Load detection

[bmarvo]

Okay so I'm designing a portable cell phone charger with a battery pack. What I want to do is detect when the phone is connected so I can turn
on an LED indicating whether or not the battery has sufficient charge. I immediately think that current sensing on the output is the way to go.

So I found this device: http://www.st.com/internet/com/TECHNICAL_RESOURCES/TECHNICAL_LITERATURE/DATASHEET/CD00283176.pdf

I could use something like that with a comparator to detect when the load is attached. It does seem like overkill using a precision device.

Anyone know of a more elegant solution?

Here is an image of a very basic version of what I'm talking about.

[chrome]

Small resistor in line with the power supply going to the phone, measure over this resistor with a opamp in differential mode, feed this to a comparator, done.

[bmarvo]

Excellent. Prototyped it and it does the job

[T4P]

What chrome said is basically a current shunt monitor ... like a INA168
His solution is cheaper 

[cebrax]

I am really interested in this. I want to make a detector to detect IC insertion into an 8-pin DIP socket. Whenever the IC is inserted, I want to sense if there is any current flowing into this IC's Vcc pin, and so I will be able to detect an IC insertion (or call it a load connection). However, I want to build this only with transistors. Is this possible?

[AndyC_772]

Depends on the IC. If it's a CMOS gate, for example, there could be so little current that measuring it could be a real challlenge whatever components you decide to try and use.

Do you have a specific IC in mind?

[cebrax]

Yes, I think it is a CMOS IC. I have a specific IC in mind, X9C102P, but I don't want this detector to be working for only this specific IC, that means I do not want to detect it polling other pins.