[SI-LIST] Re: DC Power supplies Connected in parallel
- From: Vinothkumar D <Vinothkumar.D@xxxxxxxxxx>
- To: "si-list@xxxxxxxxxxxxx" <si-list@xxxxxxxxxxxxx>, "erfan@xxxxxxxxxxxxxxx" <erfan@xxxxxxxxxxxxxxx>
- Date: Mon, 13 Aug 2012 04:46:00 +0000
Erfan,
Use a OR-ing diode at both the outputs when you are paralleling the power
supplies of same voltages. If it is a simple DC regulated power supply , it
will always have a simple current limiting and acrow bar protection which will
shutdown the +5V supply. Incase of SMPS, the output reference/feedback section
circuits will damage.
Suppose if the +5V is locally sensed , then the feedback error amplifier will
see the output 12V and will damage the complete error amplifier section.
From your previous communication, I can understand that you wanted to increase
the current rating by paralleling for two dc power supplies. When you are
directly shorting two DC 12V supplies for e.g. each can source 2A, Suppose one
output is +12.05 and another voltage is +12.00V then the highest voltage 12.05V
supply will source the load till 2A , then it reduces to 12.00 the other one
starts sourcing and you get 4A load. To have better load sharing use an OR-ing
diode or controller with mosfet to have better load sharing.
Regards
Vinothkumar.D
L&T- Integrated Engineering Services,
Mobile : +91 - 9742797772.
E-mail ID : Vinothkumar.D@xxxxxxxxxx
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] On
Behalf Of Paul Levin
Sent: Sunday, August 12, 2012 4:30 AM
To: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Re: DC Power supplies Connected in parallel
On the other hand, if the 5V supply has working over-voltage protection, that
5V OVP circuit may save the 5V supply by simply blowing the fuse of the 12V
supply.
I say *working* because I just experienced a +/-15V power supply "with
over-voltage protection" run its positive output up to +22V, just a tad past
where I would have expected the OVP level to be set (and also a tad past what
most of my parts could tolerate.)
Paul Levin
Director of Engineering
InnoSense LLC
Torrance, CA
________________
On 8/11/2012 11:49 AM, O. Laney wrote:
> Power supplies can't be treated as theoretical sources of the pspice
> kind plus output impedance. Your typical positive supply can only
> source current and can't sink it. If the outputs of a 5V and 12V
> supply are tied together, the 12V supply will pull the 5V supply above
> its set point and the regulation loop in the 5V supply will turn off
> the pass transistor. Whether the 5V output can pull clear to 12V
> without something breaking down is a matter of supply design. For
> instance, the output caps in the 5V supply will likely be rated for
> less than 12V and might not survive the overvoltage for very long. The
> pass transistor might break down from the inverted voltage (...or not.
> The raw voltage is probably 9 to 12V.)
>
> Orin
>
> ------ Original Message ------
> From: "Erfan" <erfan@xxxxxxxxxxxxxxx>
> To: si-list@xxxxxxxxxxxxx
> Sent: 8/11/2012 2:13:59 AM
> Subject: [SI-LIST] DC Power supplies Connected in parallel
>> Hai Everyone,
>>
>>
>> I have few questions regarding the DC power supplies.
>>
>>
>>
>> What happens when 2 DC-power supplies are connected in parallel which
>> has 2 different voltages let say one has 12V and other has 5V. What
>> happens to their voltage and current, current has to get added up to
>> my knowledge does it really happen in this case? What happens to voltage do
>> I see 12V or 5V?
>> what happens in case of grounds are isolated and not isolated? If I
>> have to generate more current using 2 DC supplies in parallel then
>> what care or configuration I should use. Wanted to know the practical
>> limitations of using them.
>>
>>
>>
>> Kindly through some light in this regard.
>>
>>
>>
>> Regards,
>>
>> Erfan
>>
>>
>>
>>
>>
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