then though). What is going on? My output inductor is a factory made toroid type 47.0 uH, 3.6 IDC, 0.055 OHM (different than my schematic shows).
Fish,
Remember the AT/ATX PSUs sense the +5V line more heavily than the +12V line, and when the +5V line is unloaded, the +12V output may dip to 9-10V. Try loading the +5V output to get a little more stiff +12V line to feed your new SMPS with. Also, if you have a battery you could stick in between the AT/ATX PSU and your SMPS, this will go a long way in stiffening your +12V supply. Just a thought.
As for the output imbalance, how are you sensing? Between +31V and output ground? Or from +31V to -31V? This topic (of asymmetrical output sensing) came up in another thread, and this may be a contributing factor. What output restifiers are you using? Double-Anode/Cathode diodes? or four individual diodes? It has been my experience that the forward voltage drop on the negative double diode is a bit higner than the positive diode pair.
Here's another idea:
Your AT/ATX PSU is switching at ~36kHz. What frequency do you have your SMPS Switching at? What is the controller? SG3525? TL494? Other? Perhaps the interaction of the two switching frequencies could be a cause. I'm really fishing here now, but these are all worth checking out.
Remember the AT/ATX PSUs sense the +5V line more heavily than the +12V line, and when the +5V line is unloaded, the +12V output may dip to 9-10V. Try loading the +5V output to get a little more stiff +12V line to feed your new SMPS with. Also, if you have a battery you could stick in between the AT/ATX PSU and your SMPS, this will go a long way in stiffening your +12V supply. Just a thought.
As for the output imbalance, how are you sensing? Between +31V and output ground? Or from +31V to -31V? This topic (of asymmetrical output sensing) came up in another thread, and this may be a contributing factor. What output restifiers are you using? Double-Anode/Cathode diodes? or four individual diodes? It has been my experience that the forward voltage drop on the negative double diode is a bit higner than the positive diode pair.
Here's another idea:
Your AT/ATX PSU is switching at ~36kHz. What frequency do you have your SMPS Switching at? What is the controller? SG3525? TL494? Other? Perhaps the interaction of the two switching frequencies could be a cause. I'm really fishing here now, but these are all worth checking out.N-Channel said:
I am using 4 IR Ultrafast Diodes (MUR1620CTPbF) they are of the dual anode type... I am measuring the voltage as +31/GND and -31/GND the controller is a SG3525... I will put a dummy load on the +5V and see if that helps.
I have a 500W linear 12.6V power supply buy it is at my parents house and I wont be around there for another week, so I hope this ATX supply will work till then.
Your ATX should work fine. As Eva has stated in another thread, the full 20+A should be available from the 12V output because it shares the same winding as the +/-5V winding.
Is your '3525 on the primary or secondary side? I ask this because from what you wrote, you must be using both the (+) and (-) inputs of the '3525's error amp to sense the output rails, which can only be done if the controller is located on the secondary side.
Is your '3525 on the primary or secondary side? I ask this because from what you wrote, you must be using both the (+) and (-) inputs of the '3525's error amp to sense the output rails, which can only be done if the controller is located on the secondary side.
Fish,
Also noticed something else: In an old Unitrode App note on synchronizing the '3525 to another '3525 (though not the subject here, I felt it was worth mentioning), I read where Unitrode (and possibly all the '3525 manufacturers) recommends grounding any unused SYNC pins, to prevent noise pickup. I will modify any existing designs I can to do this, but for future '3525-based designs, I will incorporate this into the design.
Just a thought.
Steve
Also noticed something else: In an old Unitrode App note on synchronizing the '3525 to another '3525 (though not the subject here, I felt it was worth mentioning), I read where Unitrode (and possibly all the '3525 manufacturers) recommends grounding any unused SYNC pins, to prevent noise pickup. I will modify any existing designs I can to do this, but for future '3525-based designs, I will incorporate this into the design.
Just a thought.
Steve
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