Interesting Observation

241

02:18:17

I notice that a simple ultra-low-noise regulator like this one (which eliminates virtually all traces of power supply noise) does not necessarily produce a super-stable output voltage without some form of negative feedback since the exact output voltage is highly dependent on the load. A larger load and the voltage drops. A smaller load and it rises. This means that if this regulator is regulating the supply of something like a preamp or other device sensitive to supply noise, nothing else should run of the same regulated supply, as that something else may not be a constant load and thereby produce noise in the power supply of the noise sensitive device.

published 7 years ago

hurz

7 years ago

do you expect a super-stable voltage of a simple emitter follower? BTW, 100k and PNP is a nice noise generator (termal noise). I dont get what and why is this a surprise for you? You should built more circuits practical to face temperatur problem which you will have with this design!

jason9

7 years ago

How well can capacitors prevent thermal noise? If capacitors aren’t effective against thermal noise, what can I do about it other than keep it in a bath of liquid nitrogen? I could reduce the 100k but then the PNP will push too much into the zener.

hurz

7 years ago

high ohmic designs are more noisy then low ohmic ones. Preamplifier or mic amplifier are as low ohmic as possible. This about Thermal Noise. Thermal runaway, which you designed with the 100kOhm and PNP transistor is a second issue. Use a voltage divider for the PNP to bias or even better a zener/led/diodes as voltage reference, while this would also need an emitter resistor, cuz they are all higher then one Vbe of 0.7V

hurz

7 years ago

check this http://everycircuit.com/circuit/6298094535442432

ViolationMad

7 years ago

I've seen this zener setup recently on the "ham it up" upshifter. It creates really a lot of noise.

hurz

7 years ago

yes, all semiconductor are very noisy. So good preamps do use as less as possible semiconductors. Sure we talk about thermal noise, some people mix this with nonlinear effects.

jason9

7 years ago

I see. I hadn’t considered thermal runaway and that design you gave not only prevents thermal runaway but also solves the thermal noise problem. I see I still have much to learn, because if I didn’t I would’ve come up with a similar design myself, and not failed to consider thermal noise and runaway.

hurz

7 years ago

sure, no problem

fahad77

7 years ago

💐

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