Doubling up a regulator for more current ??

[unclejed613]

transformer voltages are rated in volts RMS, not peak. the DC voltage will depend on the type of rectifier, and for a bridge rectifier it will be 1.414 times the RMS voltage. transformer voltage ratings are not used as marketing tools, as the specs have long been standardized, and the transformers are rated in engineering terminology, not consumer terminology. if a transformer doesn't meet published specs, it doesn't sell, unlike consumer audio, which can have a listed power output of the amplifier wattage multiplied by the square of the marketing executive's shoe size.

 

[madhippiescientist]

Soooo...the 14v will do (I'm going to reduce it to 10V), or should I maybe buy a 12v ? <12*1.414=16.96v). Or maybe a 10v ??? (10*1.414=14.14). I just wish to get it close to the regulator's 10V output, but still have ample area for load drop. As long as I get one that's 3A, and take into account the load drop (if I happen to draw upwards of 3A), I need it to still supply enough voltage for the regulator (LDO) to do the job. So, unclejed613, what voltage secondary do you suggest I use?

 

[unclejed613]

transformers with 12V secondaries are by far the most common. because they are so common they are cheaper because they are made in vast quantities.

 

[Mike odom]

don't squeeze it down until it doesn't work. Don't forget your line voltage varies, and most designs I work on we plan on the line voltage being as low as 108V. I just finished a design for a radar power supply for the FAA, and it works down to 95V (thru 265V) but it has a switcher on the front end with pfc (power factor correction).

12V and 14V secondary transformers at the same amperage probably cost about the same. For the same VA size, you may lose a little current with the 14V vs 12V. I wouldn't go higher than 16V because you don't want to throw away too much on overhead and heat your regualtor. I would stay with 14V.

 

[madhippiescientist]

Thank You Mike !

My LT1528 arrived today, so now I'll be off to the races!! If you'all don't hear from me (in this post) anymore, it's because I got it all to work. I appreciate every one of your inputs and feedbacks, and bearing with me and my needy requirements throughout this post. 10V3A, here I come !!!