Can you highlight the part of the datasheet that you do not understand?

Thank you
What I meant by the simple explanation was that, for example, if I put the voltmeter probes on the gate and drain or gate and source pins, what is the allowed voltage?
Or is this measurement wrong and I should put the probes on the MOSFET and GRAND or + pins?
I didn't understand this from Dataasht and first I have to see if the MOSFET condition is standard or not and then go to the next possibilities
Thank you for the simple explanation

 

Thank you
What I meant by the simple explanation was that, for example, if I put the voltmeter probes on the gate and drain or gate and source pins, what is the allowed voltage?
Or is this measurement wrong and I should put the probes on the MOSFET and GRAND or + pins?
I didn't understand this from Dataasht and first I have to see if the MOSFET condition is standard or not and then go to the next possibilities
Thank you for the simple explanation

Voltmeter probes on a MOSFET gate are not going to tell you much and is probably a waste of time. It has to be an oscilloscope or nothing. Without an oscilloscope you have no hope of understanding or trouble shooting what is happening. I'm surprised you don't know this already

 

I certainly agree that waveforms will be helpful. So if the gate driver is adequate for charging and discharging the gate in an appropriate amount of time, what is the purpose of R8(6.8KΩ)?

It's nearly always recommended in application notes. I believe that it is there to make sure that the gate capacitance can't charge up when the IC has no power (which seems unlikely to me). It's generally 10k to 47k, so would be of no use in speeding up the gate discharge. If the output stage is MOS (UC3843 is bipolar) there is a MOSFET reverse diode clamping the gate to the V+ supply, which would adequately prevent the gate charging up when there is no supply.

 

Voltmeter probes on a MOSFET gate are not going to tell you much and is probably a waste of time. It has to be an oscilloscope or nothing. Without an oscilloscope you have no hope of understanding or trouble shooting what is happening. I'm surprised you don't know this already

Don't be surprised
I am an amateur and my field of study is art!!!! but I am interested in electronics.
I want to supply my power supply with this circuit
What exactly does VGS or VGD mean in the datasheet?
Voltage between gate and source? Voltage between gate and drain?
I wanted the input of the circuit to be 30V, so according to the advice of friends, we changed R6 to 680 ohms and put an 18V zener between pin 7 of the IC and the grand, and I set the voltage of the capacitors to suit this input.
Now I want to know, is this enough? Or is it still harmful for MOSFET?

 

C8, C9; Under light loads, you can operate without these two caps.

I removed these capacitors
But it has no effect on the result and output

 

.

C8, C9; Under light loads, you can operate without these two caps.
View attachment 273470

If you do it ceases to be a SEPIC converter and becomes a flyback converter. Then you need a RCD suppression network on the MOSFET drain, as the capacitors coupling to the secondary are removing the effects of the leakage inductance.

 

Don't be surprised
I am an amateur and my field of study is art!!!! but I am interested in electronics.
I want to supply my power supply with this circuit
What exactly does VGS or VGD mean in the datasheet?
Voltage between gate and source? Voltage between gate and drain?
I wanted the input of the circuit to be 30V, so according to the advice of friends, we changed R6 to 680 ohms and put an 18V zener between pin 7 of the IC and the grand, and I set the voltage of the capacitors to suit this input.
Now I want to know, is this enough? Or is it still harmful for MOSFET?

So, you are saying that you tried to run a marathon before learning to crawl and walk. I'm sorry you chose that path. You may have to go back and fill in some of the gaps that are missing.

Voltage is always measured between two points. One of the points is a reference which can be GROUND. It can also be any other point in a circuit. The measured difference can be positive or negative. Vgs is indeed the voltage difference between the gate and the source. Sometimes the source will be at GROUND and sometimes it will be something else.

 

I certainly agree that waveforms will be helpful.

Without an oscilloscope, I cannot help more. There are things we need to see what a meter does not see. Often, we can trouble shoot without the proper tools. In this case there is something wrong that is not clear.

So if the gate driver is adequate for charging and discharging the gate in an appropriate amount of time, what is the purpose of R8(6.8KΩ)?

When things are working property there is no function for the 6.8k. If the IC is not powered up well (supply=2V) it cannot pull down the output. The resistor holds Gate=0V in this case.

 

Without an oscilloscope, I cannot help more. There are things we need to see what a meter does not see. Often, we can trouble shoot without the proper tools. In this case there is something wrong that is not clear.

Thank you so far

 

So, you are saying that you tried to run a marathon before learning to crawl and walk. I'm sorry you chose that path. You may have to go back and fill in some of the gaps that are missing.

