The Zeners already have a Zz = 9Ω @58mA and Zzt = 400 Ω @ 1mA or the threshold value.

The sum for Vf=0.7V and Vz=4.3 add up to 5.0V yielding a convenient regulated +/-5V clipped signal.

The Vz tolerance is +/-5% at 58mA but would rise 9mV/mA with more current and drop by 400mV/mA at Vzt. THus for stable operation using more current towards the rated current is preferred.

Also nobody really uses zeners for this due to the soft limiting characteristics using a Zener to change gain and limit the voltage .

Why is this a terrible design example?

• there are no specs for Voltage tolerance and squareness of peaks.
• Zeners are poor tolerance to begin with due to the exponential VI curve
• The Source impedance must be higher than Zeners to reduce the limit the gain and thus the voltage output, thus the current is low and the knee is very rounded.

The Zeners already have a Zz = 9Ω @58mA and Zzt = 400 Ω @ 1mA or the threshold value.

The sum for Vf=0.7V and Vz=4.3 add up to 5.0V yielding a convenient regulated +/-5V clipped signal.

The Vz tolerance is +/-5% at 58mA but would rise 9mV/mA with more current and drop by 400mV/mA at Vzt. THus for stable operation using more current towards the rated current is preferred.

Also nobody really uses zeners for this due to the soft limiting characteristics using a Zener to change gain and limit the voltage .

Why is this a terrible design example?

• there are no specs for Voltage tolerance and squareness of peaks.

• Zeners are poor tolerance to begin with due to the exponential VI curve

• The Source impedance must be higher than Zeners to reduce the limit the gain and thus the voltage output, thus the current is low and the knee is very rounded

• the Zener voltage drops well below rated Vz by more than 10% so it will never be 4.3+0.7=5V , rather more like 4.4V with 1K source

• at this point you ought to be re-examining the real requirements and specs.

  Why do I need this?
  Why do we take for granted examples in books and websites are perfect? Trust but verify. Never assume unless you know for sure.

The Zeners already have a Zz = 9Ω @58mA and Zzt = 400 Ω @ 1mA or the threshold value.

The sum for Vf=0.7V and Vz=4.3 add up to 5.0V yielding a convenient regulated +/-5V clipped signal.

The Vz tolerance is +/-5% at 58mA but would rise 9mV/mA with more current and drop by 400mV/mA at Vzt. THus for stable operation using more current towards the rated current is preferred.

This ideal source impedance is ΔV/ΔIz= 10V/58mA = 172 Ohms which will not be affected by the AC input signal of +/-25mV over +/-5V output swing.

My answer is in theory of course theoretical as the Op Amp cannot possibly drive this current alone , even with high negative feedback and Zout near zero because of internal current limits.

Also nobody really uses zeners for this.

Why is this a terrible design example?

• there are no specs for Voltage tolerance and squareness of peaks.
• Zeners are low tolerance to begin R less than Zener knee resistance, Zzt of 400 Ohms @ 1mA and a source R=400 Ohms so the voltage drops to -1 and will always have a rounded edge due to the dynamic impedance ratio of he 2 diodes in series.

The Zeners already have a Zz = 9Ω @58mA and Zzt = 400 Ω @ 1mA or the threshold value.

The sum for Vf=0.7V and Vz=4.3 add up to 5.0V yielding a convenient regulated +/-5V clipped signal.

The Vz tolerance is +/-5% at 58mA but would rise 9mV/mA with more current and drop by 400mV/mA at Vzt. THus for stable operation using more current towards the rated current is preferred.

Also nobody really uses zeners for this due to the soft limiting characteristics using a Zener to change gain and limit the voltage .

Why is this a terrible design example?

• there are no specs for Voltage tolerance and squareness of peaks.
• Zeners are poor tolerance to begin with due to the exponential VI curve
• The Source impedance must be higher than Zeners to reduce the limit the gain and thus the voltage output, thus the current is low and the knee is very rounded.

The Zeners already have a Zz = 9Ω @58mA and Zzt = 400 Ω @ 1mA or the threshold value.

The sum for Vf=0.7V and Vz=4.3 add up to 5.0V yielding a convenient regulated +/-5V clipped signal.

The Vz tolerance is +/-5% at 58mA but would rise 9mV/mA with more current and drop by 400mV/mA at Vzt. THus for stable operation using more current towards the rated current is preferred.

This ideal source impedance is ΔV/ΔIz= 10V/58mA = 172 Ohms which will not be affected by the AC input signal of +/-25mV over +/-5V output swing.

My answer is in theory of course theoretical as the Op Amp cannot possibly drive this current alone , even with high negative feedback and Zout near zero because of internal current limits.

Also nobody really uses zeners for this

The Zeners already have a Zz = 9Ω @58mA and Zzt = 400 Ω @ 1mA or the threshold value.

The sum for Vf=0.7V and Vz=4.3 add up to 5.0V yielding a convenient regulated +/-5V clipped signal.

The Vz tolerance is +/-5% at 58mA but would rise 9mV/mA with more current and drop by 400mV/mA at Vzt. THus for stable operation using more current towards the rated current is preferred.

This ideal source impedance is ΔV/ΔIz= 10V/58mA = 172 Ohms which will not be affected by the AC input signal of +/-25mV over +/-5V output swing.

My answer is in theory of course theoretical as the Op Amp cannot possibly drive this current alone , even with high negative feedback and Zout near zero because of internal current limits.

Also nobody really uses zeners for this.

Why is this a terrible design example?

• there are no specs for Voltage tolerance and squareness of peaks.
• Zeners are low tolerance to begin R less than Zener knee resistance, Zzt of 400 Ohms @ 1mA and a source R=400 Ohms so the voltage drops to -1 and will always have a rounded edge due to the dynamic impedance ratio of he 2 diodes in series.