EL851 Series 4-Pin DIP High Voltage Phototransistor Optocoupler Datasheet - Package 6.35x4.57x3.3mm - VCEO 350V - CTR 50-600% - English Technical Documentation

1. Product Overview

The EL851 series represents a family of high-voltage phototransistor optocouplers designed for robust electrical isolation in demanding applications. These devices integrate an infrared emitting diode optically coupled to a silicon phototransistor detector, housed within a compact 4-pin Dual In-line Package (DIP). The primary function is to transmit electrical signals between two isolated circuits using light, thereby preventing high voltages or noise from propagating from the output side to the input side, or vice versa. The series is characterized by its high collector-emitter voltage rating, making it suitable for interfacing with power supply circuits and other high-voltage systems.

1.1 Core Advantages and Target Market

The EL851 series offers several key advantages that define its position in the market. Its most prominent feature is the high V_CEO rating of 350V, which allows it to withstand significant voltage differences between the input and output sides. This is complemented by a high isolation voltage (V_ISO) of 5000 V_rms, ensuring reliable safety barriers in industrial and telecommunication equipment. The devices are compliant with major international safety standards including UL, cUL, VDE, and various other regional approvals (SEMKO, NEMKO, DEMKO, FIMKO, CQC), facilitating their use in global markets. Furthermore, the series is designed to be halogen-free (for copper leadframe versions) and complies with RoHS and EU REACH regulations, addressing modern environmental and regulatory requirements. The target applications include telephone line interfaces, power supply circuit interfaces, controllers for Solid State Relays (SSRs) and DC motors, and programmable controllers where signal isolation and noise immunity are critical.

2. In-Depth Technical Parameter Analysis

A thorough understanding of the device's electrical and optical characteristics is essential for proper circuit design and reliable operation.

2.1 Absolute Maximum Ratings

The Absolute Maximum Ratings define the stress limits beyond which permanent damage to the device may occur. These are not intended for normal operation. Key ratings for the EL851 include:

• Input Forward Current (I_F): 60 mA (continuous).
• Peak Forward Current (I_FM): 1 A for a 1µs pulse, useful for brief surge conditions.
• Collector-Emitter Voltage (V_CEO): 350 V, the maximum voltage that can be applied across the output transistor when the base is open.
• Collector Current (I_C): 50 mA.
• Total Power Dissipation (P_TOT): 200 mW, combining input and output power limits.
• Isolation Voltage (V_ISO): 5000 V_rms for 1 minute at 40-60% relative humidity. This test is performed with pins 1 & 2 shorted together and pins 3 & 4 shorted together.
• Operating Temperature (T_OPR): -55°C to +100°C.
• Soldering Temperature (T_SOL): 260°C for 10 seconds, relevant for wave or reflow soldering processes.

2.2 Electro-Optical Characteristics

These parameters, typically specified at 25°C, describe the device's performance under normal operating conditions.

2.2.1 Input Characteristics (LED Side)

• Forward Voltage (V_F): Typically 1.2V, with a maximum of 1.4V at I_F = 10 mA. This is used to calculate the required current-limiting resistor for the input side.
• Reverse Current (I_R): Maximum 10 µA at V_R = 5V, indicating a very low leakage when the LED is reverse-biased.
• Input Capacitance (C_in): Typically 30 pF, with a maximum of 250 pF. This can affect high-frequency switching performance on the input side.

2.2.2 Output Characteristics (Phototransistor Side)

• Collector-Emitter Dark Current (I_CEO): Maximum 100 nA at V_CE = 200V. This is the leakage current when the LED is off (no light), crucial for determining the 'off-state' signal integrity.
• Collector-Emitter Breakdown Voltage (BV_CEO): Minimum 350V at I_C = 0.1mA, confirming the high-voltage capability.
• Collector-Emitter Capacitance (C_CE): Typically 10 pF at V_CE = 0V.

2.2.3 Transfer Characteristics

• Current Transfer Ratio (CTR): Ranges from 50% to 600% at I_F = 5mA and V_CE = 5V. CTR is defined as (I_C / I_F) * 100%. A higher CTR allows for a lower input current to drive a given output current, improving efficiency. The wide range indicates a binning system; designers must account for the minimum CTR in their circuit to ensure functionality.
• Collector-Emitter Saturation Voltage (V_CE(sat)): Maximum 0.4V at I_F = 20mA and I_C = 1mA. This low saturation voltage is important when the phototransistor is used as a switch in the 'on' state, minimizing voltage drop and power loss.
• Isolation Resistance (R_IO): Minimum 10¹¹ Ω at V_IO = 500V DC, indicating excellent DC isolation between input and output.
• Input-Output Capacitance (C_IO): Typically 0.6 pF, which is very low and helps minimize capacitive coupling of high-frequency noise across the isolation barrier.
• Rise Time (t_r) & Fall Time (t_f): Typical values are 4 µs and 5 µs respectively, with maximums of 18 µs each under the test conditions (V_CE=2V, I_C=2mA, R_L=100Ω). These parameters define the switching speed of the optocoupler and are critical for digital signal transmission or PWM applications.

