Obviously to have more current is there a way to somehow connect multiple DC sources together not by using trivial series Schottky diodes, but using mosfets and LDO(Low dropout) circuits? To somehow use the mosfet body diode forward voltage drop as a one way "valve" as long as it's within 0.5V or less between any 2 sources in the array? I don't think it's possible. But I'm not sure... That's why I'm posting this question. I don't think it's possible because the mosfet is not a unidirectional switch but bidirectional? I think the N or P channel is symmetrical in the manufacturing of mosfets. I'm not sure... I don't know. But if the substrate is connected to the source then it's not symmetrical...I'm not sure...I don't know...I have many questions and very few answers and self-confidence. I'm almost sure the circuit in the picture does not work, but can somehow be made to work? Can two mosfets in anti-series be used somehow? I don't know...I don't know anything. Can somebody help me?
\$\begingroup\$ Connecting 2 batteries in series increases current. \$\endgroup\$– Miss MulanApr 5, 2022 at 13:18
Actually when multiple dc sources have to be connected to increase the current, the problem is not as simple as it looks.
First, you have to look into the actual problem which stems from basic electrical principle, ie.,
- Different rating Voltage Sources should not be connected in parallel and Current sources should not be connected in series.
- What is acceptable is like this: One controlled voltage source fixing the parallel combination voltage and other sources behaving as current sources.
simulate this circuit – Schematic created using CircuitLab
- Droop control is usually employed in parallel combination of voltage sources.(You can check the literature for that). Most commonly, it is used in grid where multiple sources are connected.
So, the problem comes down to a basic one. We have to control the dc link using one source acting as voltage source and other sources to behave as current sources(if more than one acting as voltage source, control problem comes into the picture with possibility of circulating current).
This implies we would need, a voltage to current converter (Power electronic circuits have to be dealt with). Now this becomes a little complicated in which you will have to study up a bit on it. It is difficult to tell all the things here.
Following are the references you can read in which they implemented such a thing:
Unitrode IC Application Design
Many more available on internet.
The questions that you asked:
- Connecting only via schottky diode won't solve your problem. Since then only 1 voltage source will be providing power.
- For the case of MOSFET's circuit that you have shown, same thing applies
\$\begingroup\$ Please don't get me wrong. I don't disagree, but I need to add something. In theory you are correct if the DC sources have same parameters except the voltage, but in practice the DC voltage sources might not have same internal resistance (some panels are older, others newer, others are shaded, other are not, some are polycrystalline, others are monocrystalline). If the DC sources are roughly the same voltage (19 +/- 1V), and the load is high it will drop the voltage of the higher DC sources first, until current then begins to be drawn from lower voltage sources. \$\endgroup\$ Jul 9, 2020 at 9:34
\$\begingroup\$ I think what I'm trying to say it that connecting via schottky diodes the Voltage-current output curve is not a uniform smooth curve (I’m guessing it has ups, downs and inflexion points). True, the current distribution will not be even, but at least we draw current from all the sources, in the idea for example to somehow eliminate the backflow of current from the sunny panel to the shaded one(which begins to act as a load "stealing" current from the rest of the array). \$\endgroup\$ Jul 9, 2020 at 9:34
\$\begingroup\$ If Schottky diodes are used, Let's say you have 2 sources, one of 19.7V and other of 19.3V output of sources, (Considering Vdrop of Schottky = 0.3-0.6V for higher power), the common point of voltage would have to be lower than <18.7 for both to be active. Then, your theory would work, but the thing is you will have no control over the power drawn from the panels. It would come down to internal resistance and load power as you said. The above answer showcases if you want a little complex solution with full panel power utilization. But Yes, the solution would become involved to implement. \$\endgroup\$– DivBJul 9, 2020 at 9:44
\$\begingroup\$ So it all comes down to the implementation scale. It will depend on the application you want to use for, what the power ratings are(For higher ones, complex solution have to be looked for), what range of voltage sources are being used(One solar panel may be covered(No power from this one) but others may not be). \$\endgroup\$– DivBJul 9, 2020 at 9:47
\$\begingroup\$ Your links in your answer are informative. Thank you! Never heard of ”ORing” before. Never heard of ”Ideal diode controllers” before. I'm still learning stuff... \$\endgroup\$ Jul 9, 2020 at 9:58