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Switching Regulator Power Supply

Hi All,

I need to design and build the circuit and printed circuit board to receive the power. I have got 40 volts input and I do not know how much input current because the guy who is working on it still experiemnt with his part of the system.

The load or the circuit needs atleast 4 volts and 400mA current to work properly. I thought that I can convert the 40 volts downto 5 volts or so using the following buck regulator

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and then using the following Power Controller and Li Ion charger to toggle between charging the Li-ion battery or providing the Load circuit with LT3970 's DC 4 volts output. Am I right?

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My questions and problems are as follows

  1. Am I going in the right direction with this?

  1. What I understood from the LTC4055's data sheet is that I do not need to use the pins "IN1" and " IN2" because I have only one input and I can use "Wall" input pin for the input voltage that ranges between 2 to 40 volts. But If I go with Wall pin than what would be the status of the following pins a. HPWR b.CLPROG c.ACPR d. Susp

3.LT 3970 's data sheet, page number 16, Figure "5V Step Down Converter" . Is this what I need? How can I choose the values for the inductor change current and the input capacitor?

I would appreciate if someone gives a good advise.

Thanks John

Reply to
john
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Did you look at the National Semiconductor LM2575T-ADJ ? That part can take 40v in, and give you 4V out, at up to 1500mA, IIRC. Requires just (2) programming resistors, an inexpensive inductor, filter caps, and a fast diode. Inexpensive solution for a low-voltage switcher. In my opinion. Haven't designed a P/S in over a year, so there may be better solutions by now.

Best of luck.

-mpm

Reply to
mpm

If you have a nominal 40 volts in, that's the wrong part for the job. 40V is the absolute maximum rating. It also only supports 350mA out. You need a higher voltage and higher current part. Look at the LT1766, rated for up to 60V in and 1.5A out. That gives you some headroom.

I'm not sure where the battery fits into this. What are you trying to do? Charge the battery, or provide a UPS capability?

You can download LTSpice from the Linear site. It has good models of all Linear Technology power parts (which is why they give the software away), and you can simulate your design. See

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and then

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They also have some Excel spreadsheets to help with component value calculation.

John Nagle

Reply to
John Nagle

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