MPPT-2420-LC with switchable boost output

As Martin confirmed the MPPT-2420-LC hw and fw are capable to work in buck or boost modes.

I found interesting to modify the hw and fw in such a way that the device should be capable to charge a battery in buck mode during day time, than in dark condition it should operate in boost mode to supply a high power LED light so energy stored in the battery will be used for lighting.
I opened this topic to share this project with anyone who might be interested in this feature.

I’m sharing my first draft schematics and some thoughts.

  • The Q2, R2 and D1 are unnecessary and should not be placed for this modification, I’m just planning to leave it there in case the boost feature is not needed or if someone wish to keep the current protection circuit.
    For boost mode Q2 S-D should be connected to allow current flow.

  • To detect day/night conditions I need a way to measure the PV voltage continuously. I thought not to interrupt the SOLAR-, so I’m planning to use the reverse protection from MPPT_Charger_12A.
    PV_Voltage output can be used for monitoring purpose.

  • I added LOAD(LED) output which can be turned on with DCDC_LOAD(LED)_OUT.
    I’m planning to use relatively high voltages

    for LED’s around 40-50V and current will be around 2-3A so using a P-channel MOSFET shouldn’t be a problem (it’s relatively hight RDS(on) is still OK for this application)

Any comments / ideas are welcome!


I’ve got some concerns. Not sure if the circuit will work as intended.

  • Q2 can be used also for boost mode, as it is continuously on as soon as the power stage is switching. It is kept on during off-time of the LS FET by the MOSFET’s internal gate capacity.
  • The idea with the PMOS Q6 from previous design was to allow reverse polarity protection even though the pull-down of the Q5 gate faces “outwards”. Unfortunately, it didn’t work on a test board. But I didn’t further investigate why, as I moved the reverse current blocking to the low-side, which is easier. So this circuit might not protect from reverse polarity.
  • You need the power stage to be on also for driving the LEDs. But this means that also Q2 and Q5 will be on, so current will flow into your solar panel during the night.

A simple solution could be to use a dedicated driver for Q2 so that you can switch it independent of the power stage and keep SOLAR- floating during the night.

The gate of Q7 will also need some protection with a Zener diode, as the max. voltage will be exceeded if DCDC_LOAD(LED)_OUT is pulled down to GND.

Yes, Q2 can be used for booth buck or boost but once the converter is idle (for example on sunset or sunrise when there is not enough solar energy to charge a battery but a LED light not needed) Q2 will switch off hence Solar- to GND is disconnected and floating so it is not possible to measure the solar voltage anymore. I need to monitor the solar panel continuously to be able to decide when to switch on or off the LED.

Thanks for the info about the earlier protection circuit. I was trying to simulate it earlier and was not working as expected but I thought I might be wrong because it is a proven circuit :slight_smile:

It looks like I need to find another solution to monitor the PV even in idle mode and also a protection circuit.

Great idea !! What a great way to make full use of the hardware day and night.

Here another idea which based on spice simulation should work.


I’m wondering if you also tried your smaller MPPT 1210 in boost mode? Does the fw support it?

On another thread I read that you may have some blank PCBs for the MPPT 1210 (also 2420-LC maybe?). I might be interested in both if you still any, it would be easier to start development on real hw.


Nice solution. Only issue I can see is that the gate of Q5 could see too low voltage if DCDC_IN is above 30V.

Yes, I did also try the boost mode with the MPPT 1210 and it works. The firmware is the same for all charge controllers anyway.

Don’t have any PCBs for the 2420 anymore, but there are some of the 1210 left. Send me an email if you are interested.

hmm, I’m not sure If I understand the Q5 issue.

Imagine you are in boost mode and the voltage DCDC_IN is at 40V vs. GND. Now if ~LED_EN = 1, Pin 3 of T2 and the anode of D6 are at GND potential. The Zener diode D6 drops the reverse bias voltage of approx. 10V, so the cathode of D6 = gate of Q5 will be at -30V vs. its source, which is more than the absolute maximum of ±20V.

See also Second input to 20 amp charge controller.


I sent you an e-mail on 29th of august.
Have you received it?