3. Performance Curve Analysis

While specific graphical data is referenced in the PDF (Typical Electro-Optical Characteristics Curves, Figure 9), the key interpretations are based on the provided tabular data and test circuit.

The switching time test circuit shows a standard configuration where a pulsed current drives the input LED, and the output phototransistor's response is measured across a load resistor (R_L). The rise time (t_r) is the time for the output current to go from 10% to 90% of its final value when the LED turns on. The fall time (t_f) is the time to go from 90% to 10% when the LED turns off. The typical values in the 4-5 µs range indicate this device is suitable for moderate-speed switching applications, such as relay driving or lower-frequency data line isolation, but may not be ideal for very high-speed digital communication.

4. Mechanical and Package Information

4.1 Package Dimensions and Options

The EL851 is offered in three primary lead form options, each with specific dimensions and applications.

• Standard DIP Type: The default through-hole package.
• Option M Type: Features a wide lead bend with 0.4-inch (approx. 10.16mm) lead spacing, suitable for boards requiring wider pin spacing.
• Option S1 Type: A surface-mount (SMD) lead form with a low profile. This is the SMD variant of the device.

While exact numerical dimensions are provided in the PDF drawings, the overall package body size is approximately 6.35mm in length, 4.57mm in width, and 3.3mm in height for the standard DIP type, making it a compact component.

4.2 Polarity Identification and Marking

The pin configuration is standardized:

1. Anode (Input LED positive)
2. Cathode (Input LED negative)
3. Emitter (Phototransistor emitter, typically connected to ground/common on output side)
4. Collector (Phototransistor collector, the output)

The device is marked on the top with "EL" (denoting the manufacturer), "851" (the device number), followed by a 1-digit year code (Y), a 2-digit week code (WW), and an optional "V" for VDE-approved versions. Proper identification of pin 1 (often indicated by a dot, notch, or beveled edge on the package) is crucial for correct orientation during assembly.

4.3 Recommended Solder Pad Layout

For the S1 (surface mount) option, a recommended pad layout is provided. The suggested dimensions are for reference, and designers are advised to modify them based on their specific PCB manufacturing processes, solder paste application, and thermal management requirements to ensure reliable solder joints.

5. Soldering and Assembly Guidelines

The device can withstand a soldering temperature of 260°C for up to 10 seconds. This is compatible with standard wave soldering for through-hole packages and lead-free reflow soldering profiles for the SMD option. It is critical to adhere to this time-temperature limit to prevent damage to the internal die, wire bonds, or the plastic package material. Standard ESD (Electrostatic Discharge) precautions should be observed during handling and assembly. The storage temperature range is -55°C to +125°C.

6. Packaging and Ordering Information

6.1 Model Numbering Rule

The part number follows the format: EL851X(Z)-V.

• X: Lead form option.
  • None: Standard DIP-4 (100 units/tube).
  • M: Wide lead bend, 0.4" spacing (100 units/tube).
  • S1: Surface mount lead form (low profile).
• Z: Tape and reel option (only applicable with S1).
  • TA, TB, TU, TD: Different tape and reel specifications affecting packing quantity (1000 or 1500 units/reel).
• V: Optional suffix denoting VDE safety approval.

6.2 Tape and Reel Specifications

Detailed tape dimensions (A, B, D0, D1, E, F, P0, P1, P2, t, W, K) are provided for the S1 option. These dimensions are critical for PCB assembly machines to correctly pick and place the components from the reel. The tape width (W) is 16.0mm ±0.3mm, and the pocket pitch (P0) is 4.0mm ±0.1mm.

7. Application Notes and Design Considerations

7.1 Typical Application Circuits

The EL851 is well-suited for several key applications:

• Telephone Line Interface: Isolating the sensitive logic circuitry of a modem or telephone system from the high-voltage ringing signals and potential surges on the telephone line.
• Power Supply Feedback Loop: Providing isolated feedback of the output voltage in switch-mode power supplies (SMPS), allowing regulation while maintaining safety isolation between the primary (high-voltage) and secondary (low-voltage) sides.
• SSR and DC Motor Control: Driving the gate or input of a Solid State Relay or acting as an isolated interface between a microcontroller and a motor driver H-bridge, protecting the logic controller from motor-induced noise and voltage spikes.
• Programmable Controller (PLC) I/O Modules: Isolating digital input/output channels to protect the central processing unit from field wiring faults, noise, and differing ground potentials.

7.2 Critical Design Factors

1. CTR Degradation: The CTR of optocouplers can degrade over time, especially when operated at high temperatures and high LED currents. For long-term reliability, design the circuit to function with the minimum specified CTR after accounting for an appropriate degradation margin (often 50% over the product's lifetime).
2. Input Current Limiting: An external resistor must always be used in series with the input LED to limit the forward current (I_F) to a safe value, typically well below the 60mA absolute maximum. The resistor value is calculated as R_limit = (V_supply - V_F) / I_F.
3. Output Load Resistor: The value of the load resistor (R_L) connected to the phototransistor collector affects both the output voltage swing and the switching speed. A smaller R_L allows for higher speed but reduces output voltage gain. The test condition of R_L=100Ω provides a reference for the specified switching times.
4. Noise Immunity: While the device provides excellent galvanic isolation, the very low input-output capacitance (0.6 pF) helps minimize high-frequency noise coupling. For extremely noisy environments, additional filtering on the input and output signals may still be necessary.
5. Heat Dissipation: Ensure the total power dissipation (P_TOT = V_F*I_F + V_CE*I_C) does not exceed 200 mW, considering the maximum operating ambient temperature. Derating may be required at temperatures above 25°C.

