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High Voltage Regulated Tube Supply
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johnnyc
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31st October 2009
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High Voltage Regulated Tube Supply

I've mostly dealt with tube guitar amps but want to start building some tube recording gear. Anyone have a good resource/schematic for a regulated tube supply? Is there a 317 equivalent for 250-300V?
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31st October 2009
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I'm not aware of any IC that will do it. I doubt there is one.

I saw a design once that used a 6V6 as a servo. I think it was in Glass Audio. But, to be honest, given the scarcity of anything other than linear unregulated power supplies in tube designs, it sounds like overkill - not that overkill is a bad thing.
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31st October 2009
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What....

No sag!
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I don't have a schematic but IIRC the Peavey valve Comp/limiter regulated the supply. Probably used a common low voltage regulator chip with some glue parts around it to scale output up, and feedback back down..

There may be some ideas in regulator app notes for general direction to take.

JR
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1st November 2009
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You may use this one. Actually bias shunt regulator is an output current sensor for soft start of B+ since they are in series. Speed of increase of B+ depends on the current that is drawn from it by load, so it starts going up faster as soon as tubes are warmed up. Very intelligent and gentle start-up.

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1st November 2009
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Quote:
Originally Posted by johnnyc View Post
I've mostly dealt with tube guitar amps but want to start building some tube recording gear. Anyone have a good resource/schematic for a regulated tube supply? Is there a 317 equivalent for 250-300V?
TL783.

The 723 can be used in a floating configuration for regulating high voltage.
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1st November 2009
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International Power (and probably others) sells an open frame linear module adjustable between 215 and 265 VDC at 100 mA. Mouser stocks it as part number 597-B250-0.1 for $46.15.

Now that I look, MPJA also stocks that same unit for $43.84:

215-265V @ .10A LINEAR POWER SUPPLY IHB250-0.10-MPJA, Inc.

Bri
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1st November 2009
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IMHO, unregulated (but well filtered) is the way to give life to all tube circuits. Because they behave dynamically with regards to the circuits demands, they're voltage will drop with high current demand - ie, sag, but the tubes in the circuit understand this and all their characteristics change along with it - in a way that a transistor will not. With tube rectification the power supply behaves even more sympathetically with the circuit. well, that's what I hear at least

nothing like an all tube circuit powered by a saggy tube power supply! that's where the magic is
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some good stuff to get me started. thanks guys.
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2nd November 2009
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Quote:
Originally Posted by Lee Cardan View Post
IMHO, unregulated (but well filtered) is the way to give life to all tube circuits. Because they behave dynamically with regards to the circuits demands, they're voltage will drop with high current demand - ie, sag, but the tubes in the circuit understand this and all their characteristics change along with it - in a way that a transistor will not. With tube rectification the power supply behaves even more sympathetically with the circuit. well, that's what I hear at least

nothing like an all tube circuit powered by a saggy tube power supply! that's where the magic is
It is one of urban legends. Actually, only consumers of military and precision measurement / test equipments could afford voltage regulators during the all-tube era.
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2nd November 2009
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noooo don't listen to the evil man above!

electrically, I have to agree with Wavebourn

but still... I can't deny what I hear
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2nd November 2009
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For mic/line amps I'd say go with an unregulated supply(assuming you want to build from scratch). Many good broadcast quality designs from the golden era used no regulation. From my experience building pre amps, I see no need for it either. Tubes are very tolerant to supply changes - you don't really hear a difference in changes caused by normal line fluctuations in these type circuits. No real need for DC on the filaments either. There's an assortment of simple floating arrangements or the standard 100ohm pot usually works great.

As for sag, in low current apps you certainly won't hear it like you would in a guitar amp.

For the big push pull limiters using power tubes it may be a different story. The Gates SA-39 for example does use a regulated supply for the first stages as well as DC on the heaters. For more critical detail on these type circuits best bet is over at Prodigy - lots of details to consider.

Happy building
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2nd November 2009
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Quote:
Originally Posted by Wavebourn View Post
It is one of urban legends. Actually, only consumers of military and precision measurement / test equipments could afford voltage regulators during the all-tube era.
I find myself in full agreement with Waveborn's comment ...

JR

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3rd November 2009
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Quote:
Originally Posted by gyraf View Post
http://www.gyraf.dk/gy_pd/g9/g9_sch.gif

TL783 with some simple protection surroundings

Jakob E.
This is nice and simple circuit, i used it several times. The only problem is that TL783 can be hard to find. Also, this psu needs 2-3mA through it to start to function.

