[Top] [All Lists]

Re: [Amps] HV Diodes

To: Carl <>, "" <>, amps <>
Subject: Re: [Amps] HV Diodes
From: Steven Katz <>
Date: Wed, 8 Oct 2014 15:44:10 +0000
List-post: <">>
I agree with Carl.

Unless a power supply circuit board is very special, the diode leads are a 
better heatsink than PCB copper foil is.  The only important parameter there is 
Rthj-a and the wire leads of a power rectifier are better than microscopically 
thin copper foil on a printed circuit board that isn't thermally conductive.

BTW "potting" can actually improve a lot of stuff if it's done right.  The old 
Semtech assemblies previously referenced were made from highly thermally 
conductive potting material from Emerson-Cuming, and the modules that had 
built-in aluminum mounting rails like the SDHD and SDHD-KM and -KS series had 
even more thermally conductive potting material, allowing a lot of the junction 
heat to be transferred to that aluminum rail, which in turn should be tightly 
bolted to a heat dissipating surface (aluminum chassis, heatsink, etc).

The typical old Semtech rectifiers used in those didn't have Vf = 0.7V/junction 
at rated current...they were thicker "suprataxial" junctions (not double 
diffused or conventional epitaxial) and had somewhat higher Vf, typically close 
to 1.0V/junction at rated current (and at room temp, 25C).  But running them 
hotter drives the Vf down lower, and while that also drives Ir (leakage) 
current up higher, those were very low leakage devices that would not run away 
thermally even at Tj > +175C.


-----Original Message-----
From: Amps [] On Behalf Of Carl
Sent: Wednesday, October 08, 2014 8:37 AM
To:; amps
Subject: Re: [Amps] HV Diodes

I wouldnt use smaller than a string of 1N5408's as they have a much higher 
surge current capability as the rather obsolete 1N4007 in the era of much 
higher filter cap C and dirty AC utility lines.

The diode leads are the heat sink and a minimum of 1/2" in free air is 
recommended by the manufacturers. Ive no idea how potting would modify that. 
My own method is to simply mount them on perf board when possible and thats 
easy in the Alpha 77DX in place of the "petrified blocks".


----- Original Message -----
From: "KA4INM radio" <>
To: "amps" <>
Sent: Wednesday, October 08, 2014 9:36 AM
Subject: Re: [Amps] HV Diodes

> On 10/08/14 06:35, Chris Wilson wrote:
>   When companies pot a string of 1N4007's (1 kV at 1 Amp) they rate the 
> string at .75 Amp.  The diodes, lacking the posts or copper foil to act as 
> heat sinks, run hotter when potted.  Short leads to the circuit board 
> copper conduct heat away from the silicon die better than long leads.
>> Hello Han,
>> On Wednesday, October 8, 2014,  you wrote:
>>> hi George-san and all
>>> I think HV6-1 is equivalent to GI HVPR10-MX12.
>>> I have measured forward voltages of these diode modules
>>> using a CVCC power supply with 100-mA current.
>>> Assuming each of the diode in a string exhibits 0.7 V forward
>>> voltage one can presume how many series diodes are in
>>> the module.
>>> GI HVPR10-MX12 6.36 V: 9 diodes
>>> EDHD 15k 10.67 V per a leg: 15 diodes x 2 (which I am using)
>>> SEMITECH KV-PAC SDHD-15k 12.97 V per a leg: 18 diodes x 2
>>> Toshiba S5166A (13 kV 500 mA) 14.0 V: 20 diodes
>>> I think 10 x 1kV 1A diodes in series is OK as an alternative.
>>> de Han JE1BMJ
>> Has  anyone  experimented  with  home "potting" diode strings to make
>> their  own  blocks?  I  am  curious  about diode lead length, physical
>> orientation, and potting compound used. thanks.
> -- 
>   Ron  KA4INM - Youvan's corollary:
>                 Every action results in unwanted side effects.
> _______________________________________________
> Amps mailing list
> -----
> No virus found in this message.
> Checked by AVG -
> Version: 2014.0.4765 / Virus Database: 4037/8348 - Release Date: 10/08/14

Amps mailing list
Amps mailing list

<Prev in Thread] Current Thread [Next in Thread>