What is the VAR-2273 Constant Current Stimulus Isolator?

The VAR-2273 (Model A365) is a precision constant current stimulus isolator from World Precision Instruments, designed for demanding electrophysiology applications in neuroscience and muscle physiology research. Battery-operated and optically isolated from ground, the A365 delivers highly accurate, artifact-minimized stimulation currents across three selectable ranges — making it an indispensable tool for in vitro brain slice recordings, in vivo stimulation, and any preparation where stimulus precision and electrical isolation are critical.

The A365 is gated by any standard pulse generator, stimulator, or computer output. Its output current tracks control settings to better than 1%, and automated bipolar pulsing delivers zero net charge to biological preparations — protecting tissue integrity across long experimental sessions.

Key Features

• Three Selectable Current Ranges: Output up to 10 mA across three ranges (0.1 mA, 1.0 mA, 10 mA), enabling fine control for both sub-threshold probing and suprathreshold stimulation of excitable tissue.
• 100V Compliance Voltage: Maintains accurate current delivery even through high-impedance electrodes or tissue, ensuring reliable stimulation regardless of load resistance.
• 2500V Optical Isolation: Optocoupler-based isolation of 2500V completely eliminates ground loops and stimulus artifacts, protecting both the preparation and recording amplifier.
• Bipolar Pulsing with Zero Net Charge: Automated bipolar output mode ensures zero net charge delivery to the biological preparation, preventing electrode polarization and tissue damage during chronic stimulation protocols.
• Battery Operation: Runs entirely on internal batteries, eliminating mains-frequency noise from the power supply and enabling use in environments where AC-powered equipment would introduce interference.
• Load-Independent Output: Current output is fully independent of load resistance — the instrument automatically adjusts compliance voltage to push the desired current through any impedance within specification.
• Fast Rise and Fall Times: Rise time of 6 µs and fall time of 10 µs allow faithful reproduction of brief, high-frequency stimulus trains without waveform distortion.
• Multiple Configurations: Available as SYS-A365R (rechargeable battery), SYS-A365D (dual-channel), and A365RC (remote-controlled) to fit a wide range of experimental setups.