LM358N

The LM358N from Texas Instruments is the industry-standard dual general-purpose operational amplifier optimized for single-supply operation. Its key advantage is the input common-mode voltage range that includes ground (0V), allowing it to amplify signals that go all the way down to the negative rail without requiring a dual supply. The output also swings close to ground (typically to 5mV with a 10kΩ load), eliminating the need for a negative supply in many applications. The 3V minimum supply voltage makes it compatible with 3.3V logic systems, while the 32V maximum allows use in automotive and industrial applications. The 1.2MHz gain-bandwidth product and 0.5V/µs slew rate are sufficient for DC and low-frequency AC applications (audio up to ~100kHz at unity gain). The N suffix denotes the commercial temperature range (0°C to +70°C) in PDIP-8. The LM358 is one of the most produced and lowest-cost op-amps in the world, available from TI, onsemi, STMicroelectronics, and dozens of other manufacturers.

The LM358N contains two independent operational amplifiers on one chip. Each op-amp is a high-gain differential amplifier with inverting (−) and non-inverting (+) inputs and a single output. In open-loop (no feedback), the gain is approximately 100,000 (100V/mV), so even a tiny voltage difference between the inputs drives the output to saturation. In closed-loop (with feedback), the gain is determined by the external resistor network: for an inverting amplifier, AV = −Rf/Rin; for a non-inverting amplifier, AV = 1 + Rf/Rin. The input stage uses PNP transistors that allow the common-mode input to go below ground by approximately 0.3V, and the internal biasing allows single-supply operation. The output stage is a Class-AB push-pull that can both source (up to 20mA) and sink (up to 10mA) current. When the output needs to go to 0V (ground), the sink capability pulls it close to ground, though not exactly to 0V under load. For a voltage follower (unity gain buffer), connect the output directly to the inverting input; the output then follows the non-inverting input exactly, with high input impedance and low output impedance.

LM358N uses the PDIP-8 (N) package with industry-standard dual op-amp pinout: Pin 1 = Output A, Pin 2 = Inverting Input A (-), Pin 3 = Non-inverting Input A (+), Pin 4 = GND/VEE, Pin 5 = Non-inverting Input B (+), Pin 6 = Inverting Input B (-), Pin 7 = Output B, Pin 8 = VCC. This pinout is shared by all dual op-amps in DIP-8 including LM358, LM2904, RC4558, NE5532, and TL072. The single-supply operation (3V-32V or ±1.5V to ±16V) allows inputs to go to ground without phase reversal. Output swings to within 0-20mV of ground in single-supply configuration. For surface-mount, LM358DR (SOIC-8) provides identical pinout.

• Inverting Amp: Input through Rin to IN−; Rf from IN− to OUT; IN+ to GND; gain = −Rf/Rin; inverts and amplifies
• Non-Inverting Amp: Input to IN+; Rf from OUT to IN−; Rin from IN− to GND; gain = 1 + Rf/Rin; amplifies without inversion
• Voltage Follower: OUT connected directly to IN−; input at IN+; gain = 1; high-Z input, low-Z output buffer
• Schmitt Trigger: Positive feedback from output to IN+ through resistor divider; creates hysteresis; cleans noisy digital signals
• Difference Amp: Both inputs used; output = gain × (IN+ − IN−); measures voltage across a shunt resistor

LM358 is the industry-standard dual general-purpose op-amp with 1.1MHz GBW and 3-32V single-supply operation. Input common-mode range includes ground for single-supply sensor interfacing. LM358B offers modern 36V rail-to-rail output. For quad needs, LM324 provides 4 channels. For audio, NE5532 offers 10MHz GBW and low noise. LM2904 extends temperature range to 125C for automotive applications.