Slim, 2.1-mm High Relay Incorporating a MOS FET Optically Coupled with an Infrared LED in a Miniature, Flat SOP Package # G3VM351G MOSFET Output Photorelay Technical Documentation
## 1. Application Scenarios
### Typical Use Cases
The G3VM351G is a MOSFET-based solid-state relay (SSR) designed for low-power switching applications requiring high reliability and electrical isolation. Common implementations include:
- Signal Switching : Digital I/O interfacing between microcontrollers and external circuits
- Measurement Equipment : Switching between multiple sensors or test points in automated test systems
- Communication Systems : Modem/telephone line switching, data bus isolation
- Battery-Powered Devices : Power management in portable equipment due to low drive current requirements
- Safety Systems : Emergency stop circuits and interlock systems requiring fail-safe operation
### Industry Applications
- Industrial Automation : PLC I/O modules, sensor interfaces, control panel switching
- Medical Equipment : Patient monitoring devices, diagnostic equipment isolation
- Telecommunications : PBX systems, network switching equipment
- Consumer Electronics : Audio/video switching, smart home controls
- Automotive Electronics : Low-voltage control circuits, infotainment systems
### Practical Advantages and Limitations
Advantages:
- Electrical Isolation : 1500Vrms input-output isolation prevents ground loops and noise transmission
- Long Lifespan : No mechanical contacts eliminates wear-out mechanisms
- Fast Switching : Typical turn-on time of 0.2ms enables high-frequency operation
- Low Drive Current : 3mA typical LED current reduces controller power requirements
- Zero Crossing : Built-in zero-crossing function minimizes EMI generation
- Compact Package : DIP4 package saves board space compared to mechanical relays
Limitations:
- Current Handling : Maximum 120mA output current restricts high-power applications
- Voltage Rating : 60V maximum load voltage limits high-voltage applications
- On-Resistance : 35Ω typical RON causes voltage drop in high-current paths
- Temperature Sensitivity : Performance degrades above 85°C operating temperature
## 2. Design Considerations
### Common Design Pitfalls and Solutions
Pitfall 1: Insufficient LED Drive Current
- Problem : Inadequate phototransistor activation causing high RON
- Solution : Ensure minimum 3mA forward current with current-limiting resistor calculation: R = (Vcc - Vf) / If
Pitfall 2: Thermal Management in High-Frequency Switching
- Problem : Internal heating during rapid switching cycles
- Solution : Implement duty cycle limitations and provide adequate PCB copper for heat dissipation
Pitfall 3: Voltage Spike Damage
- Problem : Inductive load switching causing voltage transients
- Solution : Use snubber circuits or TVS diodes across output terminals
### Compatibility Issues
Input Side Compatibility:
- Microcontrollers : Compatible with 3.3V and 5V logic levels
- CMOS/TTL : Direct interface possible with proper current limiting
- Incompatible Systems : Requires external drivers for high-voltage control signals (>1.5V reverse voltage rating)
Output Side Considerations:
- Load Types : Optimal for resistive loads; inductive loads require protection circuits
- Voltage Matching : Ensure load voltage <60V and peak voltage <80V
- Current Limitations : Do not exceed 120mA continuous current
### PCB Layout Recommendations
General Layout:
- Maintain minimum 8mm creepage distance between input and output circuits
- Place decoupling capacitors (0.1μF) close to input and output pins
- Use ground planes for noise reduction but maintain isolation barrier
Thermal Management:
- Provide adequate copper area around output pins for heat dissipation
- Consider thermal vias to internal ground layers for improved cooling
- Avoid placing near heat-generating components (regulators, power devices
