hii, i need help for my project which is i have design a closed loop flyback converter with 3W, 350mA, 10.5V for my output and the input should be varying from 9V-24V, my current should be constant 350mA and also my 10.5V, but as you can see, my output voltage and current also increased. The output current just constant with the voltage and not with the varying input voltage. I also want to know, why my voltage is -ve?

 

Why are you using a flyback converter for that?
Normally a flyback is used when you need input-output isolation, or need an output voltage much higher than the input voltage.
Also flybacks have poorer conversion efficiency than buck or boost converters.

You say its a closed-loop converter but the output is open loop and the LED current will vary with the characteristics of the particular LEDs you use.
Your output is constant-voltage, not constant-current.

 

If you post files we can all look at the details.
I see no hint of feed back.
What is I1 doing?

 

What is the purpose of R8? A heater?

 

Why are you using a flyback converter for that?
Normally a flyback is used when you need input-output isolation, or need an output voltage much higher than the input voltage.
Also flybacks have poorer conversion efficiency than buck or boost converters.

You say its a closed-loop converter but the output is open loop and the LED current will vary with the characteristics of the particular LEDs you use.
Your output is constant-voltage, not constant-current.

True, just looking at the parts datasheet it appears per a typical application to want a feedback path, thus the sense winding.

 

If you post files we can all look at the details.
I see no hint of feed back.
What is I1 doing?

its actually when i deleted that, i cant get the result but its okay now

 

What is the purpose of R8? A heater?

its r load, for the leds, when i dont use the R8, the current for the leds is not the same

 

Why are you using a flyback converter for that?
Normally a flyback is used when you need input-output isolation, or need an output voltage much higher than the input voltage.
Also flybacks have poorer conversion efficiency than buck or boost converters.

You say its a closed-loop converter but the output is open loop and the LED current will vary with the characteristics of the particular LEDs you use.
Your output is constant-voltage, not constant-current.

i just doing some research for my project for this flyback converter. yea i also dont know what im doing , completely lost hahah

 

If you post files we can all look at the details.
I see no hint of feed back.
What is I1 doing?

 

i also dont know what im doing

Then look into buck or buck-boost converters designed to drive LEDs with load current, not voltage feedback.
That would be the most efficient way to power them.

 

Slowed down the switching frequency. Change inductance. Added feedback for 350mA.

------------------
edited
Sorry I attached the wrong file. LT1234_led_ron.

 

Slowed down the switching frequency. Change inductance. Added feedback for 350mA.
View attachment 294671

I see you added an LTSpice circuit with the LT3065 linear regulator. Could you add the LTSpice circuit you created in the picture for the LT1243? Being you have it working better, I am just curious about it's simulation. Thanks.

 

If you are not to concerned about efficiency, you can also use a Linear regulator with current feedback (this is modified from the circuit ronsimpson posted using the LT3065). I just changed it to use current feedback.

 

1) Should not have 24V directly on VCC so I added R11, which charges up C8. There is a little delay. When the supply is running it is powered by the LED voltage. I would make C8 10uF but it makes the delay in SPICE too long.
2) Changed the use of R4 to make the PWM regulate at 1V. Changed R9 to compensate. Now there is only 1V loss in R9.

 

 

1) Should not have 24V directly on VCC so I added R11, which charges up C8. There is a little delay. When the supply is running it is powered by the LED voltage. I would make C8 10uF but it makes the delay in SPICE too long.
2) Changed the use of R4 to make the PWM regulate at 1V. Changed R9 to compensate. Now there is only 1V loss in R9.
View attachment 294689
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Thank you so much everyone!!! i really appreciate it :')
May god bless u all, thank you so much!

 

Welcome to AAC.

Because it concern course work your thread has been moved to the Homework Help forum. AAC rules limit the kind of help that members can provide in such cases to guidance concerning your own solution. For that reason all course work related posts must be to the Homework Help forum to make the nature of the question clear.

Good luck on your project.

 

1) Should not have 24V directly on VCC so I added R11, which charges up C8. There is a little delay. When the supply is running it is powered by the LED voltage. I would make C8 10uF but it makes the delay in SPICE too long.
2) Changed the use of R4 to make the PWM regulate at 1V. Changed R9 to compensate. Now there is only 1V loss in R9.
View attachment 294689

what should i consider if i want to change the output voltage? because the output voltage is to high

 

The circuit given is current-regulated. It will automatically supply the correct voltage to give 350mA through the LEDs

 

The circuit given is current-regulated. It will automatically supply the correct voltage to give 350mA through the LEDs

Thank You!!