I just built this psu and i have some questions; there are two caps before and after 5W resistor near gretz. Author says they can have even 400uF. This would make psu quite big as there are two more 450V caps.
I would like to know if i can replace the second cap near first 5W resistor with something much smaller, 10u or 47u? What would the effect of, say, 47u cap be? I guess i have enough filtering with nice big cap at the input and output.
What about the cap near zener string, does it really need to be that big? I've seen some other schematics with much much smaller caps at that position. Would that make big difference? Why?

Miha
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4th November 2009
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Quote:
Originally Posted by rotation View Post
I just built this psu and i have some questions; there are two caps before and after 5W resistor near gretz. Author says they can have even 400uF. This would make psu quite big as there are two more 450V caps.
I would like to know if i can replace the second cap near first 5W resistor with something much smaller, 10u or 47u? What would the effect of, say, 47u cap be? I guess i have enough filtering with nice big cap at the input and output.
What about the cap near zener string, does it really need to be that big? I've seen some other schematics with much much smaller caps at that position. Would that make big difference? Why?
You can't know how much capacitance you need without knowing your expected range of current draw.

The size of the capacitors determines how much filtering you get. If the caps are too small, you'll have some ripple (hum) left on the supply, which could find its way into your audio. Smaller capacitors will also increase the extent to which a variable current draw can modulate the DC supply voltage - something alluded to earlier in this thread ("sag" has become a part of the sound of tube guitar amps, but something you generally don't want in line-level circuits). On the other hand, if the capacitors are too big, your transformer and rectifier may have trouble charging them at start-up and you'll get nuisance fuse blows. So how much capacitance do you need? Enough to avoid audible hum in the audio circuit, and avoid any unwanted sag in the power supply (if you want some sag, then the amount you want will still determine how much capacity you need).

In addition to the capacitance, the stiffness of the supply will be determined by the current draw, the series resistance, the "regulation" spec of the power transformer, and the mains frequency. More current draw will discharge the caps more quickly, leaving you with more ripple for a given capacitance. More series resistance will improve the filtering of the capacitors, but will produce a current-dependent voltage drop across that resistance. Likewise, the transformer represents a non-zero impedance that will drop volts proportional to current draw. And 60Hz mains power charges the caps more frequently than 50Hz mains power (and a full-wave rectifier charges them twice as often as a half-wave rectifier). You'll want to choose the value of the series resistor and the filter capacitors in the context of your current needs. It looks like this drawing was made as part of a power amp design. If you're using it to power line-level circuitry, your current draw will probably be substantially lower, and so will your capacitance requirement.

But the biggest factor in your particular circuit is that TIP50 transistor. It's behaving simultaneously as a voltage limiter and a filter known as a "capacitance multiplier". The output of the transistor at its emitter likes to stay about two-thirds of a volt below the voltage on its base. This allows the zener diode on the base to limit the output voltage without requiring the zener (and the resistor feeding it) to handle ALL of the excess power. At the same time, the voltage on the base is filtered by an additional RC filter stage that is not loaded by the output of the supply. The effect is that the capacitance on the base of the transistor is multiplied by the Hfe (DC current gain) of the transistor. This has the general effect of requiring less total capacitance in the supply, but you have to make sure the ripple coming into the transistor doesn't allow the voltage to drop, even momentarily, below the desired output.

I like this circuit a lot, and I've used it many times in a number of projects and products. It can be thought of as a "Voltage Limiter" rather than a regulator. It works best when you choose the Zener diode to set some safe upper limit to the output voltage. If the input voltage is lower than the Zener voltage, the Zener stops conducting and the Capacitance Multiplier aspect of the circuit continues filtering happily. In other words, this circuit doesn't really have a "dropout voltage" like most voltage regulators do. Feed less than 26V into a fixed 24V regulator, for example, and you get no regulation and no filtering. When this circuit gets less voltage than it's expecting, it still works just fine and still filters very effectively.

The base resistor needs to be selected carefully to produce optimum output voltage and current capacity without overheating. The base current (which is output current divided by the Hfe of the transistor) and the Zener current will both flow through the resistor, causing a voltage drop across it. In order to determine the best value, you need to know the maximum and minimum input voltages the circuit will see, the maximum and minimum current draw of the circuit being powered, and the desired output voltage (and Zener voltage). It's a fairly involved set of calculations, but relatively straightforward and only requires some basic algebra applied to Ohm's Law.

