High Voltage Regulators (Maida or zener)

[tomchr]

Originally Posted by mr2racer

Is there a high voltage regulator PC board or kit that would work with a power amp? I don't know from transistors but from what I've seen they don't look like they would work point to point. I've seen schematics for Salas and Maida. But a PC board would make it much easier.

Kevin

Kevin,

Once I get mine debugged I intend to put it on a PCB and have the PCB professionally made. I'll have spares and would be happy to sell you one. Just shoot me a PM if you're interested and can wait a few weeks while I develop this.

My needs are 470 V, 200 mA but it could be tailored to other output voltages as well. The current needs to stay within the SOA of the components used.

~Tom

[tomchr]

Oh.... Note to self: The NPN darlington needs to be operating within its SOA during start-up. I knew that... I bet that's the cause of the fried silicon.

The FJPF5027 I'm using only handles about 20 mA at 600 V Vce. Granted, it shouldn't see that much voltage for very long, but it does need to charge the capacitors in the amp...

~Tom

[aardvarkash10]

Originally Posted by mr2racer

Hey All,

Is there a high voltage regulator PC board or kit that would work with a power amp? I don't know from transistors but from what I've seen they don't look like they would work point to point. I've seen schematics for Salas and Maida. But a PC board would make it much easier.

Kevin

or try this from Giaime

[tomchr]

Yeah..... It's the in-rush that kills the Maida cascode device. My spice sim hows the 47 uF cathode cap in my 300B amp draws 650 mA inrush. The cathode resistor is 725 ohm. 470/725 = 0.65 or 650 mA...

Way above the SOA of the wimpy cascode devices I'm using. I'm currently eying out some 800 V ~ 1 kV, 10+ A MOSFET devices on Digikey.

Of course, one could change from the Loftin-White topology to using a regular grounded cathode cap. That way only 200 mA is needed during start-up. The drawback of this approach would be that the 200 mA is sourced through the 300B tube. In addition, it complicates the signal path. Simplifying - and shortening - the signal path is the whole point of the Loftin-White circuit. The original L-W circuit from 1930 also included some hum-reducing circuit but with DC heated filaments I don't really see a need for that.

~Tom

[mr2racer]

Hey Guys,

Has anyone seen these? They have stupid high voltage ratings. I don't know if they would work in a regulator. That kind of engineering is beyond me.

http://www.st.com/internet/analog/subclass/1229.jsp

Kevin

[Elvee]

A discrete, protected regulator using a MOS ballast will be much more resilient than any BJT or 317 alternative.
Here is an example of such a regulator that could easily be adapated for other voltages/polarity:
Need Negative High Voltage Regulator Circuit
It doesnt compromise on performances either.

[Rod Coleman]

Originally Posted by Elvee

A discrete, protected regulator using a MOS ballast will be much more resilient than any BJT or 317 alternative.
Here is an example of such a regulator that could easily be adapated for other voltages/polarity:
Need Negative High Voltage Regulator Circuit
It doesnt compromise on performances either.

I agree - a regulator with a single pass element should be capable of better dynamic performance than a "stacked" IC regulator. And better durability.

Have you built the circuit on the linked page? I am wondering about the aggressive pole formed by R3 and C1 - and the risk of oscillation at 500k .. 5MHz with that response. Does R4 zero it in time?

I prefer non-LDO circuits at high voltage though - the drain-output configuration in LDOs is much harder to tame, due to the open-loop behaviour, and difficulty with capacitive loads.

Thanks for linking the circuit, though - I always enjoy a good discrete design to check out.

[Elvee]

Originally Posted by Rod Coleman

Have you built the circuit on the linked page? I am wondering about the aggressive pole formed by R3 and C1 - and the risk of oscillation at 500k .. 5MHz with that response. Does R4 zero it in time?

I didn't build exactly that version of the circuit, but I tried a number of similar ones.

The schematic is bit misleading, because it upside down, but if you look more closely, you'll see that those components create in fact a zero, not a pole.

[Sheldon]

Originally Posted by tomchr

The original L-W circuit from 1930 also included some hum-reducing circuit but with DC heated filaments I don't really see a need for that.

Side topic for this thread, but the noise canceling in the original L-W was not for the filaments, but for the power supply. They didn't have access to large value caps, so quiet supplies were expensive. You could easily incorporate the cancellation circuit in you design, if you replace the 3V bias supply with a resistor. That resistor becomes part of a divider to divide down a signal taken from the output tube cathode, by the ratio of the u of the input tube. If you include a trim pot as part of the divider, you can null out the power supply noise completely.

In the original design, the input tube and output tube shared a supply and the ripple phase is the same for both, so the noise for both is nulled. In your case, the noise for the output would be nulled, but not for the driver. If you are regulating both, it's probably a moot point. If you are regulating only the driver, then it is worth considering.

Sheldon

[tomchr]

Originally Posted by Rod Coleman

I agree - a regulator with a single pass element should be capable of better dynamic performance than a "stacked" IC regulator. And better durability.

I disagree, actually. Run a sim of the loop gain and it's pretty easy to convince yourself of the advantages of the IC regulators. You do have to ensure that the cascode device will operate within its SOA under all operating conditions. If the cascode fries, so will the IC.

It's the same level of reliability for the discrete regulator. If the pass device in the discrete regulator fries due to operation outside its SOA, the regulator won't regulate.

~Tom