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Lead and Lag Oscillators [Copy link]

 
[Ask if you don't understand] [1] Why can each RC link in the topology of Figure 5-2 make the signal of the fo frequency lead by 60 degrees, while Figure 5-3 actually makes it lag by 60 degrees? [2] In Figures 5-2 and 5-3, how are the respective fo frequencies calculated?
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In fact, to figure out the first question you raised in this post, it is far from enough to rely on the little bit at the beginning of the analog circuit textbook. To figure it out thoroughly, you need knowledge of "solid state physics" and "quantum mechanics". Moreover, figuring out these problems is of little use to electronic engineers.  Details Published on 2019-1-21 20:02

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The connection of R and C in your Figure 5-2 and the connection of R and C in your Figure 5-3 are just reversed. So the RC in Figure 5-2 makes the signal phase advance, while the RC in Figure 5-3 makes the signal phase lag.
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As for the calculation of fo frequency you mentioned, there are many ways. But these calculation methods all require certain mathematical knowledge. I don't know what your mathematical knowledge is, so I don't know where to start to explain how to calculate.
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Teacher, I saw this post again and I really want to know how the frequency fo is calculated. I used to see 1/2π square root RC, which is the same as the fo in the first post, but with the square root 6 as a constant. I want to know how it is calculated. My math knowledge is just average, I have studied advanced calculus.  Details Published on 2019-1-17 16:17
 
 
 
 

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maychang posted on 2018-12-26 09:23 As for the calculation of the frequency fo you mentioned, there are many ways. But these calculation methods require certain mathematical knowledge. I don't know how much mathematical knowledge you have...
Teacher, I saw this post again and I really want to know how the frequency fo is calculated. It turns out that the most common one is 1/2π square root RC, which is the same as the fo form in the first post, but with the square root 6 constant. I want to know how it is calculated. My mathematical knowledge is also average, and I have learned advanced calculus.
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In fact, we only need to write out the transfer function of the three RC circuits (note that the three resistors are equal and the three capacitors are also equal) and solve for the frequency of the 180-degree phase shift.  Details Published on 2019-1-17 18:31
In fact, we only need to write out the transfer function of the three RC circuits (note that the three resistors are equal and the three capacitors are also equal) and solve for the frequency of the 180-degree phase shift.  Details Published on 2019-1-17 18:27
 
 
 
 

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shaorc posted on 2019-1-17 16:17 Teacher, I saw this post again, and I really want to know how the frequency fo is calculated. It turns out that I often see the 1/2π square root RC, and the fo shape in the first post...
In fact, you only need to write out the transfer function of the three-section RC circuit (note that the three resistors are equal and the three capacitors are also equal), and then solve for the frequency of the 180-degree phase shift.
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shaorc posted on 2019-1-17 16:17 Teacher, I saw this post again and I really want to know how the frequency fo is calculated. It turns out that the 1/2π root RC is more common, and the fo shape in the first post...
It turns out that the 1/2π root RC is more common. That is to write out the transfer function and solve for the phase shift of 45 degrees. Note that the source impedance is zero and the load impedance is infinite. The calculation of the three-section RC is complicated because the latter RC forms a load on the former RC.
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Thank you, teacher. This is indeed a long post. I have a few random questions, so I will ask you directly in the post. [1] If a circuit has good "switching characteristics" under a certain operating state, does the switching characteristic refer to low switching loss, "zero voltage turn-on, zero current turn-off" and other characteristics? [2] What is the reverse recovery of the diode?  Details Published on 2019-1-21 10:35
 
 
 
 

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maychang posted on 2019-1-17 18:31 I used to see 1/2π root RC more often. That is to write out the transfer function and solve for the phase shift of 45 degrees. Note that the source impedance is zero and the load impedance...
Thank you, teacher. This is really a long list. I have a few scattered questions, so I will ask you directly in the post. [1] If a circuit has good "switching characteristics" under a certain operating state, does the switching characteristic refer to low switching loss, "zero voltage turn-on, zero current turn-off" and other characteristics? [2] Diode reverse recovery problem. The diode does not conduct when reverse voltage is applied. What does this recovery time refer to? Is it that in the transition from reverse voltage to positive voltage, the diode cannot immediately change from cut-off to conduction state? The device needs a buffer time. This time is the reverse recovery time? [3] What determines whether the flyback converter works in the discontinuous current mode or the continuous current mode of the inductor?
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Does the circuit have good "switching characteristics"? Does the switching characteristics refer to small switching losses and "zero voltage turn-on, zero current turn-off"? Good switching characteristics mean that the current is very small when turning off, the resistance is very small when turning on, the delay time is short, and the current rise and fall edges are steep.  Details Published on 2019-1-21 10:59
Does the circuit have good "switching characteristics"? Does the switching characteristics refer to small switching losses and "zero voltage turn-on, zero current turn-off"? Good switching characteristics mean that the current is very small when turning off, the resistance is very small when turning on, the delay time is short, and the current rise and fall edges are steep.  Details Published on 2019-1-21 10:58
Does the circuit have good "switching characteristics"? Does the switching characteristics refer to small switching losses and "zero voltage turn-on, zero current turn-off"? Good switching characteristics mean that the current is very small when turning off, the resistance is very small when turning on, the delay time is short, and the current rise and fall edges are steep.  Details Published on 2019-1-21 10:52
 
