Help with LM2585 behavior ...

Hi,

I hope you can help with this. I have made a buck boost converter using the LM2585 (please see attached schematic). I works perfectly and allows me to output voltages from ~23 volts to ~61 volts DC with an input ranging from ~4 volts DC to ~22 volts DC.

However, I use the circuitry with solar cells and have observed that when the current drain is higher than what the solar cells can output, the LM2585 "shuts down" - which is as it should be - BUT it does not resume charging at the set voltage when the solar cells again output more.

I may manually set the output current limiter to a desired value but at some point in time the sunlight intensity will drop below this level causing the LM2585 to shut down again.

I wonder if there's a way to make the LM2585 resume operation when the solar panels again output sufficient power? Or maybe there's a better IC or circuitry to be used?

Assistance is appreciated.

Regards,

Jesper

What is the load for the LM2585?

How do you restart the converter after it shuts down?

Hi - the load is various batteries so current drain varies and can be "high". I restart the converter by removing the voltage input completely and re-connect. It's just not that feasible ...

Regards,

Jesper

Sounds like the converter gets hung in some abnormal state when the voltage is slowing reduced and then slowly increases. Don't know what you can do expect add a circuit that removes and re-applies the input voltage when it detects that the circuit has no switching signal at the SW output.

Conceptually you could AC couple the SW signal and rectify the capacitor output. Use that to trigger a 555 one-shot that would momentarily remove the power when the rectified signal goes to zero. The power could be controlled by a P-MOSFET in series with the input to the converter. You may have to add a delay (perhaps another 555 or a 556 [dual 555]) so that you allow some time for the converter to start before it shuts off the power again.

The only other option I see would be to try a different converter.

Edit: Thought of another more simple option. Add a comparator to monitor the input voltage a cut it off when it goes below the operational voltage and rapidly turn it back on when the voltage goes above the minimum operational voltage. This could be done with a comparator and a P-MOSFET in series with the converter input voltage.

Edit 2: You may be able to just switch the power to the regulator without switching the power to the inductor. Thus you wouldn't have to switch high current and also the reduction in efficiency that such a switch would cause.

Get more solar panels or build up a reserve by charging a SLA battery with the solar panel and use the battery to run your DC to DC converter. Andy

@Andy: Thanks for your suggestion. It will, however, probably not be possible to increase the amount of solarcells and SLA batteries are quite heavy (I am to use this for a bike trip). But I see the point in your idea.

@Crutschow: Hmmm...Thank you also for your ideas. I will consider your suggestions, although I had hoped that there might be a simpler solution like adding a few components and maybe making a few more connections ... Ideally, I would like to find a simple solution that measures the available power on the input and adjusts the output accordingly but I don't know if that can be done in a simple way?

'Best for your weekend,

Jesper

Jesper; What are you powering with this? LEDs? Andy