Triangular wave and square wave generator circuit diagram installed with NE555

Working principle: The circuit is as shown in the figure. VT1, VT2 and resistor R1 form a constant current source, which is used to linearly charge capacitor C2; VT3, VT4 and resistor R2 form a constant current source, which is used to linearly discharge capacitor C2.

The circuit has just been connected, the voltage on C2 is zero, pins 2 and 6 of the 555 time base integrated circuit are less than 1/3Vcc, and pin 3 outputs high level (about 10.8V), diode VD4 is forward biased, VD3 is reverse biased; VD1 is positive Biased, VD2 is reverse biased. The VT2 collector current charges C2 through VD1. When the voltage on C2 increases linearly to 2/3Vcc (ie 8V), pin 6 of the 555 is triggered, causing pin 3 to output a low level (about 0V). At this time, VD1 and VD4 are reverse biased, while VD2 and VD3 are forward biased. The charge on capacitor C2 is discharged through the collector of VT3. When the voltage on C2 linearly drops to 1/3Vcc (i.e. 4V), pin 2 of 555 is triggered, causing Pin 3 resets and outputs a high level, and so on. A highly linear triangular wave can be obtained on pins 2 and 6 of the 555 , and a square wave with a duty cycle of 50% can be obtained on pin 3.

The frequency of this circuit is in the range of 0~200kHz and above, and its stability is very high. The frequency of the circuit is obtained by calculation: f≈0.1375/(R1+R2) C2. According to the values ​​of R1 and R2 given in the circuit, f≈208kHz. In the circuit diagram , VT5 is a high-B output buffer stage. The triangular wave is taken out from the emitter of VT5, and the amplitude is about 4V. At the same time, this circuit can be applied in a flexible way: changing the size of R1 or R2 can change the rise or fall time of the triangular wave , and change the square wave accordingly. The duty cycle of the 555, or controlling the voltage of pin 5 of the 555, can change the frequency of the square wave of pin 3 (linear change).