Enter your Input Voltage, Output Voltage, and Load Current into the LM7905 / 79xx Regulator Calculator to find Power Dissipation, Junction Temperature, and Efficiency — plus plug in your Thermal Resistance (θJA) and Ambient Temperature to get an instant Heat Sink Status check on whether your regulator is running safely.
Power Dissipation
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Voltage Drop
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Junction Temperature
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Efficiency
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Heat Sink Status
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Dropout Voltage
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The LM7905 is a three-terminal negative voltage regulator that provides a fixed -5V output. It belongs to the 79xx series of negative voltage regulators and can handle input voltages from -7V to -35V while maintaining a stable -5V output with up to 1.5A current capability.
Negative voltage regulators are essential for dual-supply circuits, operational amplifiers, audio applications, and digital circuits that require both positive and negative supply rails. They provide stable negative voltages needed for proper circuit operation and signal processing.
The LM7905 requires a minimum input voltage of -7V to maintain regulation. For reliable operation, the input should be at least 2V more negative than the output voltage, so -7V minimum for -5V output.
Power dissipation equals the voltage drop across the regulator multiplied by the load current: P = (Vin - Vout) × Iload. This heat must be managed through proper heatsinking to prevent thermal shutdown and ensure reliable operation.
A typical LM7905 circuit requires a 0.33µF ceramic capacitor on the input and a 0.1µF ceramic capacitor on the output. The input capacitor improves transient response, while the output capacitor enhances stability and reduces output noise.
A heat sink is needed when power dissipation causes the junction temperature to exceed safe limits (typically 125°C). Higher voltage drops, load currents, or ambient temperatures increase power dissipation and heat sink requirements.
Alternatives include other 79xx series regulators (7906, 7908, 7912, 7915), adjustable negative regulators like LM337, or switching regulators for higher efficiency applications. Choose based on output voltage, current requirements, and efficiency needs.