Powerful audio oscillator
This project is an audio oscillator pulse to two powerful transistors. It could be used as an alarm or warning signal in a noisy place, or as a signal source for troubleshooting. It's a good circuit on which to practice your power circuit analysis.
The method we suggest is good for most circuits. It involves the establishment of current paths in the diagram, and consider them until you understand the circuit. Of course you can and should check with your analysis counters, changing values and an oscilloscope.
Use different colored pens and draw arrows directly on the diagram to indicate the following current loops. The direction of current flow should be indicated by the arrows along color lines. We give you the list of components through which the current must pass in order. (Number your colors so that they are in agreement with this list).
1. Battery (-), Q2 E to B-, 22K, 50K, key, battery (+)
2. Battery (-), Q2 E to C, Q1 to E, key, battery (+)
3. Battery (-), speaker, Q1 C to E, key, battery (+)
4. Battery (-), Q2 E to B, 0.1 uF, 100 ohms, Q1 C to E, key, battery (+)
5. 0.1 uF left, 22K, 50K, key, battery (+) to (-) speaker, 100ohms, 0.1 uF right
The first four currents flow immediately when you close the key, and are related as follows.
The current 1 initially puts the Q2 running which then allows the two to follow.
The current 2 puts 2SB running which then allows 3 and 4 to pass.
The current 3 moves the coil and the speaker cone.
The current 4 starts charging the capacitor 0.1 uF (left negative) while with the same current, the Q2 is switched more securely. All this happens in a very short time (microseconds or less). The above currents are all only about 100 microseconds, because after that time the charging current (4) of 0.1 uF decreases to the point where it allows the Q2 and thereby to Q1 out slightly saturation point.
When this occurs, the voltage at C-E of Q1 rises. This voltage increase (negative -C Q1) coupled across the 100 ohm resistor and the capacitor of 0.1 uF quickly polarized conversely Q2, stopping. This action takes a very short time (microseconds or less) because as Q2 stops, it stops as Q1, causing the voltage EC to rise further until the voltage at the speaker is zero, while the voltage of Q1 equals that of the Battery.
As soon as the stop transistors, currents 1, 2, 3 and 4 continue to spend 5 and the current begins to flow. This is the discharge current of the capacitor of 0.1 uF. Since this current must pass through the high resistance of 22K and 50K, it takes approximately 1.4 to 4.2 milliseconds before the action ceases. These long downtimes depend 50K control settings.
As soon as the 0.1 uF is discharged, it can not hold the arrested Q2, and the cycle repeats.