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Old 9th March 2006, 11:59 PM   #11
testlab is offline testlab  United States
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I have to agree that the switcher is the more elegant solution. But if linear is what you want, then use a 723 adjustable voltage regulator and a good size pass transistor.
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Old 10th March 2006, 12:24 AM   #12
Mr Teal is offline Mr Teal  Canada
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I've designed a battery charger using the UC3906 to give a bulk charge of 5A to an Optima red top gel battery. My rail voltage is about 18V, and I'm using a TO3 darlington as a pass transistor. It works quite well.

Keep in mind, if you're trying to charge 12V batteries, you'll need higher than 12V rails. To put any decent amount of charge into them, you'll need a fairly large transformer and a big filter cap as well, unless you use the approach most commercial chargers do, and use rectified, unfiltered DC.
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Old 10th March 2006, 12:27 AM   #13
Eva is offline Eva  Spain
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Mdern switching regulator ICs now available are almost as easy to use as a classic 7812. Everything is built into the IC, including switching element, diodes, control circuit, feedback, etc...

As it has been pointed out, all you have to do to get a working regulator with one of these ICs is to choose a suitable coil, input and output capacitors.

In comparison, building a regulator around a LM723 is more complex (I killed several LM723 ten years ago when I built my first high current linear supply, some junction inside the IC was geting reverse biased in a destructive way during turn-off).
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Old 10th March 2006, 01:14 AM   #14
hermanv is offline hermanv  United States
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Lead acid cells are 2.21 Volts per cell at room temperature. To charge a 12V (6 cells) lead acid battery to full capacity requires about 13.5 VDC not 12. Most automotive alternator regulators actually run closer to 14V.

Several IC houses make specialty regulators for charging lead acid because the correct charge voltage is temperature dependent.

At "full charge" the charger should switch to a constant current mode to avoid over charging.
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Old 10th March 2006, 05:00 AM   #15
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My advice..go in for a switched regulator..there r lots of chices.from Maxim (maximic.com) National etc.
MAX724 can sink in 5Amps max with greater than 85% efficiency.
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Old 10th March 2006, 01:34 PM   #16
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Quote:
Originally posted by hermanv
Lead acid cells are 2.21 Volts per cell at room temperature. To charge a 12V (6 cells) lead acid battery to full capacity requires about 13.5 VDC not 12. Most automotive alternator regulators actually run closer to 14V.

Several IC houses make specialty regulators for charging lead acid because the correct charge voltage is temperature dependent.

At "full charge" the charger should switch to a constant current mode to avoid over charging.
Actually, the battery is overcharged at the end of the process -- the attached pic from Texas Instruments demonstrates:
Attached Images
File Type: gif charge.gif (11.2 KB, 145 views)
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Old 24th March 2006, 05:19 PM   #17
JDeV is offline JDeV  South Africa
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Quote:
Originally posted by Mr Teal
I've designed a battery charger using the UC3906 to give a bulk charge of 5A to an Optima red top gel battery. My rail voltage is about 18V, and I'm using a TO3 darlington as a pass transistor. It works quite well.

Keep in mind, if you're trying to charge 12V batteries, you'll need higher than 12V rails. To put any decent amount of charge into them, you'll need a fairly large transformer and a big filter cap as well, unless you use the approach most commercial chargers do, and use rectified, unfiltered DC.
Hi Mr. Teal,
Sorry for the "off topic" interrupt. I also am playing with this UC3906 IC but need some guidance. May I look at your circuit please?

Much appreciated.
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