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Negative voltage regulation is essential in many analog and mixed-signal electronic systems, especially in circuits that require dual power supplies or stable negative voltage rails. The LM337 variable negative voltage regulator is a widely used 3-terminal adjustable linear regulator designed to provide reliable and precise negative output voltages. This article will discuss the LM337 regulator basics, pinout details, block diagram, specifications, features, application circuits, alternatives, comparisons, and practical uses.
The LM337 variable negative voltage regulator is a 3-terminal adjustable linear regulator designed to provide a stable negative output voltage. It is commonly used in dual power supply designs and analog circuits that require a negative voltage rail. As the negative counterpart of the LM317, the LM337 allows flexible voltage adjustment using only a few external components.
The device can deliver output voltages from approximately −1.25V to −37V with output currents up to 1.5A, depending on proper heat dissipation. By connecting two external resistors between the output and adjust pins, users can easily set the desired negative voltage level. The LM337 also includes built-in thermal shutdown, current limiting, and safe-area protection, ensuring reliable and secure operation.
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| Pin Number | Pin Name | Symbol | Description |
| 1 | Adjust | ADJ | Used to set the output voltage. Connect a resistor between ADJ and VOUT to adjust the negative output voltage level. |
| 2 | Output | VOUT | Provides the regulated negative output voltage. The voltage level depends on the external resistor configuration. |
| 3 | Input | VIN | Receives the unregulated negative input voltage that needs to be regulated. Must be more negative than the desired output voltage. |
• LM237
• LM337L
• LM337T
• LM337BTG
• LM337SP
• NTE957
• KA337
• MC337
• TL337
• uA337
The LM337 block diagram shows how the regulator controls and stabilizes a negative output voltage using internal transistor stages, reference circuitry, and protection networks. At the core of the circuit is a precision voltage reference (around –1.25 V) that works with an error amplifier. This amplifier compares the feedback voltage from the ADJ pin with the internal reference and continuously adjusts the drive to the output transistor to maintain a stable regulated voltage.
The series pass transistor stage, located near the VOUT terminal, handles the main load current. It acts like a variable resistor controlled by the error amplifier, increasing or decreasing conduction to keep the output voltage constant even when input voltage or load current changes. Compensation capacitors inside the circuit improve stability and prevent oscillations.
The diagram also shows current limiting, thermal protection, and safe-area protection transistors. These internal safety circuits protect the device from overload, short circuits, and overheating, ensuring reliable operation in power supply applications.
| Parameter | Value |
| Output Voltage Range | –1.25V to –37V |
| Output Current | Up to 1.5A |
| Reference Voltage | –1.25V |
| Dropout Voltage | Approx. 3V |
| Line Regulation | 0.01% / V (typ.) |
| Load Regulation | 0.1% (typ.) |
| Ripple Rejection | 60–80 dB |
| Operating Temperature Range | 0°C to +125°C |
| Storage Temperature Range | –65°C to +150°C |
| Package Options | TO-220, TO-263, TO-92 (LM337L) |
The LM337 can deliver output currents up to 1.5A, making it suitable for moderate-power negative voltage supply applications. With proper heat sinking, it can reliably power analog circuits, op-amps, and other components requiring a stable negative rail.
This feature means the output voltage changes very little when the input voltage fluctuates. Good line regulation ensures stable performance even if the input supply is not perfectly constant.
The LM337 maintains a steady output voltage even when the load current changes. This helps protect sensitive circuits from voltage variations caused by sudden load shifts.
High ripple rejection reduces unwanted AC noise from the input supply. This makes the regulator suitable for low-noise analog and audio applications.
The output voltage remains stable across temperature changes. A low temperature coefficient ensures consistent performance in varying environmental conditions.
Built-in thermal shutdown circuitry automatically turns the device off if it overheats, preventing damage due to excessive power dissipation.
The LM337 includes internal current limiting to protect against short circuits and overload conditions, improving overall circuit reliability and safety.
In the first circuit, the LM337 is configured as an adjustable negative voltage regulator. The input receives an unregulated negative voltage (−VIN), and the output provides a regulated negative voltage (−VOUT). Two resistors, including a fixed 120 Ω resistor and a variable resistor (R2), form a feedback network between VOUT and the ADJ pin. By adjusting R2, the output voltage level changes according to the regulator formula. Capacitors placed at the input and output improve stability, reduce ripple, and prevent oscillations during operation.
In the second circuit, the LM337 is paired with an LM317 to create a symmetrical dual power supply. The LM317 provides the positive adjustable output, while the LM337 provides the negative adjustable output. Both regulators use similar resistor networks to set their voltage levels, producing balanced outputs such as ±12 V or other adjustable ranges. The capacitors around both regulators improve filtering and stability, making this configuration ideal for op-amps and analog circuits that require both positive and negative voltage rails.
• Adjustable negative power supplies
• Dual ± power supply systems
• Operational amplifier circuits
• Audio amplifier circuits
• Analog signal processing circuits
• Laboratory bench power supplies
• Industrial control systems
• Instrumentation equipment
• DC power regulation modules
• Battery-powered negative voltage rails
| Feature | LM337 | LM317 | 79xx Series (e.g., 7912) | TL337 |
| Output Type | Adjustable Negative | Adjustable Positive | Fixed Negative | Adjustable Negative |
| Output Voltage Range | –1.25V to –37V | +1.25V to +37V | Fixed (e.g., –5V, –12V, –15V) | –1.25V to –37V |
| Output Current | Up to 1.5A | Up to 1.5A | Up to 1A (typ.) | Up to 1.5A |
| Adjustability | Yes | Yes | No | Yes |
| External Components | 2 Resistors | 2 Resistors | Minimal | 2 Resistors |
| Typical Dropout Voltage | ~3V | ~3V | ~2V–3V | ~3V |
| Common Use | Adjustable negative supplies | Adjustable positive supplies | Fixed negative rails | Alternative to LM337 |
| Polarity | Negative Output | Positive Output | Negative Output | Negative Output |
The LM337 variable negative voltage regulator is a dependable and flexible solution for generating adjustable negative voltages in electronic systems. With an output range from –1.25V to –37V and current capability up to 1.5A, it supports a wide range of analog and dual-supply applications. Its internal reference, error amplifier, pass transistor stage, and built-in protection features ensure stable and safe operation under varying load and input conditions.
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