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HV power supply 0-400V - 200 mA

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marvi3:
Salve, per provare dei carichi attivi per alte tensioni vorrei realizzare un alimentatore che fornisca tensioni tra 0 e 400V ed una corrente di 200-300 mA.
Ho scelto di usare un integrato ad alta tensione, LR8K4, capace di tale funzione.
sul DA non c'è traccia di idee buster per questo integrato.
In rete ho trovato questo schema di massima, e mi chiedevo se poteva essere adeguato, sia per il controllo della tensione che per il controllo della corrente, come si può fare con un 317 a basse tensioni.
Per il controllo della corrente si luò fare low side o high side?
Non sono esperto di ali ad HV e chiedo lumi in proposito.
Ho anche trovato uno schema che usa un mosfet come buster, ma ha qualcosa che non mi convince.
Vi posto i due schemi ed attendo vostri lumi in merito.

fcb:
Part translation says: "I am not an expert on wings at HV and I ask for guidance on this."

You want 0-400 @ 200-300mA.  Schematic is 50-350V and the fuse is 250mA (so assume their current limit is <250mA).

Probably need to understand more about your skill level before advising further - you'll be playing with potentially lethal voltages!

Ian.M:

--- Quote from: marvi3 (Google Translate) on June 07, 2021, 10:47:37 am ---Hi, to test active loads for high voltages I would like to make a power supply that provides voltages between 0 and 400V and a current of 200-300 mA.
I have chosen to use a high voltage integrated, LR8K4, capable of this function.
on the DA there is no trace of buster ideas for this integrated.
On the net I found this schematic diagram, and I was wondering if it could be adequate, both for voltage control and current control, as can be done with a low voltage 317.
Is it a low side or high side to control the current?
I am not an expert on wings at HV and I ask for guidance on this.
I also found a scheme that uses a mosfet as a buster, but it has something that doesn't convince me.
I place the two schemes and I await your enlightenment on this.

--- End quote ---

'Circuito_Def_08' uses two IRFP460 N-MOSFETs effectively in parallel as source followers after a linear regulator.  Their source resistors (for current sharing) and the current sense resistor add about 7 ohms output resistance, and together with the typical output characteristic of a MOSFET source follower, and as they are outside the feedback loop,  the result is likely to be poor regulation with respect to load current.   The original Fairchild IRFP460 was rated for linear operation, with a DC line on its SOA graph, but is no longer in production.  The second source ones from Vishay and Infineon don't have DC lines on their SOA graphs, so there is a risk that they will fail due to hot-spotting if you use them in this circuit.  Where is this circuit from?  The original designer may have more details on their choice of MOSFET.   Modifying it for increased output current requires a full understanding of the design but should be possible.  Modifying it for 0V-400V would be far more difficult as that adds up to an extra 100V across the MOSFETs at low output voltages, and would require a higher input voltage which the MOSFETs don't have enough voltage rating to handle.  (Consider the case of AC mains supply 10% high, a 5% regulation transformer, no load and minimum output voltage - the unregulated DC input voltage will be approx 60% higher than when the transformer is loaded to its nominal VA rating at nominal AC mains voltage!  :scared:  :-- )

'Buster_LR8' cant work.  The design needs a PNP pass transistor, but the APT13005 is NPN.  That could be fixed by adding a high voltage PNP driver transistor to make a Sziklai pair, but the  APT13005's SOA graph shows its only good for max. 100 20mA with 400V across it.     :--


--- Quote from: fcb on June 07, 2021, 11:20:45 am ---Part translation says: "I am not an expert on wings at HV and I ask for guidance on this."

You want 0-400 @ 200-300mA.  Schematic is 50-350V and the fuse is 250mA (so assume their current limit is <250mA).

Probably need to understand more about your skill level before advising further - you'll be playing with potentially lethal voltages!

--- End quote ---

As Fcb points out, there are *SERIOUS* safety concerns.  If you don't have appropriate experience with HV DC circuits, there is no substitute for hands-on tutoring from an experienced mentor, preferably one formally qualified to teach the subject.

Edit: Thanks Zero999 for spotting my SOA f---up, see below

H713:
It should also be noted that 0 - 400 V, 200 mA is a spec that can be met by a whole bunch of old tube power supplies. Heathkit, Eico, Lambda and a bunch of others all made them, and they work really pretty well.

coppercone2:
some guy writing in italian on an english forum about a 400V 80W power supply, this is a bad thread

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