KDZVTR5.1B

The KDZVTR5.1B is a 5.1V Zener voltage regulator diode from ROHM in SOD-123FL (PMDU) surface-mount package, featuring 5.368V typical Zener voltage (5.1V min, 5.7V max), 1W power dissipation, 40mA test current, 20µA max reverse leakage current, and 150°C max junction temperature. Small power mold type with high ESD tolerance. Supplied on 3,000-piece tape and reel.

The KDZVTR5.1B operates based on the Zener breakdown effect in a silicon epitaxial planar junction. When reverse-biased beyond the Zener voltage (VZ ≈ 5.1V), the diode enters breakdown region where current increases rapidly while voltage remains nearly constant. This voltage regulation property makes it suitable for reference voltage and overvoltage protection. The device is manufactured using a small power mold (PMDU) construction, which provides high ESD tolerance. At the nominal test current of 40mA, the Zener voltage is specified between 5.1V and 5.7V with a typical value of 5.368V. The 1W power dissipation rating allows continuous operation in regulator and clamp circuits. The low reverse leakage current (<20µA below VZ) ensures minimal power waste during normal operation.

以下是 KDZVTR5.1B 引脚描述的详细说明，这是一种齐纳二极管 （具体来说是 SOD-123F 或类似表面贴装封装中的 5.1V 齐纳二极管）。

Given that the “KDZVTR5.1B” is a standard two-terminal semiconductor device (a Zener diode), its pin description is very simple, but crucial for correct circuit operation.

KDZVTR5.1B Pin Description (Expanded)

The device has only two pins (terminals), but they are not interchangeable in a standard circuit. Here is the detailed breakdown:

引脚编号 引脚名称 类型 描述 1 阴极（K） 功率/参考 标记端（通常是封装上的带状或线）。 这是正常齐纳工作时的负极。它必须连接到电源的正极或需要调节的电路节点。电压参考于该引脚到阳极。2 阳极（A） 接地/回流 无标记端。 这是正常齐纳工作时的正极。它通常连接到地（0V）， 或者当齐纳击穿时，电路的负极电流从阴极流向阳极。

Functional Behavior (How to use it)

To understand the pins, you must understand the two operating modes of a Zener diode:

1. Normal Operation (Reverse Bias / Breakdown Mode):
   • The Cathode is connected to the positive voltage (e.g., +5.1V rail).
   • The Anode is connected to ground (0V).
   • When the voltage across the device (Cathode to Anode) exceeds 5.1V, the diode “breaks down” and conducts current to maintain a constant 5.1V drop. This is the intended use.
2. Forward Bias (Not normally used):
   • If the Anode is at a higher voltage than the Cathode (e.g., Cathode = 0V, Anode = +2V), the device acts like a standard silicon diode (forward voltage drop ~0.7V). It will conduct heavily, damaging the circuit or the diode itself if current is not limited.

Critical Design Considerations for these Pins

Because this is a surface-mount Zener diode, the physical pin layout and thermal behavior are important:

1. Polarity is Critical (Easy to Get Wrong)

• The Cathode is almost always marked with a black band, line, or dot on the top of the SOD-123F package. The Anode is the unmarked end.
• Wrong polarity: If you reverse the pins in a voltage regulation circuit, you will essentially place a 0.7V forward-biased diode across your power rail, which will cause a short circuit and potentially destroy the diode and the power supply.

2. Thermal Path (SOD-123F Package)

• The Anode pad is typically connected to the larger portion of the internal die. In some PCB layouts, the Anode pad may have a larger copper pour or thermal via to help dissipate heat generated during Zener operation.
• The Cathode pad is often smaller.

3. Power Dissipation

• The KDZVTR5.1B is a Zener diode, so it dissipates power.
• Current flows from Cathode to Anode during regulation. The power dissipated (P = Vz * Iz) generates heat, which must be conducted away through the solder joints on both pins.
• Do not exceed the rated current. The “B” suffix may indicate a specific current rating or tolerance (e.g., 5.1V ±5%). Check the datasheet for the maximum continuous current (Izt or Izm).

4. Circuit Connection Example (Simple 5V Regulator)

• Pin 1 (Cathode): Connect to the output of a resistor or current source (which is connected to a higher voltage, e.g., 9V).
• Pin 2 (Anode): Connect to Ground (0V) .
• Voltage at Cathode: ~5.1V relative to ground.

摘要表（快速参考）

引脚名称表示电压（调节） 电流流 1 阴极（K）能带/线路， 进入二极管 2 阳极（A），无更多负极（GND） 从二极管输出 。

Key Takeaway: The KDZVTR5.1B is a simple but polarity-sensitive device. The Cathode is the marked, positive reference pin (for regulation), and the Anode is the unmarked, ground return pin. Never reverse them in a circuit expecting regulation.

