![]() Richard. If you were using a 1M input resistor, this would correspond to voltage drops across the 1M input resistor of -0.02V, +0.04V and 8V (ouch!). Inversion of voltage level to obtain 3.3V using four LM324-N ICs quadruple operational amplifiers from Texas Instruments 10 to cover the necessary. ![]() In these opamps, the bias current goes from -20nA for 0.8V below the +Vs rail to +40uA between +Vs - 0.5V to +Vs and then 8uA up to +44V. Mouser offers inventory, pricing, & datasheets for Texas Instruments LM324-N Series Operational Amplifiers - Op Amps. This circuit is really simple and is only using a few components like a battery, an IR LED, photodiode, LM324 op-amp IC. Texas Instruments LM324-N Series Operational Amplifiers - Op Amps are available at Mouser Electronics. The purpose of this circuit is to provide a visual indication by activating an LED whenever an object is placed in front of the IR LED and the photodiode. In a normal opamp, the bias current is always in one direction and is fairly constant. Here is a simple project of an IR sensor using LM324 IC. PCN Obsolescence/ EOL: EOL 22/May/2023: PCN Design/Specification: Design 25/Feb/2022. One thing you have to watch is the changes in bias current. LM324 324A Quadruple Operational Amplifiers. The input bias current increases from 20nA to to 8uA (as the input NPN transistors saturate and so they are now just forward biased diodes into the emitters of the next PNP stage) and the offset voltage increases to 2mV, but the inputs are still fully functioning in differential mode. So they can still operate with both inputs at 44V with the opamp running from a +5V supply. The LM324B and LM2902B devices are the next-generation versions of the industry-standard operational amplifiers (op amps) LM324 and LM2902, which include four high-voltage (36 V) op amps. If I understand the specs correctly, the LT1491 and the LT1639 will not only withstand overvoltage on the inputs, but they keep operating with overvoltage on the inputs. If the design does not use this property, then replacement is probably not hard. In the context of this thread, if you want to replace a LM324 in an existing design, you have to keep in mind that the designer of the original design may be using the LM324's overvoltage capability. If you do not have overvoltage, you just have to make different design choices. ![]() In many supply designs, they get around this problem by using a reverse-biased diode that goes from the load output back to the supplies power rail which means that if the supply is off, and you attach a 12V battery, the battery is actually powering the power supply. LM324, LM324A, LM324E, LM224, LM2902, LM2902E, LM2902V, NCV2902 3 ELECTRICAL CHARACTERISTICS (VCC 5.0 V, VEE GND, TA 25C, unless otherwise noted. With almost all other opamps, I would have to add a series resistor, and the schottky diodes, and they would load the battery. This means that I can have a 12V battery on the output, and switch off the power supply, and the LM324's can cope with the 12V from the battery fine without loading the battery. As another example, I used LM324s in my power supply project. With the LT1491, a 1K series resistor with the input means it is safe for positive and negative overvoltages. With a LM324, you do not have to worry about this for positive overvoltages. What this means is that if you use conventional opamps in a circuit with multiple supply rails, and assume the supplies power up at different rates, you have to make sure that on power up, an opamp input can never go above or below the supply rails. You cannot rely on the inherent IC diode junctions as it it those junctions that cause the latchup in the first place. So if your opamp circuit does connect to an externally power circuit that under some circumstances (eg power up) can drag an input more then 0.3V above the positive rail or 0.3V below the negative rail, then you do have to add a series resistor and a pair of external schottky diodes. If the inputs exceed the specified maximums, the opamp IC can latch that usually means it self destructs.
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