AN90031

Zener diodes - physical basics, parameters and application
examplesRev. 3.0 — 7 June 2023

application note

Document information
Information

Content

Keywords

Zener voltage, voltage stabilizer, leakage current

Abstract

This application note explains the key parameters of Zener diodes and their testing methods.
Application examples for these components are included.

AN90031

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Zener diodes - physical basics, parameters and application examples

1. Introduction
When biased in the forward direction Zener diodes have the same characteristic as a silicon p-n
diode. Most important for Zener diode applications is the characteristic when biased in the reverse
direction, where Zener diodes have a small leakage current below a specific breakdown voltage.
Above the breakdown voltage, the I-V characteristic shows a steep increase of current. Zener
diodes can operate constantly as voltage stabilizers at or above the breakdown voltage, VZ. These
components are produced for many different voltages with guaranteed small ranges for VZ tested
at a defined reverse current IZ. Fig. 1 shows common symbols for a zener diode.

CathodeAnodeFig. 1.

Symbols for a Zener diodeFig. 2 shows an example of the I-V curve of a Zener diode. For positive voltages the diode is inforward conduction. Current increases quite steeply if about 0.7 V is exceeded. In reverse direction
an area is depicted where the diode is blocking. Once the breakdown voltage is reached, current
increases significantly. The voltage drop across the diode is kept almost constant in this area. An
ideal Zener diode would keep VZ constant independent on the current. In practice however the
curve is not perpendicular but there is a dynamic resistance Rdyn = ∆VZ/∆IZ larger than zero.
Breakdown area

Reverse blocking

Forward conduction
IZ

V BR

0.7

V

aaa-033931

Fig. 2.

I-V characteristic of a Zener diodeZener diodes for voltages up to about 5 V are realized with highly doped substrates. For suchp-n diodes an electrical breakdown occurs if electrons can tunnel from the valence band into the
conduction band across the depletion area of the reverse biased junction. The free charge carriers
create a sudden increase of the reverse current once the field strength is high enough.
Clarence Melvin Zener discovered the above described effect in 1934 and the diodes produced
have been named after him. For Zener diodes with a breakdown voltage higher than 5 V, a different
breakdown effect becomes dominant. This is the avalanche breakdown, which is different from theabove discussed Zener effect. The electrical field across the p-n junction accelerates electrons
in the transition area. These electrons create electron-hole pairs. Holes move to the negative

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Zener diodes - physical basics, parameters and application examples
electrode and get filled again, whereas the electrons move to the positive electrode. This motionof holes and electrons create a leakage current through a negative biased diode. With high fieldstrength the mobile holes and electrons can generate more charge carriers by freeing up adjacentbound electrons. This process of generating more charge carries happens to the extent of anavalanche, so that a high current starts to flow if a specific reverse voltage is exceeded.
Both effects, the Zener effect and the avalanche effect, are not distinguished for the naming of
Zener diodes. No matter which physical effect dominates the breakdown of the p-n junction, allvoltage reference diodes are referred to as Zener diodes.

2. Data sheet parameters
Nexperia data sheets for Zener diodes generally cover a series of products, with each type number
having a specified working voltage. These data sheets start with a section “General description”
where the package type is given. The following section “Features and benefits” mentions theworking voltage range. For Zener diodes that are offered with different tolerance selections of VZ,
which is the nominal working voltages, this information is provided as well.
The chapter “Quick reference data” contains a table with the maximum forward voltage VF at a
forward current IF = 10 mA and ambient temperature Tamb = 25 °C. In order to avoid significant selfheating this parameter is tested in pulsed mode. The maximum total power dissipation Ptot is also
given, together with the description of the related mounting condition. Table 1 below is an example[1]

from the data sheet of BZX884S .
Table 1. BZX884S Quick reference data
Tamb = 25 °C unless otherwise specified.
SymbolParameter

Conditions

VFforward voltage

IF = 10 mA

Ptot

total power dissipation

[1]
[2]

Min

Typ

Max

Unit

[1] -

-

0.9

V

[2] -

-

365

mW

Pulse test: tp ≤ 100 μs; δ ≤ 0.02
Device mounted on a FR4 PCB, single-sided 70 μm copper, tin-plated and standard footprint.

Table 2 gives the pinning of the Zener diode. As for other diodes, the cathode is clearly marked
with a bar in order to safeguard proper mounting in the desired direction. Table 3 is the ordering
information with the type number, exact name, description and version of the package.
Table 2. BZX884S Pinning
Pin
SymbolDescription
1

K

cathode[1]

2

A

anode

Simplified outline

Graphic symbol

1

1

2

2
006aaa152

Transparent
top view[1]

The marking bar indicates the cathode.

Table 3. Ordering information
Type number
Package
BZX884S series
[1]
[1]

Name

Description

Version

DFN1006BD-2

Leadless ultra small plastic package with sidewettable flanks (SWF); 2 terminals; 0.65 mm
pitch; 1 mm x 0.6 mm x 0.47 mm body

SOD882BD

The series includes 37 breakdown voltages with nominal working voltages from 2.4 V to 75 V and ±2 % and approximately ±5%
tolerances.

The next data sheet chapter is named “Marking” and contains a Marking code table, (Table 4).
All the available products with different working voltages in the two tolerance clusters are listed
together with the marking code.

