Working Process of Cycle Led Color Lamp Circuit

This circuit can realize the cycle lighting of three LEDs D1, D2 and D3. During actual welding, the triodes D1, D2 and D3 can be selected with different colors. In addition, the number of LEDs can be increased according to the output capacity of the power supply to realize a cycle of color lamp works.

Circuit working process:

1. When the power supply is powered on, the triodes Q1, Q2 and Q3 have conduction conditions, so the three triodes will rush to conduct first. However, due to the difference of components, one triode will always conduct the slowest. Then, when one of the triodes turns on first, the conduction conditions of the connected triode will be broken, which will have a series of chain reactions. We assume that the slowest conduction triode is Q2.

2. When the transistor Q1 is saturated and turned on, the collector voltage of the transistor Q1 drops to nearly 0V, so the LED D1 is off at this time; At the same time, when the collector voltage of the triode is close to 0V, the left end of the electrolytic capacitor C1 will be 0V. Due to the characteristic that the voltage at both ends of the capacitor cannot change suddenly, a negative pulse will appear at the right end of the electrolytic capacitor C1, that is, the base voltage of the triode Q2, so as to cut off the triode Q2. The LED D2 is illuminated. When D2 is lit, the voltage at both ends of capacitor C2 is VCC, which will not cause a sudden change in the base potential of triode Q3.

3. Then, with the reverse charging of capacitor C1 by the power supply, the base voltage of Q2 gradually rises. When the base voltage rises to the point where transistor Q2 can be turned on, the light-emitting diode D2 is extinguished, and the collector potential of Q2 drops close to 0V. Similarly, according to the characteristic that the voltage at both ends of the capacitor cannot change suddenly, a negative pulse will appear in the base voltage of transistor Q3 to cut off transistor Q3, The light emitting diode D3 is illuminated.

4. Then, the power supply reversely charges the electrolytic capacitor C2, and the base voltage of Q3 gradually rises. When the base voltage rises to make Q3 turn on again, the LED D3 goes out, and the collector voltage of the triode Q3 drops close to 0V. Similarly, the capacitor C3 will also make a negative pulse in the base voltage of the triode Q1, cut off the triode Q1 and turn on the LED D1.

5. In this way, the whole circuit repeats the situation that two LEDs go out and one LED is turned on. When it is turned on, the three LEDs are turned on in turn.


1. In this circuit, the electrolytic capacitor will be charged in reverse. During reverse charging, the capacitor charging voltage can only reach 0.7V, so there will be no capacitor explosion in practical use.

2. In this example, the triode must work in the saturated conduction state to make the collector voltage of the triode close to 0V.

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