Can We use PTC with LYT4228

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Hello,

We are using LYT4228 for out 50W & 75W led drivers.

Currently we are using Slow blow fuse for over current protection. But we have to replace complete driver when only fuse blows.

I wonder if I can use PTC thermister(Resettable fuse) for over current protection instead of slow blow fuse in this driver.

Is it okay to use 3.5ohm PTC with 50W & 75W Led driver ?

 

Hi,

Yes, resettable fuse is accepted to use but not paractical in terms of cost. Because normally the LED driver is designed not to fail unless there will be a component failure.

 

For the PTC rating, check the (I^2) t and note that it will decrease the efficiency. 

 

Another thing consider is if given product is with safety logo aproval then it will require reevaluation if a fuse is replaced.

 

Regards,

PI-Jono

1) We are selling our lights in india where some of area has worst power conditions.

Here typically volatege range is 220 +/- 10%.
But some time it may rise upto 400V and that time varistor(Vmax = 300V) blow the fuse.

We have checked many failed drivers and found that only fuse & varistor are blown.
All other components are working fine.

2) I am going to use 3.5-6 Ohm PTC which will waste 0.5Watt in 75Watt driver.
Efficiency drop is less than 1%. We can afford it for high reliblity driver.

3) We do not have problem of reevaluation driver. But one queation.
Is there any saftey problem to use PTC in LED driver ?
Is there chance to fail in standard safty test ?

Hi,

Now I got the point why a resettable fuse is your preffered.

Since there is a huge spike in input, the varistor and fuse are subject to stress.

There is no problem in safety using a resettable fuse but the safety testing is more stringent. they will wait for the fuse to recover then observe the effect on the board.  Note that resettable fuse is slower than the normal fuse so safety design is more challenging.

Since PTC is slower than normal fuse, the varistor may fail during this 400VAC event.  Assuming you address the fuse the varistor is istill your problem. Therefore, you need to increase the rating for the MOV also.

 

Regards,

PI-JOno