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Zener diodes - physical basics, parameters and application examples
The naming of later generation Zener diodes is quite easy to interpret. At the beginning the
Zener diode family name can be found. In the given example BZX884S. This is followed by acharacter for the tolerance. An indicator “B” stands for 2% tolerance, the character “C” for about
5%. Nexperia introduced a larger portfolio of Zener diodes with an “A” tolerance rating for the VZ,
which means 1% accuracy in order to address a growing demand for higher precision. Diodes
in packages SOT23, SOD323 and SOD123F can be chosen. After the tolerance indicator, theworking voltage is added, e.g. 2V4 for VZ = 2.4 V. Integer voltage ratings show a number with no"V" as separator.
Table 4. Marking Codes
Type number
Mark.
Code

Type number

Mark.
Code

Type number

Mark.
Code

Type number

Mark.
Code

BZX884S-B2V42A

BZX884S-B15

2U

BZX884S-C2V4

4K

BZX884S-C15

4C

BZX884S-B2V7

2B

BZX884S-B16

2V

BZX884S-C2V7

4L

BZX884S-C16

4D

BZX884S-B3V0

2C

BZX884S-B18

2W

BZX884S-C3V0

4R

BZX884S-C18

4E

BZX884S-B3V3

2D

BZX884S-B20

2X

BZX884S-C3V3

4S

BZX884S-C20

4F

BZX884S-B3V6

2E

BZX884S-B22

2Y

BZX884S-C3V6

4T

BZX884S-C22

4G

BZX884S-B3V92F

BZX884S-B24

2Z

BZX884S-C3V9

4U

BZX884S-C24

4H

BZX884S-B4V32G

BZX884S-B27

3A

BZX884S-C4V3

4U

BZX884S-C27

4J

BZX884S-B4V72H

BZX884S-B30

3B

BZX884S-C4V7

4Y

BZX884S-C30

4M

BZX884S-B5V1

2J

BZX884S-B33

3C

BZX884S-C5V1

5B

BZX884S-C33

4N

BZX884S-B5V6

2K

BZX884S-B36

3D

BZX884S-C5V6

5C

BZX884S-C36

4P

BZX884S-B6V2

2L

BZX884S-B39

3E

BZX884S-C6V2

5F

BZX884S-C39

4Q

BZX884S-B6V8

N3

BZX884S-B43

3F

BZX884S-C6V8

5G

BZX884S-C43

4V

BZX884S-B7V5

2M

BZX884S-B47

3G

BZX884S-C7V5

5J

BZX884S-C47

4W

BZX884S-B8V2

2N

BZX884S-B51

3H

BZX884S-C8V2

5K

BZX884S-C51

4Z

BZX884S-B9V1

2P

BZX884S-B56

3J

BZX884S-C9V1

5L

BZX884S-C56

5A

BZX884S-B102Q

BZX884S-B62

3K

BZX884S-C10

3Y

BZX884S-C62

5D

BZX884S-B11

2R

BZX884S-B68

3L

BZX884S-C11

3Z

BZX884S-C68

5E

BZX884S-B122S

BZX884S-B75

3M

BZX884S-C12

4A

BZX884S-C75

5H

BZX884S-B13

2T

-

-

BZX884S-C13

4B

-

-

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2.1. Limiting values
Table 5 contains the Limiting values. The maximum forward current IF is defined as well as the
maximum total power dissipation Ptot, followed by the maximum junction temperature Tj and theallowed temperature ranges for ambient Tamb and storage Tstg.
Table 5. BZX884S Limiting values
In accordance with the Absolute Maximum Rating System (IEC 60134).
SymbolParameterIF

forward current

Ptot

total power dissipation

Tjjunction temperature

Tamb
Tstg
[1]

Conditions

Min

Max

Unit

-

200

mA

-

365

mW

-

150

°C

ambient temperature

−55

+150

°C

storage temperature

−65

+150

°C

Tamb = 25 °C[1]

Device mounted on a FR4 PCB, single-sided 70 μm copper, tin-plated and standard footprint.

2.2. Thermal characteristics
Table 6 provides the Rth(j-a) value for the device mounting on a standard footprint, single-sided PCB
with 70 µm copper plating. This value could also be calculated with (150 K - 25 K)/0.365 W.
Table 6. BZX884S Thermal characteristics
SymbolParameter

Conditions

Rth(j-a)in free air[1]thermal resistance from junction
to ambient

[1]

Min

Typ

Max

Unit

-

-

340

K/W

Device mounted on a FR4 PCB, single-sided 70 μm copper, tin-plated and standard footprint.

2.3. Characteristics
In Table 7 “Characteristics”, the maximum forward voltage drop at IF of 10 mA is given, this istested in pulsed mode.
Table 7. BZX884S Characteristics
Tj = 25 °C unless otherwise specified.
SymbolParameter

Conditions

VFforward voltage

IF = 10 mA[1]

Pulse test: tp ≤ 300 μs; δ ≤ 0.02.

Min
[1] -

Typ

Max

Unit

-

0.9

V

Table 8 and Table 9 list several very important parameters of the Zener diodes. The first column
is the name extension, followed by a column for the accuracy ranges provided per diode. Therd
3 column informs the minimum and maximum VZ values at a reverse current of 5 mA for VZ< 27 V. Above and equal VZ = 27 V the testing current is reduced to 2 mA as otherwise thepower dissipation would become quite high with P = VZ * IZ in case of a high breakdown voltage.
Additional operating cases are tested in mass production to ensure that the whole VZ – IZ curve iscorrect in the reverse blocking area as well as in the forward conduction and the breakdown areas.
The differential resistance is defined as rdif = ∆VZ/∆IZ and listed in the fourth column. This is thesteepness of the VZ – IZ curve. Ideal would be a dynamic resistance of 0 Ohm or a perpendicular
curve. In this case VZ would not change with reverse current and the breakdown voltage would staystable, independent of the current applied.

