Precision Current Regulation Made Simple: J500 & SST500 Diodes
- JC - Linear Systems
- Sep 23
- 2 min read
When designing circuits for test instrumentation, medical electronics, or any system where stable, low current is crucial, the choice of a current-regulating diode (CRD) can make all the difference.
Linear Systems’ J500 and SST500 series provide engineers with reliable, tightly specified constant-current performance — even across wide voltage and temperature ranges — while simplifying circuit design.
What is a Current Regulating Diode?
A current-regulating diode (also called a constant current diode) is a two-terminal device that limits current to a fixed value, regardless of voltage fluctuations within its operating range.
Internally, most CRDs use a JFET with the gate tied to the source. Once the device reaches saturation, the current remains steady over a wide voltage swing. This gives designers a simple, compact, and reliable current source without additional circuitry.
Key advantages:
Reduced part count compared to op-amp or resistor-based current sources
Stable performance across voltage changes
Compact and easy to integrate in low-power and battery-driven designs
The J500 & SST500 Series at a Glance
Feature | J500 Series | SST500 Series |
Package | TO-92 (through-hole), plus bare die | SOT-23 (surface mount), plus bare die |
Current Range | ~0.19 mA to 5.6 mA (nominal) | ~0.19 mA to 5.6 mA (nominal) |
Operating Voltage | Up to 50 V | Up to 50 V |
Temperature Range | −55 °C to +150 °C | −55 °C to +150 °C |
Forward Capacitance | ~2.2 pF (typical) | ~1.5 pF (typical) |
Why It Matters
Tight, predictable performance — essential for sensitive applications in medical instrumentation and precision test gear.
Package flexibility — TO-92 for prototyping and robust handling, SOT-23 for space-constrained SMT designs.
High reliability — Wide voltage and temperature ratings ensure stable performance even in harsh environments.
Simplified design — Drop-in constant current without biasing networks or active components.
Application Examples
Driving LEDs or photodiodes with a fixed current, even as supply voltage changes
Providing a stable bias for RTDs, thermistors, or strain gauges
Current sources in battery-powered medical devices
Simplifying constant-current references in test and measurement equipment
Choosing Between J500 & SST500
Prototyping / through-hole builds → J500 (TO-92 package)
Compact SMT designs → SST500 (SOT-23 package, lower parasitics)
Custom packaging or tighter screening → Bare die options available directly from Linear Systems
Final Thoughts
Linear Systems’ J500 and SST500 current regulating diodes deliver stable, predictable current regulation in easy-to-use packages. With options ranging from TO-92 to SOT-23 to bare die, and current levels spanning ~0.19 mA to 5.6 mA, these CRDs simplify circuit design while ensuring high performance across demanding applications.
📄 Explore datasheets on our Current Regulating Diodes page
✉️ Contact our applications team at support@linearsystems.com for design guidance
📦 Request samples to evaluate the J500 and SST500 in your next design
Prefer to speak with someone directly? Give us a call at (510) 490-9160 and our team will connect you with the right person.
Precision current regulation is critical in modern systems, and components like the J500 and SST500 diodes make achieving it straightforward and reliable. From my experience, though, real progress happens when precise components are paired with intelligent system design. That’s why I value EMSYS Design’s mission: emsys.com their hardware is built to streamline installations and reduce maintenance costs, while their software helps users spend less time analyzing data and compiling compliance reports. Together, this approach ensures that current regulation and battery service are not only precise, but also efficient and future-ready.