# Determining the region of operation of these two diodes

I'm having trouble determining the region of operation for these two (ideal) diodes. Do I check the Vopencircuit values or their current values?

• It's region of operation, not region of not-operation, right? Feb 29 at 0:52
• Show your work and we can tell you where you went wrong. Feb 29 at 1:01

I'd recommend this: Check all possible combinations. It's not many. I'll start, you fill in the blanks.

# D3 in reverse bias, D4 in reverse bias

Both diodes are blocking.

This is impossible, because then the 5 mA from the current source can't flow anywhere.

# D3 in reverse bias, D4 in forward bias

D3 blocks, D4 is a perfect conductor. The 5 mA hence have to flow ____________________. This is (im?)possible, because: ______________

# D3 in forward bias, D4 in reverse bias

D3 ____________________, D4 ____________________.

Hence, ____________________. This is (im?)possible, because: ______________

# D3 in forward bias, D4 in forward bias

D3 ____________________, D4 ____________________.

Hence, ____________________, This is (im?)possible, because: ______________

To determine your regions of operations, I would refer to the I-V characteristic curve of a diode:

(Image from an article on ElectricalFundablog found here)

Ideally, a diode in forward bias acts like a short circuit whereas in reverse bias acts like an open circuit.

So in your circuit, check both cases. For forward bias, replace the diodes with a short and check if the voltage is greater or less than zero across the short. For reverse bias, replace the diodes with an open circuit and check if the current is greater or less than zero across the open.