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The maximum reverse or leakage current is given in the next column, this is specified at about 2/3
of VBR.
The next column contains the thermal coefficient SZ in mV/K valid for an IZ of 5 mA or . The
breakdown voltage dependent on junction temperature can be calculated with the simple formula
below:VZ = VZ(nominal) + S Z × (Tj 25 °C)(1)For low voltage zener diodes SZ is a negative coefficient, so VZ decreases over temperature.
The breakdown mechanism is the Zener effect. Above about 6 V the sign of SZ changes and theavalanche effect becomes dominant.
Finally, there is a column for the diode capacitance Cd tested at VR = 0 V and f = 1 MHz.
Table 8. Characteristics per type; BZX884S-B2V4 to BZX884S-C24
Tj = 25 °C unless otherwise specified.
BZX884S

2V4
2V7
3V0
3V3
3V6
3V9
4V3
4V7
5V1
5V6
6V2
6V8
7V5

Sel

Working
voltageVZ (V)

Differential resistance
rdif (Ω)

IZ = 5 mA

IZ = 1 mA

IZ = 5 mA

Min

Max

Typ

Max

Typ

Max

Max

VR (V)

Min

Max

Max

B

2.35

2.45

275

600

70

100

50

1.0

-3.5

0.0

450

C

2.20

2.60

B

2.65

2.75

300

600

75

100

20

1.0

-3.5

0.0

450

C

2.50

2.90

B

2.94

3.06

325

600

80

95

10

1.0

-3.5

0.0

450

C

2.80

3.20

B

3.23

3.37

350

600

85

95

5

1.0

-3.5

0.0

450

C

3.10

3.50

B

3.53

3.67

375

600

85

90

5

1.0

-3.5

0.0

450

C

3.40

3.80

B

3.82

3.98

400

600

85

90

3

1.0

-3.5

0.0

450

C

3.70

4.10

B

4.21

4.39

410

600

80

90

3

1.0

-3.5

0.0

450

C

4.00

4.60

B

4.61

4.79

425

500

50

80

3

2.0

-3.5

0.2

300

C

4.40

5.00

B

5.00

5.20

400

480

40

60

2

2.0

-2.7

1.2

300

C

4.80

5.40

B

5.49

5.71

80

400

15

40

1

2.0

-2.0

2.5

300

C

5.20

6.00

B

6.08

6.32

40

150

6

10

3

4.0

0.4

3.7

200

C

5.80

6.60

B

6.66

6.94

30

80

6

15

2

4.0

1.2

4.5

200

C

6.40

7.20

B

7.35

7.65

30

80

6

15

1

5.0

2.5

5.3

150

AN90031application note

Reversecurrent
IR (μA)

Diode
capacitanceCd (pF) [1]

IZ = 5 mA

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SZ (mV/K)© Nexperia B.V. 2023. All rights reserved

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Zener diodes - physical basics, parameters and application examples
BZX884S

8V2
9V1
10
11
12
13
15
16
18
20
22
24

[1]

Sel

Working
voltageVZ (V)

Differential resistance
rdif (Ω)

Reversecurrent
IR (μA)

Temperature
coefficient
SZ (mV/K)

Diode
capacitanceCd (pF) [1]

IZ = 5 mA

IZ = 1 mA

IZ = 5 mA

Min

Max

Typ

Max

Typ

Max

Max

VR (V)

Min

Max

Max

C

7.00

7.90

B

8.04

8.36

40

80

6

15

0.7

5.0

3.2

6.2

150

C

7.70

8.70

B

8.92

9.28

40

100

6

15

0.5

6.0

3.8

7.0

150

C

8.50

9.60

B

9.80

10.20

50

150

8

20

0.2

7.0

4.5

8.0

90

C

9.40

10.60

B

10.80

11.20

50

150

10

20

0.1

8.0

5.4

9.0

85

C

10.40

11.60

B

11.80

12.20

50

150

10

25

0.1

8.0

6.0

10.0

85

C

11.40

12.70

B

12.70

13.30

50

170

10

30

0.1

8.0

7.0

11.0

80

C

12.40

14.10

B

14.70

15.30

50

200

10

30

0.05

10.5

9.2

13.0

75

C

13.80

15.60

B

15.70

16.30

50

200

10

40

0.05

11.2

10.4

14.0

75

C

15.30

17.10

B

17.60

18.40

50

225

10

45

0.05

12.6

12.4

16.0

70

C

16.80

19.10

B

19.60

20.40

60

225

15

55

0.05

14.0

14.4

18.0

60

C

18.80

21.20

B

21.60

22.40

60

250

20

55

0.05

15.4

16.4

20.0

60

C

20.80

23.30

B

23.50

24.50

60

250

25

70

0.05

16.8

18.4

22.0

55

C

22.80

25.60

IZ = 5 mA

f = 1 MHz; VR = 0 V

Table 9. Characteristics per type; BZX884S-B27 to BZX884S-C75
Tj = 25 °C unless otherwise specified.
BZX884S

