Discussion in 'Electronics Homework Help' started by 07potatoes36, Mar 24, 2013.

1. ### 07potatoes36

2
0
Mar 24, 2013
in the attachment there are four circuit diagram (A,B,C,D)
questions:
1). What are the condition for the diode to conduct in circuit A,circuit B,circuit C , circuit D?
example : in A the VRA must be bigger than VA for the diode to conduct.

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2. ### Laplace

1,252
184
Apr 4, 2010
Are these ideal diodes, or must there be a forward voltage drop (0.7 volt?) before they are considered to be conducting? Is the external applied voltage (+,-) the same for each case? For starters I would zero out the battery voltage and analyze whether the applied voltage (+,-) would cause the diode to conduct, then determine whether the polarity of the battery voltage would aid or oppose the applied voltage. Then determine the point where the battery voltage just begins to enable or suppress conduction. Note there may be a case where the diode always conducts or never conducts regardless of the value of the battery voltage. I would think that the value of the resistor is not relevant to whether the diode conducts or not so I am assuming that 'VRA' is the value of the external applied (+,-) voltage.

3. ### 07potatoes36

2
0
Mar 24, 2013
VRA is the Voltage of Resistor in circuit A.
(+,-)?yes its another source..its a semiconductor diode perhaps and i have no idea what model it is... i just copy the question from the whiteboard...i ask the lecturer but he ask me to find the topic in youtube .. and here is the link... (please watch at 16:00)
the cirsuit diagram is exactly the same ...but i dont understand sigh...

4. ### Laplace

1,252
184
Apr 4, 2010
With the above perspective this becomes exceedingly simple. Identify the point where diode conduction begins - in all cases this is when the voltage across the diode equals zero, i.e., VRx=Vx where x is A, B, C, or D. You merely need to determine the region of conduction, when VRx is (more positive, less positive, more negative, less negative) than Vx.

It does not matter if VRx is taken to be the voltage into the resistor or the voltage at the resistor/diode connection node. At the point where diode conduction begins there is no current flowing so the voltage drop across the resistor is zero and both ends of the resistor are at the same voltage.