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Old 29th October 2004, 12:51 PM   #21
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I'm not sure where you guys are looking for the TL494 and the SG3535 but at Jameco they are both less than $.50 a piece.
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Old 29th October 2004, 01:20 PM   #22
sdoom is offline sdoom  Germany
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Of course the TL494 can drive MOSFET directly without driving-transistors. That application can be found in older Harman car amplifiers (JBL and Concord white series) . Here the TL494 drives up to 6 IRF540N directly.

But small driving-transistors are recommended , if one or more of the MOSFET fail and cause a short, the TL494 will be saved if driving-transistors are being used.

Amplifiers made in Asia often use the 2SA1266 or 2SA1015 transistors for driving the MOSFET. Those are standard transistors as a BC557 is in Germany.

The more stable version of the TL494 is the TL594 , often used in Hifonics amplifiers series 8 .

Price changes with the manufacturer. The Texas Instruiments TL494 will def. be more expensive than a korean KIA494 , overhere the TL is sold for 50cents.

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Old 29th October 2004, 02:07 PM   #23
RX5 is offline RX5  Philippines
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im from tacloban city, leyte,philippines.....

i have ordered the SG3525 in alexan, manila and costs P150.00... for the TL494, i could get it here locally at about P60.00.... big difference....

could you maybe post a circuit? that would really help me a lot....

tnx
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Old 29th October 2004, 02:23 PM   #24
sdoom is offline sdoom  Germany
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Here is a small SMPS with a TL494, used for a 250W RMS amplifier (korea-standard) .



Maybe this helps.

TL494_DC_converter
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Old 29th October 2004, 04:11 PM   #25
RX5 is offline RX5  Philippines
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tnx for the link...
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Old 30th October 2004, 11:08 AM   #26
djQUAN is offline djQUAN  Philippines
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I have not gotten around to making an online schem of my SMPS, I'm in manila,

that I think is still expensive. I get TL494's for 40 pesos and SG3525 for 75 pesos.
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Old 31st October 2004, 03:40 PM   #27
RX5 is offline RX5  Philippines
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djQUAN,

posted is a scheme of TL494 in simple osc mode... maybe you could edit it with any bitmap editor and add "softstart" capability... and how to calulate the "deadtime" of it...
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File Type: jpg tl494.jpg (44.5 KB, 1362 views)
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Old 1st November 2004, 12:53 PM   #28
djQUAN is offline djQUAN  Philippines
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I'll try drawing the schem on paper and scan it to post online. I don't have a scanner here so I'll do it in my friend's house. I'll try to post it as soon as I can.
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Old 1st November 2004, 06:35 PM   #29
RX5 is offline RX5  Philippines
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Project report:

finally ,after many months of waiting and sourcing parts, my SMPS works:

1> chip used was SG3525.. simple oscillator mode with softstart only
no voltage regulator using the 4N35 optoisolator

2> diodes used were 200V 3A (R30D) could not find any high power rated in our area, got these from faulty PC Power supply

3> mosfets used: total of 4 IRFZ44 (2 per side) mounted on small heatsink

4> core used U-U core (from TV flyback transformer)<thick ones, not the slim> , or big E-I core or toriod, very rare to find

5> output cap used : 4,700uF/50V per side

6> softstart value of cap used: 4.7uF instead of 33uF

i turned the power on, after about 1/4 second, i hear a "sssssssssssssst"!!! but sound extinguished after 1/8sec.... twas the SMPS powering up and charging the 4,700uF...

output was around 37V per side.... when i was using 1A regulated 12V but when i used a PC AT power supply(12V@8A), output was 51V.. under no load.... so, i think ill put/add voltage sensing using 4N35, but i think that would make the SMPS efficient enough?? comments pls...

---==== NOW TESTING TIME ====----

amp used 100W rms amp , published in our local country... supply was +40,gnd,40 @4A... i used this amp as my subwoofer amp... connected to my PC through an active sub filter... I first tried the 1amp 12V supply, for safety sake... all went well, until you put it to full power(amp)... sound output is moderate... and i hear a "ssssssssssst" every second or two, on full sound output!! well its understandable because my 12V power supply cant supply the current demand!!

i was still afraid to use the 12V 8A PC PC because my SMPs still got no voltage sensing circuit.. maybe it will blow my amp.. maximum supply valtage must be under 100V... still gonna add it, sensing circuitry.... the other thing im worried about are the fast recovery rectifier diodes (R30D).. looks like 1N5401.... thay arent mounted on heatsinks like the BYw diodes.... i cant source them locally....

anyway, my SMPS works... no heating of SMPS parts .. just my 12V 1A power supply.. hehehehe

btw, SG3525 is way much better and easier to use than TL494.. but it could be done... need more time though....

thats all for now.....
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Old 2nd November 2004, 10:11 AM   #30
djQUAN is offline djQUAN  Philippines
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how many turns did you use for the primary and secondary windings?

check out ESP's P108.
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