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himanshuraval 8th March 2004 07:57 AM

car smps based on TL494
any body have full design of TL494 based car smps with toroid data

maylar 8th March 2004 08:34 PM

I Doubt it. Not a very popular chip.

weissi 8th March 2004 08:57 PM

you´ll find it in almost every cheap computer psu.... that´s for the popularity...

maylar 9th March 2004 12:25 AM

Really? I would have thought open collector designs went away a long time ago.

creamed_emu 13th March 2004 09:13 AM

I've just finished a +/- 35v smps using the tl494. It runs beautifully. right now its driving 2 lm3886 50W amps with no drop in voltage. It runs from 12vdc and sucks around 13 amps when fully driving 2 8ohm subs. I tried a toroid but due to the small physical size of it it could supply more than 20watts. i am now using a AT PC ferite transformer wich i can get around 150watts.

Super simple, cheap circuit that allmost anyone can build.

If u want more info just email me or add me to your msn contact list.

li_gangyi 13th March 2004 11:59 AM

Maybe u would want to put some schematics here...I got a bunch of those outta scrap PSUs

fr0st 14th March 2004 02:50 AM

Rod Elliot has a SMPS based on the SG3525. You can get them from Oatleys or national on a sample order (I think).

creamed_emu 14th March 2004 03:24 AM

2 Attachment(s)
I've just re-drawn the schematic that i've used in my design. The 2 ic's are a tl494 (also known as 7500 in some pc power supplies) and a 4050 hex buffer. the capacitor and resistor attached to pins 5 and 6 of the 494 are to set the push pull frequency. you may need to change these depending on the type of core you use and the number of primary turns you have wound. these seemed fine for me even using a number of different cores.

The 4050 is a buffer to give nice n quick rise and fall times for the output stage to keep the output transistors/mosfets out of their linear range to increase efficiency and reduce heat.

The transformer i used was out of a 200w at pc power supply, as was the tl494 and pretty much everything else (except the 4050) to seperate the cores without cracking the ferite i usually boil them in water for around 5 min and take them out and seperate them as quickly as possible. then you unwind the windings (save the wire, it could be usefull) and let the cores cool.

To wind the transformer you wind 4 turns of wire (because of the high frequency its best to combine a number of thinner wires to create the one wire to handle the current, i used 6 .8mm wires twisted into the one large wire using a power drill) then leave around 10cm of wire and cut them. then wind another 4 turns of wire over(or beside) the first 4 in the same direction and leave 10cm and cut them. now join the lead from the first primary (the one from the fourth turn) and join it to the start of the 1st winding of the second primary. so you have a 8 turn center tapped primary. get it?

Now for the secondary. using the same technique as the primary, wind around 18-20 turns of wire then another 18-20 turns. so u have a 40 turn center tapped primary. ok, that should be the transformer done, replace the cores and add a little glue to hold them together and your done.

The output stage can be what ever you want, i first used mosfets but they kept getting destroyed probably due to spikes and at $4 each i didnt want to waste any more money, so i used the transistors used in the pc powersupply. theyre good for around 8 amps each with good heatsinks. you cant drive them directly so u need to get another smaller npn transistor and connect the emmitor to the base of the big transistor, the collector of the small to the collector of the big transistor. the emmiter of the big transistor goes to ground, and the collector goes to the primary of the transformer. you can find these npn transistors in the pc power supply also. The center tapped winding goes to the 12v rail. same with the other side of the push pull configuration.

on the secondary side, just put a bridge rectifier with a few caps after it, center tap goes to ground. connect the positive output to the feedback terminal. with the variable resistor towards the output side, power it up (through a fuse, of course and not with a car battery just yet, use a 12v dc supply). there should be 5v on the output. now turn the variable resistor back and it should increase, not linearly though.

I think that has covered everything. if not, or if i didnt explain things as clearly as i hoped just email me and ill try some more. if theres enough requests ill create a website with detailed instrustions and a whole lot of pics for u guys, hope i helped.


palesha 3rd April 2004 07:53 PM

Dear Ben,
Nice description. But better post full schematic of powersupply. We will like to see ur layout of the PCB. More interestingly what ferrite core u hv used and ur observation & experience about calculating the winding turns. This r the problematic areas.

MOER 4th April 2004 08:16 AM

The TL494 is probably the most popular PWM chip. It is inexpensive and does a great job. We have used it for over 20 years with no problems. So I have no idea where "Maylar" gets his info.

Zed Audio
Los Angeles CA:smash:

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