How to detect 5V?

Hi,

Are you sure the power good line isn't a logic level signal (i.e. two states, high and low)? Usually, they output something undefined when the PSU output voltage is very low (e.g. just powering up), then they indicate power bad for the milliseconds that the supply is still coming up, then they indicate power good, then they remain there unless the output voltage is not within some threshold in which case the signal indicates power bad by changing logic level again.

So, if you have enough power to drive your circuit from the main supply, then you can trust the logic level of the power good signal.

You could just drive an LED from the main PSU using a resistor and a transistor. Connect the Power Good output via a resistor to the transistor base. Or (even more straightforward, it should only have an extremely dim state during the undefined stage when the voltage is very low), just connect the LED directly to the Power Good line through a resistor.

Ow so you say the PG line would just be 0 or 1 (0 or 5V)... That would idd simplify things!

I read somewhere that the PG line could be 3V so I guessed it was an analog signal.. Did not find anything else on it so I decided to trust that.. Might do some more research!

If it's idd just a digital signal that simplifies everything!

I'll update the thread when I find out more about this!

It is a guess, it depends on your power supply (google the part number in case you can find user documentation for it).

It isn't necessarily 5V, but usually is a voltage, e.g. a 12V supply may output 11V if the power is good, and 0V if the power is bad.

However, you still need to check the documentation, there is no real standard on this. Also, don't assume that the signal means that

the output is exactly 5V or 12V or whatever your supply is rated at. It could be out by 1 volt or more. It is a crude "go/no-go" indicator.

While TINA-TI seems to work nicely on top of wine for Linux users, I also found a different package, Qucs, which runs natively on Linux (at least, Intel/AMD).  This might eventually be a better fit for the SoCs like RPi since it would probably use less resources.  I am looking through their circuit libraries with the tool on Xubuntu:

Go here if you are interested (executables and source code): http://qucs.sourceforge.net/

Although not needed for this project, there is an awesome silabs part that I found recently, called TS9001 (a couple of variants, open drain or usual totem pole type).

It is adjustable, so needs additional resistors, but has ultra-low current consumption, the kind of thing that could be used to build a rechargeable or primary cell monitor that could be permanently or semi-permanently! connected, it has about 0.6uA typical, 1.3uA worst-case (25 degrees C) current consumption (and a tiny bit more that would be eaten up with the additional resistor circuit) which was awesome.

That's a neat idea. For a battery monitor, you could alternatively arrange it with a red LED to the supply to indicate that the battery was below the threshold.

One thing to watch is that the output drive isn't as good as you'd get with a microcontroller I/O pin - 5mA max according to the datasheet.

For Linux desktop users, just install the wine package first.  Then, you can install and run TINA-TI as if it were a Windows desktop.  Note that I tested on a Xubuntu desktop system.  If I had a RPi Raspbian desktop, I'd try it there too but I am running OpenELEC.

If the measure needs to be precise, there are dedicated ICs: 'Supply Voltage Supervisors'. They are 3-pin devices that can directly drive an LED if voltage is above a certain threshold.

For 5 V monitoring, there's the TPS3809I50D (trips at 4.55 V).

The EEVBlog µCurrent uses a 2.64V one of that family as battery monitor:

Thanks for the explanation! I really appreciate the effort you put into it!

Putting a 5V zener was a silly mistake idd! And my electronics profesor would kill me if he had known I forgot Kirchoff haha

I'll definitely try out the Spice Simulators. (We actually worked with them at university once, so shouldn't be to hard to master... )

Thanks for the explanation! I really appreciate the effort you put into it!

Putting a 5V zener was a silly mistake idd! And my electronics profesor would kill me if he had known I forgot Kirchoff haha

I'll definitely try out the Spice Simulators. (We actually worked with them at university once, so shouldn't be to hard to master... )

Although not needed for this project, there is an awesome silabs part that I found recently, called TS9001 (a couple of variants, open drain or usual totem pole type).

It is adjustable, so needs additional resistors, but has ultra-low current consumption, the kind of thing that could be used to build a rechargeable or primary cell monitor that could be permanently or semi-permanently! connected, it has about 0.6uA typical, 1.3uA worst-case (25 degrees C) current consumption (and a tiny bit more that would be eaten up with the additional resistor circuit) which was awesome.

That's a neat idea. For a battery monitor, you could alternatively arrange it with a red LED to the supply to indicate that the battery was below the threshold.

One thing to watch is that the output drive isn't as good as you'd get with a microcontroller I/O pin - 5mA max according to the datasheet.

If the measure needs to be precise, there are dedicated ICs: 'Supply Voltage Supervisors'. They are 3-pin devices that can directly drive an LED if voltage is above a certain threshold.

For 5 V monitoring, there's the TPS3809I50D (trips at 4.55 V).

The EEVBlog µCurrent uses a 2.64V one of that family as battery monitor: