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TL494 Based SMPS controller


This circuit is from a cheap car electronic crossover. I have modified it a bit to accommodate several versions that could be designed around the basic circuit. It has to be noted that making your own SMPS can be very difficult and needs lots of experience in power electronics especially on the high power version. I could offer only limited help since I do not go online often.


Don't mind the drawing. I hand-drew it in my notebook since I didn't have time to go and play with the computer.


for the controller circuit, Rt and Ct (timing components) are not labeled with component values. This was intended since different applications require different values (for a start, 6.8k and 2.2nF oscillates at around 35-40kHz). the 33uF cap connected across pin 14 and pin 4 controls the soft start function of the PWM controller. the 1k resistor from pin 4 to ground controls the dead-time. the four 1k resistors along with the two transistors buffers the remote turn-on signal from the headunit and provides the PWM control circuitry with a switched +12V. the drivers shown connected at the output of the TL494 is only needed for MOSFET output stages. If you are going to use the output stage shown (which can only handle up to a few hundred mA), just connect the 510R resistors directly to the TL494 outputs. output diodes can be 1N4148 for low power preamps/crossovers and should be UF4004 or similar (ultrafast diodes!) for slightly higher current. Not shown, you will also need to bypass the B+ and Gnd terminals with about 100-470uF and 100nF ceramic caps for input and outputs.

I have made car SMPS's using the basic circuit. a few low power units for crossovers/line drivers and one 200W unit for two P3A amplifiers and one 500W unit for a mono P68 amp. I also have built a 600W unit with eight 110A MOSFETs for an AMP2 board from 41Hz audio.

Incase anyone is wondering, "SMPS" stands for "Switch Mode Power Supply".

For use with high power amplifiers, use the output stage similar to Rod's P89 car SMPS project. just use the drivers and connect to 100R gate resistors. To add some form of protection to your new SMPS, use the circuit I contributed to ESP. I have also described in the article how to simply "tap" this circuit to the TL494 circuit.

And now, for something new......

PCB foil side (in bitmap)

PCB component overlay (in bitmap)

I assume that you have read all the notes above before doing the PCB. If not, go and read it again. Anything to know about the circuit in the PCB is in the notes above......

All PNP transistors are now MPSA56 and all NPN transistors are MPSA06. the PCB also uses a different MOSFET driver circuit. it now uses a totem pole since there are three MOSFETS per phase and six in total.

The rectifiers used are those dual diodes similar in PC power supplies BUT MUST HAVE HIGHER PIV RATINGS! they must have about 200V PIV rating or greater. These are in TO-220 case with three pins, the middle is the common cathode.

MOSFETs to use are IRFZ44, 50N06, IRF3205 to name a few. Specs to look for are a Vds of 50V or greater, peak drain current greater than or equal to 30A.

For the transformer, The board has enough space for a decent sized EE core. There is a marked rectangle in the PCB under the trafo, cut this out for EE cores. This allows the windings to go below the board for a lower profile. Toroids will also work fine and the cutout could be used for additional ventilation. a guide to use is 6 + 6 turns for the primary and compute for the secondary. There are lots of info in the net about computing for the secondary turns with your needed output voltage.

The connectors to use? well, for the 12V power, I suggest you solder 8GA wires directly to the board. for the outputs, soldering right sized wires is adequate but a high wattage iron is definitely required.

Although not included in the PCB, a fuse is very necessary as with the currents involved, damage is certain incase something goes wrong. Also, you do not want to be driving around and a fire starts in your car. This is not a joke, I'm serious as this project involves considerable electric currents/voltages.

It must be noted that I will not be held responsible for any property damage. I'm assuming that you know exactly what you're doing and fully understand the consequences of dealing with high current/high power equipment.

If you decide to build this SMPS, let me know how it turns out.


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