# Single Transistor LED Flasher Circuit Using Negative Resistance | Summary and Q&A

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June 8, 2020
by
The Organic Chemistry Tutor
Single Transistor LED Flasher Circuit Using Negative Resistance

## TL;DR

The video explains how to create a simple LED flasher circuit using a single NPN transistor, a resistor, a capacitor, and a battery.

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### Q: What components are needed for the LED flasher circuit?

The circuit requires a battery, a resistor, a capacitor, an NPN transistor, and an LED. The values of the resistor and capacitor can be adjusted for the desired flash rate.

### Q: How does the circuit use negative resistance?

In this circuit, the NPN transistor is connected in reverse, causing it to operate in the negative resistance region. As the voltage increases, the current decreases, and vice versa.

### Q: Why is the breakdown voltage of the transistor important?

The breakdown voltage determines the voltage at which the transistor will start conducting, allowing the LED to light up. It is approximately 7.3 volts in this circuit.

### Q: Can the flash rate of the LED be adjusted?

Yes, the flash rate can be adjusted by changing the values of the resistor and capacitor. Decreasing the values will increase the flash rate, while increasing them will decrease the flash rate.

## Summary & Key Takeaways

• The circuit consists of a battery connected to a resistor, which is connected to a capacitor, and an NPN transistor. The LED is connected to the collector of the transistor.

• The circuit operates using negative resistance, where there is an inverse relationship between voltage and current.

• The breakdown voltage of the transistor determines at what voltage the LED will start conducting. The flash rate of the LED can be adjusted by changing the resistor or capacitor values.