I'm attaching a link to the schematic diagram for the Free Charge Controller (http://freechargecontroller.org/images/a/ab/Charge_controller_4_04b.pdf). I have built a prototype power assembly and I have verified that the square wave is coming out of mosfets M1 and M2 as described in the documentation "Testing the Power Circuitry" (http://freechargecontroller.org/Documentation). I understand that the circuit is some variation of what is called a half bridge drive. Here is a link to the page where the test program I am starting with is (http://thesolarpowerexpert.com/free-charge-controller-kit-part-4-testing-the-power-circuitry/) the source code is available as well in the documentation "Testing the Power Circuitry".
The code to the program is telling me that sending the Arduino high signal to 8 turns on the high side and sending a high signal to 9 turns on the low side. This makes sense to me since pin 7 of IC2 (The half bridge driver) is connected to the gate of M2 and the gate of M1. I'm pretty sure I understand correctly that D1 prevents electrons from flowing from the direction of M1's gate back to M2. I don't yet understand the purpose of the resistor R1 which is soldered between source and the gate pins of Mosfet M1. Could someone explain this?
I think I understand that when mosfets M1 and M2 (which are chained) are turned on that electrons are allowed to travel onto the conduit which runs between pin 6 of IC2 and is called the VS line and the batteries positive power terminal. I don't yet understand the function of the VS line. I have tried to look at the data sheet for the IC. I am attaching a link to it (http://www.irf.com/product-info/datasheets/data/ir2104.pdf) but I'm finding I'm not really good enough at reading these data sheets to glean enough from it to understand why the VS line is there and how it is supposed to react.
So I see that the COM pin of the half bridge driver is connected to the VCC the VB and then back to the VS conduit? Why? I see the com is described as the low side return however I don't really understand where power is being returned from. Also the purpose of the capacitors C11 and C3?
Any help in understanding the schematic would be greatly appreciated.
Thank You
Best Answer
The purpose of M1 is to stop the battery from discharging into the solar panel when its voltage drops in low light. M1's Source and Drain are connected 'backwards' so that its body diode will be turned off (whereas M2's body diode will be turned on under those conditions). Resistor R1 discharges M1's Gate capacitance to ensure that the FET turns off when there is no PWM drive, while D1 keeps it charged up during normal operation. In effect M1 is acting as a blocking diode, but with lower loss.
The VS line is 'ground' for the high-side driver's output circuit. M2's Gate drive voltage toggles between VS and the 'bootstrap' voltage at VB (produced by D2 and C2).
C11 and C3 filter out noise on the power supply to IC2. They may appear to be duplicating the function of C10 and C4, but do the job better by being physically closer to IC2.