The one thing you should keep in mind about this circuit as it's drawn is that there's no short-circuit protection. In theory, if you size the base resistor just right, you get some degree of current limiting. But if you short the output, you'll dissipate some watts in the transistor and may destroy it. As long as the rated Vce of the transistor is higher than the input voltage, destruction won't be automatic.
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4th November 2009
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Huh, very detailed reply, it's nice from you, thanks. I will need some time for calculations and thinking, but i will come back.
I'm powering tube mic preamp, i have 230V at the output of trafo, around 320V rectified, 3x91V/5W zeners and 273V output. Current consumption is around 20mA, i'm not sure how much it changes.? All values in psu are the same as on schematic.
I completely forgot i have capacitance multiplier here. Datasheets state different Hfe for different working points, from 25-150. I'm not sure how i calculate this, but even if i take Hfe of 25 and 47u cap, i get a lot of capacitance. I guess i can take away output cap and replace base cap with 47u.


People taught me to not believe in "regulated vs unregulated psu are sounding different". I tried Jakob's version, this psu, and several other well designed CRC unregulated psu-s. There WAS noticeable difference in sound. I'm not going to comment what i heard in highs, but i'm 100% sure there was a difference in bass, it became a little tighter with regulated. I think that regulated also changed the way my circuit handled transients.
This psu made biggest difference, it sounds like something is wrong. I probably used too much capacitance, don't really know. My cap to base of TIP50 is 330u at the moment, and the rest of caps are all 150u or more.

Miha
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5th November 2009
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I wouldn't take away the output capacitor. It doesn't need to be very big, but leave it in there. And I don't think excess capacitance is going to make your preamp sound bad. It's more likely that your resistor values are too high, resulting in current limiting right when you need more current.

What's the value of the series resistor (unlabeled on the schematic)? If it's 10K like the base resistor, that could be your problem. Your load current, transistor base current, and Zener current all go through this resistor. 20mA across a 10K resistor will drop 200V.

Assuming that's not the case:
If the output current is 20mA and the Hfe of the transistor is 25, then your base current is 0.8mA. If your input voltage is 320V and your Zener voltage is 273, then you have 47V dropped across your 10K base resistor, which gives you 4.7mA through the resistor (and 221mW dissipated in the resistor). 4.7mA - 0.8mA leaves 3.9mA of Zener current, so your Zeners are each dissipating 355mW. You might want to look at the data sheet for your Zener diodes and find their nominal current. Their Zener voltage will be more precise around the center of their nominal current. If 3.9mA is significantly less than nominal, then variations in input voltage or output current (and therefore base current) which cause small changes in Zener current could result in fluctuating Zener voltage. You can confirm these estimates by measuring some combination of the actual Zener voltage, actual voltage across the base resistor, actual transistor Hfe, etc.

Also figure out where your nominal mains voltage (the mains voltage that produced your 230VAC at the transformer secondary) sits relative to your country's expected range of mains voltage. If you plan to take the unit to other countries, you'll want to consider their local fluctuations as well. Then look at your circuit and determine possible load current fluctuations. For example, you can measure the current while delivering a full-scale audio signal into a worst-case output load. These will help you find your top and bottom limits to the transistor circuit's proper operation. You may find you need to lower the value of the base resistor or select a higher-Hfe transistor in order to improve performance and avoid premature current limiting.
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6th November 2009
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Ok, i measured some things; series resistor is 1k8/5W, input AC is 254V, voltage at the base of TIP50 is 275V, zeners are 3 1N5377. Zener and output voltages seem to be almost the same. Some of the components get just a little warm, they seem to be ok.
This was measured with another tube, E88CC, this tube circuit is now pulling 18mA which is normal. Sound is good now, i think old tube was causing problems.

I have one question about zeners i'm using; i'm not sure how many mA i need through them to make them function properly. Datasheet only states test current which is 15mA. I'm not sure how i calculate this current from given current and voltage, i got 0.027mA calculating 270/10000. Is this correct.

I think this is cheap and useful circuit, easy to build. That's why i'm going to learn how to calculate thing properly. I need it quite often for projects i'm making.

Miha
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8th November 2009
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Quote:
Originally Posted by rotation View Post
Ok, i measured some things; series resistor is 1k8/5W, input AC is 254V, voltage at the base of TIP50 is 275V, zeners are 3 1N5377. Zener and output voltages seem to be almost the same. Some of the components get just a little warm, they seem to be ok.
This was measured with another tube, E88CC, this tube circuit is now pulling 18mA which is normal. Sound is good now, i think old tube was causing problems.

