I'm designing a small solar charger with these characteristics:


  • Voc = 5,65 V
  • Vmp = 4,25 V (Voc -25% approx.)
  • Isc = 250 mA


STMicroelectronics SPV1040 High efficiency solar battery charger with embedded MPPT


  • Type Li-Po (Model LP804367, FULLWAT)
  • Nominal Voltage 3.7 V
  • Nominal Capacity 2400 mAh
  • Standard Charge Current 480 mA
  • Max Charge Current 4800 mA
  • Charge cut-off Voltage 4.20+/-0.05 V
  • Discharge cut-off Voltage 2.75 V

I used the ST Electronics eDesignSuite tool and THIS is the schematic of the design calculated with this tool enter image description here


When I have entered the characteristics of the solar panel in the eDesignSuite tool, I have introduced as open circuit voltage the value Voc = 5.2 V which is the maximum input voltage allowed by the IC SPV1040T. However, the Voc value of the solar panel used is 5.65 V, so I thought of using a zener diode in parallel with the capacitor Cin to not exceed this the maximum voltage allowed at the IC input (5.2 V).

  1. Is this correct or is there a better solution than using a zener diode to clamp the input voltage?
  2. Could the zener diode decrease to the efficiency of the MPPT algorithm?
  3. If using a diode zener is a feasible solution, could this zener diode be used? (1SMA5918BT3G)

1 Answer 1


Sorry, that chip is largely unsuitable for your needs. It is a boost converter i.e. generates an output voltage that is higher than the input supply voltage. Given that your SP ranges between 4.25 volts and 5.65 volts AND you only require a maximum output voltage of 4.2 volts, you should be looking for a buck (rather than boost) controller.

The block diagram below shows the transistors that prove to me it's a boost converter: -

enter image description here

  • \$\begingroup\$ Thanks! Do you know any buck controller charger for solar power source? As much as I look for I do not find any for the characteristics of my design. \$\endgroup\$
    – FranMartin
    Commented May 4, 2018 at 13:39
  • \$\begingroup\$ @FranMartin it's not an area I have had much experience in so nothing springs to mind. \$\endgroup\$
    – Andy aka
    Commented May 4, 2018 at 13:40

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