[ARC5] Solid State 6AL5

[Dennis Monticelli]

Classical Si has its BV limitations.  Those rectifiers must be SiC.
Increased demand from the solar and EV industries have probably driven down
prices to where they are cost-effective for slow non-PWM applications too.
Good for us hobbyists.

Dennis AE6C





On Thu, Feb 8, 2018 at 1:48 PM, Peter Gottlieb <kb2vtl at gmail.com> wrote:

> I doubt anyone uses 1N4007’s in anything HV these days. Look at Mouser and
> you can find cheap 4kV diodes in stock and I see that single component 10
> kV ones are around as well.
>
>
> Peter
>
> On Feb 8, 2018, at 4:23 PM, Dennis Monticelli <dennis.monticelli at gmail.com>
> wrote:
>
> The fast diode problem is unequal release of stored charge.  Quite a bit
> of instantaneous current flies around when fast diodes are suddenly
> reversed in a PWM circuit.
>
> Yes, a dead short in one diode of a string increases the reverse BV of the
> survivors, thus stressing them further.  I generally design for 50% of BV
> rating when using common Si power diodes in 60Hz applications.  1N4007's
> are so cheap these days while 1KV rated resistors are not.
>
> I wonder how modern day HV 60Hz rectifier modules are built? Do they do
> anything to match BVs or leakages before assembly?  Do they use resistors?
> I haven't broken one open.  My guess is that they a simple test to throw
> out the out-liers to insure they are using only the middle of the
> distribution and then dispense with resistor balancing.
>
> Dennis AE6C
>
> On Thu, Feb 8, 2018 at 12:23 PM, Peter Gottlieb <kb2vtl at gmail.com> wrote:
>
>> Yet, I still find manufacturer app notes, such as STMicro AN443, that
>> talk about this, although in the context of fast diodes.
>>
>> application-notes.digchip.com/005/5-10702.pdf
>>
>> One diode shorts in that HV bridge and the whole rest of them will not be
>> far behind.
>>
>> I’m not saying you’re wrong, just that I’d like to see a manufacturer or
>> academic reference justifying eliminating the resistors before I’d accept
>> it in anything beyond hobby use.
>>
>>
>> Peter
>>
>> On Feb 8, 2018, at 3:04 PM, Dennis Monticelli <
>> dennis.monticelli at gmail.com> wrote:
>>
>> FYI.  The practice of using equalization resistors dates way back to when
>> early Si manufacturing had uniformity issues.  If you are using modern
>> 1N4007's (particularly from the same batch) don't bother with the
>> resistors.  Just design with the usual BV margins and you will be fine.
>>
>> Dennis AE6C
>>
>> On Thu, Feb 8, 2018 at 12:00 PM, Peter Gottlieb <kb2vtl at gmail.com> wrote:
>>
>>> In my test set the 5R4 is set up as a full wave rectifier from a 1700
>>> volt CT winding. At one point I thought the tube was weak and I’d replace
>>> with diodes. I have a bunch of 1N4007 but looking at the voltages I
>>> realized I needed three diodes for each plate!  And then equalization
>>> resistors, but with their max rated voltages I needed a lot of them. This
>>> started to be more trouble than it was worth and I was able to locate a
>>> replacement tube in my stash and just went with it.
>>>
>>>
>>> Peter
>>>
>>> > On Feb 8, 2018, at 2:47 PM, Richard Knoppow <1oldlens1 at ix.netcom.com>
>>> wrote:
>>> >
>>> >    I don't remember if I ever measured the resistance of the 5R4
>>> replacement I have and don't know where it is now. However, the B+ with it
>>> installed was substantially higher than with the tube rectifier and it was
>>> small so I don't think it had anything but diodes in it.
>>> >
>>> >> On 2/8/2018 10:17 AM, John Watkins via ARC5 wrote:
>>> >> My solid state 6AL5s have just diodes and possibly a resistor in
>>> series with them (2 diodes).  They measure 16 Ohms forward resistance using
>>> a Simpson VOM on the Rx1 scale.off the upper end on both Rx1 and Rx100 for
>>> reverse.  Nothing in mine for heater load.  That is a no connection.  I
>>> haven’t removed the amber epoxy yet to see if the diodes have a 1N number.
>>> Will report on that when I get back to town.
>>> >> John WD5ENU
>>> >
>>> >
>>> > --
>>> > Richard Knoppow
>>> > 1oldlens1 at ix.netcom.com
>>> > WB6KBL
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>
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