Am back with another oscialltor circuit, sawtooth waveform this time. I have designed a mini sawtooth generator using simple NPN and PNP transistors. The most highlighting feature about this circuit will be its miniature size and easy to use on the go. You will find more effective sawtooth generators than this but when scaling up the size factor this design might hold the advantage.
The short description is that the circuit uses two constant current sources instead of passive resistor for a more linear rise. While using a resistor in your circuit you will obtain more of a exponential rise. In order to get rid of that i have used these two current sources in here. The two current sources are the two upper transistors. You can use a simple 9V battery to power up this circuit like me or you can go for other power sources.
The two transistors at the bottom form a emulated thyristor. Here this thyristor kind of formation serves the purpose of switching in our circuit. I have used the capacitor C1 for the purpose of charging and discharging. The charging capacitor triggers the thyristor at some point defined by the forward drop of the LED D1 (around 2V) connected to the base of transistor Q2, leading to a fast discharge. As the capacitor discharges very rapidly, the voltage that sustains the thyristor open, drops below the thyristor on threshold, thus disengaging it. Thus in turn forms a smooth Sawtooth wave. The cycle then repeats over and over again, thus we will get a sawtooth waveform in the output point.
Here is the output sawtooth wave i have obtained from my circuit, works like a charm from the first time. Hope this circuit was useful to you, try this out and write me your feed backs.