An Introduction to LM393 Low Power Dual Voltage Comparator
28 November 2023
Ⅱ. What are the features of LM393 comparator?
Ⅲ. Pin configuration of LM393 comparator
Ⅳ. Functions of LM393 comparator
Ⅴ. Technical parameters of LM393 comparator
Ⅵ. Typical circuit of LM393 comparator
Ⅶ. How to use the LM393 dual voltage comparator?
Ⅷ. Applications of LM393 comparator
The LM393 is a widely utilized voltage comparator integrated circuit (IC) available in DIP-8 and SOIC-8 packages. It comprises two independent and accurate voltage comparators, each exhibiting an offset voltage of no more than 2.0mV. This versatile IC is compatible with both single and dual power supplies, and its current remains unaffected by the power supply voltage magnitude. With a broad supply voltage range, the LM393 finds suitability across various applications. Notably, the LM393's low operating current consumption renders it well-suited for deployment in portable and battery-operated devices. Its output drive logic system is adaptable for integration into digital circuits. The LM393 boasts a maximum output current of 20mA, providing ample capability to drive transistors and logic systems.
Replacements and equivalents:
• LT1013
• LM2903
• LM324
• LM339
• Its output is compatible with DTL, TTL, MOS, CMOS, etc.
• The LM393 boasts rapid switching speeds, enabling swift responses to alterations in system signals. This contributes to heightened system response speed and efficiency.
• It has relatively low input bias current, which helps reduce the effect of this current on the connected circuitry.
• It can work in both single power supply and dual power supply modes. The single power supply is 2 to 36V and the dual power supply is 1 to 18V.
• The LM393 boasts a significant input impedance, resulting in minimal impact on the circuit under observation by reducing loading effects.
LM393 is an 8-pin integrated circuit, including positive and negative power inputs (VCC and GND), two comparator input ports (IN+ and IN-), output A and output B, and two bias adjustment ports (VREF1 and VREF2). Among them, IN+ is a non-inverting input and IN- is a non-inverting input.
1. The output load resistor can be connected to any power supply voltage within the allowable power supply voltage range without being limited by the Vcc terminal voltage value.
2. When the limit current of 16mA is reached, the output transistor will exit and the output voltage will rise quickly.
3. The output saturation voltage is limited by the γ SAT of the output transistor of approximately 60ohm. When the load current is small, a low offset voltage (approximately 1.0 mV) clamps the output to zero level.
In conventional PWM applications, a sawtooth wave and a control voltage are typically compared using a comparator to generate PWM pulses. In this setup, comparator 2 of the LM393 serves as the PWM comparator. The non-inverting input is connected to the control voltage input, while the inverting input is linked to the sawtooth wave input. The resulting PWM dimming signal is transmitted to the ENN pin of the IRS2540/1 via the output terminal (pin 7) using an isolation diode, as illustrated in the accompanying circuit diagram.
The sawtooth wave is generated by comparator 1 of LM393. Ignoring capacitor C1, comparator 1 is a multivibrator that outputs a square wave. In order to obtain a sawtooth wave, we connect a capacitor C1 in parallel between the output terminal of comparator 1 and the COM terminal. This actually describes the charging process of the output terminals R1 and C1 of comparator 1. If the capacitance of this capacitor is large enough, since the charging of C1 requires R1, and the discharging of C1 is the output transistor of the comparator, the rise and fall of the voltage at the output end of the comparator will become asymmetrical, forming a "sawtooth wave" oscillation waveform. Since the power supply of the circuit is VBUS, we need to use RS to step down, and need VD2 voltage stabilization and power supply bypass capacitors C3 and C4.
The LM393 is characterized by high gain and a wide bandwidth. Similar to most comparators, the presence of parasitic capacitance coupling from the output to the input can lead to oscillation, particularly when the comparator state changes. This oscillation manifests as a gap in the transition of the output voltage. Implementing standard PCB design practices can help minimize the coupling of parasitic capacitances from input to output. To further mitigate this issue, it is recommended to reduce the input resistance to less than 10KΩ, thereby decreasing the feedback signal. Additionally, a slight increase in positive feedback (hysteresis range between 1.0 to 10mV) can facilitate fast switching, effectively preventing oscillation caused by parasitic capacitance. It's essential to note that directly plugging into the IC and adding resistors to the pins may induce input and output transitions to oscillate over short periods unless hysteresis is specifically required. In cases where hysteresis is unnecessary, especially when dealing with a pulse waveform characterized by rapid rise and fall times, the hysteresis characteristic can be omitted. Furthermore, any unused pins of the comparator should be connected to ground to ensure proper functionality.
The LM393 bias network ensures that its quiescent current is independent of the supply voltage range of 20 to 30V. Typically, we do not need to add bypass capacitors to the power supply because the differential input voltage can be greater than VCC without damaging the device. The protection part should ensure that the input voltage is prevented from excursion to the negative terminal by -0.3V.
The output section of the LM393 is an NPN output transistor with open collector and grounded emitter, which can be provided with a multi-collector output or function. The output load resistor can be connected to any supply voltage within the allowable supply voltage range without being limited by the VCC terminal voltage value. When no load resistor is used, this output can simply be considered an open circuit to ground SPS. The sink current in the output section is limited by the driver and device B values. When the limit current (16mA) is reached, the output transistor will stop working and the output voltage will rise quickly. The output saturation voltage is limited by the γ SAT of the output transistor of approximately 60Ω. When the load current is small, the output transistor's low offset voltage (about 1.0mV) allows the output to stabilize at zero level.
LM393 is a voltage comparator. When the resistance value of photoresistor R3 changes when exposed to light, it will be converted into a voltage signal and passed to the non-inverting input terminal INB+ of the voltage comparator. This changing voltage signal is compared with the reference voltage (generated by potentiometer R9) at the inverting input terminal INB- of the voltage comparator. When the voltage of the non-inverting terminal INB+ is greater than the voltage of the inverting terminal NB-, the output terminal OUTB of the voltage comparator outputs a high level, and the D1 light goes out at this time. When the voltage of the non-inverting terminal INB+ is less than the voltage of the inverting terminal NA-, the output terminal OUTB of the voltage comparator outputs a low level, and the D1 light turns on at this time.
Frequently Asked Questions
1. What is LM393 used for?
The LM393 series are dual independent precision voltage comparators capable of single or split supply operation. These devices are designed to permit a common mode range−to−ground level with single supply operation.
2. What is the input voltage of LM393?
Input offset voltage specifications as low as 2.0 mV make this device an excellent selection for many applications in consumer, automotive, and industrial electronics.
3. What is the substitute for LM393 IC?
The LM393 applications are very similar to the LM311 Comparator IC, only the specifications change a bit. Other than that the LM311 can be considered as a close replacement for LM393. Like all voltage Comparators the LM393 also has an Inverting Pin and a Non-Inverting Pin.
4. Can LM393 be used as amplifier?
An LM393 IS an amplifier but it is designed to be used as a comparator and it therefore is designed to have a very high gain and an open collector output.
5. What is the difference between LM358 and LM393?
Can I use LM393 instead of LM358? The LM358 and LM393 might seem outwardly similar, but the LM358 is an operational amplifier with linear output, and the LM393 is a comparator with a digital output, and they cannot be interchanged.
