# Diode Circuits: Find Q-Point for D1

• Engineering
• Gotejjeken
In summary, for the given circuit, the Q-point for diode D1 is (0V, 1mA) for the ideal diode model and (0V, 0.88mA) for the constant voltage drop diode model. The direction of current flow through the diode depends on the polarity of the voltage across it, and in this case, it is defined as flowing out of the node for I3.
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## Homework Statement

For the figure below, use the ideal diode model and the constant voltage drop diode model (assume a turn on voltage of 0.6V) to find Q-point for diode D1:

[PLAIN]http://gotejjeken.webs.com/ckt.jpg

KCL/KVL

## The Attempt at a Solution

For the ideal model, I assumed the diode was on, and thus acted as a wire. Doing that, I get a Q-point of (0V, 1mA), as there is 1mA flowing into the node from the 10V source and 2mA flowing out of the node from the 20V source, so there must be 1mA coming in through the diode branch.

For the CVD model, I get a Q-point of (0V, 0.88mA), as there is 1.06mA coming in from the 10V source, and 1.94mA flowing out through the 20V source, leaving 0.88mA to flow in through the 0.6V source.

I am a bit concerned about my definition of the I3 current (I1 and I2 are defined by the problem). If I define it flowing out of the node instead of in, the current is negative, which doesn't make sense for either model of the diode. If I assume the diode is off, I get a positive voltage across it with no current, which also doesn't make sense.

I always get confused with circuits that have multiple sources like this, can anyone check my reasoning over and see if it is sound?

Last edited by a moderator:

Your reasoning seems sound and your calculations are correct. However, one thing to keep in mind is that the direction of current flow through the diode will depend on the polarity of the voltage across it. In this case, since the voltage across the diode is positive, the current will flow in the direction you have defined (out of the node for I3). If the voltage across the diode were negative, the current would flow in the opposite direction. So, it is important to consider the polarity of the voltage when defining the direction of current flow through a diode. Other than that, your approach and calculations seem correct.

## 1. What is a diode circuit?

A diode circuit is an electrical circuit that contains one or more diodes, which are electronic components that allow current to flow in only one direction. Diodes are commonly used in electronic devices to convert alternating current (AC) to direct current (DC) or to protect against reverse current flow.

## 2. How do I find the Q-point for D1 in a diode circuit?

The Q-point, or operating point, for a diode in a circuit can be found by using a load line analysis. This involves plotting the diode's current-voltage (I-V) characteristics on a graph and finding the intersection point with the circuit's load line. The Q-point is where the diode's current and voltage values intersect on the graph.

## 3. Why is it important to find the Q-point for D1 in a diode circuit?

The Q-point is important because it determines the operating conditions of the diode in the circuit. It ensures that the diode is functioning within its safe and optimal range, preventing damage to the component. Additionally, the Q-point helps in analyzing the overall performance of the circuit.

## 4. What factors affect the Q-point for D1 in a diode circuit?

The Q-point for D1 can be affected by several factors, including the value of the load resistor, the input voltage, and the characteristics of the diode itself. Any changes in these factors can shift the Q-point and affect the performance of the circuit.

## 5. How can I adjust the Q-point for D1 in a diode circuit?

The Q-point for D1 can be adjusted by changing the values of the load resistor or the input voltage. This can be done by using a potentiometer or by selecting different resistors. Additionally, using a different type of diode with different characteristics can also affect the Q-point. Careful analysis and experimentation are required to find the optimal Q-point for a specific diode circuit.

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