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| From | Winfield Hill <hill@rowland.harvard.edu> |
|---|---|
| Newsgroups | sci.electronics.design |
| Subject | Re: buck converter for negative voltages |
| Date | 2017-02-02 11:33 -0800 |
| Organization | Rowland Institute |
| Message-ID | <o701hv014n9@drn.newsguy.com> (permalink) |
| References | <o6ti3m0312e@drn.newsguy.com> <3pk49ct21gjuhka45gqe30g5c7s7f48upg@4ax.com> <43f62388-eb31-41b0-89e4-72f861ac6411@googlegroups.com> |
Lasse Langwadt Christensen wrote...
>
>Den onsdag den 1. februar 2017 kl. 23.27.44 UTC+1 skrev Winfield Hill:
>> Lasse Langwadt Christensen wrote...
>>>
>>> Den onsdag den 1. februar 2017 kl. skrev Winfield Hill:
>>>> John Larkin wrote...
>>>>>
>>>>> Winfield Hill wrote:
>>>>>
>>>>>> Suggestions for buck converter ICs for negative voltages?
>>>>>> Controller ICs (external MOSFETs) would be nice.
>>>>>
>>>>> I can't recall ever seeing a real negative-to-negative
>>>>> switcher! People sometimes hack a positive controller.
>>>>
>>>> LTC also suggests the positive boost-converter hack,
>>>> in design note DN1022.
>>>
>>> if you can figure out a way to flip the feedback or live with the
>>> output being relative to input, wouldn't any synchronous buck work?
>>
>> The feedback is inverted in a *boost* converter, one
>> just needs to translate it down to the negative rail.
>
> afaict it is the same issue, you need to make the feedback
> relative to ground instead of to the negative rail
Actually, besides level-shifting the feedback to the IC's
FB pin, which is referenced to -Vin, it's necessary to
invert the sign of the feedback. That becomes clear when
comparing buck-converter duty-cycle formula Vout/Vin = D,
with a boost converter, Vout/Vin = 1/(1-D). Also, it's
obvious that when -Vout increases (more negative), FB
must increase (more positive).
The inversion occurs in the level-shift transistor, Q1.
. gnd ----+---------+--------+--------,
. ___|____ | _|_ |
. | | _|_ --- R1
. | boost | /_\ | |
. | | | | |
. | SW |----+-#####--+---+------- -Vout
. | | B |
. | FB |----+----------C E--'
. |________| | Q1 pnp
. | R2
. | |
. -Vin ---+---------+-----
--
Thanks,
- Win
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buck converter for negative voltages Winfield Hill <hill@rowland.harvard.edu> - 2017-02-01 12:57 -0800
Re: buck converter for negative voltages John Larkin <jjlarkinxyxy@highlandtechnology.com> - 2017-02-01 13:35 -0800
Re: buck converter for negative voltages Winfield Hill <hill@rowland.harvard.edu> - 2017-02-01 14:02 -0800
Re: buck converter for negative voltages Lasse Langwadt Christensen <langwadt@fonz.dk> - 2017-02-01 14:16 -0800
Re: buck converter for negative voltages Winfield Hill <hill@rowland.harvard.edu> - 2017-02-01 14:27 -0800
Re: buck converter for negative voltages Lasse Langwadt Christensen <langwadt@fonz.dk> - 2017-02-01 14:39 -0800
Re: buck converter for negative voltages Winfield Hill <hill@rowland.harvard.edu> - 2017-02-02 11:33 -0800
Re: buck converter for negative voltages Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> - 2017-02-03 09:44 -0500
Re: buck converter for negative voltages John Larkin <jjlarkinxyxy@highlandtechnology.com> - 2017-02-01 14:38 -0800
Re: buck converter for negative voltages Lasse Langwadt Christensen <langwadt@fonz.dk> - 2017-02-01 14:43 -0800
Re: buck converter for negative voltages John Larkin <jjlarkinxyxy@highlandtechnology.com> - 2017-02-01 15:35 -0800
Re: buck converter for negative voltages Winfield Hill <hill@rowland.harvard.edu> - 2017-02-01 18:25 -0800
Re: buck converter for negative voltages Winfield Hill <hill@rowland.harvard.edu> - 2017-02-01 13:36 -0800
Re: buck converter for negative voltages Wanderer <wanderer@dialup4less.com> - 2017-02-01 15:04 -0800
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