Optically coupled isolators for harsh environments

Optek Technology has developed a series of reliable, optically coupled isolators that provide military electronics design engineers with the ability to optically isolate sensitive circuit elements.

The 4N2x and 4N4x series isolators provide up to 1kV electrical isolation with a high-current transfer ratio.

The optically coupled isolators are hermetically sealed metal packages - either surface-mount six-pin leadless chip carriers, or through-hole TO-78 metal cans - and are processed to TX and TXV MIL-PRF-19500/486 and /548 specifications.

Commercial-off-the-shelf (COTS) level devices are also available.

The isolators are said to be ideal for any high-reliability circuit requiring high-voltage isolation between input and output, especially in harsh environments.

The optically coupled isolators consist of a 935nm (4N2x series) or an 890nm (4N4x series) wavelength infrared-emitting diode and a NPN silicon phototransistor mounted in a hermetically sealed metal package, with a base contact provided for conventional transistor biasing.

Devices are also available with the collector pin electrically isolated from the case.

Devices within the 4N2x series all exhibit input diode forward current (IF) of 40mA (max), 10mA (typical); collector-emitter voltage (VCE) is rated at 35V (max); with 1kVDC voltage isolation.

The devices' operating temperature range is from -65C to +125C.

4N22 series devices feature a minimum current transfer ratio (CTR) of 25 per cent.

4N23 series devices feature a minimum CTR of 60 per cent.

4N24 series devices feature a minimum CTR of 100 per cent.

Devices within the 4N4x series all exhibit input diode forward current (IF) of 40mA (max); collector-emitter voltage (VCE) is rated at 40V or 45V (max), depending on package style; with 1kVDC voltage isolation.

Their operating temperature range is from -55C to +125C.

4N47 series devices feature a minimum CTR of 50 per cent.

4N48 series devices feature a minimum CTR of 100 per cent.

4N49 series devices feature a minimum CTR of 200 per cent.

The 4N2x series (TX, TXV) devices are processed to MIL-PRF-19500/486 standards; and the 4N4x series (TX, TXV) are processed to MIL-PRF-19500/548 standards.

Burn-in condition for all devices is as follows: VCE = 10V, IF = 40mA, PD = 275mW, TA = 25C.

Packaging options for the 4Nxx series optically coupled isolators include a standard TO-78 metal can through-hole package; and a surface-mount leadless chip carrier (designated with a 'U' suffix to the part number).

Both package types are hermetically sealed and are compatible with high-temperature soldering processes.

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