27
30

Sel

Working
voltageVZ (V)

Differential resistance
rdif (Ω)

IZ = 2 mA

IZ = 0.5 mA

IZ = 2 mA

Min

Max

Typ

Max

Typ

Max

Max

VR (V)

Min

Max

Max

B

26.50

27.50

65

300

25

80

0.05

18.9

21.4

25.3

50

C

25.10

28.90

B

29.40

30.60

70

300

30

80

0.05

21.0

24.4

29.4

50

C

28.00

32.00

AN90031application note

Reversecurrent
IR (μA)

Diode
capacitanceCd (pF) [1]

IZ = 2 mA

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Zener diodes - physical basics, parameters and application examples
BZX884S

33
36
39
43
47
51
56
62
68
75

[1]

Sel

Working
voltageVZ (V)

Differential resistance
rdif (Ω)

Reversecurrent
IR (μA)

Temperature
coefficient
SZ (mV/K)

Diode
capacitanceCd (pF) [1]

IZ = 2 mA

IZ = 0.5 mA

IZ = 2 mA

Min

Max

Typ

Max

Typ

Max

Max

VR (V)

Min

Max

Max

B

32.30

33.70

75

325

35

80

0.05

23.1

27.4

33.4

45

C

31.00

35.00

B

35.30

36.70

80

350

35

90

0.05

25.2

30.4

37.4

45

C

34.00

38.00

B

38.20

39.80

80

350

40

130

0.05

27.3

33.4

41.2

45

C

37.00

41.00

B

42.10

43.90

85

375

45

150

0.05

30.1

37.6

46.6

40

C

40.00

46.00

B

46.10

47.90

85

375

50

170

0.05

32.9

42

51.8

40

C

44.00

50.00

B

50.00

52.00

90

400

60

180

0.05

35.7

46.6

57.2

40

C

48.00

54.00

B

54.90

57.10

100

425

70

200

0.05

39.2

52.2

63.8

40

C

52.00

60.00

B

60.80

63.20

120

450

80

215

0.05

43.4

58.8

71.6

35

C

58.00

66.00

B

66.60

69.40

150

475

90

240

0.05

47.6

65.6

79.8

35

C

64.00

72.00

B

73.50

76.50

170

500

95

255

0.05

52.5

73.4

88.6

35

C

70.00

79.00

IZ = 2 mA

f = 1 MHz; VR = 0 V

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Data sheet graphs
Following the characteristic tables a number of graphs are included.
Fig. 3 shows the I–V curve of BZX884S-B/C6V8 for forward direction with a logarithmic scale for IF
aaa-028551

103
IF
(mA)
102
10
1
10-1
10-2
10-3
0.4

0.6

0.8

VF (V)

1.0

Tj = 25 °C
Fig. 3.

Forward current as a function of forward voltage, typical values BZX884S-B/C6V8

Fig. 4 depicts how the temperature coefficient SZ varies over the working current IZ. For lower
working voltages there is a quite significant influence on this coefficient. From Fig. 5 it can beconcluded that SZ becomes almost constant over IZ for working voltages above 7.5 V.
mld4440.5
SZ(mV/K)

mld44512
15

SZ(mV/K)

4V7

0

13
12
11
10
9V1
8V2
7V5
6V8
6V2
5V6
5V1

8
4V3

- 0.5
2V4

4

2V7

3V9

-1

3V6

- 1.5

-2
10- 1

0

3V3
3V0

1

10

IZ (mA)

-4
10- 1

102

Tj = 25 °C to 150 °C
Fig. 4.

application note10

IZ (mA)102

Tj = 25 °C to 150 °C

Temperature coefficient as a function ofworking current; typical values BZX884S-B/
C2V4 to B/C4V7

AN900311

Fig. 5.

Temperature coefficient as a function ofworking current; typical values BZX884S-B/
C5V1 to B/C15

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Zener diodes - physical basics, parameters and application examples
For Zener diodes the I–V characteristic in reverse direction shows how effectively the component
can be used to stabilize a voltage. For low Zener voltages, the breakdown voltage increases
significantly versus reverse current as Fig. 6 shows. In this diagram the reverse direction I–V
curves from 2.4 V up to 6.8 V are depicted.
Fig. 7 and Fig. 8 show the reverse direction characteristics for higher voltage Zener diodes fromthe BZX884S series. These devices get quite close to an ideal Zener diode which would have aperpendicular I–V characteristic at the nominal VZ voltage, so reverse current IZ would not have an
impact on the breakdown voltage.
IR(A)

aaa-006665

10-1

2V4

10-2

2V7

10-3

3V0
3V3

3V6 3V94V3 4V7 5V1

IR(A)

aaa-006666

10-1
7V5

10-2

10 12

15

18

22

8V2
10-3

10-4

9V1

11 13

16

20

24

10-4

10-5
5V6

10-6

6V2

10-5

6V8

10-6

10-7

10-7

10-8
10-9

0

2

4

6

VR (V)

10-8

8

Tj = 25 °C
Fig. 6.

0

5

10

15

20
VR (V)

25

Tj = 25 °C

Reverse current as a function reverse voltage;
typical values (BZX884S-B/C7V5 to B/C24)
IR(A)

Fig. 7.

Reverse current as a function reverse voltage;
typical values (BZX884S-B/C27 to B/C75)
aaa-006667

10-1

30 36

10-2

27

33

43
39

51
47

62

75

56

68

10-3
10-4
10-5
10-6
10-7
10-8
10-9

Fig. 8.

