# Zener Diode vs Precision Voltage Shunt

What is the difference between a zener diode and a precision voltage shunt? From the name I am guessing that the precision voltage shunt is more precise. I am using the shunts to limit the output of a sine wave generator.

• What do the data sheets tell you and what confuses you? – Andy aka Jan 30 '18 at 13:59
• So from the data sheets, the zener has +- 200mv and the precision one is +- 40mv. I am just wondering if there are other differences between the two devices, performance in temperature variation for example. Just wondering if there is physically something different or just that they are zener diodes held to a higher tolerance in selection. edited: Zener : centralsemi.com/… Voltage Shunt : ww1.microchip.com/downloads/en/DeviceDoc/20005757A.pdf – Alex Bussiere Jan 30 '18 at 14:09
• Without links to data sheets it's anybody's guess except yours. – Andy aka Jan 30 '18 at 14:10
• The IV behavior before the zener voltage is quite a bit different between a shunt reference ic and a zener diode. A zener diode may have lowish leakage before the breakdown voltage. A shunt reference has active circuitry to power. – sstobbe Jan 30 '18 at 14:56

If you look at an average zener diode like the MM3Z3V6T1G, and a voltage regulator like the LP2980, you can see the difference pretty quickly.

First off, the zener voltage is listed as 3.4V-3.8V. That's already +-5%.

Next, you have the IV curve of the zener.

Notice how the Zener breakdown curve on the left is not a straight vertical line, but is instead somewhat diagonal. The gradient of this line is the zener resistance. In the attached datasheet, it lists the resistance as 90 Ohms (at 5mA). This means that the voltage will vary depending on the current through it, by almost 100mV per mA. Say you want to use it at 0mA and 3 mA, thats a variance of another 8%.

In contrast, the regulator is guaranteed to have an absolute max variance of +-2.5%, and keep that constant between 0mA and 50mA. These are maximums, and the actual value will likely be a fair amount lower.

Basically, with Zeners you're almost guaranteed to get variations of +-10%, whereas with actual regulators its more like <1%.

Just to add, Andy is correct that this is a voltage regulator, but the same logic applies to a shunt like the LT1389, except that it's even more accurate at a guaranteed +-0.5%.

• The LP2980 is a precision voltage regulator and not a precision shunt -1 – Andy aka Jan 30 '18 at 14:18

A precision voltage reference is a complete circuit that uses something called a Band Gap Reference.

A bandgap voltage reference is a temperature independent voltage reference circuit widely used in integrated circuits. It produces a fixed (constant) voltage regardless of power supply variations, temperature changes and circuit loading from a device Wikipedia

A zener diode is a simply a diode which is designed and binned with a particular breakdown voltage. Like all diodes, it's characteristics vary with applied current and temperature.

A precision reference is really more like an accurate voltage regulator.

• @Bimpelrekkie lol..oops. Different website... Thanks for the heads up – Trevor_G Jan 30 '18 at 14:14
• OP asked about a "precision voltage shunt", not a precision series reference. – The Photon Jan 30 '18 at 16:43
• @ThePhoton hmm.. from how I understand them they are the basically the same thing.. see this one – Trevor_G Jan 30 '18 at 16:51
• The difference is that the shunt reference needs a resistor between Vin and its "cathode", and current draw will be constant regardless of load current (while in regulation). Like a shunt regulator. A series reference is connected directly to Vin and only draws (about) as much current as the load draws (like a series regulator). – The Photon Jan 30 '18 at 16:57
• Your last sentence is actually correct if you assume "voltage regulator" means "shunt regulator", but I think at least 99.9% of readers will assume series regulator instead. – The Photon Jan 30 '18 at 17:03