Small board design help!

Thread Starter


Joined Jun 30, 2021
Good morning everyone, I'm trying to make a quite simple electronic component, but being a newbie I'm not really sure about what I'm doing.
The componenti, given two input, one constant from a battery and the other variable from a solar panel, provide a constant sufficient voltage to the output. Also, using a second solar panel is able to close the whole circuit during the time this second panel cannot produce energy at all.
I'm attaching an image of the scheme so far designed.
My question is: Is there something wrong in it?
If I simulate it in a specific software everything seems going fine but on a real built circuit actually it seems not working.
Thank everyone will dedicate a few minutes to take a look at this.


Audioguru again

Joined Oct 21, 2019
Your schematic makes no sense:
1) What is the voltage and current of each of your voltage sources?
2) What is the transistor part number and what is its function? What will limit the transistor base current?
3) What is Lp1 and what are its voltage and current ratings?


Joined Jun 5, 2013
The description is also difficult to make sense of.

It sounds like you want to power something with a solar panel, but not when there is no light, as determined by another solar panel. But what is the battery for then? And why do you need two solar panels? It sounds to me like you could simply connect a solar panel to the load and get the same effect.

Edited: Please explain exactly what the circuit is supposed to do.


Thread Starter


Joined Jun 30, 2021
Thanks everyone for the time, I really appreciate it.

I understand I need to go more into details.
The component's input are:
1) a battery of about 6w
2) a solar panel able to produce up to about 8w

The output (in the previously attached image Lp1, in the scheme is just a lamp for testing purposes) is a device ables to work from 5w to the 8w of the solar panel.

Connecting the device directly to the solar panel it can work only when there is sun enough to produce at least 5w of electricity. The purpose of the component is to extend the working time of the device even when the solar panel does not produce enough energy, introducing a battery energy supply.

The component makes use of:
1) a voltage regulator (7805) to guarantee a fine not to high max voltage
2) a NPN (2N2222) to prevent the battery to flow continuously energy even when not necessary (at night time)
3) a second small solar panel that open and close the gate of the NPN.

Both inputs are connected to the circuit with simple usb cables.

I wish all is more clear now, but please tell me if I'm still omitting something.

Thanks everyone very much for the help.


Joined Oct 2, 2009
Batteries are not rated in watts.
They are rated in output voltage and current capacity (charge) in mAh or Ah, i.e. current x time.

Thread Starter


Joined Jun 30, 2021
Thank you, Mr Chips.

I wasn't aware of that.

The used battery is a very common usb battery, so usual usb values of electricity should be considered (even on my test it resulted a little bit different but I can have mistaken something...).

Thanks very much.