LM723 Current Limiting Questions

Posted on Feb 6, 2014

I get that the LM723 current sense and current limit pins (2 & 3) see a voltage created by the very low restistance current limiting resistors and that when this voltage reaches a certain value, the IC shuts down or limits the power supply output. How or where is thisvoltage parameter noted in the device specs I believe that I read somewhere that 0. 6 volts is the trigger point, but I can`t find anything like this in the spec sheet. What

LM723 Current Limiting Questions
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happens as this voltage reaches and exceeds 0. 6 volts Does the device reduce output voltage If so, does it do this until the voltage drops back to 0. 6 volts and stop there If you take a look at the equivalent circuit (on page 2) you will see that the current limit and current sense pins are simply tied to the base and emitter of an NPN transistor which has its collector tied to the output of the error amplifier. Simply speaking, when the current limit pin of the 723 is more than 0. 6V more positive than the current sense pin, the output of the error amplifier is pulled low, reducing drive to the output series pass transistor. This may be done in a number of ways. The datasheet shows the sense resistor placed in the output prior to the voltage sensing, but it can also be done in the ground return. Table 2 on page 7 gives tot he formula for calculating the sense resistor value. Vsense is probably something like 0. 6V. but it may be specified somewhere. Note that it varies with temperature, the table on page 4 illustrates that. Okay, I`ll grant that the LM723 has been around for quite a while. Is there a similar, newer device that will do a better job for me This is a 22 volt, 10 amp, low ripple power supply. I`ve attached an article with schematic that I have built. It works reasonably well but even with 10, 000 mf filtering, I`m still getting about 0. 5 volts of ripple at 8 amps output. There are *many* newer chips. You...

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