Page 52
www.us-tech.com
March 2026
Surge Protection: Keeping Voltage Spikes Under Control with TVS Diodes
By Dr. Heinz Zenkner and Gerhard Stelzer, Würth Elektronik eiSos GmbH & Co. KG T
ransient overvoltages can occur unexpectedly in many applica- tions. The consequences range from malfunctions to irreversible destruction of the circuit. TVS diodes protect sensitive circuit
components and effectively divert interference currents. TVS diodes (transient voltage suppressors) are used to protect cir-
cuits from high voltage spikes. They are designed for reverse bias opera- tion and work by diverting interference currents when the reverse volt- age exceeds the so-called avalanche breakdown potential. They are basi- cally high-power Zener diodes and represent a special form of avalanche diodes. TVS diodes can handle large power peaks (hundreds or thou- sands of watts), whereas Zener diodes have a tighter voltage tolerance. TVS diodes generally have a higher parasitic capacitance than Zener diodes. They are available in either unidirectional or bidirectional ver- sions. Unidirectional TVS diodes block up to the rated voltage in one di- rection and behave like a normal forward-biased diode in the other direc- tion. Bidirec tional TVS diodes block up to the rated voltage in both direc- tions (good for protection against alternating currents). Unidirectional TVS diodes have a much shorter turn-on time
than their bidirectional counterparts (e.g., 5 ps compared to 5 ns). The illustration on the right side of Figure 1 shows how a bidi-
rectional TVS diode can be conceptualized; it is a circuit consisting of two TVS diodes connected in an “anti-series” configuration. Figure 2 shows shows the typical current-voltage characteristics
of the diodes. The parameters of the current-voltage characteristics have the following meanings:
DC operating voltage (VDC), channel operating voltage (Vch) The maximum operating voltage must not exceed VDC. The TVS
diode presents a high impedance to the protected circuit when the voltage applied to the diode is below this threshold value. Above this value, excessive leakage current flows, which can lead to permanent failure of the TVS diode.
Reverse breakdown voltage (VBR) This is the voltage threshold at which the TVS diode begins to
conduct a defined current of 1 mA and is also referred to as the break-
down voltage. The value of VBR according to the data sheet should be above the maximum operating voltage of the circuit to be protected so that the TVS diode is in the reverse state under normal operating conditions of the device.
Clamping voltage (VClamp) he overvoltage tran-
sient is limited to the value
defined by VClamp, i.e., to the maximum voltage value that occurs in the protected cir-
cuit. The voltage VClamp is defined for a specific peak pulse current (IPeak).
Peak pulse current (IPeak) This is the maximum
surge current that the TVS diode can withstand without damage. The peak pulse cur- rent is defined based on the transient waveform of the surge current, which is specified as 8/20 µs in most industrial applications, where 8
Figure 1: symbols for unidirection- al and bidirectional TVS diodes (left), functional equivalent of a bidirectional TVS diode (right).
µs represents the rise time (t1) to the peak value and 20 µs represent- ing the pulse duration until the current drops to 50% of the peak val- ue (t2).
Leakage current (ILeak) The leakage current is measured at VDC and is the current that
flows in the reverse direction as residual current.
Power dissipation (PDISS) The power dissipation PDISS indicates how much power the diode
can absorb. A distinction is made between peak pulse power dissipa- tion and steady-state power dissipation.
From zero to cured. In runway time.
Bectron PT 4700 N Conformal Coating. Curing within seconds Low energy and space requirements
Find out more:
elantas.com/BectronPT4700N
Sustainable health protection
Figure 2: current-voltage characteristics of unidirectional (left) and bidirectional (right) TVS diodes.
Peak pulse power dissipation The maximum peak power that the TVS diode can dissipate dur-
ing a transient event for a defined pulse waveform, here for the 10/1000 µs pulse (10 µs rise time, 1,000 µs decay to half amplitude).
Steady-state power dissipation The power that the TVS diode can continuously absorb under
normal operating conditions. “Snapback” Effect An ideal TVS diode completely blocks the current, i.e., the cur-
rent is zero when the input voltage is less than the breakdown volt- age. When the input voltage is greater than the breakdown voltage, the TVS diode ideally has a resistance close to zero so that the tran- sient voltage can be effectively suppressed. A standard TVS diode clamps by starting to conduct at a certain voltage and limiting the voltage drop across the diode. This diode has “non-ideal” behavior due to leakage currents and a finite internal resistance (Figure 2). A TVS diode can be implemented using semiconductor technolo-
Continued on page 54
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56 |
Page 57 |
Page 58 |
Page 59 |
Page 60 |
Page 61 |
Page 62 |
Page 63 |
Page 64 |
Page 65 |
Page 66 |
Page 67 |
Page 68 |
Page 69 |
Page 70 |
Page 71 |
Page 72 |
Page 73 |
Page 74 |
Page 75 |
Page 76 |
Page 77 |
Page 78 |
Page 79 |
Page 80 |
Page 81 |
Page 82 |
Page 83 |
Page 84 |
Page 85 |
Page 86 |
Page 87 |
Page 88 |
Page 89 |
Page 90 |
Page 91 |
Page 92 |
Page 93 |
Page 94 |
Page 95 |
Page 96 |
Page 97 |
Page 98 |
Page 99 |
Page 100
