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Bauteile

Voltage Characteristics Of Z-diodes

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Z-Diodes are often used for simple voltage stabilized circuits. It is very important to use the Z-diode with the correct parameters.
This article shows an example for the voltage characteristics of two Z-diodes.

The reverse voltage of a Z-diode depends extremly on its reverse current. In data sheets the Z-voltage is given for a given reverse current.
If the reverse current is much more different than that value the Z-voltage is very different.

The following figures shows the Z-voltage over the reverse current from 0.5..30 mA of two Z-diodes with a nominal Z-Voltage of 2.7 V

comparison of two 2.7 V Z-diodes at 5 mA
Figure 1: comparison of two 2.7 V Z-diodes at 5 mA reverse Current

Figure 1 shows that both Z-diodes have their nominal Z-voltage at a reverse current of about 5 mA.

Comparison of two 2.7 V Z-diodes
Figure 2: Comparison of two 2.7 V Z-diodes

Figure 2 shows the whole voltage characteristics. It shows that at 2.5 mA the Z-voltage is only at 2.5 V. At 10 mA the voltage is at 2.9..3 V.

Akkus

Observations On Batteries

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This article takes a look on the costs of batteries compared to accumulators and additional chargers.

Energie costs

Batteries are one of the most expensive energie sources.
Lets make a calculation:

  • Battery: Alkaline, size: AA
  • Voltage: U = 1.5V
  • Capacity: K ≈ 2Ah

For one battery the stored energy is:

E = U ⋅ K = 1.5V ⋅ 2Ah = 3Wh

To get one kilowatthour energy out of batteries you need:

1kWh = 333 Batteries
3Wh

If one battery is 1,00 € then per kilowatt hour you pay:

333 peaces ⋅ 1,00 €/peace = 333 €/kWh

In comparision one kWh out of solar energy that is currently payed with 0,57€ is indeed cheap.
So it makes sense to use accumulators and a good charger if you use equipment with high energy demands like digital cameras or remote controlled model vehicles.

Today there are size AA accumulators that have a capacity of more than 2500 mAh. With a durability of 1000 charge cycles that can be achieved with a good charger that means a accumulator can provide 2500 Ah during its live span.

The accumulator voltage is 1.2 V. That results in 3 kWh energy during live span. If the accumulator costs 5,00 € and the charger is 40,00€ then the costs per kWh are:

45 € / 3kWh = 15,00 €/kWh

If you use more than one accumulator the costs decrease even more:

for  4 accumulators: 60€ / 12kWh = 5,00€/kWh

Of course there are the costs for the electrical energy from the grid. For 0,20 € per kWh this are 2,40 €, in sum this is for 4 accumulators  7,40 €/kWh. The losses when charging and self discharge losses of the accumulators are neglected for this observations.