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a2005r2003 5th September 2006 07:12 PM

Who can help me to making a mains switching power supply for my STK 4192 power Amp. 6A + & - 35v?

cerrem 5th September 2006 08:28 PM

I would recommend a Push-Pull converter in Current Mode..
With a 70V secondary with Center Tap... This way you get you + and - 35V ..... 6 Amps is straight forward.....
What is the mains voltage in your country????
240V ???
The toplogy and basic circuitry has been around for-ever...All you need to do is design the values of the components...I can help with that..
Look at the LTC3721-1 controller.....


ifrythings 6th September 2006 03:20 AM

A push pull converter is not the best solution for what you want.
STK4192 is a 100W IC so that falls right in the range of the flyback converter.

A simple flyback converter using UC3842or(3) can be made with very few components.

UC3842 ON semi's datasheet has some good examples and info if your intrested.

N-Channel 9th September 2006 04:44 AM

A 100W chip will certainly need more than 100W that a flyback will output. I would recommend NOT going with a center-tap push-pull because at 240VAC, your main switching transistors or MOSFETs would have to be able to stand off close 1kV. 240V x 1.414 x 2.6 = 883V.

Let's say the 100W chip needs 200W to run properly, and we assume you're doing two channels for stereo. In that case, you would need a power supply capable of outputting over 400W comfortably, and 600W without too much difficulty. At power levels over 150W, the peak drain and rectifier currents of the flyback topology become way too high to.

At this point, I would recommend a half-bridge, very similar to what is inside almost every AT & ATX pc power supply, or possibly a full-bridge topology for peak power levels over 500W. For your PWM controller IC, I would consider any of the five most common PWM ICs suited to run push-pull, half-bridge, or full-bridge layouts: TL494, SG3524, SG3525, MC-33025, or the SG1846. The '494 and '3524 are voltage-mode only (the '3524 does have a current-sense amplifier, but it is current-limiting, not current-mode), the '3525 is a voltage-mode, but pin access at the chip's comparator enables pseudo-current-mode operation. The MC33025 can be run either voltage- or current-mode, and the SG1846 is strictly current-mode. The '33025 is a newer generation of, and close cousin to the '3525, but with faster outputs and higher-speed oscillator (1MHz).

There are MANY threads on deisgning SMPSs in the Power Supply Design forum, and I encourage you to do a search function to see them all. A good threat, like this one, will usually attract the PSU Gurus to throw their two cents in, like EVA, jackinnj, poobah, richey00boy, and others. EVA always has some nuggets of golden advice she showers us every so often, and has designed many AC Mains powered SMPSs for audio and other uses.

I did a SG3525 controlled half-bridge a while back, and it actually worked! Since then, I have cannibilized its parts from it for other projects. For your needs, +/- 35V @ 6A is not unreasonable, nor uncommon. 70V x 6A = 420W output. Taking a worst-case scenario, if your psu is 80% efficient, you will need at least 525W to get the full desired outout from the your psu to the amp.

Looking foprward to your reply. Anyway, I hope these comments give you some insight as to how to best proceed.



koolkid731 12th September 2006 04:36 AM

No audio amp runs steadily at max power. Crest factor is typically 10dB. Therefore size your PSU accordingly, first.

SMPS is time consuming and full of switching noise. Why would a DIY ever choose to make one? It would be cheaper to buy one?

N-Channel 15th September 2006 11:40 AM

No switchers for audio???
I dunno. Ask every manufacturer of car audio amps over, say, 25W. They all use SMPSs.

poobah 15th September 2006 04:04 PM

Practicality of Flyback falls away over 50 Watts... unless there other motivating factors. Your inductor will be HUGE.

You are definately in P-P/ half bridge land.

I wouldn't consider a custom switcher for a one-off DIY design... unless learning switchers is an ambition. The reason is that there are really no "off-the -shelf" magnetics elements for you. If you wish to learn switcher design AND design and make your own magnetics, they go for it!

Don't expect it to be a whole lot cheaper than a linear supply... probably the opposite. Cannibalizing parts is an option... but that is easier AFTER you know what you are doing.

Methinks N-channel knows a wee more than he lets on about SMPS!


a2005r2003 27th September 2006 05:44 AM

tanx all of u.
i finaly convert atx 250w psu to give 2*35v. but its driver Transistors became very hot (with heatsink & fan). it is very abnormal. why did the tr. become very hot?!?!?!?!?!?!?

Eva 27th September 2006 09:21 AM

Because you have modified a SMPS without knowing exactly what you are doing. You have a (design) fault either in the transformer or in the output filter.

Also, you are quite lucky because the switching transistors are just overheating instead of exploding.

m-tech 27th September 2006 11:17 AM


Originally posted by a2005r2003
tanx all of u.
i finaly convert atx 250w psu to give 2*35v. but its driver Transistors became very hot (with heatsink & fan). it is very abnormal. why did the tr. become very hot?!?!?!?!?!?!?

I tried this too, and have same problem.
Number of primary turns ( on the output ransformer) is the same as on original - 40 turns, onlu the secondary is modified ( I put 2x15 turns ). Also increased output inductor, but problem is still here.

My English is bad, so I hope you understand me.

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