Output voltage vs output current

In summary, the output characteristics of a transistor in CE mode can be explained by the equation V[SUB]CE = V[SUB]CC - I[SUB]C R[SUB]C. This equation shows that as V[SUB]CE increases, I[SUB]C decreases and vice versa, due to the reverse collector-emitter voltage attracting charge carriers from the emitter side to the collector side. However, at saturation, the collector current should increase proportionally with the collector-emitter voltage until it reaches its maximum value. This seems contradictory to the equation, as it suggests that at maximum collector-emitter voltage, the collector current is zero and vice versa. This can be explained by the fact that the transistor always has a small
  • #1
ananthu
106
1
In the output charecteristics of a transistor in CE mode, according to the eqation
VCE = VCC - IC RC it comes as when VCE increases IC
decreases and vice versa. But it is only because of the reverse collector-emitter voltage, the charge carriers are attracted to the collector side from the emitter side. Hence when the collector-emitter voltage increases collector current should also proportionally increase until it reaches the saturation value. Then why do we have a completely contradictory result in the above equation? According to this equation when collector-emitter voltage is maximum the collector current becomes zero and when the collector-emitter voltage is zero, the collector current becomes maximum! I need a logical explanation for it. My question is when the the collector-emitter voltage is zero how the collector current could become maximum as they can not reach the collector side at all as the accleration given to them by the collector-emitter voltage will also be zero?
 
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  • #2
The transistor does not have zero volts across it at saturation.
It always has a small voltage between collector and emitter.

I only has minimum voltage across it at that time because there is a series load resistor that drops most of the voltage reaching the transistor.
 
Last edited:
  • #3


Thank you for bringing up this interesting question. The output voltage vs output current relationship in a transistor in CE mode is a result of the transistor's characteristic curves, which are determined by its physical structure and operating conditions.

As you correctly stated, when the collector-emitter voltage (VCE) increases, the collector current (IC) decreases due to the reverse voltage attracting the charge carriers to the collector. This behavior is reflected in the equation VCE = VCC - IC RC, where RC is the collector resistance. This equation shows that as VCE increases, the collector current must decrease in order to maintain a constant voltage drop across the collector resistance.

However, at a certain point, the collector current reaches its maximum value (known as saturation) and can no longer increase, even if VCE continues to increase. This is because at saturation, the transistor is fully conducting and all available charge carriers have been collected by the collector. Therefore, even if VCE increases, there are no additional charge carriers to be attracted to the collector.

On the other hand, when VCE is zero, the collector current is maximum because there is no voltage drop across the collector resistance, allowing the maximum amount of current to flow through the transistor. In this case, the charge carriers are not being attracted to the collector, but rather they are being pushed by the external voltage source (VCC) towards the collector. This results in a maximum collector current.

In summary, the output voltage vs output current relationship in a transistor in CE mode is a result of the interplay between the reverse voltage attracting the charge carriers and the external voltage source pushing them towards the collector. This behavior is accurately described by the equation VCE = VCC - IC RC and is consistent with the observed behavior of transistors in CE mode.
 

1. What is the relationship between output voltage and output current?

The output voltage and output current have an inverse relationship. This means that as one increases, the other decreases and vice versa.

2. How does changing the output voltage affect the output current?

Changing the output voltage will cause a corresponding change in the output current. If the output voltage is increased, the output current will decrease and vice versa.

3. What is the difference between output voltage and output current?

Output voltage is the electric potential difference between two points in a circuit, while output current is the rate of flow of electric charge through the circuit. Output voltage is measured in volts (V) and output current is measured in amperes (A).

4. Why is it important to understand the relationship between output voltage and output current?

Understanding the relationship between output voltage and output current is important in designing and analyzing electrical circuits. It allows us to predict the behavior of a circuit and make informed decisions regarding the selection of components and their operating conditions.

5. How do output voltage and output current affect the performance of electronic devices?

The output voltage and output current are critical factors in determining the performance of electronic devices. The output voltage must be within a certain range for the device to function properly, and the output current must be sufficient to power the device. If either of these is not met, the device may malfunction or not work at all.

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