I have thoroughly checked the schematics of Arduino Pro Mini from multiple sources and I count find any diode on the board.
Personally, I have one Chinese Clone of Arduino Pro Mini and I found that there is one mysterious component whose one end is connected to VCC and the other end is connected to the input of the voltage regulator. I confirmed these connections using a continuity test on a multimeter.
My guess is that it is a diode and uses to limit the direction of the current. See the picture attached.
Do you think I am right? its there any other use of this diode ?
Sounds right. Is there any marking on it? A hint of a band across the body on the regular side?
When power is applied, is the voltage at the regulator end 0.4V to 0.7V lower than the other side?
Most small-board Arduinos with USB connector have a USB backflow protection diode between USB power and VCC (or regulator). The SOD-323 version of an 1N5819.
Not a problem to also use it on a board without USB. In that case it's for reverse (supply) voltage protection.
It looses of course ~0.4volt, that could be a problem if you want to power a 3.3volt board with a 3.7volt LiPo battery.
Leo..
If it is between VCC (output of regulator) and the input, it would be to allow 5V to be applied to VCC with nothing on Raw and not damage to the regulator.
CrossRoads:
Sounds right. Is there any marking on it? A hint of a band across the body on the regular side?
When power is applied, is the voltage at the regulator end 0.4V to 0.7V lower than the other side?
There is no marking on it but I have checked it is a diode. The amazing thing is that I have searched in many places and I count find any schematic diagram mentioning doides.
Wawa:
Most small-board Arduinos with USB connector have a USB backflow protection diode between USB power and VCC (or regulator). The SOD-323 version of an 1N5819.
Not a problem to also use it on a board without USB. In that case it's for reverse (supply) voltage protection.
It looses of course ~0.4volt, that could be a problem if you want to power a 3.3volt board with a 3.7volt LiPo battery.
Leo..
What if I power the Arduino pro mini board directly at the Vcc using a 3.7-volt lipo. As the battery voltage is very close and above 3.3 so the atmega328p should be fine at 8MHz and also all of the onboard components will easily handle 3.7 because the voltage is probably not beyond the rating. Yes over time the voltage will drop and that drop will be very steady so I guess it should not affect the performance of the Arduino pro-mini-board. Am I right?
CrossRoads:
If it is between VCC (output of regulator) and the input, it would be to allow 5V to be applied to VCC with nothing on Raw and not damage to the regulator.
I have studied the schematic of the Sparkfun Arduino Pro Mini board and they provide an onboard jumper that can be used to connect and disconnect the Vcc to the output of the regulator.
Yes, the diode will prevent the current from flowing into the regulator, which will help to save power. I don't think it will damage the onboard regulator. Because I have powered Arduino pro mini directly at Vcc with the voltage regulator intact and the voltage regulator seems fine. Do you think it will degrade with time?
Furthermore, A diode at the output of the regulator doest seems a smart choice to me as it will drop around 0.6 volts and will drop the voltage that we get at the Vcc.
yasinzaii:
Because I have powered Arduino pro mini directly at Vcc with the voltage regulator intact and the voltage regulator seems fine. Do you think it will degrade with time?
No. The only two concerns with the regulator are firstly that if you have a large reservoir capacitor on the input and you suddenly connect the full 5 V to the output, there may be an excessive backflow current to charge that capacitor. This is most unlikely as the input capacitor on the Pro Mini is by no means large and you are simply not going to apply the 5 V (or 3.3 V) suddenly.
The only other concern is that the regulator may leak some current - less than a milliamp - from the output to ground. This is always undesirable when operating from batteries.
yasinzaii:
Furthermore, A diode at the output of the regulator doesn't seems a smart choice to me as it will drop around 0.6 volts and will drop the voltage that we get at the Vcc.
You simply do not put a diode at the output of the regulator for this very reason and the Pro Mini does not. Only ever at the input.
JohnRob:
I have a couple of Pro Mini Clones. One has the diode (to protect from reversed input voltage coming in the RAW input)
The other board does not.
I know that if I connect the voltage source is reverse the Tantalum Capacitor connected at the raw pin will burst and become short and it will short the voltage source and may even cause a fire.
So to avoid this they have added the reverse protection doide? am I right ?
Well, to prevent damage in general, which might include the tantalum, but more the processor and whole circuit.
The only real reason for reverse polarity protection is if you have a battery (or other power supply) which it is possible for users to insert in reverse. If you assemble it wrong, more fool you!
