# Voltage regulator with zener diode

What is the maximum input value (Vi) that can be applied without zener diode gets damaged knowing that the maximum power rating of the zener diode is $P_m = 500mW$,the breakdown voltage is $V_Z = 10V$ and the ripple in the output voltage is +-3% ? Any help is appreciated! Thanks in advance!

• Do not use Zener diodes as voltage regulators. Use them as voltage references, where you draw next to no current at all and R can be chosen far, far larger. Then again, don't use Zener diodes as references, either, as they are not thermally compensated, but simply use voltage reference ICs that aren't as temperature dependent. And while you're doing that, don't do that, either, but just use a voltage regulator IC: no-one in their right mind would build a voltage source like this. May 2 '18 at 16:21
• I'm voting to close this question as off-topic because it seems like homework and/or not shown what is tried. May 2 '18 at 16:21
• 40 yrs ago when Bandgap references were becoming popular in LDO's people still used Zeners which are poorman's regulators due to wide Vi variations that the Zener must absorb to maintain regulation ( Izt= knee current) You must design according to Vi min to supply Izt and Pz to dissipate max power at Vi max. May 2 '18 at 16:24