I have one question about zeners i'm using; i'm not sure how many mA i need through them to make them function properly. Datasheet only states test current which is 15mA. I'm not sure how i calculate this current from given current and voltage, i got 0.027mA calculating 270/10000. Is this correct.
Based on the 254VAC, I would suppose the output of your rectifier is probably 358V (254 times the square root of two, minus two diode drops). You're probably dropping around 40-50V across that 1K8 resistor (but you can measure it exactly). That would give you about 315-320V at the collector (input) of the transistor. If you have 275V at the base, that would mean you're dropping about 40-45V across your 10K base resistor. That means there's 4 or 4.5mA going through that resistor (this is the mistake you were making on the Zener current calculation: You need to measure the voltage ACROSS the resistor, not the voltage from the resistor to ground).
18mA of load current out of the transistor, which we're estimating has an Hfe of about 25, gives you a base current of maybe 0.75mA. That means the remainder of the current flowing through your 10K resistor needs to be flowing through the Zener string. So they're getting around 3.5mA.

It sounds like your circuit is working fine, and you probably don't need to mess with it. But you could lower the value of the base resistor if you wanted to. Because of the Zener diodes, the voltage drop across the base resistor will still be (almost exactly) the same. The resistor current, and therefore the Zener current, will increase as base resistance decreases. The added Zener current will increase the voltage drop across the 1K8 series resistor, and the power dissipated by it. This will in turn lower the voltage dropped across the transistor (since its input voltage will decrease while its output voltage remains constant), which will reduce the power dissipated in the transistor. Since you have a 5W series resistor which is currently dissipating less than a watt, this might prove helpful in allowing the transistor to run cooler and live longer. Or you may want to leave that base resistor alone, figuring it will limit output current somewhat for safety reasons.

As output current increases, the voltage dropped across the 1K8 series resistor increases proportionally. At the same time, base current increases. At first, this increased base current simply takes current away from the Zeners. But once the Zeners have completely shut off, then any additional increase in base current will increase the voltage dropped across the base resistor (and the series resistor) which will serve to lower the base voltage and the output voltage.
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13th September 2013
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Quote:
Originally Posted by ulysses View Post
Based on the 254VAC, I would suppose the output of your rectifier is probably 358V (254 times the square root of two, minus two diode drops). You're probably dropping around 40-50V across that 1K8 resistor (but you can measure it exactly). That would give you about 315-320V at the collector (input) of the transistor. If you have 275V at the base, that would mean you're dropping about 40-45V across your 10K base resistor. That means there's 4 or 4.5mA going through that resistor (this is the mistake you were making on the Zener current calculation: You need to measure the voltage ACROSS the resistor, not the voltage from the resistor to ground).
18mA of load current out of the transistor, which we're estimating has an Hfe of about 25, gives you a base current of maybe 0.75mA. That means the remainder of the current flowing through your 10K resistor needs to be flowing through the Zener string. So they're getting around 3.5mA.

It sounds like your circuit is working fine, and you probably don't need to mess with it. But you could lower the value of the base resistor if you wanted to. Because of the Zener diodes, the voltage drop across the base resistor will still be (almost exactly) the same. The resistor current, and therefore the Zener current, will increase as base resistance decreases. The added Zener current will increase the voltage drop across the 1K8 series resistor, and the power dissipated by it. This will in turn lower the voltage dropped across the transistor (since its input voltage will decrease while its output voltage remains constant), which will reduce the power dissipated in the transistor. Since you have a 5W series resistor which is currently dissipating less than a watt, this might prove helpful in allowing the transistor to run cooler and live longer. Or you may want to leave that base resistor alone, figuring it will limit output current somewhat for safety reasons.

As output current increases, the voltage dropped across the 1K8 series resistor increases proportionally. At the same time, base current increases. At first, this increased base current simply takes current away from the Zeners. But once the Zeners have completely shut off, then any additional increase in base current will increase the voltage dropped across the base resistor (and the series resistor) which will serve to lower the base voltage and the output voltage.
Hi all

Sorry to quote a very old post here. I've just chanced upon this while searching for a simple circuit idea to regulate 0 - 300V Variable DC Power Supply. I have built the circuit I found after googling on this link "http://www.eleccircuit.com/the-variable-high-voltage-power-supply-0-300v/".

Since you guys are pretty much experts on the analog circuit, I'd like to seek help here on how to regulate the voltage output of that circuit. Thanks a lot.

I appreciate any help.
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13th September 2013
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What do you mean by "regulate"? Do you mean "control" as in a user-selectable voltage setting?

Or do you mean "stabilize" as in "hold steady". If you mean stabilize, at what voltage are you wanting to do this?
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13th September 2013
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Originally Posted by Richard Crowley View Post
What do you mean by "regulate"? Do you mean "control" as in a user-selectable voltage setting?

