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| LM317 control by PWM |
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| David Hess:
--- Quote from: Kalvin on February 02, 2019, 10:41:02 pm ---TI's LM395 "ultra reliable transistor" comes with current limiting, power limiting, and thermal overload protection. http://www.ti.com/product/LM395/description It is a complete IC turned into an NPN transistor with extra protection features. --- End quote --- The LM395 is a great solution to add integrated protection but they cost almost 10 times more than LM317s. The LM317 is not ideal for reasons not discussed here yet, but it is a simple way to add current limiting, safe operating area protection, thermal protection, and buffering at a very low cost. |
| iMo:
I think the OP has got enough hints on the topic he is interested in, he can elaborate and report the results. Let him work. |
| Zero999:
--- Quote from: Yansi on February 02, 2019, 10:26:43 pm ---SOA protection using discrete components is just as easy to implement. What other thing than a current limit following a voltage drop across the pass element would you need? Discrete transistor audio amps solve this SOA protection on common basis. :-// --- End quote --- All right not impossible, but more complex than just using the LM317 in the first place! --- Quote from: David Hess on February 03, 2019, 05:23:49 am --- --- Quote from: Kalvin on February 02, 2019, 10:41:02 pm ---TI's LM395 "ultra reliable transistor" comes with current limiting, power limiting, and thermal overload protection. http://www.ti.com/product/LM395/description It is a complete IC turned into an NPN transistor with extra protection features. --- End quote --- The LM395 is a great solution to add integrated protection but they cost almost 10 times more than LM317s. The LM317 is not ideal for reasons not discussed here yet, but it is a simple way to add current limiting, safe operating area protection, thermal protection, and buffering at a very low cost. --- End quote --- Yes the LM395 is expensive! https://uk.farnell.com/texas-instruments/lm395t/power-transistor-to-220-3-395/dp/9488278?st=LM395 Why do you think the LM317 is not ideal? The main problem I can think of is stability and the increased risk of oscillation. |
| David Hess:
--- Quote from: Zero999 on February 03, 2019, 07:29:53 pm ---Yes the LM395 is expensive! https://uk.farnell.com/texas-instruments/lm395t/power-transistor-to-220-3-395/dp/9488278?st=LM395 --- End quote --- Meanwhile the TI LM317 from uk.farnell.com is about 1/7th the price. The ST LM317 is less. --- Quote ---Why do you think the LM317 is not ideal? The main problem I can think of is stability and the increased risk of oscillation. --- End quote --- The LM317 complicates the frequency compensation and the -1.25 volt bias requirement for a zero volt output is inconvenient. |
| Zero999:
The LM395 also doesn't appear to be that straightforward to use. It still passes a quiescent current of up to 10mA, when VBE = 0! To get a true 0V out, a negative rail is required, but I suppose a current mirror circuit will get within 100mV or so. http://www.ti.com/lit/ds/symlink/lm395.pdf |
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