Dim LED with Transistor Switch - Why?

LEDresultsindimmerlight.This is because of the saturation voltage, which causes a 0.3V drop across the CE of the transistor, resulting in only 2.7V reaching the LED. To avoid this, it is recommended to use a MOSFET with low rds.
  • #1
brodywx
2
0
Hello,

I've just been playing around with a 2n3904 transistor and 3V coin battery. I noticed when powering an LED with a transistor switch the LED is significantly dimmer than when powering the LED directly.

Why is this? Is it because 0.7 volts is siphoned off just to turn the transistor on?
 
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  • #2
The saturation voltage. Even if you drive the base hard, their is a 0.3V drop across the CE of the transistor so only get 2.7V instead of 3V. If you want to get rid of this, get a MOSFET with low rds.
 
  • #3
Thank you for the reply.

I
am
learning
 

FAQ: Dim LED with Transistor Switch - Why?

What is the efficiency of a transistor?

The efficiency of a transistor refers to how well it converts input power to output power. It is typically measured as a percentage and can range from 50-98% depending on the type and design of the transistor.

How is efficiency measured in a transistor?

Efficiency is measured by comparing the output power of the transistor to the input power. This is known as the power gain of the transistor and is calculated by dividing the output power by the input power.

What factors affect the efficiency of a transistor?

The efficiency of a transistor can be affected by several factors, including the type and material of the transistor, the operating temperature, and the input and output voltage levels. The design and quality of the circuit also play a role in determining the efficiency of a transistor.

How can the efficiency of a transistor be improved?

To improve the efficiency of a transistor, one can use a more efficient type or material of transistor, operate it at a lower temperature, and use appropriate voltage levels for the input and output. Additionally, optimizing the circuit design and reducing any parasitic effects can also improve the efficiency.

Can the efficiency of a transistor be 100%?

No, it is not possible for a transistor to have 100% efficiency. This is due to the inherent losses in the conversion of power from input to output, as well as other factors such as thermal and parasitic effects. However, with advancements in technology, the efficiency of transistors continues to improve, approaching closer to 100%.

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