• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

Omit the filament windings -- LTM8033 from Linear

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#21
It would have been nice with an externally programmable start-up (soft start) time
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With many switching regulators the total current, the fet current, or the output current can be limited. Often the limit can be set by adjusting a resistor value. (I don't know about the TI part). The trick with a tube heater for a load is to set this limit for an output current slightly above the total heater load current. This will force a slow start. Watch the output voltage with a meter or a scope while adjusting the current. You need to start the process with cold tubes.
 
#22
If you invert, could buckboost? Like a filament is really gonna care inverted DC...
A TPS5430 EVM of the inverting config is mentioned, but I couldn't find it.
This appnote mentions an email you could write to request one...

http://focus.ti.com/lit/an/slva257a/slva257a.pdf

Copy and paste from the pdf:
"The buck-boost circuit shown in Figure 3 is available as an evaluation module. See the TPS5430
product folder or send an e-mail to tps5430buckboost@ti.com to request an evaluation module"

Inverted or not, I'm completely unsure if this is safe to float the usual +75V above ground?
Also not sure if you can just slap the TPS5450 (5A) part on the same PCB or not?
I am going to guess on the side of caution and say, lets not go there...

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Edit: I think I found it... Not going to say the price out loud.
http://focus.ti.com/docs/toolsw/folders/print/tps5430buckboost.html
 
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#24
If you invert, could buckboost? Like a filament is really gonna care inverted DC...
Click to expand...

I suppose that if you had +10 volts and you needed 20 volts you could use an inverter to make -10 volts from the +10 volts and then wire the 20 volt load between the +10 volts and the -10 volts. Up until recently the inverter devices were only capable of light loads. Some recent chips can put out amps, so this is possible. I am not sure about the efficiency of high current inversion though. (I read the app note and it looks like about 85%)


Inverted or not, I'm completely unsure if this is safe to float the usual +75V above ground?
Click to expand...

If the source voltage is completely floating (like a rectified heater winding) there should be no reason why the entire rectifier - filter - regulator circuit couldn't be floated. I have done this using linear regulators with good results.
 
#26
tubelab.com said:
In any buck regulator the efficiency is highest when the input and output voltages are nearly equal. It degrades as the difference between them increases.
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True. However, that's also the point where they usually have the poorest line regulation. Tradeoffs, tradeoffs. Personally, I'd have Vin be a few volts above Vout for a buck regulator.

The efficiency also varies with load current and is usually lower at low currents.

Buck: Lowers voltage. Output voltage is less than input voltage
Boost: Raises/boosts voltage. Output voltage is higher than input voltage
Buck-boost: A regulator that automatically switches from buck mode to boost mode.

Ross: The Essence of Power Electronics is actually a fairly easy read and a good intro to the basics of switchmode supplies. It's a fairly hands-on book.

~Tom
 
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