Nch+SBD# Technical Documentation: CPH5809 Phototransistor
*Manufacturer: SANYO*
## 1. Application Scenarios
### Typical Use Cases
The CPH5809 is an NPN silicon phototransistor optimized for infrared detection in the 850-940 nm wavelength range. Typical applications include:
- Object detection systems - Used in industrial automation for counting, positioning, and presence detection
- Slot sensors - Paper detection in printers, currency validation in ATMs, and ticket readers
- Proximity sensing - Mobile device screen dimming, touchless interfaces, and robotics
- Optical encoders - Motor speed control and position feedback systems
- Ambient light sensing - Automatic brightness adjustment in displays and lighting control
### Industry Applications
- Consumer Electronics : Smartphones, tablets, laptops for proximity and ambient light detection
- Industrial Automation : Conveyor belt monitoring, robotic arm positioning, safety curtains
- Automotive : Rain sensors, twilight detection, interior monitoring systems
- Medical Devices : Fluid level detection, equipment positioning, safety interlocks
- Office Equipment : Paper jam detection, toner level monitoring, document feeders
### Practical Advantages and Limitations
Advantages:
- High sensitivity with typical collector current of 20mA (at VCE=5V, Ee=20mW/cm²)
- Fast response time with rise/fall times of 15μs typical
- Compact package (mini mold type) enabling high-density PCB layouts
- Wide operating temperature range (-25°C to +85°C)
- Excellent signal-to-noise ratio for reliable detection
Limitations:
- Spectral sensitivity limited primarily to infrared spectrum
- Temperature dependence of dark current requires compensation in precision applications
- Ambient light interference may require optical filtering in high-light environments
- Limited linearity compared to photodiodes in analog applications
## 2. Design Considerations
### Common Design Pitfalls and Solutions
Pitfall 1: Inadequate Biasing
- Problem : Insufficient collector-emitter voltage leading to saturation and slow response
- Solution : Maintain VCE ≥ 5V for optimal performance, use pull-up resistors appropriate for load requirements
Pitfall 2: Ambient Light Interference
- Problem : False triggering from environmental light sources
- Solution : Implement optical filters (IR-pass/visible-block), use modulated light sources with synchronous detection
Pitfall 3: Thermal Drift
- Problem : Dark current doubling approximately every 10°C temperature increase
- Solution : Temperature compensation circuits or AC-coupled amplification for DC-sensitive applications
Pitfall 4: Crosstalk in Array Configurations
- Problem : Optical interference between adjacent sensors
- Solution : Physical barriers (septums) between devices, proper spacing (≥5mm recommended)
### Compatibility Issues with Other Components
LED Driver Compatibility:
- Requires matching with infrared LEDs in 880-940 nm range
- Incompatible with visible spectrum LEDs without optical filtering
- Ensure driver current capability matches phototransistor saturation requirements
Amplifier Interface:
- Compatible with common op-amp configurations (transimpedance, voltage follower)
- May require high-input-impedance amplifiers for low-light applications
- Watch for capacitive loading effects on response time
Microcontroller Integration:
- Direct compatibility with 3.3V and 5V logic families
- May require Schmitt trigger inputs for noisy environments
- ADC reference voltages should match expected output swing
### PCB Layout Recommendations
Optical Considerations:
- Position away from heat-generating components to minimize thermal effects
- Ensure clear optical path without obstructions from other components
- Use solder
