My take on a discrete shunt voltage regulator

[stormsonic]

Iko, thank you.
About other parts, how critical is this?
Much easier to find 2SK170 in Europe as MPSH81 (must be ordered from USA)

[ikoflexer]

That's a tough one. We need an RF part here, this is a critical position. Let's start looking for a replacement: RF, PNP, Vceo more than 20V.

Alternatively, let's look for cheap sources for the mpsh81 in Europa too.

[stormsonic]

Ebay is cheaper & faster, delivery is slower

Last time searched for MPSA18 and found 2SK389V (NOS)
Ordered 2 pcs few days ago, awaiting delivery to see if they are real Toshibas or fake

[ikoflexer]

Good score!

There's a super guy on ebay that sells mpsa18 cheap, and delivery is cheap too.

[HiFiNutNut]

In the schematic you gave me, you modelled the load to be 350mA and the CCS 650mA. Why does the CCS nearly double the load? If the load is worked out to be absolutely no more than 350mA, could I set CCS 350mA, or 400mA? Is there a technical reason behind that (rather than lowering the output impedance) or just for a safeguard ?

With regards to lowering the output impedance, you mentioned and I understand that the higher the shunt current flows, the lower the output impedance becomes. I increased the current from 100mA to 150mA in v1 and found I liked the sound better. From your modelling, how much the impedance decreases versus current increases? In page 1, does the impedance graph correspond to the schematic there which runs 200mA current?

I asked the questions because I am working out the heatsink requirement for my application. Unless the regulator uses power amplifier like heatsinks, the best individual smaller size (still quite bulky) heatsinks would be rated at around 7 degree W. Adding the insulation pad makes it 9 degree W. To dissipate a moderate 7 W (650mA) per heatsink would add 63 degrees, and plus room temporature in Summer (my home can get 33 degrees many days, not talking about extream weather of 40 degrees happened last year) the temporature can approach 100 degrees. I would prefer to run the MOSFETs at less than 70 degrees. It is for the long life of the device and more importantly, safety.

Edit: I read page 1 where you mentioned that the shunt current may be set to 10-20% of the load current. I guess that is good for class A amplifier where the load is constant current. So the CCS would be set to 110%-130% of the required constant current. However, in my application of running opamps in class B, current demand varies. But I guess it would never be more than 200mA-250mA, as I use fairly high impedance load.

[ikoflexer]

Originally Posted by HiFiNutNut

In the schematic you gave me, you modelled the load to be 350mA and the CCS 650mA. Why does the CCS nearly double the load? If the load is worked out to be absolutely no more than 350mA, could I set CCS 350mA, or 400mA? Is there a technical reason behind that (rather than lowering the output impedance) or just for a safeguard ?

It just happened to be an image of the circuit after I was simulating that load, no particular significance. Often I push the circuit to extremes to see how it behaves.

With regards to lowering the output impedance, you mentioned and I understand that the higher the shunt current flows, the lower the output impedance becomes. I increased the current from 100mA to 150mA in v1 and found I liked the sound better. From your modelling, how much the impedance decreases versus current increases? In page 1, does the impedance graph correspond to the schematic there which runs 200mA current?

Hard to quantify because Zout is a function of frequency and it doesn't lower equally everywhere. Suffice to say that increasing the shunt current by 50mA doesn't lower Zout much.

Edit: I read page 1 where you mentioned that the shunt current may be set to 10-20% of the load current. I guess that is good for class A amplifier where the load is constant current. So the CCS would be set to 110%-130% of the required constant current. However, in my application of running opamps in class B, current demand varies. But I guess it would never be more than 200mA-250mA, as I use fairly high impedance load.

I will refrain from giving exact rules because I don't think they will apply. Best is to make sure the shunt works well first at 10-20% of the load; when you're reasonably sure this is the case, then increase the current and voice the device. Before doing this in the real audio chain, it would be good to have done it with a passive load and prepare several resistors knowing what shunt current they'll give. This is how I would do it. Remember that all the generalities that people talk about with class A and B cases are that, just generalities. Those rules do apply, in general. For your specific case I think it's best that you adjust the shunt in real life for the case at hand. IMHO, if you put so much effort already into your first class system, then it's not too much to do the same with a bit of tweaking on the regulator. You can also bypass all this and set the shunt current much higher than you think you need it, perhaps to 1.5A and call it a day Just make sure you get adequate heat sinks.

[Tham]

Iko, will receive my Phonoclone 3 kit soon after a long wait...and thinking of trying it with v2 shunts. Would appreciate if you could post a schematic for a +12v and -12v version for this purpose .

[ikoflexer]

Tham, please read carefully post #1 in this thread. The schematics show there have not changed. You'll need to tweak the resistors in the voltage reference to get the output voltage you want, as well as the resistor in the mini-CCS to get the current right.

[Tham]

Iko, other than R9 & R11 to adjust for 12v output and adjustment for current output, any other changes (MOSFET, etc) necessary?

[ikoflexer]

R2 must be adjusted so you get the current you want. When you get your parts let me know what they are, if you're planning to use different mosfets, jfets, and/or bjts. Then I can say if something must be changed to make it work or not.