hi, I need a regulated 42VDC for a project I am working on, ordered a 30V trans, which when arrived gave 33V so through my regulator i go 48 VDC, which is to high for my circuit. the standard LM317 on works up to 25 VDC, not high enough. Then I found this unit, the LM317HVT, the spec sheet says can go up to 58 VDC out or so.
the question is if I buy a kit from F/Bay for a LM317 & upgrade the capacitors to say 60-100V, can I simply replace the two regulators, the hopefull adjust insert the unit between my Tans & current ultra low noise regulator & adjust the DV voltage down to 42 VDC?
Cheers
the question is if I buy a kit from F/Bay for a LM317 & upgrade the capacitors to say 60-100V, can I simply replace the two regulators, the hopefull adjust insert the unit between my Tans & current ultra low noise regulator & adjust the DV voltage down to 42 VDC?
Cheers
Yes, both ICs are pin-to-pin compatible. Your only worry should be those caps and recalculating the resistors using the formula in the datasheet. they most likely share a similar adj circuitry (like most LDOs). its not exactly a drop in replacement but at least you don't have to redo your PCB.
Hi, thanks for that, so if I used a diode 1N400x, should that be OK plus 100v caps.
Would I need to do the resistors as the unit has an adjustable voltage pot.
Cheers
Would I need to do the resistors as the unit has an adjustable voltage pot.
Cheers
Lmx17 are floating regulators, you have to be sure you do not exceed the input-output differential voltage spec. If you exceed the input voltage spec it will not be bulletproof in that it will not be short current protected but many regulators are not short circuit protected so that is a design decision to make. A resistor in series with the regulator input can zpotentially elevate this fault condition but you have to maintain a minimum I/O differential of a few voltages for it to regulate properly. If you put the resistor at the i/p you will need a small cap ~>= 100n close to the I/p pin
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It is perfectly OK to use LM317 above the rated 37vDC input; there are three things to be aware of:
1. Short circuit protection is compromised, as posts above.
2. You ABSOLUTELY need both the protection diodes shown in the datasheet, to protect the device on shutdown from reverse bias from the Vadj and Vout charged capacitors.
3. You MUST limit the transient voltage difference from Vin to Vout during start-up. And actually this is easy - just use a 15-22V, 1.5w zener diode reverse-biased from V in to V out. Yes this part also safely provides the function of one of the protection diodes identified above : )
You must also ensure your target raw Vdc supply always remains within acceptable limits above your target Vout, regulated voltage; and that total dissipation is acceptable.
I've used LM317s above 300Vdc out very reliably, on the above basis. DO read the datasheets - all you need is there.
1. Short circuit protection is compromised, as posts above.
2. You ABSOLUTELY need both the protection diodes shown in the datasheet, to protect the device on shutdown from reverse bias from the Vadj and Vout charged capacitors.
3. You MUST limit the transient voltage difference from Vin to Vout during start-up. And actually this is easy - just use a 15-22V, 1.5w zener diode reverse-biased from V in to V out. Yes this part also safely provides the function of one of the protection diodes identified above : )
You must also ensure your target raw Vdc supply always remains within acceptable limits above your target Vout, regulated voltage; and that total dissipation is acceptable.
I've used LM317s above 300Vdc out very reliably, on the above basis. DO read the datasheets - all you need is there.
I recently started using LM317.
Then started having problems with blown IC's.
1/ I was using 317 to get 3.6 volts but hadn't done calculation close enough and it was putting out 3.9 volts and blowing up microcontroller.
2/ Kept blowing up a motor driver IC. But had forgot to put capacitor across motor driver supply so 317 wasnt to blame.
3/ Kept getting a microcontroller resetting. But hadn't put 317 output cap close enough.
Its easy to blame wrong thing.
Then started having problems with blown IC's.
1/ I was using 317 to get 3.6 volts but hadn't done calculation close enough and it was putting out 3.9 volts and blowing up microcontroller.
2/ Kept blowing up a motor driver IC. But had forgot to put capacitor across motor driver supply so 317 wasnt to blame.
3/ Kept getting a microcontroller resetting. But hadn't put 317 output cap close enough.
Its easy to blame wrong thing.
