NSI50350AST3G - 350mA 50V Linear Constant Current Regulator | onsemi
MPN: NSI50350AST3G ✓ Active| Qty | Unit Price | Extended |
|---|---|---|
| 1 | $0.85 | $0.85 |
| 10 | $0.72 | $7.20 |
| 100 | $0.55 | $55.00 |
| 500 | $0.42 | $210.00 |
| 1,000 | $0.37 | $370.00 |
| 3,000 | $0.31 | $930.00 |
NSI50350AST3G Overview
A linear constant current regulator (CCR) is a two-terminal solid-state device that functions similarly to a self-biased transistor (SBT) and provides a fixed, regulated current over a wide input voltage range. Unlike a switching LED driver, a CCR has no switching frequency and therefore introduces no EMI. Within the broader power management hierarchy, a CCR sits below switching LED drivers and current-mode linear regulators, above simple ballast resistors, and is used wherever a compact, robust, low-noise current source is required for LED strings.
Key features include the SBT architecture, which eliminates the need for external components such as sense resistors, inductors, or capacitors. The negative temperature coefficient reduces regulated current as junction temperature rises, preventing the catastrophic thermal runaway that occurs when LEDs are driven by a constant-voltage source. The device is rated for up to 50 V anode-to-cathode voltage, making it suitable for multi-LED strings in automotive and architectural lighting.
Technically, the NSI50350AST3G operates as a self-biasing current source where the regulated current is set by internal bandgap-referenced transistor matching. The wide voltage compliance range (from a few volts up to 50 V) allows the regulator to drop a varying voltage as the LED string forward voltage changes with temperature and aging, while holding current constant. The 2-pin SMC package offers a low thermal resistance suitable for dissipating up to 5.8 W with proper PCB land pattern design.
Typical applications include automotive interior and exterior LED lighting, signage and architectural illumination, signage backlighting, and emergency lighting strips. The CCR is also used in indicator LEDs on industrial equipment where robust, surge-tolerant current regulation is required.
When designing with this device, ensure adequate PCB copper area for heat dissipation because the CCR drops the difference between the supply voltage and the LED string forward voltage as heat. Minimum series voltage overhead should be calculated for the worst-case cold-start condition when LED forward voltage is highest.
This page synthesizes distributor pricing, drop-in same-package alternatives, and practical thermal design notes not found in the manufacturer datasheet alone.
Drop-in alternatives for NSI50350AST3G — same package, pin-to-pin compatible. Different-package parts requiring PCB rework are excluded.
Variants in this series
Same-series models that are drop-in compatible with NSI50350AST3G (same form factor and footprint) — differing in Configuration.
Quick Comparison Tool — Select alternative parts for side-by-side comparison:
NSV50350AST3G
✅ Drop-In📋 Reference alternative (not in catalog)
NSI50350AS-D
✅ Drop-In📋 Reference alternative (not in catalog)
NSI50350AST3G Maximum Ratings & Electrical Characteristics
| Regulated Current | 350 mA ±10% |
| Maximum Anode-Cathode Voltage | 50 V |
| Maximum Power Dissipation | 5.8 W |
| Technology | Self-Biased Transistor (SBT) |
| Package Type | SMC (2-pin) |
| Configuration | High-Side or Low-Side |
| Operating Temperature Range | -55C to +175C |
| Temperature Coefficient | Negative (thermal self-protection) |
| Mounting Type | Surface Mount |
| RoHS Status | Compliant |
| Lead-Free | Yes |
| REACH Status | Compliant |
| Automotive Grade | Standard (NSV variant is AEC-Q100) |
| Pin Count | 2 |
NSI50350AST3G Pin Configuration
| Pin 1 | Anode — Input voltage / supply (connect to higher voltage side) |
| Pin 2 | Cathode — Output to LED string (connect to lower voltage / LED anode) |
Typical Applications
NSI50350AST3G is suitable for 8 applications: Automotive Tail Lamp LED Driver, Architectural LED Strip Current Limiter, Industrial Indicator LED Driver, Emergency Lighting LED Strings, Signage and Channel Letter Illumination, LCD Backlight LED Driver, Decorative LED Strip Lighting, Status Indicator on Industrial Control Boards.
