# Photovoltaic cells and CC load

Hello! I am newbie in photovoltaic electronics and recently learned about MPPT.

In my project load needs constant current. Does constant current load, needs MPPT at all? Any DC-DC current mode converter, with current feedback, will adjust duty cycle to get max current limited by feedback circuitry, even if that current is approximately solar panel max current.

Thank you!

The system resembles this:

simulate this circuit – Schematic created using CircuitLab

Power $$\P_{IN}\$$ obtained from the solar panel PV1 is:

$$P_{IN} = I_{IN}V_{IN}$$

Power delivered to the load is $$\P_{OUT}\$$:

$$P_{OUT} = I_{OUT}V_{OUT}$$

To determine what kind of DC-DC converter is appropriate for your load depends entirely on the output requirements. In your application $$\I_{OUT}\$$ is fixed and known, and the DC-DC converter will be producing whatever voltage $$\V_{OUT}\$$ is required to produce constant current $$\I_{OUT}\$$ through the load. There is no maximum voltage or minimum voltage, only the exact voltage across the load that will cause the load to pass a current of exactly $$\I_{OUT}\$$.

The DC-DC converter will therefore be regulating current by varying output voltage, just like any constant current source. The exact $$\V_{OUT}\$$ required to achieve that exact $$\I_{OUT}\$$ will be determined entirely by the load. That is, required output power $$\P_{OUT}\$$ will be some very specific amount, and will have nothing to do with the maximum power available from the solar panel.

The purpose of an MPPT controller is to draw the maximum available power from the solar panels at all times, which is clearly not the condition required by your application. Power requirement for your load is set by the load, to some very specific amount, not related to the maximum power available, and MPPT is not an appropriate system for that.

• Thank you for your response Simon. Can we get max power if all params are known, just tuning the converter? For example, solar panel is 50V, max current 9A (not short circuit), load needs 4.5A, load impedance 20 Ohm. Efficiency coefficients let’s 90%. 50V * 9A = 450W, 0.9* 450W=405W of output power, it means 405W/4.5A = 90V, 90V/20 ohm = 4.5A, exactly what we need. Can it be any step-up converter? boost, half-bridge, two-switch forward etc? I mean any converter will match impedance's of panel and load? Tuning duty cycle will change output voltage, do we need change also frequency?
– Erch
Commented Jul 18, 2023 at 15:58