Please help me look at this oscillator circuit

电路小学徒

Please help me look at this oscillator circuit [Copy link]

 

I am studying a circuit and I would like to know what controls the frequency of its oscillation, the role of the PNP transistor and the role of the diode D1. I hope you can give me some advice.

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What circuit are you studying? Do you use multium simulation? What control is given? The C pole of Q4 is not connected, and the oscilloscope has output at port B.

maychang

This is a simulation diagram. The simulation results may not be very accurate. This circuit may produce oscillations, but according to the values of the components in the diagram, it is also possible that no oscillations occur. This circuit is a relaxation oscillator, not a sine oscillator. If oscillations occur, it may be that after C3 is charged to a certain voltage, the input of U1A is high and the output of U1A is low. U1A pulls down the voltage across C3 through the emitter junction of Q4 (used as a diode), and the output of U1A becomes high again.

maychang

"I am studying a circuit" It is best not to learn about circuits on the Internet in this way. It is better to read more formal textbooks.

电路小学徒

maychang posted on 2019-5-3 17:27 This is a simulation diagram. The simulation result may not be very accurate. This circuit may produce oscillation, but according to the values of the components in the diagram, it is also possible that no oscillation occurs. ...

Regarding this circuit, there is an explanation that the leakage current of diode D1 controls all the parasitic currents of the trigger connected behind it. I don't quite understand what this means. Can you analyze the role of this diode?

maychang

Circuit Apprentice posted on 2019-5-4 10:17 Regarding this circuit, there is a sentence explaining that the leakage current of diode D1 controls all the parasitic current of the subsequent trigger. I don’t quite understand what this means. Can...

Regarding this circuit, there is a sentence explaining that the leakage current of diode D1 controls all the parasitic current of the subsequent trigger. I don’t quite understand what this means. D1 is not seen in the figure in the first post.

电路小学徒

maychang posted on 2019-5-4 10:22 Regarding this circuit, there is an explanation that the leakage current of diode D1 controls all the parasitic currents of the subsequent trigger. I don’t quite understand what this means...

...Okay, it’s D2, the diode in parallel with the collector capacitor. Do you have any insights?

maychang

Circuit Apprentice published on 2019-5-4 11:09 ...Okay, it is D2, the diode connected in parallel with the collector capacitor. What do you think?

I think this diode D2 is useless for the generation of oscillation. D2 is in the reverse state, roughly equivalent to a capacitor, connected in parallel with capacitor C3 (the diode junction capacitance is generally greater than 1pF), and only increases the capacitance of capacitor C3.

maychang

The first circuit is a variation of the square wave generating circuit below. Fundamentals of Electronic Technology. Analog Part. (Kang Huaguang. 5th edition). In the figure, "C" is a hysteresis comparator (Schmitt input comparator). Both 74LS14 and 74HC14 are Schmitt input comparators.

电路小学徒

maychang posted on 2019-5-4 12:55 The first post circuit is a variation of the square wave generating circuit below. Fundamentals of Electronic Technology. Analog Part. (Kang Huaguang. 5th Edition). In the figure, "C" is the hysteresis ratio...

Thank you

电路小学徒

maychang posted on 2019-5-4 12:55 The first post circuit is a variation of the square wave generating circuit below. Fundamentals of Electronic Technology. Analog Part. (Kang Huaguang. 5th Edition). In the figure, "C" is the hysteresis ratio...

I also asked others, who said that the diode provides a DC path so that the PNP transistor can work normally. I don't know if this understanding is correct.

maychang

Circuit Apprentice posted on 2019-5-6 16:35 I also asked other people, and they said that a diode is used to provide a DC path so that the PNP transistor can work normally. I don’t know if this understanding is correct...

“It is said that a diode is used to provide a DC path so that the PNP transistor can work normally.” There are two PNP transistors in the picture in the first post. Which one is this “other person” referring to?