maychang

shaorc posted on 2018-9-17 10:59 Regarding the dead time controlled by pin 7, I saw Figure 2 in the chip manual, which is what you said. The oscillator output passes through a transistor and is output by PIN7. ...

The second is: the origin mechanism of the dead time, is it to change the resistance to change the charging and discharging, that is, the speed of the level change? Change the resistance to control the time required for the capacitor to discharge.

maychang

shaorc posted on 2018-9-17 11:12 The high level of the chip's 10-pin input will turn on an internal transistor, which discharges the external capacitor connected between the 8-pin and the ground. The high level of the 10-pin also...

For these two questions, it is best to read the SG3525 datasheet, and it is best to read the original text. The translation of the Chinese manual may not be very accurate.

shaorc

maychang published on 2018-9-17 11:48 The second is: the origin of the dead time mechanism, is it to change the resistance to change the charge and discharge, that is, the speed of level change? Change the resistance to control the discharge of the capacitor...

Change the resistance to change the capacitor discharge time. Using the capacitor charge and discharge time as the dead time is to change a signal, because the charge and discharge time lags behind another signal. In Figure 1 on the 18th floor, PIN7, the capacitor 0.001 connected to the dead resistance 100 ohms, how does its charge and discharge affect the output of PIN11 and PIN14? In addition, is the charge and discharge time still calculated using t=RC? R is the dead resistance, and C is the 0.001uf capacitor?

maychang

shaorc posted on 2018-9-17 13:45 Changing the resistor changes the capacitor discharge time. Using the capacitor charge and discharge time as the dead time is to change a signal, because the charge and discharge time...

"Using the capacitor charge and discharge time as the dead time is to change a signal" It is not "using the capacitor charge and discharge time as the dead time". It is "capacitor discharge time" as the dead time. The capacitor is charged, and the voltage rise part is a sawtooth wave, which is used to compare with the op amp output to form a PWM waveform.

maychang

shaorc posted on 2018-9-17 13:45 Changing the resistor to change the capacitor discharge time and using the capacitor charge and discharge time as the dead time both change a signal because the charge and discharge time...

SG3525 is a relatively later chip, which was developed on the basis of the previous switching power supply control chip. To understand how the switching power supply control chip works, you may wish to look at the earlier simple control chips. Because these simpler chips have fewer internal circuits, they are easier to understand. For early chips, you can look at KA3524 or LM3524 (the internal circuits are exactly the same).

shaorc

maychang posted on 2018-9-17 14:07 "Using the charge and discharge time of the capacitor as the dead time is to make a signal change" is not "using the charge and discharge time of the capacitor as the dead time". ...

Oh, so, the voltage across the CT is the voltage of the external timing capacitor. How do we determine how much it is?

maychang

shaorc posted on 2018-9-17 14:57 Oh, so that's how it is. The voltage across CT is the voltage of the external timing capacitor. How do you determine it?

The voltage across the timing capacitor is not determined by you, but by certain internal circuit parameters determined by the internal voltage reference of the chip.

shaorc

maychang posted on 2018-9-17 15:25 The voltage across the timing capacitor is not determined by you, but by certain internal circuit parameters determined by the chip's internal voltage reference.

Thank you

shaorc

maychang posted on 2018-9-17 15:25 The voltage across the timing capacitor is not determined by you, but by some internal circuit parameters determined by the internal voltage reference of the chip.

By the way, Mr. Maychang, when I read the datasheet, especially the switching power supply control chip or the voltage regulator chip, I can't understand its mechanism at once when I see the internal structure. I am always confused by the various internal comparators, latches or logic circuits. Are there any rules when reading the manuals of similar chips?

maychang

shaorc posted on 2018-9-18 07:33 By the way, Mr. Maychang, when I look at the datasheet, especially the switching power supply control chip or the voltage regulator chip, I can't understand the internal structure...

Are there any rules when reading similar chip manuals? Complex circuits are always composed of simple circuits, or complex systems are always composed of simple unit circuits. It may be easier to understand the simple unit circuits and then analyze the relationship between the various parts of the complex circuit.

maychang

shaorc posted on 2018-9-18 07:33 By the way, Mr. Maychang, when I look at the datasheet, especially the switching power supply control chip, or the voltage regulator chip, I can't understand the internal structure...

For the switching power supply control chip, when using this type of chip, it is not necessary to analyze the work of each tube. It is enough to know the relationship between the various parts and the function of each pin. Just like a single-chip microcomputer, the user does not need to know how each data stored in the memory is added and carried in the arithmetic logic unit, and how the result of the addition is sent to the memory. It is enough to know how each memory changes when a certain instruction is executed.

maychang

shaorc posted on 2018-9-18 07:33 By the way, Mr. Maychang, when I look at the datasheet, especially the switching power supply control chip or the voltage regulator chip, I can't understand the internal structure...

Switching power supply control chip, as well as other complex chips, often only need to be regarded as a black box. We don't know the internal structure. We only know how to connect each pin, what signal the input pin needs to input, and what signal the output pin will output under what circumstances, and then we can use this complex chip. Using operational amplifiers, various gate circuits... For such a relatively simple chip, you don't have to understand the work of every tube inside the chip thoroughly.