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Old 4th April 2004, 10:07 AM   #11
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I would agree it's pretty common...can be seen in almost all PC PSUs...I supposse it quite cheap as well...
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Old 12th April 2004, 01:19 PM   #12
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yes I repeat palesha
But better post full schematic of power supply. We will like to see your layout of the PCB if you have. what ferrite core you have used toroid or EE and your observation & experience about calculating the winding turns. I also have trying on sg3525 but some problems with them so please put here your schematic and pcb layout with your experience
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Old 14th April 2004, 12:06 AM   #13
Grucho is offline Grucho  Croatia
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Hi.

I have builded smps similar to http://valveaudio.tripod.com/images/.../switcher1.JPG but u used sg3525 and 2+2 buz11 mosfet for swtching primary.
SG3525 was driving this 4 mosfets directly. (75Khz)

I used EE core etd49 , 4+4 primary and 11+11 sec.
I menaged to run 1 channel 100w amplifer (35+35volts) at full power, with two channels I have voltage drops . That because I have wounded only 11+11 on secondary . When I found some wires Ill try wounding 19+19 on secondary to get more power.

Mosfets remainde cool without load and warm when full loaded, core is always cold. Im using very small heatsinks for now.

Also I haved bug in pcb, I have connected praimary and secondary ground and got some kinda distortion + noise when playing audio. When I have separeted primary and secondary ground everything was OK.

Concurently I'm trying preamplifiers , I want to be able to bridge to channels so I must integrate inverting signal to one channel.

Now for testing purpose Im using two old 6800uF/50v capacitors, first time I was using 1000uF/200volts capacitors, and I think thats smart because if something is wrong secondary voltage can get 120+120 volts or more (especialy without load and no feedback to sg3525 error amplifer)

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Old 14th April 2004, 01:19 AM   #14
gmarsh is offline gmarsh  Canada
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Another "vote" for the SG3525 chip here. It can drive FETs directly, which is a good feature - the TL494 requires an gate driver.

Mind you, if you're driving a lot of FETs with big gate capacitances (for some sort of insane high power project or something) then you'll need an external gate drive anyway, and it doesn't really matter what you use.

Throwing another chip into the mix, we use a UC3846 chip at work for doing this kind of stuff - creating high B+ voltages from batteries. The SG3525 is voltage mode and perfectly fine (especially in open loop), but if you're using feedback and don't mind spending a few extra bucks for a current transformer then it's probably the best thing out there.

now a question; one thing I've noticed (and never really understood) is that most car audio amps lack inductors after their secondary side rectifiers, which goes completely against my training and experience building this type of power supply. Apart from cost reasons, what kind of benefits / caveats arise in doing this?
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Old 14th April 2004, 02:05 AM   #15
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Default inductor issue

Quote:
originally posted by gmarsh
now a question; one thing I've noticed (and never really understood) is that most car audio amps lack inductors after their secondary side rectifiers, which goes completely against my training and experience building this type of power supply. Apart from cost reasons, what kind of benefits / caveats arise in doing this?
Good question. Here's the good answer. The caveats are numerous. Without an inductor the input current is drawn in short pulses or bursts. This makes the input filtering much more difficult. A very large input cap is needed to supply the short bursts of current. Also, the output filter caps are stressed very severely without an inductor, and the output ripple and noise is high. The power transistor(s) doing the switching must sustain a very large rms current due to the large ac ripple current present. Likewise with the transformer windings, the rectifiers, and all wiring and pcb traces. The increased ac ripple current in the transformer results in greater losses due to skin effect, and greater core losses due to the discontinuous core flux. An inductor reduces all of these stresses and provides a quieter output. With an inductor, efficiency is much higher, particularly when the inductor is operated in the continuous conduction mode. As far as benefits go (inductorless), the only one that comes to mind is the cost of the inductor, although the headaches caused by not having one just aren't worth the small savings. The increased cost of the transformer, and input and output filter caps surpasses the pocket change saved by omitting the inductor. I would never omit the inductor. Like you, doing such goes against my experience and judgement as well.
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Old 27th October 2004, 07:16 PM   #16
RX5 is offline RX5  Philippines
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so i guess nobody ever likes TL494?? hehehe

wish i could have one diagram... id love to experiment on it.... im done with the SG3525....
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Old 28th October 2004, 03:14 PM   #17
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Quote:
Originally posted by gmarsh
Another "vote" for the SG3525 chip here. It can drive FETs directly, which is a good feature - the TL494 requires an gate driver.

Mind you, if you're driving a lot of FETs with big gate capacitances (for some sort of insane high power project or something) then you'll need an external gate drive anyway, and it doesn't really matter what you use.

Throwing another chip into the mix, we use a UC3846 chip at work for doing this kind of stuff - creating high B+ voltages from batteries. The SG3525 is voltage mode and perfectly fine (especially in open loop), but if you're using feedback and don't mind spending a few extra bucks for a current transformer then it's probably the best thing out there.

now a question; one thing I've noticed (and never really understood) is that most car audio amps lack inductors after their secondary side rectifiers, which goes completely against my training and experience building this type of power supply. Apart from cost reasons, what kind of benefits / caveats arise in doing this?
The only time you can get away with not using an output inductor is if your supply has no feedback and it runs at 50% duty cycle all the time. If you take a center tapped secondary with two out of phase square waves and rectify it, you get a fairly clean, constant DC signal even with only small amounts of filtering. Don't listen to anyone who tells you otherwise - they are probably blowing transistors, heating their output capacitors, and wondering why things are breaking.

I vote for the SG3525 as well for simple converters

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Old 28th October 2004, 06:32 PM   #18
djQUAN is offline djQUAN  Philippines
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I have a DIY car amp (200W RMS) using TL494. I don't think there is a lot of problems in using TL494 (I didn't have any, and they're rugged enough for me) than 3525 etc. SG3525's cost twice as much as a TL494. besides being cheap, I got several from old comp PSU's. I'm already in the way of making another car amp (~500W RMS) with the TL494 based PSU. SMPS is already done. just need the amp.
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Old 28th October 2004, 09:48 PM   #19
RX5 is offline RX5  Philippines
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gud day KAbayan

could you posibbly send info/diagrams on how to utilize that TL494? i have so many links/pdfs here but so little info to gather.... yup, TL494 is way much cheaper than SG3525.... by at least 1/3 the price of 3525...

- how to make it a simple oscillator(no feedback) (as simple as it gets)
-how to operate TL494 with "softstart"
- howto on Deadtime
- how to make it a regulating(needs feedback)


hope you could help me on this....

bro, pls mail me at: beamrx5 at yahoo dot com


tnx
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Old 29th October 2004, 07:24 AM   #20
djQUAN is offline djQUAN  Philippines
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my TL494 SMPS includes everything that you described. but also has three protection circuits (P108 on the ESP website)

I don't have info online but I have circuits and PCB layouts drawn on paper. where are you from?
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