onsemi KA317

Overview

KA317 from ON Semiconductor is a monolithic 3-terminal positive adjustable voltage regulator delivering over 1.5 A output current with adjustable output voltage from 1.2 V to 37 V. It integrates internal thermal overload protection, short-circuit current limiting, and safe operating area compensation, and is commonly used in lab power supplies, battery chargers, and industrial DC power rails.

For engineers reviewing the KA317 datasheet, pinout, applications, or equivalent options, key selection considerations include its TO-220 package, 1.25 V reference voltage, ±0.02 %/°C temperature coefficient, minimum load current requirement (3.5–12 mA), and 80 °C/W junction-to-ambient thermal resistance.

Technical Context

The KA317 operates as a floating linear regulator using an internal bandgap reference (1.25 V) and error amplifier to control an NPN pass transistor. Regulation is achieved by sensing voltage across an external R1–R2 divider connected to the ADJ pin, enabling precise output setting independent of load current variation.

Its protection architecture includes foldback current limiting that reduces output current under short-circuit conditions, thermal shutdown triggered at ~150 °C junction temperature, and SOA compensation to prevent secondary breakdown during high-V_CE/I_C transients - all implemented without external components.

Key Specifications

Pinout & Package

KA317 is housed in a TO-220 (dual gauge) package with three leads: Input (pin 3), Output (pin 2), and Adjustment (pin 1). The metal tab is electrically connected to the output terminal and serves as the primary heat path.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar adjustable linear regulator applications.

Compared with LM317T, KA317 offers identical regulation performance but with a dual-gauge TO-220 package optimized for mechanical reliability; versus TLV1117-ADJ, KA317 supports higher current, wider voltage range, and higher input-output differential - making it suitable for industrial power conversion where robustness and headroom matter.

Availability

KA317 is available at Aetrix Electronics and suitable for laboratory power supplies, battery charger designs, and industrial DC power rails requiring stable component supply, long-lifecycle support, and traceable sourcing.

Supply support for KA317 includes scheduled delivery planning, volume procurement assistance, BOM continuity management, traceable sourcing, and lifecycle availability coordination for OEM customers, industrial embedded developers, connected-device designers, and electronics production programs.

Manufacturer

ON Semiconductor is a global semiconductor manufacturer specializing in energy-efficient power management, analog, sensor, and connectivity solutions for automotive, industrial, cloud, and IoT applications.

The KA317 belongs to ON Semiconductor's legacy linear regulator product line - designed for robust, low-noise, adjustable DC power delivery in applications where simplicity, reliability, and thermal resilience are prioritized over ultra-low quiescent current or switching efficiency.

FAQ

What is the maximum input-output voltage differential supported by the KA317?

The KA317 supports a maximum input-output voltage differential of 40 V, as specified in its Absolute Maximum Ratings. This allows use with unregulated inputs up to 40 V above the desired output - for example, generating 5 V from a 45 V bus. Exceeding this rating risks permanent device damage, even momentarily. Designers must ensure worst-case V_IN–V_OUT remains within 40 V under all operating conditions, including transient surges.

Does the KA317 require an input bypass capacitor in all applications?

Yes, the KA317 requires a 0.1 μF ceramic input capacitor (C_I) when located more than ~6 inches from the main power supply filter, as stated in the Typical Application note. This capacitor suppresses high-frequency noise and prevents oscillation due to source inductance. Omitting C_I in distributed power systems may cause instability or erratic regulation. The KA317 datasheet explicitly states CI is "required" under those physical layout conditions.

What is the purpose of the adjustment pin current (I_ADJ) in KA317 circuit design?

The KA317's adjustment pin draws 46–100 μA (I_ADJ), which flows through the R2 resistor in the feedback divider. This current introduces a small error term in the output voltage equation: V_OUT = 1.25(1 + R2/R1) + I_ADJR2. Designers must account for this when selecting R1/R2 values - especially for high-R2 configurations - to avoid output inaccuracy. For example, with R2 = 2.4 kΩ, I_ADJR2 adds up to 0.24 V of offset.

Can the KA317 be used in constant-current mode, and how is it configured?

Yes, the KA317 can operate as a precision constant-current source by connecting the ADJ pin to the load and the output pin to a sense resistor referenced to ground. In this configuration, the regulator maintains 1.25 V across the sense resistor (R_SENSE), delivering I_OUT = 1.25 V / R_SENSE. This method is widely used in LED drivers and battery charging circuits. The KA317's tight reference tolerance and low I_ADJ drift ensure current accuracy within ±2% over temperature and time.

How does the KA317's thermal shutdown behave during sustained overload?

The KA317's thermal shutdown activates at approximately 150 °C junction temperature, halting output conduction until the die cools below the hysteresis threshold (~130–140 °C). During sustained overload, this results in duty-cycled operation - alternating between regulation and shutdown - rather than continuous current limiting. This protects the device but may cause output voltage interruption. To avoid cycling, adequate heatsinking must keep T_J below 150 °C under worst-case power dissipation.