Difference between direct coupled and transformer coupled?

[rickeystuart]

what is the difference between direct coupled and transformer coupled?(mechanical configurations with the required turns ratios of 1:25 direct coupled and 1:1.79 transformer coupled)

 

[berkeman]

Direct coupled means no transformer (and hence no turns ratio). What is the context of your question?

Welcome to the PF, BTW.

 

[Pumblechook]

Yes.. I think you need to explain a bit more?

 

[rickeystuart]

thx. when do we use transformer coupling/direct coupling??

 

[Pumblechook]

For what though?

Do you mean for audio amplifiers or RF or something else??

 

[Utwig]

Hi,

You often have transformer couplings when you want to add an element of intrinsic safety to an environment. Intrinsic safety means all your supplies are effectively isolated via the transformers, a set-up often found in warship ammunition magazines or flight decks (where fuel is present). Two of the ships I served on were ‘intrinsic safe’, mainly because they were stores ships that carried fuel, ammo and dry stores. It didn’t matter so much with the dry stores, but it was a big deal in the mags and around the flight spaces.

For ref, the ships were the RFA Fort Victoria and George.

Hope this helps,

Utwig

 

[Pumblechook]

If you mean coupling between stages within a chain of amplifiers then the availablity and cost of components has changed the way amplifiers are designed.

Transformer coupling can maximise gain by correctly matching the output impedance from one stage to the input impedance of the next. In decades gone by where expensive and power hungry valves (tubes) were used and in the early days of expensive transistors you wanted to keep the valve or transistor count down. And eqiuipment was bulky so having relatively large transformers didn't matter.

Now, transistors are so cheap that you can use hundreds, thousands and even millions (within integrated circuits) for less than the cost of only 5 or 6 transistors in the past so gain is easy to achieve. It is items like transformers which are now relatively expensive. And if you are using integrated circuits internal stage coupling has to be direct. And of course items are very small these days.. Whole radios, MP3 players can fit within the size of single small transformer.

Early audio output amplifiers used transformer for matching to speakers. They have been designed out with the use of complementary pair NPN-PNP Class B push-pull amplifiers.