What is the A4G three-pin tube in the KA3842 switching power supply circuit?

tsmt001

What is the A4G three-pin tube in the KA3842 switching power supply circuit? [Copy link]

 

There is a three-pin A4G tube in the KA3842 switching power supply circuit. As shown in the figure, two pins are connected to the two ends of 817, and one pin is connected to the 1M resistor to the 5V output end of IC8. I hope you can analyze what type of device the tube with silkscreen A4G is? The circuit diagram is drawn in real life. I added A4G as a CMOS tube first, which may not be correct. Thank you, thank you!

PowerAnts

Look carefully at the waveform in the manual, it is not difficult to find that the PWM pulse width is positively correlated with the voltage on pin 1. The addition of RC and a small MOSFET can achieve a slow rise after the pin is powered on, thus achieving soft start. The diagram copied by the original poster uses a P tube instead of an N tube. According to the parameters in the diagram, the soft start time is 2-3mS

qwqwqw2088

The picture is wrong

The physical copying should be based on KA3842. KA3842 should have the same functions as UC3842, but the manufacturers are different.

Pin 6 should be the output, the position of the MOS tube A4G is wrong.

Let's get the circuit diagram correct first.

PowerAnts

qwqwqw2088 posted on 2022-4-27 08:12 The picture is wrong. The actual copy should be based on KA3842. KA3842 should have the same function as UC3842. The manufacturer is different. Pin 6 should be the output...

Sure enough, the pin function names were all wrong! I only checked the electrical connections and didn't look at the pin names.

PowerAnts

This method is good, it can be used to dig holes for others

maychang

The 3842 pin names and numbers do not match.

Pin 8 is labeled VDD, but it is actually the output terminal of the internal reference source.

Several other pins don't match up either.

maychang

In the figure, the 3rd pin is marked as "connected to the drain of the power tube" after the resistor, which is completely impossible. The 3rd pin should be connected to the source of the MOS tube.

PowerAnts

The same function can be achieved more simply with two devices and only 7 cents

okhxyyo

PowerAnts posted on 2022-4-27 08:26 This method is good, it can be used to dig holes for others

This is really a pitfall,

tsmt001

PowerAnts posted on 2022-4-27 08:25 Sure enough, the pin function names were all wrong! I only checked the pin electrical connections and didn't look at the pin names

I just downloaded the drawing software for this switching power supply. I am asking this question while learning how to use this software. Please forgive me and thank you for your help.

tsmt001

okhxyyo posted on 2022-4-27 12:09 This is really a pitfall,

I'm still learning, please forgive me. The injury is not serious, right? ?

tsmt001

maychang posted on 2022-4-27 08:35 In the figure, after the resistor, the 3rd pin is marked as "connected to the drain of the power tube", which is completely impossible. The 3rd pin should be connected to the source of the MOS tube.

Thanks for the help, I re-uploaded the image.

tsmt001

maychang posted on 2022-4-27 08:33 The 3842 pin names and numbers do not match. Pin 8 is marked as VDD, but pin 8 is actually the output of the internal reference source. Several other pins do not match either. ...

Thank you, the level is average. The pin number of the borrowed diagram is correct. I uploaded the diagram again.

tsmt001

PowerAnts posted on 2022-4-27 08:26 This method is good, it can be used to dig holes for others

I am a beginner, please forgive me. I hope you don't fall into the pit. . .

tsmt001

PowerAnts posted on 2022-4-27 08:11 Take a good look at the waveform in the manual, and it is not difficult to find that the PWM pulse width is positively correlated with the voltage on pin 1. The addition of RC and a small MOSFET can achieve a slow rise after the pin is powered on, and realize soft start...

I don't understand, so I come to ask for help. I hope experts can give me some advice.

tsmt001

PowerAnts posted on 2022-4-27 08:47 The same function can be achieved more simply, with two devices and only 7 cents

Too profound, I don't understand

tsmt001

PowerAnts posted on 2022-4-27 08:11 Take a good look at the waveform in the manual, and it is not difficult to find that the PWM pulse width is positively correlated with the voltage on pin 1. The addition of RC and a small MOSFET can achieve a slow rise after the pin is powered on, and realize soft start...

That makes sense. Thanks!

tsmt001

qwqwqw2088 posted on 2022-4-27 08:12 The picture is wrong. The actual copy should be based on KA3842. KA3842 should have the same function as UC3842. The manufacturer is different. Pin 6 should be the output...

Thank you, I hope you can give me more advice.

tsmt001

I used the diode function of a digital meter to measure the conduction between the pins as shown in the figure. I would like to ask the teacher how the silk-screen A4G marked with a red circle works and what specific tube it is. Thank you.

PowerAnts

tsmt001 posted on 2022-4-27 22:57 I used the diode function of a digital meter to measure the conduction between the pins as shown in the figure. I would like to ask the teacher how the silk-screen A4G marked with a red circle works and what specific tube it is...

PNP transistor