8. Technical Comparison and Differentiation

Compared to standard low-voltage optocouplers (often with V_CEO ratings of 30-70V), the EL851's 350V rating is its primary differentiator. This allows it to be used directly in off-line power supply feedback circuits (where rectified mains voltage can be ~300V+) or in industrial control interfaces without requiring additional voltage clamping or step-down circuitry on the output side. Its CTR range is broad, offering options for both sensitive and standard drive requirements. The availability of both through-hole (DIP, wide bend) and surface-mount (S1) packages in tape-and-reel format makes it versatile for both prototyping and high-volume automated assembly.

9. Frequently Asked Questions (Based on Technical Parameters)

Q: What is the minimum CTR I should design for?

A: Always design your circuit to work with the minimum CTR of 50% at your intended operating I_F and V_CE. Account for potential degradation over the product's lifetime.

Q: Can I use this optocoupler to directly switch a 120VAC load?

A: No. The V_CEO rating is 350V DC. The peak voltage of 120VAC is about 170V, which is within the rating, but the optocoupler's phototransistor is not designed to handle the high currents of an AC load directly. It should be used to drive the control input of a separate high-power switch like a triac, MOSFET, or SSR.

Q: What is the difference between V_CEO and V_ISO?

A: V_CEO (350V) is the maximum DC voltage that can be applied between the collector and emitter pins of the output transistor. V_ISO (5000 V_rms) is the AC withstand voltage tested between the shorted input pins (1,2) and the shorted output pins (3,4), representing the isolation strength of the internal plastic barrier.

Q: How do I choose between the DIP and SMD packages?

A: Use the through-hole DIP packages for prototyping, manual assembly, or applications where board space is less critical and mechanical robustness from pin-through-board soldering is desired. Choose the SMD (S1) package for automated assembly, high-density PCB designs, and reduced board thickness.

10. Practical Design Example

Scenario: Isolated Digital Input for a 24V Industrial Sensor.

Goal: Interface a 24V proximity sensor to a 3.3V microcontroller, providing isolation to protect the MCU from voltage transients on the 24V line.

Circuit Design:

1. Input Side: The sensor output (sinking type) connects between +24V and the EL851's anode (pin 1). A current-limiting resistor (R_in) is placed between the cathode (pin 2) and ground. Choose R_in to set I_F to a nominal 5-10 mA when the sensor is active. For example, with V_F ~1.2V, R_in = (24V - 1.2V) / 0.005A ≈ 4.56kΩ (use 4.7kΩ standard value).
2. Output Side: The phototransistor collector (pin 4) is connected to the 3.3V MCU supply via a pull-up resistor (R_pullup). The emitter (pin 3) is connected to the MCU ground. When the sensor is active, the LED turns on, the phototransistor saturates, pulling the collector (output signal) low (~0.4V). When the sensor is off, the phototransistor is off, and R_pullup pulls the output high to 3.3V. Choose R_pullup based on desired speed and power; 1kΩ to 10kΩ is common.
3. Isolation: The 24V sensor ground and the 3.3V MCU ground are kept completely separate. The EL851's 5000V_rms isolation barrier protects the MCU from faults on the 24V line.

This simple circuit provides robust, isolated digital signal transmission.

11. Operating Principle

The EL851 operates on the principle of opto-electronic conversion and isolation. An electrical current applied to the input side flows through the infrared Light Emitting Diode (LED), causing it to emit light. This light travels across a transparent isolation gap within the plastic package and strikes the base region of the silicon phototransistor on the output side. The incident light generates electron-hole pairs in the base, effectively acting as a base current. This photogenerated base current is amplified by the transistor's current gain (h_FE), resulting in a much larger collector current (I_C). The ratio of this output collector current to the input LED current is the Current Transfer Ratio (CTR). No electrical connection exists between the input and output circuits; only light couples them, providing the galvanic isolation.

12. Technology Trends

Optocoupler technology continues to evolve. While traditional phototransistor-based devices like the EL851 remain popular for cost-effective, general-purpose isolation, newer technologies are emerging for specific needs. Digital isolators based on CMOS technology and RF or capacitive coupling offer significantly higher data rates (into the hundreds of Mbps), lower power consumption, and higher integration (multiple channels in one package). However, for applications requiring high working voltage (like the EL851's 350V), high common-mode transient immunity (CMTI), and proven reliability in harsh industrial environments, phototransistor and photo-IC based optocouplers maintain a strong position. The trend for such devices includes further miniaturization of packages, improvement in CTR stability and longevity, and integration of additional features like undervoltage lockout (UVLO) or gate drive capabilities in more specialized versions.