Power Supply "Remote Sense" Mistakes and Remedies

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Most medium to high power AC-DC power provides and some DC-DC converters embrace "Distant Sense" connection factors (+ and - Sense) which might be used to tightly regulate the provision's output voltage on the load. For the reason that output cables that join a power provide's output to its load have some resistance, as present movement will increase, so will the voltage drop throughout the cables (I x R = Voltage Drop). Furthermore, because it's best to control the voltage instantly on the load, using the 2 Distant Sense wires related from the provision to the load will compensate for these undesirable voltage drops. Check with Fig. 1 which exhibits the everyday connections when the Distant Sense perform is used.

Fig. 1: Power Supply with Twisted "Distant Sense" Wires Related to the Load

Typical "Distant Sense" Issues & Remedies

  1. Most distant sensing circuits are able to compensating for from 0.25V to 0.75V of voltage-drops throughout the output cables. Nonetheless, to make sure, at all times examine your power provide's instruction handbook to find out its most distant sense compensating vary. If the voltage drop throughout the output cables exceeds the compensating vary of the distant sense circuits, the voltage on the load will not be regulated. This drawback may be remedied by both lowering the size of the output cables or growing the dimensions (heavier wire gauge) of the output cable's to scale back the extreme voltage drop. Voltage drops throughout the output cables needs to be minimized since this can be a source of wasted power. For instance, with only a 0.5V cable drop with a 100A load, the misplaced power quantities to 50W in every cable or 100W whole.
  2. The distant sense perform routinely will increase the output voltage on the output terminals of the provision to compensate for any undesirable voltage drop within the output cables with heavy load currents. Likewise, the distant sense perform decreases the output voltage of the provision when the required load present is decreased. In some functions, the power provide's output must be adjusted by the person to voltage larger than its nominal (e.g. 5V nominal, adjusted to 5.5V). All the time alter the power provide's output whereas measuring the voltage on the load. As well as, care needs to be taken to guarantee that below full load that the distant sense perform doesn't push the Vout to a better voltage that would probably journey the OVP set-point and shutdown the provision. Subsequently, at all times learn the power provide's instruction handbook to concentrate on the provision's adjustment vary and OVP set-point.
  3. The distant sense leads carry little or no present so gentle gauge wires can be utilized. Nonetheless, steps needs to be taken to make sure that the distant sense wires don't choose up radiated noise by both twisting the + and - Sense wires collectively and/or by shielding the wires from the noise (seek advice from Fig 1). It's best to make use of totally different coloured sense wires (e.g., black and pink) in order that after they're twisted it's straightforward to find out which wire is the + and – Sense.
  4. Check with Fig. 2 under for a simplified schematic of a power provide's distant sense circuits. You will need to observe the proper polarities, i.e., the +Sense wire ought to join on the load close to the +Vload connection and the –Sense wire ought to join on the load close to to the – Vload connection. If by mistake the distant sense wires are crossed-connected (+Sense to –Vload and – Sense to +Vload) present will movement within the Sense strains and burn out the internal Rsense resistors, inflicting a malfunction of the provision. Usually, these internal Rsense resistors are round 10 to 100 Ohms with a most ranking of 0.5W.
Fig. 2: Simplified Schematic of Distant Sense Circuit with Exterior Output & Sense Wires

  1. We now have seen functions the place the person has put in a swap or fuse in collection with one or each output wires. This could trigger a significant issue if the distant sense strains stay related to the load, as a result of if the output cable swap or fuse opens, present will movement within the sense strains and trigger the internal Rsense resistors to fritter away. System debugging may cause related issues, for instance, the place the power and sense cables are positioned on separate connectors and if by error, solely the power cable connector is disconnected. 
  2. There are functions the place the person might not need to use the distant sense feature. In these instances, the distant sense strains shouldn't be left open for optimum load regulation; as a substitute, an area sense configuration should be used. Referring to Fig. 3, to make use of an area sense arrange the + and -Sense strains needs to be related to both their corresponding native sense (LS) terminals, that are supplied on many power provides, or related to the corresponding +Vout and –Vout terminals. Most power provides are shipped from the manufacturing unit with these "Native Sense" jumpers put in on the power provide (see pictures under).
Fig. 3: Schematic of Power Supply with "Native Sense" Jumpers Put in

Photograph of Power Supply with Native Sense Wires Related (see Purple & Black jumper wires)

Photograph of PSU with Sense Screw Terminals Related to Output Screw Terminals with Metallic Jumpers

In abstract, the "Distant Sense" feature routinely compensates for undesirable output cable drops, which range because the output present will increase and decreases. This feature is advantageous to the person, however is topic to errors that needs to be averted to insure the correct operation of the power provide and the end-product.