The KDZVTR5.1B is a Zener diode designed for voltage regulation applications, specifically providing a stable 5.1V output. It is commonly used in power supply circuits to protect sensitive components from voltage spikes and to maintain a constant reference voltage. Typical applications include consumer electronics, industrial control systems, and automotive modules where precise voltage clamping is required. Its compact surface-mount package makes it suitable for high-density circuit board designs.

Here is an expanded response to the point: “What chips are recommended as replacements for the KDZVTR5.1B”

The KDZVTR5.1B is a specific Zener diode (not a complex logic or power management IC) manufactured by Rohm Semiconductor. It is a 5.1V Zener diode with a power rating of 1W, housed in a surface-mount SOD-123FL package.

When looking for replacements, you are looking for functional equivalents that share the same key electrical and physical characteristics. Here is a breakdown of recommended replacements, categorized by how closely they match.

1. Exact or Near-Exact Matches (Best for “Drop-in” Replacement)

These diodes have the same voltage (5.1V), power (1W), and package (SOD-123FL). They are the safest choice.

• Rohm KDZVTR5.1B (Original) – If available, this is the ideal choice.
• Rohm UDZV5.1B – While typically a 200mW diode, Rohm also produces variants in the UDZV series. Check the datasheet carefully. The UDZ series is often for smaller signal applications (200mW), not 1W. Do not use a lower power rated UDZ as a substitute.
• Diodes Incorporated DZ23C5V1 – Package Mismatch: This is typically a SOT-23 package (3-pin, dual diode). Not a direct match.
• Good-Ark (Taiwan) SK5V1B – This is a 1W, SOD-123FL package, 5.1V Zener. An excellent direct replacement.
• Micro Commercial Components (MCC) 1SMA5918BT3G – This is a 1.5W, SMA package. Electrically fine (slightly higher power rating), but physically larger. Will require checking for board space.
• Vishay BZX84C5V1 – Package Mismatch: This is a 350mW, SOT-23 package. Not suitable for a 1W application.

The most direct and safe replacement is another 5.1V, 1W Zener diode in a SOD-123FL package.
Example Part Number: Good-Ark SK5V1B

2. Acceptable Functional Replacements (Requires Physical or Power Check)

These have the same electrical spec (5.1V) but differ in power rating or package size. They will work electrically but may not fit the PCB footprint.

• Higher Power (Safe but may be physically larger):
  • 1SMA5918BT3G (ON Semiconductor): 1.5W, SMA (DO-214AC) package.
  • BZD27C5V1 (Vishay): 800mW, SOD-123 package. Slightly lower power margin (800mW vs 1W) – use only if the circuit’s maximum current is well below 150mA.
• Lower Power (Only for low-current applications):
  • DDZ5V1B (Diodes Inc): 500mW, SOD-123.
  • MMSZ5V1B (ON Semi): 500mW, SOD-123.
  • BZX84C5V1 (Many brands): 350-400mW, SOT-23.

3. Important Selection Criteria (When Choosing a Replacement)

To ensure a safe and reliable replacement, you must verify these three parameters against your circuit’s requirements:

1. Zener Voltage (Vz): Must be 5.1V (at the specified test current, typically 5mA or 10mA). A 5.0V or 5.2V may work, but the circuit’s regulation will shift.
2. Power Dissipation (Pd): The KDZVTR5.1B is rated for 1W. Your replacement must be at least 1W (or have a sufficient margin for the actual current). Using a lower power diode (e.g., 500mW) will cause it to overheat and fail if the circuit draws more than ~100mA.
3. Package / Footprint: The original is SOD-123FL (a flat-lead, low-profile package). Common replacements include SOD-123 (slightly larger), SMA (larger), or SOT-23 (smaller, but different pinout). A SOD-123 or SMA part can often be hand-soldered with careful alignment.

Summary Table of Recommended Replacements

Recommendation Level Part Number Brand Voltage Power Package Notes Best Direct Match KDZVTR5.1B Rohm 5.1V 1W SOD-123FL Original part. Excellent Match SK5V1B Good-Ark 5.1V 1W SOD-123FL Pin-for-pin, electrical & physical match. Functional Equivalent 1SMA5918BT3G ON Semi 5.1V 1.5W SMA Electrically better (higher power margin), physically larger. Emergency Replacement BZD27C5V1 Vishay 5.1V 800mW SOD-123 Slightly lower power. Use only if circuit current is <150mA. Not Recommended BZX84C5V1 Various 5.1V 350mW SOT-23 Power rating too low. Will likely fail.

Final Recommendation

First choice: Buy the original KDZVTR5.1B from a reputable distributor (DigiKey, Mouser, LCSC).

Second choice: If the original is unavailable, use a 1W, 5.1V Zener in SOD-123FL (e.g., Good-Ark SK5V1B).

Third choice: If you must use a larger package, a 1.5W SMA Zener (e.g., 1SMA5918BT3G) will work perfectly, but ensure you have enough physical space on the PCB.