Zener diode
A. Principle: It operates in reverse breakdown mode. When the reverse voltage reaches and exceeds the steady-state voltage, the reverse current suddenly increases, while the voltage across the diode remains constant. B. Classification
Based on voltage regulation levels: Low-voltage Zener diodes (<40V);
High voltage Zener diode (>200V)
Based on materials: N-type
C. Main parameters
① Stable voltage VZ: The reverse working voltage corresponding to the specified Zener diode and reverse working current IZ.
②Stable current IE
③ Dynamic resistance rZ;
④ Maximum power dissipation PZM
⑤ Maximum stable operating current IZmax and minimum stable operating current IZmin ⑥ Temperature coefficient at, the higher the temperature, the greater the voltage regulation error
D. Uses
① Clamp protection for drain and source
silicon Zener diode voltage regulator circuit
It uses the reverse breakdown characteristic of Zener diodes to regulate voltage. Because the reverse characteristic is steep, a large change in current will only cause a small change in voltage.
Transient Voltage Suppressor (TVS) diode: 1. Characteristics:
Under specified reverse application conditions, when subjected to a high-energy transient overvoltage pulse, its operating impedance immediately drops to a very low conduction value, allowing large current to pass through and clamping the voltage to a predetermined level, thereby effectively protecting the precision components in the electronic circuit from damage. It features fast response speed (in the pS range), small size, low clamping voltage, and high reliability. Bidirectional TVS is suitable for AC circuits, while unidirectional TVS is generally used in DC circuits.
2. Classification:
According to polarity, they are divided into two types: unipolar and bipolar.
3. Symbol:
6. Main parameters of TVS
①VBR: Reverse Breakdown Voltage (also known as breakdown voltage) Definition: When a TVS (Transient Voltage Suppressor) flows a specified current of 1mA (IR), the voltage VBR measured between the two terminals of the TVS is the minimum avalanche voltage of the TVS. At 25°C, the TVS is not conducting before this voltage. When the transient voltage exceeds VBR, the transient voltage suppressor diode breaks down, suppressing the transient voltage to a certain level and providing an ultra-low resistance path for the transient current, allowing the transient current to be diverted through the transient voltage suppressor diode and bypass the protected component.
②IR: Reverse Leakage Current. When the maximum reverse working voltage is applied to the TVS, the TVS transistor has a leakage current IR, which is typically 10-100μA. This leakage current is an important parameter when the TVS is used in high-impedance circuits.
③VRWM: Maximum Reverse Working Voltage (Reverse Stand-off Voltage: the withstandable reverse voltage) is the voltage value across the device when it operates in reverse at a specified IR. In this state, the diode is not conducting. Typically, VRWM = (0.8~0.9) VBR. During use, VRWM should not be lower than the normal operating voltage of the protected device or circuit.
④VC(max): Maximum clamping voltage (TVSdiode Clamping Voltage: suppression voltage). Under the action of the pulse peak current Ipp, the maximum voltage value across the device is called the maximum clamping voltage. In use, VC(max) should not exceed the maximum permissible safe voltage of the protected device. The ratio of the maximum clamping voltage to the breakdown voltage is called the clamping coefficient. That is: Clamping coefficient = VC(max) / VBR. Generally, the clamping coefficient is around 1.3.
⑤Cj: TVS Diode Junction Capacitance (Capacitance value of a transient voltage suppressor diode) The capacitance of a TVS diode is determined by the area of the silicon wafer and the bias voltage. Under zero bias, the capacitance value decreases as the bias voltage increases. The capacitance value affects the response time of the TVS device. A larger capacitance value in a transient voltage suppressor diode leads to greater interference in the circuit, resulting in more noise or greater signal attenuation. For circuits with higher data/signal frequencies, the capacitance value should not exceed 10pF.
⑥IPP: Maximum peak pulse current.
When operating in reverse, under specified pulse conditions, the maximum pulse peak current that the device is allowed to pass.
⑦PPR: Peak power of the reverse pulse.
The pulse peak current (PPR) of a TVS depends on the pulse peak current (IPP) and the maximum clamping voltage (VC). In addition, it is also related to the pulse waveform, pulse duration, and ambient temperature.
8. Methods for testing diodes
Use a multimeter set to the R×1k range to test the condition of the tube.
① For a unipolar TVS, its forward and reverse resistance can be measured using the method for measuring a trivial diode. Generally, the forward resistance is about 4kΩ and the reverse resistance is infinite.
② For bidirectional TVS, the resistance between its two pins should be infinite when the red and black probes are interchanged. Otherwise, it indicates that the tube is malfunctioning or has been damaged.
9. Typical examples of TVS applications in circuits:
Examples of selection in direct current:
The whole machine operates at a DC voltage of 12V, with a maximum permissible safe voltage of 25V (peak value). The surge source impedance is 50MΩ, and its interference waveform is a square wave with TP=1MS and a maximum peak current of 50A.
Examples of AC circuit applications:
DC lines use unidirectional transient voltage suppressor diodes (TVS diodes), while AC lines must use bidirectional TVS diodes. AC is the mains voltage, and the transient voltages generated here are random, sometimes also affected by lightning strikes (transient voltages induced by lightning), making it difficult to quantitatively estimate the instantaneous pulse power (PPR). However, the maximum reverse working voltage must be correctly selected. A general principle is to select the maximum reverse working voltage of the TVS diode by multiplying the AC voltage by 1.4. For DC voltage, the maximum reverse working voltage (VRWM) of the TVS diode is selected by multiplying it by 1.1 to 1.2. The following diagram shows the schematic of a microcomputer power supply using a TVS diode for line protection: 1. A TVS diode is added at the 220VAC input to suppress spike interference in the 220V AC mains.
2. Add an interference filter to the transformer input line to filter out small spike interference.
3. A TVS diode was added at the VAC=20V output terminal of the transformer to suppress interference once again.
4. When the DC output reaches 10V, a TVS diode is added to suppress interference.
Parameters of transient diode ESD5Z12T1G (http://www.dzsc.com/ic-detail/9_1353.html)
Capacitance at different frequencies: 55pF@1MHz
Supplier device package: SOD-523
Manufacturer's standard lead time: 20 weeks
Power - Peak Pulse: 240W
Packaging: Cut tape (CT), Tape roll (TR)
One-way channel: 1
Mounting type: Surface mount (SMT)
Package/Case: SC-79, SOD-523
Operating temperature: -55°C to 150°C (TJ)
Applications: Automotive
Moisture Sensitivity Level (MSL): 1 (Unlimited)
Breakdown voltage (minimum): 14.1V
Maximum reverse working voltage: 12V (maximum)
Clamping voltage VC: 25V
Peak pulse current (Ipp): 9.6A (8/20µs)
Power line protection: None
Type: Zener
Series: Automotive Grade, AEC-Q101
Parts status: Available for sale
Series: Automotive Grade, AEC-Q101
Type: Zener
One-way channel: 1
Voltage-reverse off state (typical): 12V (maximum)
Voltage-breakdown (minimum): 14.1V
Voltage clamping (maximum) @ Ipp: 25V
Current-peak pulse (10/1000µs): 9.6A (8/20µs) Power-peak pulse: 240W Power line protection: None
Applications: Automotive
Capacitance at different frequencies: 55pF@1MHz
Operating temperature: -55°C to 150°C (TJ)
Mounting type: Surface mount
Package/Case: SOD-523
Package/Case: SC-79, SOD-523
Voltage-reverse off state (typical): 12V (maximum)
Voltage-breakdown (minimum): 14.1V
Voltage clamping (maximum) @ Ipp: 25V
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