An Amplified Zener Shunt Voltage Regulator?

[KK4YY]

If Steve WA1QIX doesn't mind me standing on his shoulders...

It seems that the Amplified Zener circuit that Steve posted, in a different discussion, could be easily adapted to work as a shunt voltage regulator. I attached a modification of his sketch here.

The beauty is that the same basic circuit could work as either a positive or negative shunt regulator. This eliminates the need for a P-channel MOSFET that would be needed for a negative series regulator. It could be used as a replacement for a VR tube while offering much greater current capacity.

I'm not sure that C1 would be needed in this role.

I wasn't able to find anything like this when searching the Internet, but it's likely I'm not the first to apply the circuit in this way. If I just discovered it, must be a Festivus miracle!

Comments?


Don

[Opcom]

Amplfied Zeners are perfectly great. The FET verion suggested there is the modern way to go and handles more juice than my circuit Please try it and let us know how it performs. I am not a FET expert but might have concerns about Vth and its effect on the system at different current levels.

A bipolar version for regulating bias is attached. I made this for modding some old amplifiers and it is totally reliable. The zener and its resistors draw enough current to make sure base drive is not wanting. It was put between the B+ transformer center tap and ground and handles a wide current range with stable voltage. The shunt can easily handle 200mA and if used for a negative voltage the TO-3 case, the collector, can be bolted right to the chassis very conveniently.

[KK4YY]

Patrick,

I'm not familiar with the term "Vth". Can you spell that one out for me?

The "necessity" that brought me to this was the fact that I have a tube of N-channel 'FETS and not a single P-channel. I'm also short on PNP transistors. Both "P" devices have their own challenges too. Using the two-terminal amplified zener on both sides of a dual rail supply looked like an elegant solution... if it works. I will give it a try.

Don

[KK4YY]

Attached is an updated sketch for use in my DX-100. This may be used to provide regulated +/- rails for the MOSFET source-follower modulator drivers.

Don

[Opcom]

Vth is the threshold voltage to get the FET to start conducting. Had to deal with this at work when some operation was near that point. Its exact value determines for a particular FET the device's conduction in that region of operation where low currents are wanted to be regulated. In some gear we used to test the devices there were precise adjustments for bias to accommodate this. I don't know if minute variations in that parameter will have any effect on the exact regulation.

There is a decent animation of this here:
https://en.wikipedia.org/wiki/Threshold_voltage

[KK4YY]

Patrick,

Ahh. I see. That's stated as "Vgs(th)" on the STMicro datasheet for the device I'm using. Well, it's a feedback loop so as long as it doesn't oscillate...
It may require some damping here or there as well as a good layout and a heat sink that keeps it cool. I placed C1 at 10uf to hopefully keep it more or less settled down. We'll see.


Don

[WBear2GCR]

Watch out for Vdrop WRT power dissapated... generally speaking for lower current applications,
not much to be concerned with. But dropping 100+ volts with some current flowing = many watts of heat.
Sometimes it's more effective to use a series regulator and then the shunt... it also improves the regulation
and drops noise (although noise is not a consideration here).

          _-_-

[KK4YY]

Bear,

What's a WRT???

The way I've set it up, most of the heat will be dissipated by the series dropping resistor(s) - unloading the 'FET (also protecting it from overload and decreasing the size of the heatsink). I chose 50mA as a starting point but that will be adjusted depending on the amount of current needed, which I don't know at this time. The shunt regulator draws a constant current from the supply regardless of load placed on it which, hopefully, being small, won't be an issue. But hey, if I was really worried about heat generation I wouldn't be starting with a DX-100!

If power supply noise and ripple are passed though they should be negligible even if the zeners themselves contribute some to it. We'll see. My use of a shunt regulator is a work-around so that I can use N-channel 'FETs on the negative rail. If it all goes wrong I'll have to buy a P-channel 'FET and re-do it. I may go with a series regulator on the positive rail anyway... haven't decided yet.

I'm enjoying working these things out and getting the feedback and ideas from those who post here, thanks.

Don

[KD6VXI]

With
Regards
To



--Shane
KD6VXI

[KK4YY]

Back to Texting 101 for me!

[KK4YY]

Well, I found a nice Triad N-68X isolation transformer in the junk-box yesterday. 
With it, I can use series regulators as shown in the attached schematic which I drew last evening. I can also borrow from it to run the screen of the VFO tube and ditch the VR tube on the DX-100.

Don