Voltage is always measured between two points. One of the points is a reference which can be GROUND. It can also be any other point in a circuit. The measured difference can be positive or negative. Vgs is indeed the voltage difference between the gate and the source. Sometimes the source will be at GROUND and sometimes it will be something else.

Not to the extent that you gave an example
I have basic information and I think it is normal to question some datasheet items.
I really wanted to see Vgs, is it between gate and source?
I am detailing the information and measurement between MOSFET pins as well as grand and MOSFET here
Thank you very much for your information
Please do not get tired and guide me

 

If you’re going to make any more switched-mode supplies, get an oscilloscope!

 

Vgs is indeed the voltage difference between the gate and the source

If you’re going to make any more switched-mode supplies, get an oscilloscope!

Hello
I measured the voltage of the MOSFET pins with a voltmeter, maybe it helps why the MOSFET heats up.

Vin=24.1,Vout=30.5
Vgs=0.3(While the load is not on its output),
Vsd=23.8
Vg,ground=23.5
Vgs=3.7(while the load on its output is about 2.5 amps)

 

Hi

I think there is an error in the FB circuit shown on the TS's schematic.
The internal feedback reference voltage is 2.5v and is generated internally, so the REF pin should not be connected to the feedback circuit, it is intended for the oscillator components. So that wire should be removed. Additionally, Configure R3 as a variable resistor and change it to 10K, then connect the feedback pin to the junction of R3/R4, the output voltage will then be adjustable between 5v-30v.

The previously mentioned zener should be added as well.

See below:

EDIT: increased image sizes.

 

Hi

I think there is an error in the FB circuit shown on the TS's schematic.
The internal feedback reference voltage is 2.5v and is generated internally, so the REF pin should not be connected to the feedback circuit, it is intended for the oscillator components. So that wire should be removed. Additionally, Configure R3 as a variable resistor and change it to 10K, then connect the feedback pin to the junction of R3/R4, the output voltage will then be adjustable between 5v-30v.

The previously mentioned zener should be added as well.

See below:

View attachment 273766

Would it be possible to make your schematic larger so details would be evident?

 

Would it be possible to make your schematic larger so details would be evident?

Sorry PB...

I made the images larger...

 

Sorry PB...

I made the images larger...

Thanks.

 

I think there is an error in the FB circuit shown on the TS's schematic.
The internal feedback reference voltage is 2.5v and is generated internally, so the REF pin should not be connected to the feedback circuit, it is intended for the oscillator components. So that wire should be removed. Additionally, Configure R3 as a variable resistor and change it to 10K, then connect the feedback pin to the junction of R3/R4, the output voltage will then be adjustable between 5v-30v.

A strange case!!!
I used a single coil core in the same basic schematic that I posted in the first post.
And I removed the capacitors C8 and C9, one end of the coil to the positive input and the other to the drain and diode, that is, the circuit works only as a boost.
What do you think happened?
When the circuit input was 18 volts and there was no load on it, the voltage could be adjusted from 18 to 30
But when the load was placed on it, the voltage remained constant at 15 and practically the potentiometer did not change.
When the input voltage was 22 volts and the load was placed on it, the output remained constant at 19.
It is interesting that the circuit itself always consumes 3 volts

Hello
I measured the voltage of the MOSFET pins with a voltmeter, maybe it helps why the MOSFET heats up.

Vin=24.1,Vout=30.5
Vgs=0.3(While the load is not on its output),
Vsd=23.8
Vg,ground=23.5
Vgs=3.7(while the load on its output is about 2.5 amps)

Is this value allowed for MOSFET?
And it doesn't make it hot?

 

A strange case!!!
I used a single coil core in the same basic schematic that I posted in the first post.
And I removed the capacitors C8 and C9, one end of the coil to the positive input and the other to the drain and diode, that is, the circuit works only as a boost.
What do you think happened?
When the circuit input was 18 volts and there was no load on it, the voltage could be adjusted from 18 to 30
But when the load was placed on it, the voltage remained constant at 15 and practically the potentiometer did not change.
When the input voltage was 22 volts and the load was placed on it, the output remained constant at 19.
It is interesting that the circuit itself always consumes 3 volts

Is this value allowed for MOSFET?
And it doesn't make it hot?

Post the modified schematic

 

See below:

I closed the potentiometer circuit according to your schematic and it failed
In the initial state, the potentiometer worked only in no-load mode, and as soon as the load was connected, the voltage remained constant

 

Post the modified schematic