Automotive Tail Lamp LED Driver
The NSI508P3's 350 mA regulated current and 50 V compliance make it ideal for driving multi-LED tail lamp strings from a 12 V automotive bus. In tail lamp applications, the CCR sits between the BCM (body control module) supply and the LED string, with no inductor or sense resistor required - the SBT architecture inherently regulates current across the varying forward voltage of red LEDs as they age. The negative temperature coefficient protects the LED string from thermal runaway, a critical safety feature in sealed lamp housings where ambient temperatures can exceed 80°C. Estimated: At VIN=13.5 V, VLED=9 V (3 red LEDs), the CCR drops 4.5 V × 0.35 A = 1.58 W, well within the 5.8 W dissipation rating.
Recommended
Architectural LED Strip Current Limiter
For 24 V architectural LED strips drawing 350 mA per segment, the NSI50350AST3G provides a compact, robust current regulation solution without any EMI emissions. Each CCR in the strip drops the difference between 24 V supply and the LED forward voltage as heat, simplifying the driver topology. The wide 50 V compliance range allows operation across fluctuating bus voltages common in long cable runs. Estimated: For a 24 V supply and 8 white LEDs at 2.8 V each (22.4 V string), the CCR drops 1.6 V × 0.35 A = 0.56 W - a comfortable margin below the 5.8 W limit.
Recommended
Industrial Indicator LED Driver
The NSI50350AST3G's surge tolerance and wide operating temperature range (-55C to +175C) make it well suited for industrial indicator LEDs on PLCs, machine control panels, and outdoor equipment. The CCR handles inductive transients from long cable runs without requiring a TVS clamp. With a single 2-pin SMC footprint, the device integrates easily into space-constrained indicator assemblies where using a switching IC would require additional inductors and capacitors. According to onsemi datasheets, the negative temperature coefficient prevents thermal runaway in sealed indicator enclosures.
Recommended
Emergency Lighting LED Strings
For battery-backed emergency lighting fixtures, the NSI50350AST3G provides fixed 350 mA current regardless of battery state-of-charge variation. The wide 50 V compliance accommodates dimming circuit voltage drops while maintaining regulation. The robust SBT architecture operates reliably through surge events and brownout conditions common in emergency power transitions. Estimated: For a 36 V battery bus and 10 LEDs at 3 V each (30 V string), the CCR drops 6 V × 0.35 A = 2.1 W, requiring moderate PCB copper area for thermal management.
Recommended
Signage and Channel Letter Illumination
The NSI50350AST3G serves as a current limiter for individual LED segments in channel letter signage, where it replaces traditional current-limiting resistors with a more efficient, thermally-stable solution. The negative temperature coefficient automatically reduces current as the LED heats up inside the sealed channel letter, extending LED lifetime. The 2-pin SMC package allows placement directly behind each letter segment. According to onsemi datasheets, the CCR's surge tolerance handles the inductive kick from long LED string wiring in large commercial signs.
Recommended
LCD Backlight LED Driver
For LCD backlight strings in industrial displays, the NSI50350AST3G provides constant current to multiple parallel LED strings from a single supply rail. The CCR's wide voltage compliance handles varying forward voltage across LED bins and aging. Its small 2-pin SMC footprint allows placement directly on the backlight PCB adjacent to each LED string. Estimated: For a 12 V supply and 3 white LEDs at 3.2 V each (9.6 V string), the CCR drops 2.4 V × 0.35 A = 0.84 W, requiring only minimal PCB thermal relief.
Recommended
Decorative LED Strip Lighting
The NSI50350AST3G drives high-current decorative LED strips used in retail displays, automotive interior ambient lighting, and architectural accent illumination. Its 350 mA regulation supports high-brightness LED chips used in modern decorative strips, replacing bulky constant-current driver circuits. The 50 V compliance supports long LED strings common in decorative applications. According to onsemi datasheets, the SBT technology provides flicker-free dimming when combined with a low-frequency PWM signal at the supply.
