Fuse the TVS diode for protection

[www111]

Dear all,

I want to protect a circuit that works from following power supply:
Input voltage : from 12V to 24V
Max power consumption 10W -> Imin=0.4A Imax=0.8A



My selected components for:
Fuse : littelfuse NANO2 slo-blo 0452001. (1A)
TVS : littelfuse SMBJ24A (600W)

The questions are:
1) will the fuse protect the TVS if someone connects 200V on instead of 24V
2) how can I calculate the needed TVS diode power rating if I know the nominal melting [I2t(A2sec)] of the fuse?

Best Regards.

 

[crutschow]

1) That depends upon the power rating of the TVS and the inductance of the filters.

2) To calculate the required size of the TVS you need to know the I^2t of the fuse and the inductance of the filters.
(Is that a common-mode choke filter? If so then it would provide little protection for the TVS.)

 

[www111]

1)Power rating of the diode is 600W -> datasheet of the TVS and Fuse attached
View attachment LittelFuse_Nano2_Slo-Blo_452_454_Series.pdf
View attachment Littelfuse_TVS_Diode_SMBJ_Datasheet.pdf

2) Those are BLM ferrite beads.
The I2t of the fuse is 1.98 A2sec

How can I calculate the TVS needed, in the worst case when there are no Ferrite bead only the fuse and the TVS diode?

Best Regards.

 

[schmitt trigger]

Why a slow blow?
To protect semiconductors, fast action fuses are usually the norm, unless you significantly derate the clamping current.

The TVS diode is rated for a peak current for a very short period of time. Usually in the 10 X 1000 waveform.

 

[www111]

Thanks for the info.

But is there a way if i have this slow blow fuse I2t=1.98 A2sec to calculate the proper TVS diode so that the fuse blows before the TVS if there is 200V on power in pin that i protect? (max voltage on power in pin is 24V).

Some of this is described her on page 3 but there are no formulas to calculate it https://www.vishay.com/docs/88440/failurem.pdf

Best Regards.

 

[KlausST]

Hi,

1) will the fuse protect the TVS if someone connects 200V on instead of 24V

No, the fuse is rated with 125V only.

Klaus

 

[www111]

So this means that the fuse will blow before the TVS?

the 200V not normal operation. this only happens if short occurs between the 24 power line and 200V(dc) power line for led.

 

[KlausST]

HI,

the fuse simply is not specified for voltages above 125V.
Don´t blame it on the fuse if you (accidentally) connect 200V and the fuse makes something strange.

Ask the fuse manufacturer for more information.

Klaus