20

40

60

VR (V)

80

Reverse current as a function reverse voltage; typical values (BZX884S-B/C7V5 to B/C24)

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3. Zener diode application examples
Zener diodes are often used to generate a stabilized voltage. In Fig. 9 a Zener diode ZD1 isconnected to a voltage source via a series resistor. The load resistor RLOAD is connected in parallelto the Zener diode. This load could also be a sophisticated electronic circuit requiring a stablesupply voltage. The value of series resistor R1 has to be chosen that residual current also flows
through the Zener diode with the highest expected load current. The minimum current through the
Zener diode should safeguard that the diode operates in the steep region of reverse conduction.
The current used for the measurement of VZ in the data sheet is a good value, this means about
5 mA up to VZ = 17 V and 2 mA for Zener diodes with high Zener voltages.
The power dissipated in R1 is:

R1 =V IN V Z
I Z(min) + I LOAD(max)(2)

The power dissipated in R1 is:PR1 =( V IN

VZ )

2

(3)

R1

The Zener diode has the maximum power dissipation, if no load is connected. In this case all thecurrent via R1 flows through the diode:

PZD1 = VZ × I Z = VZ ×

V IN

VZ

R1

(4)

R1
V OUT

V in

ZD1

R LOAD

aaa-033932

Fig. 9.

Voltage Stabilizer with a Zener diodeThe basic voltage stabilizer circuit shown in Fig. 9 is used for rather low power requirements. For
higher power requirements of a load circuit it is not efficient that the full current through R1 heats
up the Zener diode in case that the load is turned off or that much heat is generated if load current
consumption drops for a use case. The circuit in Fig. 10 improves this significantly. The Zener
diode ZD1 is driven in breakdown via R1. The base of the bipolar transistor Q1 is connected to thestabilized voltage across ZD1.
The output voltage at RLOAD is according to the equation:

VOUT = V Z

AN90031application note

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R1
Q1

V in

V OUT

ZD1

R LOAD
aaa-033933

Fig. 10. Voltage Stabilizer with a bipolar transistor and Zener diode voltage referencePower dissipation in the Zener diode is almost independent from load current if it is assumed thatthe base current is a small part of the current through R1 only. For output voltages of about 5 V
the circuit has a quite good thermal stability because a thermal coefficient of about - 2.0 mV/K iscompensated by a decrease of VBE with a very similar coefficient.
Another important application area for Zener diodes is clamping of undesired over-voltages. In
Fig. 11 a simple load switch is depicted. The gate oxide of MOSFETs is sensitive to over-voltages.
Internal ESD diodes of FETs should not be used for clamping in an application because the gatesource voltage VGS is above data sheet limits in this case. The breakdown voltage of the ESD
diode is higher than the specified VGS rating. In the application example a P-channel FET switches
the load current. The FET turns on once the gate gets negative voltage against the source. If
switch S1 is turned on, the voltage divider of R2 and R1 with ZD1 in parallel define the gate voltage
higher than VGS(th). The voltage at the gate is limited by ZD1 to a level which is within the VGS
rating of the FET with some safety margin. Gate voltage can be adjusted by a resistor divider
without a Zener diode. But in this case the circuit is not safe if VIN sees over-voltage events. The
resistor R1 has to be applied for discharge of the gate once the load switch is turned off. S1 isrealized with an N-channel control FET or a BJT normally.

V in

Q1
R1

V OUT

ZD1

R2

S1
aaa-033934

Fig. 11. Load switch with P-Channel FET and Zener diode for gate voltage clamping
Fig. 11 is another solution for protecting a MOSFET. The FET Q1 is switching an inductive load.
The inductance has no free-wheeling diode. Once the switch turns off, the current continues toflow. L1 creates a voltage which is high enough to break through the drain-source path of the
FET. However, with the zener diode applied between the drain and gate of the FET, the FET can
get gate drive so that the VDS rating is not exceeded. The FET runs in linear mode for a shortduration and the energy stored in the inductor is dissipated in the FET in a comparably short time.
Compared to a simple free-wheeling diode parallel to L1 a higher voltage loss across the drainsource path leads to higher power and faster decay of the stored energy in the inductor.

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+V
R1
L1
D1
ZD1
R2

Q1

aaa-033935

Fig. 12. Protection of a switch for an inductive load with a Zener diodeZener diodes can be used for all kind of applications where voltage levels have to be clamped
or kept below a limit. Fig. 13 shows a level limiter for an AC source. For a sine wave source themaxima and minima are symmetrically clipped to VZ + VF.
R1

V OUT
ZD1

AC
ZD2

aaa-033936

Fig. 13. Example for level clipping of an AC voltage by Zener diodes
Fig. 14 shows a SPICE simulation result of a 1 kHz sine wave voltage source supplied via 220
Ohm to Zener diodes with a VZ of 5.6 V in a serial structure with connected anodes. It can be seenthat the clipping levels are about 0.6 V higher than VZ as to be expected. In a similar approach
Zener diodes are often implemented as ESD and surge pulse protection for signal lines. With thevoltage clipping function they avoid excessive over-voltages that could endanger a damage ofelectronic circuits.
Zener diodes are often used as voltage references. Fig. 15 shows an example where an OP-Amp
is used as non-inverting buffer to provide the reference voltage created by the zener diode ZD1 as
output voltage with low impedance towards connected electronic loads. The current through the
Zener diode can be chosen small compared to the circuit shown in Fig. 9. In order to support suchapplications with a narrow spread of VZ at low Zener currents, dedicated low current zener diodefamilies are offered. Instead of 5 mA that are used for standard Zener diodes, these components
are selected for 50 µA. If standard Zener diodes are used for low current applications, the parts
should be tested upfront, if clamping works as desired.