 
 
 

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shaorc posted on 2019-1-21 10:35 Thank you, this is indeed a long post. I have a few scattered questions, so I will ask you directly in the post [1] If the circuit has good "switching characteristics" under a certain operating state...
The circuit has good "switching characteristics". Does the switching characteristics refer to low switching loss and "zero voltage turn-on, zero current turn-off"? Good switching characteristics refer to very small current when turning off, very small resistance when turning on, short delay time, and steep rising and falling edges of the current. As for "zero voltage turn-on, zero current turn-off", it is determined by the external circuit and has nothing to do with the switch.
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Oh, let's say the PWM signal of the switch is a square wave that goes straight up and down, which is the best. But if the rising and falling edges are not steep, but oblique lines, how can it be shown to be bad? Is it because of the loss?  Details Published on 2019-1-21 11:48
 
 
 
 

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shaorc posted on 2019-1-21 10:35 Thank you, teacher. This is indeed a long post. I have a few scattered questions, so I will ask you directly in the post. [1] If the circuit has good...
Diode reverse recovery problem, the diode does not conduct when reverse voltage is applied, what does this recovery time refer to? "Reverse recovery" usually means that when a diode passes a forward current and a reverse voltage is suddenly applied to the diode, the diode will not turn off immediately, but will flow a large reverse current (as if it is short-circuited), and the diode will recover to the off state after a short period of time. This "short period of time" is called the reverse recovery time.
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Why does a sudden application of reverse voltage cause a large current to flow, like a short circuit?  Details Published on 2019-1-21 11:51
 
 
 
 

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shaorc posted on 2019-1-21 10:35 Thank you, this is indeed a long post. I have a few scattered questions, so I will ask you directly in the post [1] If the circuit has good...
What determines whether the flyback converter works in the discontinuous current mode or the continuous current mode of the inductor? It is determined by three factors: the primary inductance of the flyback converter transformer, the on-time of the switch tube, and the load current.
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maychang published on 2019-1-21 10:52 The circuit has good "switching characteristics". Does the switching characteristic refer to low switching loss, "zero voltage turn-on, zero current turn-off" and other characteristics? Switching characteristics...
Oh, let's say the PWM signal of the switch is a square wave that goes straight up and down, which is the best, but if the rising and falling edges are not steep, but oblique lines, how can it be reflected as bad? Is it because of the loss?
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If the rising and falling edges are not steep but oblique, how can it be shown that it is not good? The heat loss of the power switch tube is relatively large.  Details Published on 2019-1-21 11:56
 
 
 
 

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maychang published on 2019-1-21 10:58 Diode reverse recovery problem, the diode does not conduct when reverse voltage is applied, what does this recovery time refer to? "Reverse recovery" usually refers to the diode passing through the forward...
Why does a large current flow through when reverse voltage is suddenly applied, just like a short circuit?
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Why does a sudden reverse voltage cause a large current to flow through the diode like a short circuit? The usual explanation is that when a forward current flows through the diode, a large number of majority carriers are stored in the PN junction space charge region (depletion layer). When a reverse voltage is suddenly applied, these majority carriers do not have time to recombine, causing a large current to flow through the diode instantly until  Details Published on 2019-1-21 12:13
Why does a sudden reverse voltage cause a large current to flow through the diode like a short circuit? The usual explanation is that when a forward current flows through the diode, a large number of majority carriers are stored in the PN junction space charge region (depletion layer). When a reverse voltage is suddenly applied, these majority carriers do not have time to recombine, causing a large current to flow through the diode instantly until  Details Published on 2019-1-21 12:11
 
 
 
 

