3-TERMINAL 1.5A​​ 




General​​ Description​​ ​​ 

The EM317 is an adjustable 3-terminal positive voltage regulator capable of supplying in excess of 1.5 A over an output voltage range of 1.2 V to 37 V. This voltage regulator is exceptionally easy to use and requires only two external resistors to set the output voltage. Further, it employs internal current limiting, thermal shutdown and safe area compensation, making it essentially blow out proof.


EM317 offers full overload protection. Included on the chip current limit, thermal overload protection, and safe-area protection. Normally, no capacitors is needed unless the device is situated far from the input filter capacitors in which case an input bypass is needed. An optional output capacitor can added to improve transient response.





  • Output current up to 1.5A

  • Output Voltages 1.2V to 37V

  • Input Regulation typ. 0.01%

  • Output Regulation typ. 0.1%

  • Peak Output Current Constant over Temperature Range of Regulator

  • Available in TO-220, TO-263, TO252 and SOT223 Packages

  • Ripple Rejection Typically 80dB

  • Direct replacements for EM317









  • Voltage Regulators

  • Power Supplies

  • Current Regulators

  • Switching Regulators

  • Current Limiter

  • Constant Current Battery Charger

  • Current Limited Charger










Typical Application Circuit






















Marking Information and Pin Configurations (Top View)​​ – Green Product




















Ordering Information



































Green products:​​ 

  • Lead-free (RoHS compliant)​​ ​​ 

  • Halogen free (Br or Cl does not exceed 900ppm by weight in homogeneous material and total of Br and Cl does not exceed 1500ppm by weight)






Absolute Maximum Ratings














Recommended Operating Conditions​​ 








Block Diagram





















Electrical Characteristics​​ ((Unless otherwise noted, VI - VO = 5V and IO= 0.5A. TJ = Full Range)












































Application Information

  • Basic Circuit Operation

The EM317 is a 3- terminal floating regulator. In operation, the EM317 develops and maintains a nominal 1.25V reference (VREF) between its output and adjustment terminals. This reference voltage is converted to a programming current flow through R2 to ground.

The regulated output voltage is given by:













Basic Circuit Configuration





Since the current from the adjustment terminal (IADJ) represents an error term in the equation, the EM317was designed to control IADJ​​ to less than 100µA and keep it constant. To do this, all quiescent operating current is returned to the output terminal. This imposes the requirement for a minimum load current. If the load current is less than this minimum, the output voltage will rise.​​ 

Since the EM317 is a floating regulator, it is only the voltage differential across the circuit which is important to performance, and operation at high voltages with respect to ground is possible.




  • Load Regulation

The​​ EM317​​ is capable of providing extremely good load regulation, but a few precautions are needed to obtain maximum performance. For best performance, the programming resistor R1 should be connected as close to the regulator as possible to minimize line drops which effectively appear in series with the reference, thereby degrading regulation. The ground end of R2 can be returned near the load ground to provide remote ground sensing and improve load regulation.





  • External Capacitors

A 0.1µF disc or 1.0µF tantalum input bypass capacitor CIN​​ is recommended to reduce the sensitivity to input line impedance. The adjustment terminal may be bypassed to ground to improve ripple rejection. This capacitor CADJ prevents ripple from being amplified as the output voltage is increased. A 10µF capacitor should improve ripple rejection about 15 dB at 120Hz in a 10V application.​​ 


Although the​​ EM317 is stable with no output capacitance, like any feedback circuit, certain values of external capacitance can cause excessive ringing. An output capacitance CO in the form of a 1.0µF tantalum or 25µF aluminum electrolytic capacitor on the output swamps this effect and insures stability.


  • Protection Diodes

When external capacitors are used with any IC regulator, it is sometimes necessary to add protection diodes to prevent the capacitors from discharging through low current points into the regulator.​​ 


The figure below shows the​​ EM317 with the recommended protection diodes for output for output voltage in excess of 25V or high capacitance values (CO​​ > 25µF, CADJ​​ > 10µF). Diode D1 prevents CO from discharging thru the IC during an input short circuit. Diode D2 protects against capacitor CADJ​​ discharging through the IC during an output short circuit. The combination of diodes D1 and D2 prevents CADJ​​ from discharging through the IC during an input short circuit.


























Typical Performance Characteristics