Tubecad HV regulator - Modifcation- OCP? - diyAudio
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Old 23rd November 2008, 12:49 PM   #1
dtproff is offline dtproff  United States
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Default Tubecad HV regulator - Modifcation- OCP?

I'm about ready to cut a board based on a version of Brodskies VH linear regulator. I made a couple modifications. Anywone see anything major wrong?

What I would like to add is an over current latch off. But I'm stumped. Getting too old for this stuf anymore. know I can add alatch to the ground side and do it that way butu I wan really hoping to use the other half of the amp on the LM2904 with a diode across it to latch off the other amp.

I like Brodskies new regulator but not the choice of linear regulator. Almost all linear regulators have very poor noise performance. I've done similar things with a TL431 shunt regulator before and they work OK but most if the linears have an issue beyound about 3KHz so I was hoping this amp based version would give a bit more performance.


Any one with a suggestion?

schematic and output waveform included.
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Old 24th November 2008, 04:27 AM   #2
dtproff is offline dtproff  United States
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So I had time to sleep on it. I think this is it.

Here is the final version of the schematic with an OCP latch off.

Let me know if anyone spots something obvious.

I'll bread board it in a couple weeks and post some results.

Tony
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Old 24th November 2008, 05:05 AM   #3
Eva is offline Eva  Spain
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The latch is both susceptible to self triggering and self destruction.

Output transistor needs a base-emitter resistor for charge removal.

U2 and D3 are likely to be destroyed on every output overload event.

D4 is useless.

The topology is not very good. Op-amp current consumption will cause deviations in output voltage.
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Old 24th November 2008, 02:02 PM   #4
dtproff is offline dtproff  United States
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Eva;

Thanks for taking the time to reply. Good comments.

I agree with you on the base emittier resistor

U2/D3 should be safe (I think) since the whole circuit runs off the current limitted IXxxx 10mA current source. Of courrse I could be wrong and am certianly willing to admit a mistake... I'm just a slow learner so if you can see a current path I'v overlooked I would appreciate the feedback.

You are correct on D4... There used to be a cap there and I still may add it back so at least for the tiime being I'll keep D4 in place.

You are currect about the converter consumption effecting the regulator that works out to 40uV/V output.

Do you have a linear HV supply handy or would you have done a buck converter?

Thanks again for taking the time to post. Comments are always appreciated.

Tony
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Old 26th November 2008, 04:14 AM   #5
Eva is offline Eva  Spain
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How about implementing current limiting with a single transistor that shunts base drive as in current sources? You could even use the remaining op-amp for thermal shutdown.

The problem is that 47uF and 100uF charged to 200V store a significant amount of energy, usually enough to blow small diodes or anything not rugged enough and trying to carry the current in case of an output short.

The latch may self destruct too because it's connected across the 10uF capacitor and peak discharge current is only limited by internal transistor resistances and high current gain roll-off.
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Old 26th November 2008, 09:36 AM   #6
dtproff is offline dtproff  United States
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After my email yesterday I did go back and look at the current through the diode. Ipk hits about 1A. That part will need to change.

I thought about using the base as a shoutdown but thought the amplifier would eventually blow up if it railed into 10V... Maybe I'll go rerun some simulations.

I also have a version of this linear design using a TL431 to replace the expensive IXYS part. We'll see which part gets implemented next week. I am still in China through the end of next week so I won't be back in the states and working on the bread board for at least 10 days.

I do have a DC/DC buck that I could put in it's place. I'll post the schematic sometime this week after I run a few more simulations. I may even breadboard it since it is a fairly simple design as long as the loop is ignored and a simple Zener is used as the regulator reference voltage.

BTW if you need an easy thermal shutdown, the PTC thermal switch works well and only needs a simple 2N7002 for an implementation instead of an op amp. See Epscos P/N B59701A0110A062 and I believe that Thinking Electronics has an alternate.

I wanted you to know that I do appreciate your responses.

Tony
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Old 26th November 2008, 10:25 AM   #7
Eva is offline Eva  Spain
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Power integrations TinySwitch ICs are great as buck regulators, both the LNK3xx and the TNY2xx. An HCPL4504 may be employed to level shift the error signal without dV/dt problems, as conventional optocouplers suffer from false triggering.

Output noise due to pulse density modulation may be made very small with an high value output capacitor and additional LC stages.

Up to .25A 400V output with no heatsinks (TNY268)
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Old 26th November 2008, 01:29 PM   #8
dtproff is offline dtproff  United States
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I've done the same thing using a NCP1012 and an optoisolator as the level shifter.

It's a good circuit and fairly bullet proof. What I didn't like is the zener I used as a Vref. It's stability over temp is pretty bad. I may end up using a TL431 but will have to generate another voltage to run it off of I don't like pulling 1mA from the 250V rail for one stinking part.

Anyway that's my thinking tonight. Maybe I'll change my mind again bfore I get home to bread board this thing.

Tony
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