Hi guys,
What happens to a voltage regulator when started up on a variac?
I am about to test a tube power supply with a regulated 12.6v heater supply (lt1086) and a 265v regulated b+ (treg)
My question is will this hurt the regulators in some way?
My guess would be that there is no ill effect. That the regulators simply won't regulate when their input voltage is below their minimum drop out.
My punny brain can conjure some horror scenarios when this would cause wild current flow but I am guessing this is my feeble mind displaying it's feebleness.
What happens to a voltage regulator when started up on a variac?
I am about to test a tube power supply with a regulated 12.6v heater supply (lt1086) and a 265v regulated b+ (treg)
My question is will this hurt the regulators in some way?
My guess would be that there is no ill effect. That the regulators simply won't regulate when their input voltage is below their minimum drop out.
My punny brain can conjure some horror scenarios when this would cause wild current flow but I am guessing this is my feeble mind displaying it's feebleness.
Some circuits won't start up nicely that way, but most standard circuits will.
Connect DVMs to the B+ and filaments while you raise the Variac, and be ready to kill the power if misbehavior happens.
Connect DVMs to the B+ and filaments while you raise the Variac, and be ready to kill the power if misbehavior happens.
Usually, the regulator will start up fine but not provide any regulation until the voltage across it exceeds its minimum drop-out voltage. So basically you get an output voltage that's slightly lower than the input voltage until the input voltage is high enough for the regulator to provide the desired output voltage.
This is not hugely different from what happens on a normal startup except the startup never finishes. I haven't personally had issues browning out regulators like that, but that's not to say that you can't find a design out there that'll be rather cranky and possibly oscillate if it doesn't have enough input voltage to regulate properly.
Startup and power-down issues can be hard to deal with in the circuit design and they're often ignored until something bad happens. So ideally, you'd simulate the regulator with a slow ramp for its input voltage. In lieu of that, use @rayma's method above.
Tom
This is not hugely different from what happens on a normal startup except the startup never finishes. I haven't personally had issues browning out regulators like that, but that's not to say that you can't find a design out there that'll be rather cranky and possibly oscillate if it doesn't have enough input voltage to regulate properly.
Startup and power-down issues can be hard to deal with in the circuit design and they're often ignored until something bad happens. So ideally, you'd simulate the regulator with a slow ramp for its input voltage. In lieu of that, use @rayma's method above.
Tom
Post your schematic here, it should be easy to see any questionable features that could cause problems.
A basic Zener follower B+ regulator should be ok. But your prudence is admirable.
A basic Zener follower B+ regulator should be ok. But your prudence is admirable.
The LT1086 will likely just provide the input voltage less a bit until you give it enough input voltage. I'm not familiar with the B+ regulator.
Tom
Tom
The t reg is from the diyaudio store although mine is a v4 direct from Jan before the store stocked it.
I can only post the schematic as a pdf as I have no way of changing to a jpeg.
Before the t reg is a standard rcrc filter. Rectifiers with quasimodo snubber > 100r > 470uf > 100r > 470uf
I don't have the schematic for my exact implementation of the lt1086 on my cellphone, but it's a bog standard implementation. Rectifiers with quasimodo snubber> filter cap> regulator> output cap.
I used 470uf output cap iirc, 220uf adjust cap and protection diodes across the regulator. The datasheet said protection diodes are unnecessary but I figured why not use them anyway.
I can only post the schematic as a pdf as I have no way of changing to a jpeg.
Before the t reg is a standard rcrc filter. Rectifiers with quasimodo snubber > 100r > 470uf > 100r > 470uf
I don't have the schematic for my exact implementation of the lt1086 on my cellphone, but it's a bog standard implementation. Rectifiers with quasimodo snubber> filter cap> regulator> output cap.
I used 470uf output cap iirc, 220uf adjust cap and protection diodes across the regulator. The datasheet said protection diodes are unnecessary but I figured why not use them anyway.
