Active(switch mode) v passive(fully indutive) transformers

Topics relating to lighting control gear, including magnetic & high frequency ballast and ancilliary devices such as starters, ignitors and switchgear.
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MetalHalideHater
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Active(switch mode) v passive(fully indutive) transformers

Postby MetalHalideHater » Fri Apr 13, 2012 1:56 pm

I just tested a pair of transformers:one was a 12v 5a switch mode power supply, which feeds the transformer on a frequency several thousand times higher than the normal ac the passive feeds the tranny on. This means the transformer can be a lot smaller and thus more effective. However, to raise the frequency, transistors are used. These are often very small and light power supplies.
The second was a 12v 5a passive one with just a transformer, bridge rectifer and a capacitor for smoothing.
In terms of reliability, the passive one will win hands down because there are no sensitive components, like the switch mode active. However, when I did voltage testing, I was a tad shocked. The passive one provided 14v at no load, and 7v at 5a. The active provided 15.5v at no load and 15.45v at 5a. My question is:does anyone know of the "real world" reliability of both types of transformer?

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Re: Active(switch mode) v passive(fully indutive) transforme

Postby FrontSideBus » Fri Apr 13, 2012 4:50 pm

I'm no expert but I'd put my money on the transformer and the four diodes to last the longest.
The switched mode PSU would probably give the best power as long as it had active pfc. Passive pfc switch mode supplies pollute the mains with harmonic distortion!
Regards, Mark Jones.

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Tom
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Re: Active(switch mode) v passive(fully indutive) transforme

Postby Tom » Fri Apr 13, 2012 5:10 pm

Yep I'm with Mark on this! Good old fashioned linear power supply with proper magnetic tranny and rectifier bridge all the way! it's like comparing magnetic ballasts with HF I suppose! I think we've all heard of a PC PSU going bang at some point!

Its the same with audio. Personally I prefer amplifiers with proper power supplies over switch mode, despite being 3 times heavier! They tend to sound better mainly because a big lump of a transformer coupled with a bridge rectifier and a couple of big fat smoothing caps will always cope better with the power demands of loud music! My amps weigh a mighty 40 odd kilos in their 19" rack flight case but the weight is worth it! :)
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Re: Active(switch mode) v passive(fully indutive) transforme

Postby MetalHalideHater » Fri Apr 13, 2012 5:20 pm

FSB:you're right about the harmonic distortion-I forgot about that.
@Tom-yep definitely. My valve amp has a big wire wound (passive ballast) weighs a ton and the sound is fantastic!

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Re: Active(switch mode) v passive(fully indutive) transforme

Postby FrontSideBus » Fri Apr 13, 2012 9:21 pm

The transformer in my AV amp is so big, the lights dim from the inrush current :D
Regards, Mark Jones.

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Re: Active(switch mode) v passive(fully indutive) transforme

Postby f36t8 » Fri Apr 13, 2012 10:01 pm

Conventional transformer + rectifier + capacitor PSUs are also non-linear loads and thus also pollute the mains with harmonics the same way switchmode PSUs without active PFC does. Consider the input stage of a typical SMPSU and compare it to a conventional supply: power is rectified and stored in capacitors. Since current is only drawn trough the rectifier when the instantaneous voltage on the input is greater than that of the instantaneous voltage of the filter cap, the current waveform is massively distorted. The transformer on the conventional supply makes little difference.

On the other hand, SMPSUs can also cause radio interference problems because of the switching noise, which is not present in linear (or unreguleted) conventional PSUs.

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Re: Active(switch mode) v passive(fully indutive) transforme

Postby frutas » Fri Apr 13, 2012 11:55 pm

I've seen conventional PSU's go for years and years with no problems, but many switch mode power supplies give a reasonable service life if decent quality. Again I think it's cheaply made rubbish thats the worst.

Audio is deffo an area where conventional PSU's rule and everyone is right to say they sound better. Many claim that toroidal transformers are best here too and minimise noise.

But switch mode power supplies have allowed things like PC's to run reasonably well and not weigh a tonne. I've worked maintaining hundreds of PC's in a University and only known of a couple of fails in about 5 years and these were running all day in enclosed cabinets with audio amplifiers and video equipment adding heat, so some are OK!

The maddest thing is the Panasonic inverter drive microwaves - thats one crazy HV switch mode! And this here is what you call a proper power supply and a work of art :) http://www.electricstuff.co.uk/50KVpsu.html

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Re: Active(switch mode) v passive(fully indutive) transforme

Postby FrontSideBus » Sat Apr 14, 2012 12:12 am

I frigging hate inverters! Used to have a microwave. It was over 20 years old and the only reason that it was binned because it looked rubbish in the new ultra modern kitchen. New all bells and whistles microwave lasted six months before the inverter drive blew! Same goes for washing machines with induction motors and air conditioners. They are let down by the electronics.
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Re: Active(switch mode) v passive(fully indutive) transforme

Postby Tom » Sat Apr 14, 2012 12:36 pm

LOL our microwave is a Panasonic Inverter! Had it 5 years now. Been a good machine so far TBH. The one we had before was an ancient Toshiba one from the 80s! With the tumbler rolling minutes counter!

Deffo established now that proper linear PSUs are best for audio. And any decent amp will have a toroidal in it too like Chris mentioned. I have to admit I've been tempted by switch mode powered amps just to save my back when loading to and from the van! But my current beasts just sound so SWEET!! I'll just have to keep avoiding upstairs gigs where there's no lift!
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