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V

aaa-033938

8
OUT

6
4
2
0
-2
-4
-6
-8

0

1

2

4

3

5
6
time (ms)Fig. 14. Symmetrical clipping of 1 kHz sine wave with BZT52H-B5V6
+V
R1
IC1
ZD1

V OUT

R2
R3

aaa-033937

Fig. 15. Zener diode as voltage reference with an OP-Amp buffer

4. Avalanche breakdown considerations
The major application for Zener diodes is to operate them in reverse polarity. If the reverse
bias voltage is below the breakdown voltage the diode can be considered as a capacitor. The
capacitance depends on the size of the active areas and the distance of the depletion zone in thereverse mode. The depletion zone in a silicon crystal is not a perfect electrical insulator. A few
electrons can get into the depletion zone or some electrons in the depletion zone can lose theirbounds. These free electrons get accelerated to the positive voltage side which is the cathodeof the Zener diode. If the field strength is high enough a free electron can pick up enough kinetic
energy in the electric field to punch free another bond electron. This mechanism leads to a chain
reaction of creating more and more free electrons which is the so-called avalanche breakdown.
From the description of the avalanche mechanism, it is obvious that leakage current is a major
precondition beside providing an electrical field strength high enough for an avalanche breakdown.
The more free electrons are present the bigger is the probability to start an impact ionization andbecause of this an avalanche breakdown.
With a very simple test circuit a Zener diode can be operated at different operating points withregards to the Zener current IZ. The diode under test is put in series with a resistor R1 and a DC
voltage higher than VZ is connected. The voltage at the diode is investigated with an oscilloscope,
see Fig. 16.

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430 kΩ

DC adjusted todrive averagetarget current

V TEST
connected
to oscilloscopeDC
ZD1

aaa-036776

Fig. 16. Zener diode noise test circuit
IZ can be adjusted according IZ = (Vin – VZ) / R1. If the current is chosen smaller than 500 µA thevoltage at the Zener diode will show an overlay of “noise”. For low currents the avalanche condition
stops if not enough impact ionizations happen statistically to keep the desired Zener current stable
at the value according to the above formula. If conduction stops the voltage at the diode rises
and the diode capacitance gets charged via R1. Due to the higher field strength an avalanche
breakdown gets started again. Because the start of an avalanche breakdown has a statisticalspread, a random noise of triangle-shaped overswings can be observed. The signal even falls
below VZ after the steep falling edges where the breakdown has started again so that the diodestops conducting and needs to get re-triggered with a rising ramp signal again.
In Fig. 17 an example of a 27 V Zener diode is shown. 470 kΩ had been used as series resistor.
If the maximum overswing shall be found it is important to adapt the series resistor such that theovershoot waveforms look like triangles. If the resistance of the series resistor is chosen too low,
the waveforms show the typical flat run-in of a capacitor charging voltage curve, because theovershoot cannot get bigger than Vin - VZ.

Fig. 17. Avalanche noise for a 27 V Zener diode operated with 50 µA with 470 kΩ in series
Fig. 18 shows a test with 50 µA current applied via 43 kΩ. With a low series resistance, acomparably low voltage Vin is required to achieve a desired average current for the test circuit andthe overswing voltage can get clipped. The clipped pulses show then a statistical variation of the
breakdown delay. These delays can get bigger compared to a test with same current where thevoltage at the Zener diode can ramp up to a higher voltage without clipping effects. The highest
overswing can be captured by adjusting the trigger level of an oscilloscope to higher values step bystep until no bigger trigger events can be found anymore. Because of the statistical nature of theAN90031application note

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avalanche breakdown the oscilloscope should get enough time to wait for a trigger event which canbe seen as maximum overswing.

Fig. 18. Avalanche noise for a 33 V Zener diode operated with 50 µA with 43 kΩ in series
The diagram in Fig. 19 shows the maximum noise levels found for a 24 V Zener diode in
dependence on the current tested with 1.5 MΩ series resistance. Maximum noise is seen with
IZ = 20 µA to 40 µA. For currents larger than about 0.3 mA the noise almost disappears. For
currents lower than about 20 µA the noise pulses decrease in voltage. This is because the risetimes become larger and the charge time for the diode capacitance increases. Then there is moretime for a start of an avalanche breakdown while the voltage rises, the breakdown delay is not big
enough for seeing the maximum values for these very small currents.
aaa-036828

12
BZX84-C24

V Z(noise)
(V)
8

4

0

0

100

200

300

400

I Z (µA)

500

Fig. 19. Maximum noise level for BZX84-C24 as a function of IZ
In the described test set-up, the Zener diodes are exposed to a constant bias voltage via a series
resistor. Alternatively, turn-on tests can be performed where a test pulse is applied to the device
under test (DUT) while the waveform is captured. Nexperia performs tests where 100 V or 150 V
pulses are provided with a low frequency (~ 1 Hz) to a DUT which is connected via 10 kΩ to thegenerator. The series resistor and the diode capacitance Cd define the rise rate of the test pulse. In

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Fig. 20 a 'scope trace of such test is shown. The clamping of the input voltage shows a statisticalspread. Fig. 20 shows a worst case captured with a significant overswing voltage. In area 1 thesignal ramps up according to the time constant 10 kΩ × Cd. Then the Zener diode becomes
conductive and a short undershoot can be seen in area 2. After this the Zener diode shows thedesired nominal clamping voltage in area 3.

