simulate this circuit – Schematic created using CircuitLab

I am looking to understand this circuit better. The main question is:

  1. Is it true that the battery will start draining and stop when its Voltage is 12.16V (D1 Zener voltage) and will not continue to drop voltage?
  2. The simulator tells me that around 12.16 Volts the current will be Zero. Is this real, that the circuit current really becomes Zero at around 12.16V in real life?

Something is telling me that the simulations are too theoretical :)

Also, there are Zener Diodes of almost all voltages, right? or does the industry limit the availability of these?

The simulators all have DC Sweep but all are from 0 to a positive voltage not, for example, from 24 Volts to 10Volts. How can I simulate a voltage dropping as in a battery in a simulator?

  • \$\begingroup\$ Thank you for the reply. Let's remove the voltmeter and the amperemeter, these are there for the simulation only. The real-life example is exactly as in the schematic but without the meters. I want to drain a battery to a certain voltage (The Zener voltage). \$\endgroup\$
    – Nandostyle
    Jun 26 '21 at 21:00
  • \$\begingroup\$ I just modified the circuit (removed the meters). \$\endgroup\$
    – Nandostyle
    Jun 26 '21 at 21:02
  • \$\begingroup\$ Is the 24 volt battery a lead acid type? If so is it standard or deep discharge type? I ask because a keyword search yields information as follows: standard 24 volt lead acid battery is 12 cells rated 2 volts per cell nominal and should not be discharged below 1.95 volts per cell. Most battery chemistries have a low voltage cutoff to protect against damage from deep discharge. This is separate from your effort to understand the circuit which is a Zener diode voltage regulator. You can study how this operates via keyword search and watch some videos. \$\endgroup\$ Jun 26 '21 at 21:08

You are correct that it is not so simple in practice, although it is fairly close. Here's a short list of some of the things that makes your circuit deviate from the simulation:

  • Every component has a manufacturing tolerance, or variation. The datasheet tells us that VZ can vary between 11.4 and 12.6 volts right from the start.
  • A Zener diode does not magically start and stop conducting fully at the Zener voltage, it has a gradual curve. Sometimes this is given in the datasheet.
  • Even below the Zener voltage there will be a leakage current, the datasheet again tells us that it is around 5 µA for this device, but I expect it to vary between components, and vary strongly depending on the temperature.

About the Zener voltage selection, you can probably get whatever you want if you order hundreds of thousands, but since it is impractical to stock many different voltages, manufacturers typically limit their selection to a fixed set.

  • \$\begingroup\$ How can I simulate a voltage dropping as in a battery in a simulator? \$\endgroup\$
    – Nandostyle
    Jun 27 '21 at 23:15

See This Question and Answer

Zener Diode Voltage and Curve Equation

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The simulator creates an approximation for the Zener diode curve. The circuit uses the Zener diode in the region of voltage regulation when the voltage from the battery exceeds the magnitude of the Zener voltage shown as VZ. The 100 ohm resistor limits the current flow and locates the operating point at the intersection of the Zener curve and the 100 ohm load line (not shown in the figure).

See Also This Question and Answer

What is the Q-point of the zener diode?

An answer there incorporates this link which explains the operation of your circuit in general terms:


The Q-point is shown in Figure 4 on page 2 of the 9 page reference. An accurate simulation would reproduce the typical curve for the specific Zener diode and use an algorithm to find the Q-point based on the specified value of series resistance.


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