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| lm78xx series question and some more stuff |
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| Kilroywashere:
Hello world, I'm building a lab power supply and I only have 1 Lm317, I want to have a current limit of up to 1 amp . I know that you can use a 78xx series to provide a constant output current, I was wondering can I just use a 7805 as my current regulator or will 1 amp be too much for this thing to handle ? (get super hot and such) I wanted to save the Lm317 for the voltage adjustment, or is it better to use it for current if you only have one? Also some designs I look at have two 1n4001 diodes and a transistor leading into -10volts (I guess to bring the output to 0 v?) is it better to have some sort of duel + - power rails powering the thing? |
| Vovk_Z:
--- Quote from: Kilroywashere on January 23, 2020, 12:47:23 am ---I guess to bring the output to 0 v?) --- End quote --- - yes. |
| MarkF:
Do you want to just limit the current to 1A or do you want an adjustable current limit? If you want an adjustable current and are okay with a minimum of 1.2V of the LM317, you can do something like this: If you just want a fixed 1A current limit, take a look at this battery charger circuit: The sense resistor value can set a fixed current limit with the minimum LM317 voltage output. You will probably want a full-wave bridge and a large cap for the input. But you get the idea. (You can use any NPN transistor, 2N2222, 2N3904, etc. But will need to select a different sense resistor value.) --- Quote from: Kilroywashere on January 23, 2020, 12:47:23 am ---Also some designs I look at have two 1n4001 diodes and a transistor leading into -10volts (I guess to bring the output to 0 v?) is it better to have some sort of duel + - power rails powering the thing? --- End quote --- You only need a negative if you want to pull the minimum output voltage down to 0V. |
| MarkF:
A LM317 circuit that goes down to 0V. |
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