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Electronics => Projects, Designs, and Technical Stuff => Topic started by: migsantiago on July 02, 2010, 09:27:54 pm

Title: DC backup - 19V 4A
Post by: migsantiago on July 02, 2010, 09:27:54 pm
Hello

I would like to build a power supply that delivers 19VDC and 4A. This power supply will be fed from a 120VAC input at 60Hz. When there's an AC interruption, the power supply should continue feeding its output by using 2x12V lead-acid batteries. It should also have the battery recharging circuit.

Can you please recommend me a circuit or application note to follow? I've looked in google but I can only find laptop power supplies.

Thanks!!  ;D
Title: Re: DC backup - 19V 4A
Post by: NiHaoMike on July 02, 2010, 09:34:11 pm
27.6v power supply for float charging along with a buck converter to convert it to 19v.
Title: Re: DC backup - 19V 4A
Post by: migsantiago on July 02, 2010, 10:43:10 pm
Hello NiHaoMike

If I use the 27.6V for float charging, should I add a recharge current controller or just let the battery draw all the current it needs? I've seen some recharging supplies which feature PWM to control the amount of current been supplied to the battery, but, is it really necessary?
Title: Re: DC backup - 19V 4A
Post by: NiHaoMike on July 02, 2010, 10:48:23 pm
Put a shunt in series with the battery in order to limit charge current.
Title: Re: DC backup - 19V 4A
Post by: migsantiago on July 03, 2010, 02:11:04 am
Quote from: NiHaoMike on July 02, 2010, 10:48:23 pm
Put a shunt in series with the battery in order to limit charge current.

OK, I'll study how to calculate that shunt according to the Ah rating of the battery. Thanks.
Title: Re: DC backup - 19V 4A
Post by: NiHaoMike on July 03, 2010, 03:59:37 am
Quote from: migsantiago on July 03, 2010, 02:11:04 am
OK, I'll study how to calculate that shunt according to the Ah rating of the battery. Thanks.
Simply put it in series with the negative side and use an opamp circuit to create a feedback loop.
Title: Re: DC backup - 19V 4A
Post by: migsantiago on July 03, 2010, 12:52:45 pm
Yes, I know that  :)  ;D

But I want to know how much current will flow, depending on the Ah rating of the battery and its actual charge value in Volts.
Title: Re: DC backup - 19V 4A
Post by: NiHaoMike on July 03, 2010, 01:04:00 pm
Quote from: migsantiago on July 03, 2010, 12:52:45 pm
Yes, I know that  :)  ;D

But I want to know how much current will flow, depending on the Ah rating of the battery and its actual charge value in Volts.
You first pick a shunt as small as possible while still getting a large enough voltage drop to measure, then compare it to a reference voltage. It's usually something small, on the order of 50mv or less.
Title: Re: DC backup - 19V 4A
Post by: Pyr0Beast on July 08, 2010, 10:57:11 am
Diode to discharge and shunt to recharge.
Use Schottky diode.

Tho I would rather go with boost design. You don't need additional higher voltage to drive the upper mosfet.