I'm currently planning my second SMPS project for an automotive amp. My first was based on the ESP pages design with some minor changes. It worked very well and got me thinking, why not build an amp with all the channels and onboard signal filtering I need in one chassis? I have three way components for my doors, coaxials for the rear and one dual voicecoil subwoofer for a total requirement of 10 amplifiers plus filters. I have decided to use LM3886's and opamp filters for simplicity.
Problem is the power supply has to be large. I have decided on a half bridge topology delivering +/-35V rails at something like 600watts. Undecided on whether or not to regulate. To get the needed power I think I will have to go with two transformers. I have two 5cm toroid cores that I picked up for this purpose and now I'm wondering whether it would be better to wire the primaries in a series or parallel scheme? A search turned up little in this regard. I think series forces equal currents, parallel offers lower inductance. Anyone gone this road before? Any advice on how to proceed? Thanks.
Problem is the power supply has to be large. I have decided on a half bridge topology delivering +/-35V rails at something like 600watts. Undecided on whether or not to regulate. To get the needed power I think I will have to go with two transformers. I have two 5cm toroid cores that I picked up for this purpose and now I'm wondering whether it would be better to wire the primaries in a series or parallel scheme? A search turned up little in this regard. I think series forces equal currents, parallel offers lower inductance. Anyone gone this road before? Any advice on how to proceed? Thanks.
Instead of using half-bridge on my last project, I used push-pull. But since I did not need the output isolated from the input to get voltages similar to the ones you seek, I placed diodes from the drains of the MOSFETs to the output filter capacitors to shunt spikes since I like simple winding techniques that don't provide especially low leakage inductance. That gives the efficiency of push-pull for 12v power input with the spike clamping of half-bridge.
The trade-off is that active current limiting might be needed to prevent transformer saturation whereas in half-bridge the coupling capacitor does that job. The problem with coupling capacitors at low voltage is relatively high impedance at high frequencies.
Later on, I decided to make the nonisolated output of my supply 48v. That voltage is twice 24v, which is the voltage on the MOSFET drains in a push-pull circuit. I used a capacitive voltage doubler that was driven by each winding of the transformer. The transformer had no secondary winding. This approached eliminated leakage inductance problems and gives high efficiency with simple transformer winding techniques.
I just remembered that you want -35v in addition to +35. These ideas will not work for you since your amplifier does not have bridge tied load outputs. But since I already spent time writing here, I guess other hobbyists may find the ideas useful.
The trade-off is that active current limiting might be needed to prevent transformer saturation whereas in half-bridge the coupling capacitor does that job. The problem with coupling capacitors at low voltage is relatively high impedance at high frequencies.
Later on, I decided to make the nonisolated output of my supply 48v. That voltage is twice 24v, which is the voltage on the MOSFET drains in a push-pull circuit. I used a capacitive voltage doubler that was driven by each winding of the transformer. The transformer had no secondary winding. This approached eliminated leakage inductance problems and gives high efficiency with simple transformer winding techniques.
I just remembered that you want -35v in addition to +35. These ideas will not work for you since your amplifier does not have bridge tied load outputs. But since I already spent time writing here, I guess other hobbyists may find the ideas useful.
Thanks for the replies Electrone. I had considered stacking the cores but thought maybe dual transformers was the better way to go. I've seen it done in several commercial amps. I have little experience designing switching supplies from scratch. When I said I was thinking of using a half bridge I meant the generic term as in using two switches. Push-Pull is what I was actually thinking. Bit of a faux pas I suppose. Have you stacked cores in the past? Do I simply double the core cross section when calculating primary windings? Giving up isolation for increased efficiency is worth considering, thanks.
On another note, I have a few freebee software calculators I downloaded from core vendors for designing chokes and transformers. Can everyone post names of their favourites please? So far I've accumulated: Mini Ring Core Calculator 1.2, Magnetic's Current Transformer Design, Magnetic's Common Mode Inductor Design and Magnetic's Current Transformer Design.
On another note, I have a few freebee software calculators I downloaded from core vendors for designing chokes and transformers. Can everyone post names of their favourites please? So far I've accumulated: Mini Ring Core Calculator 1.2, Magnetic's Current Transformer Design, Magnetic's Common Mode Inductor Design and Magnetic's Current Transformer Design.
You're welcome, Kevin. Thanks for thinking about those things.
I think that your idea is right to just double the cross sectional area figure, and pretty much the power capability.
I have been twiddling with this simple calculator lately.
http://www.bcae1.com/trnsfrmr.htm
I think that your idea is right to just double the cross sectional area figure, and pretty much the power capability.
I have been twiddling with this simple calculator lately.
http://www.bcae1.com/trnsfrmr.htm
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