[ARC5] [Milsurplus] If You Need a Regulated Low B+ Supply
Brooke Clarke
brooke at pacific.net
Mon Feb 15 13:19:37 EST 2010
Hi John:
National Semi has an app note about noise generation in switch mode
power supplies and the key factor is the topology used. Some
arrangements are inherently noisy while others tend to generate a lot
less noise and can be easily filtered.
For one off circuits I just get the eval board for the IC which is a
ready made power supply. But if you want to roll your own supply it
often turns out that NS has chosen some very special inductors. Those
inductors make the IC look very good in terms of specs like efficiency
and small circuit size (comes with higher switching frequencies). They
often are only available in full rolls of SMT parts. But for me size is
not a big factor so going to a much larger inductor to get efficiency
and give up the size is an easy choice.
Have Fun,
Brooke Clarke
http://www.PRC68.com
J. Forster wrote:
>> Well, you're talking about following or replacing the slow switcher with a
>> linear reg. Sure you can do that and it works well, but that will cost
>> you
>> the efficiency you were after in the first place by going with a switcher.
>>
> Low frequency does not automatically mean poor efficiency. If you really
> want efficiency at low frequencies, you might consider a tape wound
> torroid, rather than an E-I filament transformer. I've easily done>90% at
> the 50 Watt level. The transformer is not cheap though.
>
>
>> Providing feedback for regulation is usually best, but the key is at what
>> freq do you sample. Do it rapidly and you have more EMI to content with,
>> do it slowly and then some other means is needed to deal with the poor
>> dynamic regulation, be "vitamin C" or a secondary linear regulator. No
>> free lunch I'm afraid.
>>
> A simple pass regulator on the output can have KHz BW if you want,
> irrespective of inverter frequency. Certainly more than enough to stifle
> key chirp.
>
> Bottom line, the stacked switcher blocks are OK, if you can live with the
> EMI. In my experience, it is pretty hard to suppress the spikes well, even
> with twisted pairs, ferrites, capacitors, and shielded boxes with
> feedthroughs.
>
> -John
>
> ============
>
>> Dennis AE6C
>>
>> On Sun, Feb 14, 2010 at 11:35 AM, J. Forster<jfor at quik.com> wrote:
>>
>>
>>> Not at all.
>>>
>>> If you want regulation, there are a number of ways to do it. IMO, the
>>> simplest would be a FET or BJT version of the "Beta-C" circuit with the
>>> capacitor replaced with a Zener or Zener string.
>>>
>>> You could also regulate the inverter input and feed back an output
>>> sample.
>>> Isolation of the B- line is usually not needed, unless you are stacking
>>> supplies. Some exceptions are the R.1155 and WS19 HT2.
>>>
>>> -John
>>>
>>> ===============
>>>
>>>
>>>
>>>
>>>> True, you can slow switch at 60Hz but if dynamic load regulation
>>>>
>>> matters
>>>
>>>> it
>>>> can become an issue. You would have to rely purely on big oversized
>>>>
>>> caps
>>>
>>>> vs
>>>> the feedback loop to hold the voltage steady in the presence of CW or
>>>> voice
>>>> peaks.
>>>>
>>>> Dennis AE6C
>>>>
>>>>
>>>> On Sun, Feb 14, 2010 at 11:14 AM, J. Forster<jfor at quik.com> wrote:
>>>>
>>>>
>>>>> One solution to the EMI problem from switchers is to use a low
>>>>>
>>> frequency
>>>
>>>>> square waves, of the order of 60 Hz, rather than 10s of KHz. This
>>>>> enables
>>>>> you to use much slower rise/fall switching times and conventional
>>>>> filament
>>>>> transformers run backwards. They are bigger and require bigger HV
>>>>>
>>> caps,
>>>
>>>>> but are a lot quieter.
>>>>>
>>>>> Best,
>>>>> -John
>>>>>
>>>>> ================
>>>>>
>>>>>
>>>>>
>>>>>
>>>>>
>>>>>
>>>>>> While the diagram says "new" this part and the associated circuit
>>>>>>
>>>>> dates
>>>>> to
>>>>>
>>>>>> 1991 when it went into the early GM airbags. I know because my
>>>>>>
>>> work
>>>
>>>>> group
>>>>>
>>>>>> designed it. However, it is still sold along with a plethora of
>>>>>>
>>> other
>>>
>>>>>> "Simple Switchers" which have gone through five generations now.
>>>>>>
>>> If
>>>
>>>>> you
>>>>>
>>>>>> go
>>>>>> to the National Semiconductor website you will a cluster of
>>>>>>
>>>>> easy-to-use
>>>>>
>>>>>> design tools that allow virtually anyone to design the switching
>>>>>>
>>> reg
>>>
>>>>> they
>>>>>
>>>>>> need right on-line. All the popular configurations are covered.
>>>>>>
>>> You
>>>
>>>>> can
>>>>>
>>>>>> then order the components along with the PCB from the distributor
>>>>>>
>>> link
>>>
>>>>> or
>>>>>
>>>>>> just roll your own by buying the chip from DigiKey.
>>>>>>
>>>>>> BTW, you can still stack "common-ground" DC/DC converters by
>>>>>>
>>> feeding
>>>
>>>>> them
>>>>>
>>>>>> raw DC from independent windings on the transformer.
>>>>>>
>>>>>> Remember that most switcher circuits are not designed to have low
>>>>>>
>>>>> enough
>>>>>
>>>>>> EMI
>>>>>> to guarantee happiness in our radios. Pay close attention to short
>>>>>>
>>>>> lead
>>>>>
>>>>>> dress, good grounding and use shielded inductors vs the cheap
>>>>>>
>>> solenoid
>>>
>>>>>> types. For best results, extra input& output filtering and a
>>>>>>
>>> metal
>>>
>>>>> box
>>>>>
>>>>>> may
>>>>>> be needed.
>>>>>>
>>>>>>
>>>>>> Dennis AE6C
>>>>>>
>>>>>> On Sat, Feb 13, 2010 at 11:50 AM, David Stinson
>>>>>>
>>> <arc5 at ix.netcom.com>
>>>
>>>>>> wrote:
>>>>>>
>>>>>>
>>>>>>> This cute little circuit is an example of the kind of DC/DC
>>>>>>> converter you cannot stack, since in and out have a
>>>>>>> common ground:
>>>>>>>
>>>>>>> http://www.nbglin.com/dc.htm
>>>>>>>
>>>>>>> Still a neat circuit, though. I'm gonna get me a
>>>>>>> couple to use as "Borg Implants."
>>>>>>>
>>>>>>> 73 Dave S.
>>>>>>>
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>>>>>> ______________________________________________________________
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>>>>>>
>>>>>>
>>>>>
>>>>>
>>>>>
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>>>
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