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12V / 6A Power supply. Help with Buck and Boost converters + OR'ing circuit

Hello all.
I would like to receive some suggestions of ICs / considerations about this design.
The picture below states how this power supply should work.


1) IC 1 probably will be a LT3650-8.4 from Linear Technology. It supports up to 32V of input voltage (40V peak). Suggestions of other ICs for this purpose?

2) The power supply INPUT has only two states: (A) Floating (cut-off) and (B) 17 to 30VDC present at the input.

3) The OR'ing circuit at the OUTPUT, as the picture shows, doesn't mean it will be done with diodes. It can be done with MOSFETs, relays, or any kind of logic control like, for example: When the INPUT is connected to a 17 to 30VDC PSU, a logic LOW is present in an ENABLE pin of the BOOST converter, so that this remains in idle state (Output in high impedance). When there is no power supply connected at the INPUT, the same ENABLE pin goes logic HIGH, so the BOOST converter goes to active mode and presents 12V at its output.

4) The intention of using batteries is, case the INPUT be floating, maintain the circuit connected to the 12V OUTPUT working for at least 10 minutes (If more, better), through the BOOST converter

5) Which BUCK and BOOST controllers from ANALOG Devices could I use for this design (IC 2 and IC 3)?

6) How can I do the Or'ing circuit between Buck and Boost controllers? Some suggestions of ANALOG DEVICES ICs?

7) There are no restrictions if heatsinks are required. No restrictions with the final physical dimensions of the PCB. Just need to work.

8) No problem if external MOSFETs are required, both on Buck and Boost converters

9) Final cost of this PSU is not so important.

10) Preference to SMD packages in all the circuit, if possible.

11) The 12V OUTPUT can be designed to deliver more than 6A. No problem about that.

12) No need of insulation (Flyback / forward topology, for example). The topology can be modified to Flyback / Forward also

For the time, all I found is a Buck converter from Linear Technology, based on a LTC1624. Example of a 12V x 10A output with Vin range of 13 to 28V using this converter:

Thanks in advance.

  • esm,

    instead of designing 2 power conversion stages (a buck and a boost) you could design a single stage SEPIC converter that can handle 6V to 30V.

    You would supply this with diode ORing at the input instead of the output.

    The ADP1621 could be used for this.

    Use the Coupled-SEPIC ADIsimPower tool to get you in he right direction.

    ADP1621 Coupled-SEPIC Design Tool v. 1.0

    A synchronous controller would probably be better bur we do not have one at this point that can handle the floating synch driver.

    The ADP1621 can also be used for the boost converter in your block diagram.

    Unfortunately we do not have a battery charger for your application.

  • Hi.

    I was thinking about you said. Yes I can do the ORing circuit at the input, with one (or maybe two) suitable Schottky diode or maybe a synchonous rectifier.

    I will check the datasheet of ADP1621 and also the design tool soon.

    Does Analog Devices have a similar solution (another IC), but based on Buck-Boost topology?

    Remembering the output must be 12V @ 6A, but 4,5A is enough also.

    And the input voltage is 6 to 30VDC (6VDC due to 2 li-ion cells connected in series).

    I saw on ADP1621's datasheet that the supply voltage is only 2.9 V to 5.5 V. Do you have sure this IC is suitable for my design?

    Is there any evaluation board for the ADP1621 ?

    Another question is:

    Does Analog Devices have Li-Ion Charger IC capacble to charge 4 Li-Ion cells connected in series?

         (Answer, not at this time - 6/2012)

  • The ADIsimPower tool will direct you on how to extend the operating range of the part above its specified range of operation (basically a resitor is used to power the internal 5V zener)

    Free evaluation boards are available to order directly from the downloaded ADIsimPower XLS tool.