Suitable IC for flyback constant current LED driver in boundary conduction mode

[Patrick_66]

Hello everyone, can someone help me check whether these 3 IC can be used for flyback constant current LED driver in boundary conduction mode?

RT7306, RT7306, LT3799

Other than that, I have one more question will the equation be the same to calculate the Lm for DCM, CCM, and BCM in the flyback converter? Thank you for your time.

 

[cupoftea]

Lenz's Law is one of the main equations to calc L's in SMPS.

 

[KlausST]

Hi,

or the most basic inductance formula: L = V(t) * dt / di
or speaking with the units: H = Vs/A or more clear V * s / A

example: if you apply 2V across an inductance for 10us ..and the current changes by 100mA (during this 10us) then:

L = 2V * 10us / 100mA = 20uVs / 100mA = 20 uVs/A / 0.1 = 200 uH

The only thing to remember is that L should be rather constant until the core saturates.
On saturation L will drop, thus the current will rise faster. Much faster. Sometimes a regulation loop is not fast enough to react on this speed.
-> overcurrent --> destruction.
Thus it´s very important to chose an inductor with a saturation above normal regulation conditions.

Klaus

 

[Patrick_66]

Hello Sir, can I follow the way to find the inductance value based on this video stated below without caring about the operating condition (CCM,DCM,BCM) since I will be using an IC that ensures the system in BCM mode and regulates the output current at the same time? Is this how it works? Please advise me. One more question, if I add another LED in series to the system will the output change since the IC is regulating the output current and not the output voltage? Thank you for your time and help. Appreciate it.

 

[KlausST]

since I will be using an IC that ensures the system in BCM mode

if you use an IC, then read it´s datasheet. It tells you all you need to know and tells you how to calculate part values.
Maybe the manufacturer additionally provides application notes or design notes. Just vist the internet site for the IC.

Klaus

 

[Patrick_66]

if you use an IC, then read it´s datasheet. It tells you all you need to know and tells you how to calculate part values.
Maybe the manufacturer additionally provides application notes or design notes. Just vist the internet site for the IC.

Klaus

Hello Sir, may I ask does the datasheet even teaches you how to calculate the inductance values for the coupled inductors or is there a fixed equation for the inductor values in BCM, CCM or DCM? One more question, can I use the method used in this webpage to calculate the coupled inductance value even though the system is a constant voltage LED driver, with a different IC and operating in DCM mode? Because I want to build a flyback converter for a constant current LED driver in boundary conduction mode. Thank you for your time and guidance.

 

[KlausST]

may I ask does the datasheet even teaches you how to calculate the inductance values for the coupled inductors

Simple answer:
Read it, then you will know. It´s high time to do so.

An inductance is an inductance. Coupled or not it will basically follow the basic forumla given in post#3.

It seems you did not even try to read a datasheet. You don´t show the math you did.
A forum is not meant that others do your job. We like to help. But helping means you do the main job. You show what you have done and we will correct it if needed.

Klaus

 

[Patrick_66]

Simple answer:
Read it, then you will know. It´s high time to do so.

An inductance is an inductance. Coupled or not it will basically follow the basic forumla given in post#3.

It seems you did not even try to read a datasheet. You don´t show the math you did.
A forum is not meant that others do your job. We like to help. But helping means you do the main job. You show what you have done and we will correct it if needed.

Klaus

Hello Sir, I will go and have a look in detail of the datasheet. If I still have something that I'm unclear in the datasheet can I come and ask you ? Thank you for the advise and now I will do my part in understanding the datasheet. Have a nice day sir thanks for all your help so far.