Ok. So rather than using the zener as a shunt regulator, I'd like to use it as a level shifter.
Will this work? I can't see why it won't as long as the load is large enough to cause zener action, but low enough not to cause the Pd of the zener to be exceeded. Am I wrong? Vin - Vzener = Vout?
Will this work? I can't see why it won't as long as the load is large enough to cause zener action, but low enough not to cause the Pd of the zener to be exceeded. Am I wrong? Vin - Vzener = Vout?
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You are absolutely right. The reason why it is not used very frequently is that the zener characteristic is not very abrupt, few zener diodes can handle much current and input voltage swings (at the power source) are transferred to the output. An integrated voltage regulator can do much better and still for a low price.
Thank you.
All it will do it replace a 15k resistor for a 6E2. Right now, the tubes bounce and play with each other because the more current drawn, the lower the plate voltage. I figure this would "stiffen it up" so to speak.
All it will do it replace a 15k resistor for a 6E2. Right now, the tubes bounce and play with each other because the more current drawn, the lower the plate voltage. I figure this would "stiffen it up" so to speak.
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A "drop-zener" is better than a "drop-resistor". If it is good enough for avoiding tube-bounce, you know (or will know) better than I (no tube experience).
You need to check that the zener has enough current through it to reach the knee in the curve. Zeners can be noisy, so it may need to be bypassed.
As long as you remain reasonable (for example, Vout>0.5*Vin), it can work, but it will magnify problems in relative terms: the absolute regulation will be the ~same, but the relative one wil be degraded.
The same for noise, ripple, etc: you will add x dB's to the initial value, x being dependent on the ratio of the initial to the final voltage
The same for noise, ripple, etc: you will add x dB's to the initial value, x being dependent on the ratio of the initial to the final voltage
Good to know... As you can see from the schematic in post 1, it basically needs to get rid of 50V at maybe 5 - 10 mA... The part is 5W, so I figure it's up to the task...
Are you using this to power an audio circuit? If so, be aware that zener diodes generate considerable noise. In fact, some "white noise" and "pink noise" generators use the base-emitter junction of a BJT in zener mode (reverse biased) to generate the noise.
A Zener bias current of 249uA is too low. Look up the datasheet to determine whether this is enough.
KodaBMX,
Using a zener circuit from B+ is what I have been doing with my submini amp, for screen supply.
In my case I have a similar drop, from the B+ 300V down to 245V for the screens. A rule of thumb i was taught is that the current through the zener should be about 10times larger than the current expected to be drawn at the zener tap.
In my case i use about 6k in series with a zener string of 1N53** 5W zeners (I have a string of several, 1N5378 - 100V, then 2 1N5359 - 24V)
This is all bypassed with about 100uF. It isnt well designed, on paper.
One tube screen (Ig2max=2mA), so the resultant zener regulator needed something like 20mA flowing to maintain good regulation of screen under full load. I used 16k and brought this down to 8k to maintain regulation.
Three tube screen to supply and 6mA max meant that to avoid the supply sagging, series resistance had to be dropped to 4k!
5W zeners are then, in some cases overloaded, with 300/4k......75mA constant draw through the reg. I ended up with higher resistor, so that I'm not wasting 75mA just to power the screen circuit.
So....thems the breaks,
Regardless of the use as shunt reg, or series dropper, the concerns are the same.
I'd bypass to ground at the zener-resistor node, to clean up noise.
The cap may be frustratingly slow to charge to regulated voltage in the same way it is in my circuits using zeners as a shunt reg.
Hopefully is works series mode...never tried it!
But I will try in the cathode circuit if it is reliable enough
Using a zener circuit from B+ is what I have been doing with my submini amp, for screen supply.
In my case I have a similar drop, from the B+ 300V down to 245V for the screens. A rule of thumb i was taught is that the current through the zener should be about 10times larger than the current expected to be drawn at the zener tap.
In my case i use about 6k in series with a zener string of 1N53** 5W zeners (I have a string of several, 1N5378 - 100V, then 2 1N5359 - 24V)
This is all bypassed with about 100uF. It isnt well designed, on paper.
One tube screen (Ig2max=2mA), so the resultant zener regulator needed something like 20mA flowing to maintain good regulation of screen under full load. I used 16k and brought this down to 8k to maintain regulation.
Three tube screen to supply and 6mA max meant that to avoid the supply sagging, series resistance had to be dropped to 4k!
5W zeners are then, in some cases overloaded, with 300/4k......75mA constant draw through the reg. I ended up with higher resistor, so that I'm not wasting 75mA just to power the screen circuit.
So....thems the breaks,
Regardless of the use as shunt reg, or series dropper, the concerns are the same.
I'd bypass to ground at the zener-resistor node, to clean up noise.
The cap may be frustratingly slow to charge to regulated voltage in the same way it is in my circuits using zeners as a shunt reg.
Hopefully is works series mode...never tried it!
But I will try in the cathode circuit if it is reliable enough
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It's called motorboating. You most probably have several coupling cap + loads that have a similar RC product. That means multiple roll offs at the same or almost same frequency. The result is motorboating.
Try to double a coupling capacitor somewhere and halve one somewhere else. That should stop it.
Jan
A 51V "zener" isn't using the zener effect, its an avalanche breakdown device (zener breakdown is limited to about 7V or so - higher voltage "zener"s are a combination of tunneling and avalanche, with avalanche taking over eventually. The avalanche devices have much better voltage regulation and more noise - so a parallel capacitor is usually used.
Nothing to do with motorboating or RC filters this time (there is no RC filter at all), just the fact that the voltage ranges from 230V - 265V depending on the deflection of the beam in the 6E2.
Semantics really... A VR tube doesn't use the zener effect either, but the end result would be the same, no?
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