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LT3083 as a Voc Clamp to power LTC4015


I am using the LTC4015 with Solar Panels that have Open Circuit Voltage (Voc) as high as 42V, but the maximum voltage that can go into the LTC4015 is about 36V. So I am looking for a Voltage clamp / Regulator that can output 36V/3A from a 42V/3A power input. 

 For this requirement my search lead me to LT3083, and specifically to the high voltage regulator mentioned on the datasheet (Page20).  

Following are my questions

1. Is this a good solution for the requirement I have? or are there better alternatives?

2. For the above schematic to output 36V/3A apart from Rset, any other parts on the schematic will need changing?

3. I dont completely understand the input section FET circuitry, can someone explain this part?


  • Hi Deepak,

    I am not familiar with LT3083, but I can give some LTC4015 perspective. It may work. Your idea is basically to protect the circuit when above 36V, knowing you will not get much power in that case, but then operate the regulator in dropout the entire time. This will essentially cause the regulator to be a pass-through for the solar panel (minus the dropout voltage). It just might work with the LTC4015's MPPT scheme, but it is not something we have tested.



  • I apologize but I am the product applications engineer for the LT3083 but I don't recommend using the LT3083 or any other non-switching device to drop the 6V between your solar panel and the LTC4015 because the non-switching device used that way will dissipate (waste) too much power.  Contact Technical Support from the Analog Devices web site and see if they can recommend a part that is a better fit than the LTC4015.

  • It should be noted that the customer is not looking for high efficiency while the LT3083 is active. My understanding is that this is mostly meant for OV protection and to get a little power through (unlike OV protection alone). The solar panel will have low current capability in the voltages where the LT3083 is active (operating near the solar panel's open-circuit voltage), so the actual power dissipated may be acceptible.

    We do have some other solar chargers with higher voltages. You might consider LTC4013. However, we do not have any higher-voltage charger with the digital telemetry that the LTC4015 has.



  • ARad,

    Thanks for the reply, however as Zack has mentioned in his reply, we will be using the LT3083 to clip excess low current / high impedance current from solar panels (the open circuit voltage) part of it. Once the panels are loaded the voltage will automatically drop to below 36V and the LTC3083 will not really be regulating in this region. 

    In this case is this acceptable? 

  • I apologize again but your system seems complicated to me and I don't have the resources to give you a good answer.  I would at least make sure the system functions properly including stability in an LTspice simulation with reasonable models for the panel and load.  Perhaps another way to answer is to say that I don't know of any reference designs - in articles, datasheets or my support history - where the LT3083 is used as you suggest.  That does not mean it is not possible to use the LT3083 as you suggest because normally I get support requests when there is a problem - not when things work.

  • ARad,

    Thanks for the effort. However, we did a quick test with the LT3083 and we found it not to be suitable for the requirement, primarily because of thermal performance.