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I need a 350V, 1A PSU

poormystic

Jul 23, 2023
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Hi people
I want to play with high voltage piezoelectric transducers. To drive these highly capacitive devices I need a low impedance, stable 350V d.c. supply. I'd like to have 1A of smooth 350V current available.
Naturally I remembered *steve* who often said that Google is your friend (but maybe all that's changed). I found through my Google search that wonderful amplifiers can be had at about 8 big ones, but (did you guess) that doesn't suit.
So a DC supply looks like my best option, and really I would like to do better than variac control.
 
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Bluejets

Oct 5, 2014
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Depends on your country and your mains supply voltage.

If you use a 1:1 240v ac transformer and rectify and smooth the output , it will get you to around 340V DC.
Or say a 240-12 and then reverse with another 12-240 it should be around the same.
Do NOT try connection direct to mains as the fault current will blow your head off (if you are lucky).
 

AnalogKid

Jun 10, 2015
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Fixed 350 Vdc or adjustable over a range?

What is the minimum output current expected? Some supplies have a minimum output current requirement; below that amount, the output regulation becomes unstable, the output impedance increases, etc.

What does "smooth" mean? Filtered but with some residual ripple, or regulated?

Where are you located?

Also, what is your experience base and/or skill set for working with electric circuits that can kill you in less time than it takes to fall to the floor?

AND, why do you think [imath]800 is too much to pay for a single piece of a 400 W power supply?[/imath]2 per watt for a low quantity of a specialized product with full safety certifications is cheap.

ak
 
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Bluejets

Oct 5, 2014
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AND, why do you think 800istoomuchtopayforasinglepieceofa400Wpowersupply?800 is too much to pay for a single piece of a 400 W power supply?800istoomuchtopayforasinglepieceofa400Wpowersupply?
Seems to me 800 is wayyyyyy over the top also.............
 

poormystic

Jul 23, 2023
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For clarification ~ I'd like my supply to be better than just a Variac-fed diode bridge and capacitors - I want proper regulation.
At this stage, because I can't afford the cost of the manufactured supplies, I am thinking of an unregulated supply followed by an adjustable regulator based on a common 3- terminal regulator. However I think there's a lot to go wrong with that kind of engineering - puts the base of a transistor so far up in the sky that something's bound to go wrong. My instincts just don't like it.
Ok so I could also do all my regulation at low voltage as AC and then transformer it up to what I want, but then I'm dealing with huge low voltage currents, and a step-up transformer must be made to order. Hence the attraction to the idea that I might be able to post-regulate. I'm not really convinced it's a good idea.
 

poormystic

Jul 23, 2023
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As
Fixed 350 Vdc or adjustable over a range?

What is the minimum output current expected? Some supplies have a minimum output current requirement; below that amount, the output regulation becomes unstable, the output impedance increases, etc.

What does "smooth" mean? Filtered but with some residual ripple, or regulated?

Where are you located?

Also, what is your experience base and/or skill set for working with electric circuits that can kill you in less time than it takes to fall to the floor?

AND, why do you think [imath]800 is too much to pay for a single piece of a 400 W power supply?[/imath]2 per watt for a low quantity of a specialized product with full safety certifications is cheap.

ak
I am a qualified and registered technician with 6 years government/corporate experience and lots of little engineering projects under my belt. I do know what I'm about - just looking for ideas is all
:)
 

Harald Kapp

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Here's a linear regulator for up to 450 V.
Drawback: only 10 mA output current. But you can boost the current by using an external pass transistor as shown e.g. here.

Note that the power dissipation will probably very high and the components need good cooling (heatsink, fan). Also observe all applicable safety regulations (insulation, fusing, overload protection etc.). You're dealing with dangerous levels of voltage and power.

Safety first is the maxim.
 

bertus

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Nov 8, 2019
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hello,

have a look at this page for an idea:

bertus
 

AnalogKid

Jun 10, 2015
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A power Factor correcting (PFC) front end is a regulated boost converter. Usually these are non-isolated. One of these plus a 1:1 isolation transformer could do what you want. You might have to post-regulate it to reduce the high-frequency ripple.

Is a 350 V output switcher a possibility, of do you require a linear supply?

ak
 

AnalogKid

Jun 10, 2015
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Here's a linear regulator for up to 450 V.
Harris used to make something similar, in a TO-220 package for higher output current. I think they are all obsolete now.

Note that the grand old LM317 will work in this application. It's 43 V rating is for the voltage from its input to its output, not from its input to GND.
 

AnalogKid

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Based on that post, here's a plan.

1:1 or 1:2 isolation transformer plus a low voltage transformer gets you a peak voltage after rectification of 370 V. With lotsa filter capacitance, the ripple voltage minimums are around 355 V to 360 V. An LM317 regulates this to a flat 350 V.

ak
 

poormystic

Jul 23, 2023
30
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Jul 23, 2023
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Hi people
I want to play with high voltage piezoelectric transducers. To drive these highly capacitive devices I need a low impedance, stable 350V d.c. supply. I'd like to have 1A of smooth 350V current available.
Naturally I remembered *steve* who often said that Google is your friend (but maybe all that's changed). I found through my Google search that wonderful amplifiers can be had at about 8 big ones, but (did you guess) that doesn't suit.
So a DC supply looks like my best option, and really I would like to do better than variac control.
Here's a linear regulator for up to 450 V.
Drawback: only 10 mA output current. But you can boost the current by using an external pass transistor as shown e.g. here.

Note that the power dissipation will probably very high and the components need good cooling (heatsink, fan). Also observe all applicable safety regulations (insulation, fusing, overload protection etc.). You're dealing with dangerous levels of voltage and power.

Safety first is the maxim.
Thank you very much for your time on this. I've seen that there are kind professional people on this forum.
:)
 

poormystic

Jul 23, 2023
30
Joined
Jul 23, 2023
Messages
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Based on that post, here's a plan.

1:1 or 1:2 isolation transformer plus a low voltage transformer gets you a peak voltage after rectification of 370 V. With lotsa filter capacitance, the ripple voltage minimums are around 355 V to 360 V. An LM317 regulates this to a flat 350 V.

ak
Yes, that's about where I was at when I stalled because of the LM317.
Now I've heard of the LR8N-3G, courtesy of Harald Kapp.

I looked at the circuits he pointed me to, and I'm settled-at-the-moment on using a Variac into an isolation transformer and then straight into the diode bridge and smoothing caps.
Then, the rough DC at up to 350V can lose a few volts to the high voltage regulator he recommends and voila! A regulated supply!
 
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poormystic

Jul 23, 2023
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hello,

have a look at this page for an idea:

bertus
Thank you very much for this suggestion, although the power supply doesn't quite fit my needs.
Things are supposed to get a bit industrial 'round here, and lotsa watts are going to happen :)
(Exactly what I'm up to I'll keep mum about just yet ;) )
 

AnalogKid

Jun 10, 2015
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The LR8 has a max output current of 30 mA, and there is no application circuit in the datasheet to boost this. Also, its minimum input-to-output differential voltage is 12 V, while the LM317's is around 2 V at a 1 A output current..

ak
 

poormystic

Jul 23, 2023
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The LR8 has a max output current of 30 mA, and there is no application circuit in the datasheet to boost this. Also, its minimum input-to-output differential voltage is 12 V, while the LM317's is around 2 V at a 1 A output current..

ak
Mr Kapp kindly provided a link to a suitable current amplifier, which comprises a fat transistor arranged around the 3 terminal regulator.
I feel pretty happy about the circuit he suggested.
:)
 
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