Simple HV series regulators

[Elvee]

Here are some examples of simple, cheap, medium performance regulators.

They are in the same league as Maida's for example, but are completely discrete.
This means a slightly increased complexity, but also more flexibility and less failure mechanisms.

Key attributes are:

• Quiescent current <1.5mA
• Low drop-out (limited to the threshold voltage of the pass element)
• Only one high-voltage or power device: the pass element itself
• No minimum or maximum current: they regulate from an open output to a maximum load limited only by the pass element/heatsinking
• Stable, rugged, quiet and tolerant

The ripple rejection is shown at 100Hz, for an input voltage of 350V to 450V, first with a load of 10K (30mA), then with no-load, and finally with 1K (300mA)

Next is the output voltage, with a load current varying between 10mA and 110mA, at 1KHz.
And finally, the same in the frequency domain.

Notes: R8 has no physical existence, its purpose is to indicate the proper layout: R5 placed upstream of D1/output node.
The circuit has been tested with an IRF830

[Elvee]

Next version uses bypasses to improve rejection/output impedance.

Protection diodes have been added, to improve the survivability in case of unexpected events that may discharge the capacitors into the semi's.

Same pictures as above, plus a variant utilizing a different compensation scheme.
For that one, the performances are somewhat improved, but at the expense of the transient behavior.

[Elvee]

Finally, any of the previous circuits can be fitted with a current limiter, to improve survivability.

Since in high voltage circuits, the SOAR could easily be exceeded, it will generally be necessary to include a folback mechanism.

Here, R9 determines the current limit, and R11 the amount of folding: for R11=∞, there is no folding, only pure current limit.
R11 cannot be made too small, as the circuit may have difficulties starting up.

If Q3 is in thermal contact with M1, it will also modulate the limit according to the temperature of the pass element, and may act as a thermal shutdown.

The first pic shows the output current at the onset of the limiting, and the second shows what happens when it is exceeded.

[Elvee]

One more thing, the behavior in temperature, between -25°C and +75°C:

[esl 63]

Elvee, can you make your regulator work at 4 times your voltage? I need a good voltage regulator for GM70 triode, 1200volts... can not find a regulator for those voltages.

[quadtech]

Nice. How about soft start too?

[Elvee]

Originally Posted by esl 63

Elvee, can you make your regulator work at 4 times your voltage? I need a good voltage regulator for GM70 triode, 1200volts... can not find a regulator for those voltages.

There are two aspects to consider here.
One is the input to output differential, and the other is the absolute voltage above ground.

In principle, to regulate high voltages, you don't need high voltage devices: in order to regulate 1200V with a 1225V input, a LM317 would in theory suffice.
In practice, it would be destroyed in a matter of seconds.

Regarding the absolute level of voltage above ground, this regulator is well suited to handle it: there is no voltage-translation circuit from the ground, just resistors, and this makes it very resilient.

To build your regulator, you have basically two options: either you build a circuit that is only capable of handling the input/output differential, with comfortable regulations margins, using a 800V device for example, but then you are not allowed soft-start or current limitation, or anything that requires the MOS to block the full voltage, or you use a 1500V+ device that will allow you the full feature, and will also increase the general ruggedness.
Something like this for example:
http://www.st.com/internet/com/TECHN...CD00050744.pdf

Here is the basic regulator adapted for 1200V. A 600V transistor is sufficient, provided you don't have a large decoupling cap to charge at the output.

With a 1500V MOS, it will be more tolerant to mishaps.

But if you really want something bullet-proof, you can turn to glass: the schematic is highly flexible, and can readily be transfered to vacuum, either a power triode or a pentode, see example.

[Elvee]

Originally Posted by quadtech

Nice. How about soft start too?

That feature is already included: it is inherent to the bypassed versions, see below the start up sequence:

[tim845]

Nice. Would you qoute the value of R2, R3, R4 in post #7.

[Elvee]

Originally Posted by tim845

Nice. Would you qoute the value of R2, R3, R4 in post #7.

e6 = megohm: 10 to the 6th power.
I forgot to change to a more "civilized" unit.