Recommended
Status Indicator on Industrial Control Boards
The NSI50350AST3G simplifies status indicator design on industrial control boards by replacing resistor-based LED current limiters with a 2-pin self-regulating CCR. No external resistors are needed - the CCR sets the LED current automatically. The robust SBT design tolerates the voltage variations common in 24 V industrial control systems. Estimated: For a 24 V supply and a single high-brightness LED at 3.2 V, the CCR drops 20.8 V × 0.35 A = 7.28 W - exceeding the 5.8 W rating, so this CCR needs a buck pre-regulator or lower supply for single-LED use.
Recommended
Recommended Products Summary
Engineering reference data for NSI50350AST3G — comparison, design guidance, and compliance information.
Selection Guide
Comparison with Alternatives
| Parameter | This Product | NSV50350AST3G | NSI50350AS-D |
|---|---|---|---|
| Package | SMC-2 | SMC-2 (same) | SMC-2 (same) |
| Brand | onsemi | onsemi | onsemi |
| Regulated Current | 350 mA ±10% | 350 mA ±10% | 350 mA ±10% |
| Maximum Voltage | 50 V | 50 V | 50 V |
| Maximum Power Dissipation | 5.8 W | 5.8 W | 5.8 W |
| Automotive Grade | Standard | AEC-Q100 qualified | Standard |
| Technology | Self-Biased Transistor (SBT) | Self-Biased Transistor (SBT) | Self-Biased Transistor (SBT) |
| Temperature Coefficient | Negative (thermal self-protection) | Negative (thermal self-protection) | Negative (thermal self-protection) |
| Unit Price (qty 1000) | $0.37 | $0.45 (est.) | $0.37 (est.) |
Key Differentiators
- True two-terminal constant current source - no external components required (vs LM3405 switching LED driver)
- Negative temperature coefficient prevents LED thermal runaway (vs Resistor-based current limiting)
- 50 V compliance supports long LED strings from 24 V and 36 V buses (vs NSI45020AT1G (20 mA, 45 V))
Design Notes
Estimated: The NSI50350AST3G dissipates (VIN - VLED_string) dimensionless × 350 mA as heat. At VIN=24 V driving a 9.6 V LED string (3 white LEDs), power dissipation is approximately 5 W, approaching the 5.8 W maximum. The onsemi datasheet recommends a minimum SMC land pattern of 1 sq inch of 1 oz copper on a 2-layer board; designs exceeding 3 W continuous dissipation should use a 4-layer board with thermal vias or a copper pour on both layers. Junction temperature should be calculated as TJ = TA + (PD × theta-JA), with TA+TJ-RISE staying below 150°C for reliable operation.
Recommended: For the SMC-2 footprint, follow JEDEC SO-253 land pattern with cathode pad (pin 2) as the primary thermal pad. Add 4-6 thermal vias (0.3 mm drill, 0.5 mm pitch) connecting the cathode pad to an internal copper plane for improved heat spreading. Place the CCR adjacent to the LED string with minimal trace length, since long traces add parasitic inductance that can cause voltage transients across the CCR during LED turn-on/off. Polarity is critical - reverse bias will permanently damage the device; verify pin 1 (anode) connects to the higher potential.
Critical: Three common pitfalls when designing with the NSI50350AST3G: (1) Exceeding the 50 V maximum voltage - this destroys the device. Ensure worst-case transient voltage stays below 50 V, especially in automotive load-dump conditions. (2) Insufficient voltage overhead - if VIN is less than VLED_string by less than the CCR's saturation voltage (typically 1-2 V), the CCR will fail to regulate. Calculate the minimum VIN at cold-start when LED forward voltage is highest. (3) Reverse polarity - the SMC-2 has no reverse blocking; add an external diode or use the NSI50350AST3G only in known-polarity applications.
Recommended: Place the CCR directly in series with the LED string - do not parallel multiple CCRs to share current, as the negative temperature coefficient causes current hogging (the hotter CCR takes less current, not more). If higher current is needed, use a single higher-current onsemi CCR or place LED strings in parallel, each with its own CCR. Keep high-dV/dt switching traces away from the CCR anode-cathode loop to avoid injecting noise; though CCRs are inherently EMI-free, the surrounding switching converter can still couple noise into the LED string.
Compliance Information
RoHS and REACH compliant per onsemi product page. Standard grade - not AEC-Q100 qualified (use NSV50350AST3G for automotive). Lead-free reflow compatible per JEDEC J-STD-020.
