At 13:02 2016-08-09, alan.b.pearce@stfc.ac.uk wrote:
>>=20
>> Hi!
>> I need a very high voltage (50kV), high current (preferably > 6A)=20
>diode, but I
>> have no need for it to have a fast recovery time.
>>=20
>> Can you please suggest a suitable, and not too expensive, diode, if it e=
ven
>> exist?
>> Microwave diodes I found are all low-current, and are thus not suitable.
>
>AFAIK all microwave diodes are low voltage and low current, unless=20
>they are designed for microwave generation in which case they are speciali=
sed.
>
>>=20
>> Or, would it be safe to make it chaining several smaller voltage=20
>rect. diodes?
>
>That is the normal method of making high voltage diodes, e.g. for CRT=20
>EHT generation.
>
>I was going to suggest using a diode stack off a CRT EHT coil, but I=20
>believe they are often integrated in and distributed through the coil=20
>to help even out the reverse voltages.
>
>Making your own high voltage stack is fraught with problems and you=20
>will need to consider equalising capacitors and maybe resistors across=20
>each diode to limit the reverse voltage each individual diode sees.

And that's what I was worrying, when I asked if it was safe to just chain
diodes together. Capacitors and resistors will not make it behave like a
normal diode.


>You would be better off purchasing a pre-built stack such as one of these =
....
>http://ppmpower.co.uk/products/uncategorized/rectifier-blocks-with-ins
>ert-mounting/

Thanks, I will take a look at it.


>That link contains several with listed PIV of 60kV, but less than 1A.=20
>There is one at 50kV at 3.5A average forward current. Why do you need=20
>6A, or is that a peak current?

Peak current is much higher.. it's for a plasma jet experiment I'm making. =
:)

Peak current will be in the order of 50A at least (better if more), so I
thought it'd be better to use a diode with enough average current capabilit=
y.

The idea is to generate enough HV to cause a spark, and then - as the
impedance of the gap is now very low - to "inject" high DC current. But
I need a diode to block the HV.

On a side note, what is the impedance I can expect from an arc? So to
calculate the voltage required to make x Ampere flow through it.


--=20
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