The 1N5919B Zener diode datasheet gives the power rating as 3W. It drops 5.6V across i.e. its Zener voltage is given as 5.6V.

Power = V * I and in this case I would say Imax = Pmax / Vz --> Imax = 3000/5.6 = 536mA.

The datasheet says Imax is 267mA.

Why is that the case? Is that related to temperature? How can it be formulated/explained?

(I would love to test this in LTspice but cannot find the model)

  • \$\begingroup\$ I found a spice model using the Wayback Machine: web.archive.org/web/20150708192143/http://www.onsemi.com/… \$\endgroup\$
    – ErikR
    Oct 16, 2022 at 16:54
  • \$\begingroup\$ How did you make the search? I go to web.archive.org and serached for d1n5919b nothing found. \$\endgroup\$
    – cm64
    Oct 16, 2022 at 17:30
  • \$\begingroup\$ The Mouser product page has links to spice models at the bottom of the page. Copy that link and search for it in the Wayback Machine. \$\endgroup\$
    – ErikR
    Oct 16, 2022 at 17:34
  • \$\begingroup\$ Can you really find 1N5917BRLG ? I will try tahnks \$\endgroup\$
    – cm64
    Oct 16, 2022 at 17:35
  • \$\begingroup\$ Is that supped to be here: mouser.dk/ProductDetail/onsemi/… \$\endgroup\$
    – cm64
    Oct 16, 2022 at 17:40

3 Answers 3

  • You can apply a short power pulse to the device that is about 100 watts for no more than 1 ms.
  • The table on page 1 says the steady state power dissipation is 1 watt at an ambient of 50°C.
  • And, if you check what power is implied by 267 mA and 5.6 volts you get 1.5 watts.
  • This 1.5 watt figure is the same for all the zeners in the main table.
  • This ties in with what other suppliers specify such as the Digitron Semiconductors data sheet.

They explicitly rate the 1N5913B as 1.5 watts at an ambient temperature of 25°C. So, I'd use a simulator if you know what pulse widths of power you might expect to see and follow the maximum surge power diagram (figure 3 in the ON semi data sheet).

But, if you looked at Figure 1 in the data sheet and applied decent heat removal on the device leads you can get a greater steady-state power level: -

enter image description here

I've added the red and green stuff for the 1 watt 50°C point.


The LTSpice model won't manage total power capability.

Note the datasheet says that 3 W is the maximum allowed power dissipation and has disclaimers about reliability etc. Clearly it is not recommended to operate sustained at 3 W, but you can temporarily. Similarly IZM is the maximum sustained current (and dissipates about 1.5 W), but short excursions above this are OK (perhaps charging a capacitor etc.).

As with any electronic component, stressing significantly above 'reasonable' ratings will degrade lifetime. 'reasonable' is complex and depends on lots of factors which vary in importance depending on the application.


The maximum ratings show two steady state power dissipation specifications.

  1. 3 watts with a lead temperature of \$75 ^{o}\text{C}\$. This requires heat sinking.
  2. 1 watt with an ambient temperature of \$50 ^{o}\text{C}\$. No heat sink required.

The electrical characteristics show that \$I_{ZM}\$ is measured at a lead temperature of \$30 ^{o}\text{C}\$. If the lead temperature is lower, then the max current can be higher. If the lead temperature is higher then the max current is lower.

The lead temperature is controlled by power dissipation and heatsinking.

@Andyaka's answer provides the finer detail available to reconcile these various specifications so I won't repeat them here.

Maximum ratings enter image description here


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