zener diodes

[glinjik]

hi folks is it possible to put two 1/2watt Zener diodes in parallel in place of a 1watt zener?

[chris_leyson]

Unlikely because one would always have a lower threshold voltage and even if they were matched it would be risky. Current sharing resistors might help. Which Zenner diodes are you thinking of using ?

[glinjik]

18v 1 watt its part no 1n4746a

was thinking 1/2 watt 18v the voltage is not really important it can be 12-24v

[glinjik]

its for this soft start module VD2

[wraper]

its for this soft start module VD2

If you make it with 400V dropping capacitor (C1) as it's in the circuit, very likely it will fail after some time. X2 ~250V+ safety capacitor or 630V DC rated film cap should be used.

[glinjik]

thank you i will change it for an x2 cap

[glinjik]

i suppose i could add in a emf filter and mov as an improvement

[srb1954]

hi folks is it possible to put two 1/2watt Zener diodes in parallel in place of a 1watt zener?

Not really a good idea. Unless the Zeners are closely matched the lower voltage one will take the lion's share of the current and dissipate a greater proportion of the power.

A better option is to put two lower voltage Zeners in series. If each Zener is half the desired total voltage them they will share power approximately equally without any need to have them closely matched.

[ledtester]

I recognize that circuit from a Kasyan TV video.

Here's a variation... pretty much same idea but they add a resistor in front of the zener and a bleeder on the dropper cap:

https://www.eeweb.com/inrush-current-limiter-soft-starter-for-ac-dc-loads/