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The basic rule for the power supply of electric circuits is to design the board by using a solid pattern to lower the impedance of the power supply and avoid voltage drops.
When incorporating the module into the system
In board design, power can be supplied with low impedance by solid traces.
However, final products and systems made by combining system power supplies, FA cameras, motors, etc. in the housing are connected with cables and supplied with power.
At this time, the cable (wiring) may become long, and the impedance of the power supply may become high, or the inductance may become large.
Effect of long cable inductance
Unstable power supply (oscillation)
Thin and long cables and wires have a large inductance component.
If there is a large inductance in the power supply cable, the power supply may become unstable (oscillate), so be careful.
For details, see [Power Supply Column] No. 1 The DC/DC converter makes noise! Please refer to.
Possibility of overvoltage breakdown
If the inductance becomes large, not only will the power supply become unstable, but overvoltage may occur when the power is turned on, which may destroy the power supply of the system (on the board). Be very careful with systems that frequently turn the power on and off (e.g., turn the power on at the start of work and turn it off at work).
For more information on damage caused by overvoltage, see [Power Supply Column] Part 2: Long Wiring Is the Culprit? Please refer to.
Effect of Long Cable Impedance
Complexity of system installation
For example, security cameras may be installed with a long cable in a location away from the original system.
Also, when building a production line in a factory, when combining systems, there may be cases where the control system section and the drive section are connected with a long cable.
In that case, when supplying power with a long cable, it is often the case that fine adjustment of the power supply voltage is performed using a volume or the like at the time of installation. The quality of the power supply depends on the experience of the installing operator.
Environmental changes and aging deterioration
The power supply voltage value, which was finely adjusted at the time of installation, may naturally fluctuate due to changes in the environment (changes in temperature) or deterioration over time.
Naturally, we anticipate that, and check the initial values and during maintenance, but it is a work that leaves us uneasy about whether the settings are correct or the frequency of maintenance is appropriate.
Set voltage automatic adjustment solution
Analog Devices has a product called Power System Management (PSM).
By using this product, it is possible to dynamically adjust the voltage accuracy within ±0.5% of the set voltage.
Suppose ①VOUT of the DC/DC converter set to output 3.3V outputs 3.23V.
The PSM (LTC2977) reads ①VOUT value as 3.23V on ②VSENSE line.
Since the DC/DC converter output is 0.07V lower, the voltage for adjustment is output from the PSM to the ③VDAC line to adjust the DC/DC converter output to 3.3V.
(4) By applying a voltage for adjustment to the VFB line, the DC/DC converter output (1) VOUT becomes 3.299V.
Systems with this PSM will automatically adjust when the output voltage varies due to the connected load.
There is also a product called the LT6110 that specializes in compensating for cable drop.
This is useful, for example, when the DC/DC converter (LT3976) and the load are connected through 20 feet of 18 AWG copper wire, as in the following schematic.
Using the LT6110 dramatically improves load regulation characteristics.
See Design Note DN529 for more details.
By using these products, it is now possible for operators to manually adjust the voltage or adjust the voltage value during periodic inspections, all of which can be done automatically.
This makes it possible to reduce operator man-hours and improve system safety performance.
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Power System Management product information
LTC2977 Product Information
LT6110 product information