Fig. 20. BZX84-C33 pulse test with 100 V via 10 kΩ
Zener diodes with a low breakdown voltage are based on the name-giving Zener effect as
described in the introduction section of this application note. If the Zener effect is dominating the
breakdown, the leakage current of the Zener is comparably high like the I-V curves in Fig. 6 andFig. 7. With enough leakage current and therefore a high number of impact ionizations, the noise
issue for low IZ cannot be observed.
Above about VZ = 6 V both breakdown effects, the Zener tunnel effect, and the avalanche
breakdown, start to play a role and at about 10 V the avalanche breakdown becomes dominant.
This fact can be seen in the I-V diagrams in Fig. 7 as well. From 10 V onwards, the I-V curves arealmost perpendicular even for a very small current once VZ is reached. For voltage types bigger
than 10 V, the avalanche breakdown is dominating, and the slope of the I-V curve is very steep.
Nexperia offers two kinds of Zener series to address the noise topic:*

The standard series BZ , TDZ, NZH, and HPZR are optimized for an extremely low leakage
current. The leakage current is in the region of only a few pA. While this is an advantage for some
applications, this can cause noise or overswing for other applications. The corresponding series
are:
•
•
•
•

BZX884S
BZX884
BZX585
BZX384••••

BZX84J
TDZxJ
BZT52
NZH

•
•
•
•

BZT52HBZB84
BZX84
BZB784••••

BZX84W
BZV90
BZV49
HPZR

*

and if applicable their ‘Q’-version ( = under development).

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Zener diodes - physical basics, parameters and application examples
The PZU, PDZ, and 50 µA Zener series have a moderately increased leakage current (IR > 1 nA
before the breakdown). The probability of an impact ionization is clearly increased and the noiseand overswing is reduced accordingly. The corresponding series are:*•

BZX8850•PZUxBA•••PZU884PZUxBL*
BZX58550•••

BZX38450
PDZ-B
PZUxB

*

*

*

•

BZX8450•

BZX845**and if applicable their ‘Q’-version ( = under development).
For the usage of Zener diodes in applications the low leakage parts should be run with an IZ of
more than 0.5 mA. Then there is no noise issue to be expected anymore. For VZ < 10 V also the
low league current series work stable at low currents. Selecting components with a moderately
higher leakage current that use a gold-kill process reduce the noise level also for Zener voltages
above 10 V significantly.
The low leakage types can become problematic if voltages shall be clipped exactly without
overshoots or turn-on delays when it is not possible to apply a sufficiently high bias current. In
these cases, the above listed Zener diodes should be selected.

5. Zener diodes package overview
Nexperia offers zener diodes in a wide range of packages. Section 5 shows all options from thesmall DFN1006 packages up to the bigger variants such as SOT223 with high power capability.
The values in column 3 apply for mounting the devices on an FR4 Printed-Circuit Board with astandard footprint. The board uses single-sided copper with tin-plating.
Table 10. Nexperia’s packages for Zener diodes, configuration and Ptot ratings
Package name
Configuration

Ptot (mW)

DFN1006BD-2(SOD882BD)

single365

DFN1006(D)-2(SOD882)

single250

SOD523

single300

SOD323

single300/400/490

SOD323F

single310

SOT23

single, dual

250/300

SOT323Single, dual

250/275/300/350

SOD123

single365/590

SOD123F

single500/830

SOT89

single1000

SOT223

single1500

SOD80C(MiniMelf)single500

SOD27(DO-35)

single500

SOD66(DO-41)single1000/1300

6. References
1. BZX884S series data sheet.

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7. Revision history
Table 11. Revision history
Revision
Date
numberDescription

3.0

2023-06-07

Section 4 added.

2.0

2022-06-27

Fig. 12 updated.

1.0

2021-10-01

Initial version.

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8. Legal information
Definitions
Draft — The document is a draft version only. The content is still underinternal review and subject to formal approval, which may result in
modifications or additions. Nexperia does not give any representations or
warranties as to the accuracy or completeness of information included hereinand shall have no liability for the consequences of use of such information.

