SCRs (Silicon Controlled Rectifiers)# 2N5064 Silicon Unijunction Transistor (UJT) Technical Documentation
*Manufacturer: MOTOROLA*
## 1. Application Scenarios
### Typical Use Cases
The 2N5064 is a silicon unijunction transistor (UJT) primarily employed in timing, oscillator, and trigger circuit applications. Its unique negative resistance characteristic makes it particularly suitable for:
Timing Circuits
- RC Timing Networks : Used in conjunction with capacitors and resistors to create precise time delays ranging from microseconds to several minutes
- Pulse Generators : Generates sharp output pulses with fast rise times for triggering other circuit elements
- Sawtooth Waveform Generation : Produces linear ramp voltages for sweep circuits in oscilloscopes and display systems
Oscillator Applications
- Relaxation Oscillators : Creates stable low-frequency oscillations without requiring complex feedback networks
- LED Flashers : Simple blinking circuits for status indicators and warning lights
- Audio Tone Generators : Produces audible frequencies for alarms and signaling devices
Triggering Applications
- SCR/Triac Gate Drivers : Provides precise firing pulses for thyristor control circuits
- Voltage Sensing : Acts as threshold detector in over-voltage protection circuits
- Sequential Switching : Controls timing sequences in multi-stage circuits
### Industry Applications
Industrial Control Systems
- Motor speed controllers
- Process timing equipment
- Machine automation sequences
- Power supply sequencing circuits
Consumer Electronics
- Appliance timers (washing machines, dryers)
- Camera flash circuits
- Electronic toys and games
- Simple alarm systems
Power Electronics
- Phase control circuits for AC power regulation
- Battery charger controllers
- Light dimmer circuits
- Soft-start circuits for motors
Test and Measurement
- Function generator timing bases
- Calibration pulse sources
- Bench test equipment triggers
### Practical Advantages and Limitations
Advantages
- Simple Circuit Implementation : Requires minimal external components compared to IC-based timing solutions
- Cost-Effective : Lower component cost than equivalent timer ICs in simple applications
- High Pulse Current Capability : Can deliver substantial gate current for thyristor triggering (up to 50mA peak)
- Temperature Stability : Intrinsic standoff ratio (η) exhibits good temperature stability (typically ±0.002/°C)
- Wide Operating Range : Functions reliably across industrial temperature ranges (-65°C to +125°C)
Limitations
- Parameter Dispersion : Significant variation in intrinsic standoff ratio (0.55 to 0.82) requires circuit tolerance
- Frequency Limitations : Maximum oscillation frequency typically limited to 100kHz
- Aging Effects : Gradual parameter shifts over extended operational periods
- Modern Alternatives : Largely superseded by 555 timers and microcontroller-based solutions in new designs
- Limited Precision : Timing accuracy dependent on external RC components and UJT characteristics
## 2. Design Considerations
### Common Design Pitfalls and Solutions
Timing Accuracy Issues
- Problem : Significant variation in oscillation frequency due to UJT parameter spread
- Solution : Use trimmable resistors or select UJTs with tighter parameter tolerances
- Alternative : Implement feedback stabilization or use temperature-compensated components
False Triggering
- Problem : Spurious triggering from noise or supply voltage transients
- Solution : Add decoupling capacitors near UJT and implement proper grounding
- Enhancement : Use noise suppression techniques and Schmitt trigger conditioning
Load Sensitivity
- Problem : Timing variation when driving different load impedances
- Solution : Buffer output with emitter follower or operational amplifier
- Isolation : Use optocouplers for complete load isolation in critical applications
### Compatibility Issues with Other Components
Power Supply Considerations
- Vol
