I want to use LT1084 with higher inputvoltage (43V) than it was designed for (30v).Ive seen TL317 used with a couple of hundred volts by raising the adjust b pin.But how do I do it,with a zener or??
Use something like the Maida topology discussed widely across the forum.
http://www.diyaudio.com/forums/tubes-valves/209067-21st-century-maida-regulator.html
The design can be adopted to relatively low voltage operation even just above the ratings of the part which results in much better reliability than standing the device on a zener.
What is the target output voltage?
If the current is low you can place a zener in series with the input, I've seen it done, but personally I think it less than optimum due to potential dissipation and other issues in the zener. Minimum current needs to be enough that the zener always operates correctly, with maximum current within the allowable dissipation limit of the zener.
http://www.diyaudio.com/forums/tubes-valves/209067-21st-century-maida-regulator.html
The design can be adopted to relatively low voltage operation even just above the ratings of the part which results in much better reliability than standing the device on a zener.
What is the target output voltage?
If the current is low you can place a zener in series with the input, I've seen it done, but personally I think it less than optimum due to potential dissipation and other issues in the zener. Minimum current needs to be enough that the zener always operates correctly, with maximum current within the allowable dissipation limit of the zener.
The problem arises that at time zero the capacitor required for stability on the output of the device is at zero volts (and looks like a short) and the voltage across the regulator may temporarily exceed the safe maximum; the part fails.
Yes the limmit is 30v it says in the data sheet.
The current i need is 10mA it is 2 2sk117GR that I am going to use as MC amp.
The AC voltage that I have on hand is 30v and the output I figure is 30-35v dc.
Or else I have to find another trafo with lower AC..
The current i need is 10mA it is 2 2sk117GR that I am going to use as MC amp.
The AC voltage that I have on hand is 30v and the output I figure is 30-35v dc.
Or else I have to find another trafo with lower AC..
You have point there,even if the datashet says it can only take max 37volts...
By the way haven´t LT1084 better specs for audio?
By the way haven´t LT1084 better specs for audio?
It is a floating regulator, it's the input to output differential that is limited to 37V. search LM317 high voltage. As for whether LT1084 is better for audio I have no idea, but I know the LM317 is very good and is used for high end audio all the time
I found this:High Voltage Regulator
Maybee I can change LM317 for LT1084 any one know if the noise is better for LT1084?
Maybee I can change LM317 for LT1084 any one know if the noise is better for LT1084?
I've been searching too. It seems the advice has changed. On the TI data sheet it used to say the LM317 could be used at high voltage so long as the differential limit wasn't exceeded. Now the concern seems to be that the smoothing capacitor after the regulator can present a momentary short on the output thus exceeding the voltage rating. I can only tell you my personal experience. I used LM317 and LM337 to regulate power supply for amplifier, a small voltage drop of about 3V to +/-60V feeding 4700uF capacitors and it worked fine for years. The LT1084 looks to be very similar to the LM317, just higher current rating. What voltage supply do you need?
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The LM317HV will handle up to a 60V differential and would be a better choice here I think. If you were using the standard 35V part you got lucky. 😀
Note that neither of these chips would be my first choice to power an MC amplifier stage, something quieter is in order.
That said there are ways to clean up the LM317HV noise performance, see here: Finesse Voltage Regulator Noise! |
Thanks for coming back Kevinkr, I'm confused, I'm sure the advice has changed, original data sheet said they could be floated at high voltage. I've even seen them used in valve circuits. At 60V I was only dropping 3V
Yes,I´ve used the finesse before in an headphonenamp.But I wonder If Salas shunt have even lower noise as I have a couple of pcb`s laying around..
I remember seeing those same application circuits, in many cases over time they proved to be unreliable. I've seen more than a few popped LM317 in HV regulator circuits.. 😀
Thanks. I was starting to think I was going mad. Perhaps they were made out of tougher stuff in the good ol' days. Or, more likely, I was lucky!
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