Solar Charge Controller Circuit

Thread Starter


Joined Mar 19, 2016
Hello All,

I have been designing a solar charge controller for 12 volt battery. The circuit is shown below. The parameters of the buck converter are as follows:

D1: Schotkey diode MBR1645
L: 8uH
Ci: 470uF
Co: 2000uF
Can anybody please validate the above design. The parameters are as follows:

Vin(min): 15V
Vout: 12 V
Iout: 15 A
Switching Frequency: 50kHz
Iripple: 30%
Vripple: 10%

The 1kHz PWM wave feeds the Dickson Charge Pump for driving the gate of the IRF44Z.



Joined Sep 9, 2010
You should learn to use LTspice. It can simulate your circuit for you and also produce a schematic that's easier to read. It has a learning curve but will save you time in the long run if you're designing circuits.


Joined Jun 22, 2012
Where's the 12v feed coming from on the left?? Dont see the point of the two transistors back to back...
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Joined Sep 17, 2013
There is nothing shown for monitoring either the battery voltage or the charging current. How will you know what PWM duty cycle to generate in order to control the charging?


Joined Mar 14, 2008
I also suggest learning LTspice (free download from Linear Technology) to simulate your circuit.
It has a fairly steep learning curve but the tutorial and examples will greatly help, as well a help from several of us on this forum.
Simulating your circuit will save you a lot of grief in getting it to operate after you build it.
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Thread Starter


Joined Mar 19, 2016
Will try and learn LT Spice (already downloading it)

@ Alec_t,
I am controlling the PWM with a micro controller that tracks the voltage of the battery via a voltage divider (not shown in the circuit diagram)

Also, the voltage and and current of the panel is monitored via a voltage divider and a current sensor (also not shown in the circuit diagram)

When the voltage of the battery is below 14 V, the PWM is at maximum duty cycle which charges the battery at Vmp of the panel. When the battery voltage rises upto 14 V, the duty cycle is reduced so as to keep the battery at trickle charge.

At the same time, a P&O algorithm monitors the panel power and if the panel is being loaded, it adjusts the duty cycle to keep the panel at Vmp.

@wayneh, D1 is included it so as to protect the battery in case the panel voltage drops suddenly (even if for a small time due to clouds passing over and the monitoring sequence has just completed) In such a case, the current might flow from the battery to the panel and can damage it. I know it sounds far fetched but wanted to be safe. This is precisely the reason I am asking the community for help. If you think if is redundant, please explain the logic so that I can remove the component and improve the circuit.


Joined Sep 9, 2010
Never mind. In the normal configuration with the source pin to the right in your drawing, the body diode would allow conduction in the reverse direction, if not for D1. I was confusing this with some work I did on an active rectifier a while back, where you turn the drain and source around and use forward conduction through the body diode to your advantage. Not relevant here.