Once, transistor Q3 is set ON, the 12 transistor drives the LEDs according to the signal sent by diodes. The third part of the circuit consisting of transistors Q4 to Q15 connected with LED depends entirely upon the ON/OFF signal from transistor Q3. This DC signal enters the base of transistor Q3 and thus, activates it. After the 10♟ electrolytic capacitor filters the amplified electrical signal, diodes D1, and D2 rectify it into a DC signal. Now, this amplified signal goes through the filtering and rectification part. Furthermore, the sensitivity can also be decreased by replacing the variable resistor of 100KΩ with 200KΩ or 300KΩ. Moreover, the sensitivity of the overall circuit is adjusted through the 100KΩ potentiometer. This electrical audio signal is then amplified by the transistors Q1 and Q2. Electret microphone catches the sound from the surroundings and converts it into an electrical signal. The main part of the circuit is the transistors Q1, Q2, and Q3 that are accountable for sound detection and amplification. The main manufacturers and their DataSheet can be downloaded here.Here, the project consists of 36 LEDs, 15 transistors, and a combination of resistor and capacitor. There are also foreign Russian equivalents:Ĭomplementary pair with 2N3906 PNP. If necessary, you can replace this BJT with a 2N3903, but you need to understand what parameters are important in this case and study the technical characteristics of both transistors. You can replace the 2N3904 transistor with the following equivalents: Electrical characteristics 2N3904 (T = +25☌) The maximum storage and operation temperature must be in the range of -50 … +150☌.Īttention! The table below scrolls.Total power dissipation – 625 Milliwatt (mW).Max Collector-Emitter Voltage |Vce| – 40 V.The tests were carried out at a temperature of +25☌. Now consider the maximum specs, since they are the most important and they should be looked at when looking for a replacement and designing new devices. The appearance, geometric dimensions and pin diagram of 2N3904 are shown in the figure. If you position the transistor so that the side with the marking is directly in front of you, and the legs look down, then the legs will be located like this: There are also equivalents in SOT-223 and SOT-23 (MMBT3904), they are marked as “1A”. The pinout 2N3904 will be considered in the TO-92 Package.
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