What will happen if I connect a diode with a battery 1V or more without any resistor?

What will happen if I connect a diode with a battery 1V or more without any resistor?
(it is forward biased)
Is the diode broken down?

depends on the current rating of the diode and the battery.

If battery is a heavy duty high current capable, then the diode will most likely break. If the diode is a very high current capable then internal resistance of battery will limit the current to some (high) value, and everything will heat up quite a bit.

If you had a really heavy battery or power supply (behaving as almost ideal voltage source), with output voltage somewhere between 1.2 and 2 volts, it might work without frying the LED. You would have to know the current characteristics of the LED and your voltage source would have to match the voltage where the LED passes the right current - about 20mA.

In the end you may get a (theoretically) working circuit, with very poor regulation - tiny voltage drops on battery due to discharging would result in significant current drop on the LED; heating of the LED would change the current characteristics due to non-zero temperature coefficient.

So you should always have a resistor in the path of diode current, if using voltage source, to linearize the current characteristics. That resistor may be the parasicic resistance of the used battery (if sufficient), as menioned by kripacharya

I don't know of a popular battery physic with 1V cell voltage. Is it a theoretical question?

I don't know of a popular battery physic with 1V cell voltage. Is it a theoretical question?

Click to expand...

yes. My initial intention is to find the limit for Vbe and Vce in the image.
Please see the figure bellow:

I want to know the limits for Vbe and Vce in this circuit.

That's what I call a theoretical question: A setup that would be never found in a real circuit.

Generally speaking, you can calculate Ib and Ic based on specified device characteristics, e.g. datasheet information.
If Ib, Ic or power dissipation exceed the transistor ratings, it may be damaged.

Some points to consider in a real setup:
- real batteries/voltage sources have an inner resistance
- transistor characteristics will change with temperature and possibly cause an instable operation point