Smps transformer

The limitation of car supply voltage (12V) forces to convert the voltages to higher in order to power audio amplifiers.
For powering correctly an amplifier the best is to use a symmetric supply with a high voltage differential. This supply is intended for two channels with 50W max each (of course it depends on the amplifier used). It is a classic push-pull design , taking care to obtain best symmetry (to avoid flux walking). The transformer must be designed to reduce skin effect, it can be done using several insulated magnet wire single wires soldered together but conducting separately. The transformer must be of correct size in order to carry the power needed, on the net there are many charts showing the power in function of frequency and core size for a given topology. For rectification i preferred to use shottky diodes since they have low forward voltage drop, and are incredibly fast.
I used the cheap 1N5822, the best alternative for low voltage converters (3A for current capability). The output capacitors are 4700uF 25V, not very big, since at high frequency the voltage ripple is most due to internal cap ESR fortunately general purpose lytics have enough low esr for a small ripple (some tens of millivolts). I used d2pak 70V 80A 0.004 ohms ultrafets (Fairchind semiconductor), very expensive and hard to find.

Try to use the lowest resistance mosfet you can put your dirty hand :-) on or the efficiency will be lower than rated and you will need even a small fan.
I used the trusty TL494 PWM controller with frequency set at around 40-60 Khz adjustable with a potentiometer. How i said before the power tracks must be heavy gauged or you will scarify regulation (since it depends of transformer step up ratio and input voltage) and efficiency too. This supply given me up to 85% efficiency (sometimes even 90% at some loads) with an input of 12V because i observed all these tricks to keep it functional and efficient.
The cross regulation is good but keep in mind that only the positive output is fully regulated, and the negative only follows it. Keep in mind that this circuit will adsorb many amperes (around 10A) so take care to reinforce power tracks with lots of solder and use heavy wires from the battery or the voltage will drop too much at the input.
In principle any fet will work, but the lower the on-resistance, the lower the on-state conduction losses, the lower the heat produced on the fets, the higher efficiency and smaller the heatsinks needed. The fet driver i used is the TPS2811P, from Texas instruments, rated for 2A peak and 200ns.
Don't forget to place a 10A (or 15A) fuse on the input because the car batteries can supply very high currents in case of shorts and this will save you face from a mosfet explosion in case of failture or short, remember to place a fuse also on the battery side to increase the safety (accidental shorts->fire, battery explosion, firemen, police and lawyers around).
An o-scope would be useful, to watch the ripple and gate signals (watching for overshoots), but if you follow these guidelines you will avoid these problems. Place a small load between the negative rail and ground (a 3mm led with a 4.7Kohm resistor) to avoid the negative rail getting lower then -20V.

In my case i used 5+5 , 10+10 turns obtaining a step up ratio of 2 (12->24) and downregulating the voltage to 20 via duty cycle dynamic adjust performed by the PWM controller TL494. The primary and secondary windings are centertapped, this means that you have to wind 5 turns, centertap and 5 windings again. Is important that the gate drive is optimized for minimal inductance or the switching losses will be higher and you risk noise coupling from other sources. The output signals is designed with two pull-up resistors on the collector of the PWM chip output transistor pulling them to ground each cycle alternatively. This power supply operates from a universal input and provides a 19.7 Volt, continuous 65 W output. The high effi ciency of this design allows for operation at a high ambient temperature (65° C) without the need for any external heatsinking. Havya Kullan?m? Lehim Nas?l Yap?l?r TDA7377 Amfi Devresi Metal Dedektoru Devresi ICL8038 LM386 Daha fazla yaz?..

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Comments to «Smps transformer»

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