Mag Amp, the use of magnetic amplifiers to regulate forward converter output(s).

[David_]

Hello.

I recently found out about magnetic amplifiers and the usage of such a circuit to regulate previously unregulated isolated rails in SMPS converters, but so far I have only found texts that speak very vaguely about what Magnetic amplifiers(MagAmps) can do and can't do.

Some texts I read have given the impression that mag amps is mostly for current regulation or minor voltage regulation, but others give the impression that I could exclude any secondary side feedback and replace that with a magnetic amplifier to regulate the voltage just as much as a secondary feedback to the PWM controller could?
Of course this depend on how the specific converter where designed but I have a forward converter that if successful will regulate the isolated output between 10V and 60V with the maximum duty cycle somewhere around 45%, but I have gotten very interested in if magnetic amplifiers could be used to give me more than one fully regulated isolated outputs?

As I understands it a magnetic amplifier would delay the switching action to change the on/off times, the difficult part appears to be designing the saturable core reactor(is that synonymous with magnetic amplifier?) to balance the volt seconds. It needs to reset it self over different amount of times depending on how long the delay action is delaying and how much energy that takes... Or something like that, I will continue to read but there are some aspects which I would like to discuss if someone have any knowledge of this.

Regards

 

[FvM]

There's a lesson in the Unitrode/TI magnetic seminars about magnetic amplifiers in SMPS http://focus.ti.com/lit/ml/slup129/slup129.pdf
Also the classical article magnetic amplifiers another lost technology **broken link removed**

 

[David_]

Great tips, thank you.

I think there will be quite some time before my first mag amp design is done for tests even since I read that it is supposed to be hard to design these things, though it is easy to find manufacturers that produce cores with square B/H loops I have a hard time finding some place to buy them and order them to Sweden(I don't want to but products for 10 dollars and pay double that in shipping costs) and so far I have not found any on digikey or any other such site that also sells other things I need.
But at this point I can get over high shipping costs so if anyone know of anywhere I can order as a private person please let me know.
Though it might be some time till then I will return here when I have some design to show.

Regards

 

[schmitt trigger]

In the mid-1990s I worked for a power supply manufacturer.
Some of its products used mag amps for post regulation.

The reason we stopped using them is because they were very expensive. And the high-mu wound tape core was brittle and easily damaged.

With the cost of IC post regulators going steadily down, a point was reached where continuing to use them was not economically justifiable.

But I agree with you, technically, they are very interesting.