voltage regulation from 24v ac to 15v dc

[ziad khan]

gentlemen i m having a 12-0-12 transformer. which gives 24volt ac at its outermost two lead and 12v ac with eighter of the two and the middle black one. now i want to regulate this voltage to 15volts dc for charging my 12v dc battery.
what i have tried is used the bridge rectifier to get 24 dc from outermost wires but can't configure the L7815cv voltage regulator to get the desired results of 15volt dc. the output amperage rating is 1.5A.
help will be highly appreciated.
thx

 

[kak111]

Hope this help...................



**broken link removed**

 

[alexxx]

If you take 24V AC from the transformer, then you will have √2*24=34V DC. Minus let's say 1.3V from the rectifier diodes, it goes to 32.7V. The current rating is 1.5A you say, so on the regulator it would be P=V*I=49W!!!
If you take input form 0-12V AC, then √2*12=17V, so the regulator doesn't have the dropout voltage it needs to produce 15V. Either way the 7815 cannot provide the 1.5A that you need.

Maybe you should consider using a different transformer (but still 7815 could not give you 1.5A), or use a step-down switching supply with current rating >1.5A.
Finally if you have a 12V lead-acid battery, the constant voltage would be 13.7V or so and not 15V.

 

[kak111]

15volts dc for charging my 12v dc battery.

If you take input form 0-12V AC, then √2*12=17V

Lead acid battery chargers for 16...20Vdc supply............

Lead Acid Battery Charger Circuit | Circuit Diagram

**broken link removed**

Lead Acid Battery Charger Circuit

 

[alexxx]

Yes but will 7815 produce 15V if input is 17V?

 

[kak111]

No , but 1. question was included "for charging my 12v dc battery."
my answer was "Lead acid battery chargers for 16...20Vdc supply"

 

[Tahmid]

gentlemen i m having a 12-0-12 transformer. which gives 24volt ac at its outermost two lead and 12v ac with eighter of the two and the middle black one. now i want to regulate this voltage to 15volts dc for charging my 12v dc battery.
what i have tried is used the bridge rectifier to get 24 dc from outermost wires but can't configure the L7815cv voltage regulator to get the desired results of 15volt dc. the output amperage rating is 1.5A.
help will be highly appreciated.
thx

For 1.5A, you shouldn't use 7815 at the input voltage you have. Too much power wasted, plus the 7815 can't provide continuous 1.5A. Use a switching regulator. A simple one to look at would be LM2576. Take a look at LM2576. Datasheet : **broken link removed**

For high output current requirement, where the difference between output voltage and input voltage is large, switching regulators are preferred.

Another nice option is L4973. The beautiful thing about this chip is that it is available in 18-pin PDIP package.

Datasheet for L4973: http://www.datasheetcatalog.org/datasheet2/9/0pzw1soiwuh017jsfs11afpsiu7y.pdf

Hope this helps.
Tahmid.