Disclaimers
Limited warranty and liability — Information in this document is believed
to be accurate and reliable. However, Nexperia does not give any
representations or warranties, expressed or implied, as to the accuracy
or completeness of such information and shall have no liability for theconsequences of use of such information. Nexperia takes no responsibility
for the content in this document if provided by an information source outsideof Nexperia.
In no event shall Nexperia be liable for any indirect, incidental, punitive,
special or consequential damages (including - without limitation - lost
profits, lost savings, business interruption, costs related to the removalor replacement of any products or rework charges) whether or not suchdamages are based on tort (including negligence), warranty, breach ofcontract or any other legal theory.
Notwithstanding any damages that customer might incur for any reason
whatsoever, Nexperia’s aggregate and cumulative liability towards customer
for the products described herein shall be limited in accordance with theTerms and conditions of commercial sale of Nexperia.
Right to make changes — Nexperia reserves the right to make changes
to information published in this document, including without limitation
specifications and product descriptions, at any time and without notice. This
document supersedes and replaces all information supplied prior to the
publication hereof.
Suitability for use — Nexperia products are not designed, authorized or
warranted to be suitable for use in life support, life-critical or safety-criticalsystems or equipment, nor in applications where failure or malfunctionof an Nexperia product can reasonably be expected to result in personal
injury, death or severe property or environmental damage. Nexperia and its
suppliers accept no liability for inclusion and/or use of Nexperia products insuch equipment or applications and therefore such inclusion and/or use is at
the customer’s own risk.
Applications — Applications that are described herein for any of theseproducts are for illustrative purposes only. Nexperia makes no representation
or warranty that such applications will be suitable for the specified use
without further testing or modification.
Customers are responsible for the design and operation of their applications
and products using Nexperia products, and Nexperia accepts no liability forany assistance with applications or customer product design. It is customer’ssole responsibility to determine whether the Nexperia product is suitableand fit for the customer’s applications and products planned, as well as
for the planned application and use of customer’s third party customer(s).
Customers should provide appropriate design and operating safeguards tominimize the risks associated with their applications and products.
Nexperia does not accept any liability related to any default, damage, costs
or problem which is based on any weakness or default in the customer’s
applications or products, or the application or use by customer’s third party
customer(s). Customer is responsible for doing all necessary testing for thecustomer’s applications and products using Nexperia products in order toavoid a default of the applications and the products or of the application or
use by customer’s third party customer(s). Nexperia does not accept any
liability in this respect.
Export control — This document as well as the item(s) described herein
may be subject to export control regulations. Export might require a priorauthorization from competent authorities.
Translations — A non-English (translated) version of a document is forreference only. The English version shall prevail in case of any discrepancy
between the translated and English versions.

Trademarks
Notice: All referenced brands, product names, service names andtrademarks are the property of their respective owners.

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List of Tables
Table 1. BZX884S Quick reference data............................. 3
Table 2. BZX884S Pinning...................................................3
Table 3. Ordering information.............................................. 3
Table 4. Marking Codes....................................................... 4
Table 5. BZX884S Limiting values....................................... 5
Table 6. BZX884S Thermal characteristics..........................5
Table 7. BZX884S Characteristics....................................... 5
Table 8. Characteristics per type; BZX884S-B2V4 to
BZX884S-C24...................................................................... 6
Table 9. Characteristics per type; BZX884S-B27 to
BZX884S-C75...................................................................... 7
Table 10. Nexperia’s packages for Zener diodes,
configuration and Ptot ratings............................................ 18
Table 11. Revision history.................................................. 19

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List of Figures
Fig. 1. Symbols for a Zener diode....................................... 2
Fig. 2. I-V characteristic of a Zener diode............................2
Fig. 3. Forward current as a function of forward
voltage, typical values BZX884S-B/C6V8............................ 9
Fig. 4. Temperature coefficient as a function of working
current; typical values BZX884S-B/C2V4 to B/C4V7........... 9
Fig. 5. Temperature coefficient as a function of working
current; typical values BZX884S-B/C5V1 to B/C15............. 9
Fig. 6. Reverse current as a function reverse voltage;
typical values (BZX884S-B/C7V5 to B/C24)...................... 10
Fig. 7. Reverse current as a function reverse voltage;
typical values (BZX884S-B/C27 to B/C75)........................ 10
Fig. 8. Reverse current as a function reverse voltage;
typical values (BZX884S-B/C7V5 to B/C24)...................... 10
Fig. 9. Voltage Stabilizer with a Zener diode..................... 11
Fig. 10. Voltage Stabilizer with a bipolar transistor and
Zener diode voltage reference...........................................12
Fig. 11. Load switch with P-Channel FET and Zener
diode for gate voltage clamping.........................................12
Fig. 12. Protection of a switch for an inductive loadwith a Zener diode............................................................. 13
Fig. 13. Example for level clipping of an AC voltage by
Zener diodes...................................................................... 13
Fig. 14. Symmetrical clipping of 1 kHz sine wave with
BZT52H-B5V6.................................................................... 14
Fig. 15. Zener diode as voltage reference with an OPAmp buffer..........................................................................14
Fig. 16. Zener diode noise test circuit................................15
Fig. 17. Avalanche noise for a 27 V Zener diodeoperated with 50 µA with 470 kΩ in series........................ 15
Fig. 18. Avalanche noise for a 33 V Zener diodeoperated with 50 µA with 43 kΩ in series.......................... 16
Fig. 19. Maximum noise level for BZX84-C24 as afunction of IZ...................................................................... 16
Fig. 20. BZX84-C33 pulse test with 100 V via 10 kΩ......... 17

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Contents
1. Introduction................................................................... 2
2. Data sheet parameters................................................. 3
2.1. Limiting values.............................................................5
2.2. Thermal characteristics................................................5
2.3. Characteristics............................................................. 5
3. Zener diode application examples............................ 11
4. Avalanche breakdown considerations......................14
5. Zener diodes package overview................................18
6. References.................................................................. 18
7. Revision history..........................................................19
8. Legal information........................................................20© Nexperia B.V. 2023. All rights reserved

For more information, please visit: http://www.nexperia.com
For sales office addresses, please send an email to: salesaddresses@nexperia.com
Date of release: 7 June 2023

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