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shaorc posted on 2019-1-21 11:48 Oh, let's say the PWM signal of the switch is a square wave that goes straight up and down, which is the best, but if the rising and falling edges are not steep, but a slant line, how...
If the rising and falling edges are not steep, but a slant line, how can it be shown that it is not good? The heat loss of the power switch tube is relatively large.
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shaorc posted on 2019-1-21 11:51 Why does a sudden reverse voltage flow a large current like a short circuit?
Why does a sudden reverse voltage flow a large current like a short circuit? The usual explanation is: when a forward current flows through a diode, the PN junction space charge region (depletion layer) stores a large number of majority carriers. When a reverse voltage is suddenly applied, these majority carriers do not have time to recombine, causing a large current to flow through the diode instantly. It is not until the majority carriers recombine and the space charge region (depletion layer) becomes wider that the reverse current stops and the diode enters a reverse equilibrium state.
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Teacher, in response to this question, I looked back at the materials and understood that in many figures, the area with a slash is the PN junction. The circle on the right is the hole that penetrates from the P semiconductor. The black dot on the left is the internal electric field formed by the free electrons that penetrate from the N semiconductor, which hinders the continued penetration on both sides. [1] P  Details Published on 2019-1-21 16:52
 
 
 
 

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shaorc posted on 2019-1-21 11:51 Why does a sudden reverse voltage cause a large current to flow like a short circuit?
This instantaneous large reverse current will obviously eventually turn into heat and dissipate. Therefore, the high-frequency rectifier tube in the switching power supply cannot use ordinary rectifier diodes, but must use so-called fast recovery diodes (when the rectifier voltage is high) or Schottky diodes.
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Thank you, teacher. Regarding the third question, what determines whether the flyback converter works in the discontinuous current mode or the continuous current mode? It is determined by three factors: the primary inductance of the flyback converter transformer, the switch on time and the load current. There is a post in the forum explaining this.  Details Published on 2019-1-21 15:10
 
 
 
 

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maychang published on 2019-1-21 12:13 This instantaneous large reverse current will obviously eventually turn into heat and dissipate. Therefore, the high-frequency rectifier tube in the switching power supply cannot use ordinary rectifier diodes, but must...
Thank you teacher for the third question before. What determines whether the flyback converter works in the discontinuous current mode or the continuous current mode of the inductor? It is determined by three factors: the primary inductance of the flyback converter transformer, the conduction time of the switch tube, and the load current. Is there a post in the forum to explain this?
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"Is there any post in the forum explaining this?" It seems not. But there are a lot of materials explaining this matter. Almost all books on switching power supplies will talk about it. You can download it and take a look.  Details Published on 2019-1-21 16:20
"Is there any post in the forum explaining this?" It seems not. But there are a lot of materials explaining this matter. Almost all books on switching power supplies will talk about it. You can download it and take a look.  Details Published on 2019-1-21 15:29
 
 
 
 

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shaorc posted on 2019-1-21 15:10 Thank you teacher for the third question before, what determines whether the flyback converter works in the discontinuous current mode or the continuous current mode of the inductor current...
"Is there a post in the forum to explain this?" It seems not. However, there are a lot of materials to explain this matter. Almost all books on switching power supplies will talk about it. You can download it and have a look.
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Thank you teacher  Details Published on 2019-1-21 16:19
 
 
 
 

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maychang posted on 2019-1-21 15:29 "Is there any post in the forum explaining this?" It seems not. But there are a lot of materials explaining this, almost all books on switching power supplies...
Thank you, teacher
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shaorc posted on 2019-1-21 15:10 Thank you teacher for the third question before. What determines whether the flyback converter works in the discontinuous current mode or the continuous current mode of the inductor current...
In fact, it is easiest to explain the discontinuous current and continuous current working modes from the energy relationship. In steady state, the energy stored in the transformer during the on-time of the flyback converter switch is completely released during the off-time of the switch. The next switching cycle starts only after the energy stored in the transformer drops to zero. The current must be discontinuous, otherwise it is continuous.
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maychang posted on 2019-1-21 12:11 Why does a sudden reverse voltage cause a large current to flow through the diode like a short circuit? The usual explanation is: when a forward current flows through the diode, the PN junction space charge region ( ...
Teacher, in response to this question, I looked back at the information and understood that in many figures, the area with a slash is the PN junction. The circle on the right is the hole that penetrates from the P semiconductor. The black dots on the left are the internal electric field formed by the free electrons that penetrate from the N semiconductor, which hinders the continued penetration on both sides. [1] How come the holes (circles) and free electrons (black dots) in the PN junction don't neutralize each other? Instead, such an area is formed. [2] Do the three terms "space charge region", "depletion layer" and "barrier layer" all refer to the PN junction?

IMG_20190121_164158.jpg (36.03 KB, downloads: 0)

IMG_20190121_164158.jpg
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Start from Section 2.2 “Formation and Characteristics of PN Junction” on page 31.  Details Published on 2019-1-21 20:02
Start from Section 2.2 “Formation and Characteristics of PN Junction” on page 31.  Details Published on 2019-1-21 17:19
 
 
 
 

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