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For a solar powered project I'm using a 5V solar panel to keep a 3.7V Li Ion battery topped up.

The Li Ion charge regulator IC is an MCP73831T and can handle a Vin from 3.75V to 6V. This is fine for the most part but the solar panel can actually output up to 10V when in direct sunlight. And so I wanted some sort of over voltage protection for the charge regulator IC which doesn't compromise too much current.

I looked into standard voltage regulators but these require a much higher input voltage. LDO regulators could work but I don't think they would be able to handle the power dissipation.

I also looked at Zener diodes but these work by conducting current once their reverse breakdown voltage is reached. I'm worried that this will reduce the current used for the charging the battery and so isn't an efficient solution. (Correct me if I'm wrong)

I was wondering if there was some sort of voltage clamp IC or circuit which operates normally until the voltage gets too high and then it can regulate it. Looking for an efficient solution since the solar panel can only produce 500mA max and I want as much of this to be used for charging the battery when it's available.

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  • \$\begingroup\$ If the power you get from the solar panel matters, you want a Maximum Power Point Tracking(MPPT) charger or a charger with a better voltage range. With the charger you have the only really easy option I see without another voltage converter is to make an artificial load to waste power and hold down the input voltage. \$\endgroup\$ – K H Jan 31 at 11:07
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    \$\begingroup\$ ” MCP73831T and can handle a Vin from 3.75V to 6V. This is fine for the most part but the solar panel can actually output up to 10V when in direct sunlight.” In other words, it’s everything but fine. Get a regulator which can handle your full peak open circuit voltage plus margin. It will be cheaper and simpler in the end. \$\endgroup\$ – winny Jan 31 at 12:16
  • \$\begingroup\$ @KH Thanks for the suggestion. Just done some reading on MPPT and it seems the way to go with this. \$\endgroup\$ – zt42 Jan 31 at 12:27
  • \$\begingroup\$ @winny Thanks. The solar panel won't always have an output of 10V though. And so I need a device which can still operate at lower voltages as well (i.e. a voltage clamp). Regulators aren't very good at that this since they usually have a minimum Vin value. \$\endgroup\$ – zt42 Jan 31 at 12:31
  • \$\begingroup\$ ”The solar panel won't always have an output of 10V though” Sorry to rain on your parade, but that’s a rookie mistake way of thinking. Assume worst case scenario and design for that. Your average transistor blows within ms if you apply overvoltage. \$\endgroup\$ – winny Jan 31 at 13:54
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Looking for an efficient solution since the solar panel can only produce 500mA max and I want as much of this to be used for charging the battery when it's available.

Use a buck-boost pre-regulator like this one from Analog Devices/Linear Technology: -

enter image description here

You can work this from any input voltage in the range 2.5 volts to 15 volts. Texas Instruments will no-doubt have similar offerings. If you need a bit more power (and efficiency) then consider this one: -

enter image description here

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    \$\begingroup\$ This is a good solution. Even better would be to find a replacement for the MCP73831T that can handle 10v. \$\endgroup\$ – user69795 Jan 31 at 17:45
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    \$\begingroup\$ This is exactly what I need. Looks like it'll do the job. Thanks! \$\endgroup\$ – zt42 Jan 31 at 22:11

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