Or do you mean "stabilize" as in "hold steady". If you mean stabilize, at what voltage are you wanting to do this?
Hi Richard

I meant "Load Regulation". The power supply I build is a simple 0-300V adjustable DC supply which I had mentioned in the previous post. When I apply 300V to my load, it cannot handle the low resistance and the output voltage drops to 270 ~ 280, which is obviously a bad thing. So I am seeking some help on how to stabilize the output voltage for different loading.

Thanks a lot for all the help.
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13th September 2013
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It sounds like first, you need a power source capable of supplying more current, THEN you can work on stabilizing the voltage. What is the load? What is the source of the power? An adjustable circuit would seem like the wrong choice if you want a fixed voltage output.
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16th September 2013
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Originally Posted by Richard Crowley View Post
It sounds like first, you need a power source capable of supplying more current, THEN you can work on stabilizing the voltage. What is the load? What is the source of the power? An adjustable circuit would seem like the wrong choice if you want a fixed voltage output.
Hi Richard

Sorry for my late reply, as I was too busy over the weekend to turn to my PC.

Regarding the circuit, I am using AC mains (230 V), then having it rectified through the diode bridge before having it filtered through the capacitor. So I think the power source can supply more current.

As for the load, it is a solution or gel (varies from single channel to multi channels), which is used in Gel Electrophoresis technique. Since the number of channels vary from time to time, the load will inevitably change. The problem has been that the circuit cannot provide relatively constant output voltage. Do you know of any idea how to work on stabilizing the output voltage? I built a variable supply because of the project's need.

Thanks a lot for your help.
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16th September 2013
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Are you saying that you are using a DIRECT connection to the power mains? No transformer? Do you understand that this is a VERY DANGEROUS and likely LETHAL practice? Even WITH an isolation transformer such a high voltage is very dangerous.

I had several specific suggestions, but I don't think that I want to be a party to something SO DANGEROUS! Seriously! You MUST NOT DO THAT!

I discovered several good circuits and a good website on high voltage regulator circuits with a simple Google search, but NONE of those circuits will protect someone from a LETHAL electrocution!

Gel electrophoresis? Rather far away from audio electronics which is the main focus of this forum. Google says that the voltage of 5-8V per centimeter is typical. What on earth are you doing that needs 300V? Does the current change during the process? Else why wouldn't you be able to set it at 300V and just leave it?

PS: It is typically quite helpful to know where people are. For example we don't know what your mains power line voltage is. At least complete the user profile to reveal where you are on the planet.
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16th September 2013
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Quote:
Originally Posted by Richard Crowley View Post
Are you saying that you are using a DIRECT connection to the power mains? No transformer? Do you understand that this is a VERY DANGEROUS and likely LETHAL practice? Even WITH an isolation transformer such a high voltage is very dangerous.

I had several specific suggestions, but I don't think that I want to be a party to something SO DANGEROUS! Seriously! You MUST NOT DO THAT!

I discovered several good circuits and a good website on high voltage regulator circuits with a simple Google search, but NONE of those circuits will protect someone from a LETHAL electrocution!

Gel electrophoresis? Rather far away from audio electronics which is the main focus of this forum. Google says that the voltage of 5-8V per centimeter is typical. What on earth are you doing that needs 300V? Does the current change during the process? Else why wouldn't you be able to set it at 300V and just leave it?

PS: It is typically quite helpful to know where people are. For example we don't know what your mains power line voltage is. At least complete the user profile to reveal where you are on the planet.
Hi Richard

Yes, of course, I used an isolation transformer.

Attached is the complete circuit I have set up. And yes, I know this is an audio electronics forum, but I chanced upon a high voltage circuit diagram from the earlier posts by Wavebourn, Ulysses, etc. discussing on the circuit functionalities in details. Hence, I figured I would drop a few notes here to seek help from the experts because the basic idea is the same whatever the load is.

Regarding the requirement of 300V, it is mainly used to drive the process of moving some protein across the gel solution filled-channel. During the process, the resistance of the channel changes (from low to high), hence, the current also changes. As a consequence, the voltage drops substantially for a few seconds to a min or so right after turn-on before getting back to 297 or 298 or 299V. Obviously, that original cct was only designed for about 100mA but I replaced the current-limiting resistor R2 with 1.44 ohms hoping to increase the current, but still, the voltage output is not stable at all.

Also, the reason I set this up as adjustable is because the user sometimes needs 200V.

Oh, yeah I live in Singapore where the mains voltage is 230V.

Hope that helps clear the doubts.

Thanks.
Attached Thumbnails
High Voltage Regulated Tube Supply-300vsup.gif  
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