Specifications

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T
3
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3
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2
2
Use Remote Sensing to Compensate for
Load-Lead Effects
When your power supply leaves the
factory, its regulation sense terminals
are usually connected to the output
terminals. This limits the supply’s
voltage regulation abilities, even with
very short leads. The longer the leads
and the higher the wire gauge, the
worse the regulation gets (Figure 1).
Compare the output impedance of a
well-regulated 10 A supply, which
might have an output impedance of
0.2 mΩ, with the resistance of copper
wire:
AWG wire size Resistance in mΩ/ft (at 20° C)
22 16.1
20 10.2
18 6.39
16 4.02
14 2.53
12 1.59
10 0.999
And regulation gets even worse if
you use a relay to connect power to
the load.
Remote sensing, in which you con-
nect the sense terminals of the power
supply’s internal feedback amplifier
directly to the load, lets the power
supply regulate its output at the load
terminals, rather than at its own out-
put terminals (Figure 2). The supply
voltage shifts as necessary to com-
pensate for the resistance of the load
leads, relays, or connectors, thereby
keeping the voltage at the load con-
stant.
To implement remote sensing, dis-
connect the local sense leads from
the output terminals. Use twisted
two-wire shielded cable to connect
the power supply sensing terminals
to the sense points on the load.
(Don’t use the shield as one of the
sensing conductors.) Connect one
end of the shield to ground and leave
the other end unconnected.
Sensing currents are typically less
than 10 mA, and as a general rule,
you should keep the voltage drop in
the sense leads to less than 20 times
the power supply temperature coeffi-
cient (usually stated in mV/°C). This
is easy to achieve with readily avail-
able shielded two-wire cable.
Figure 1: The effects of six feet of AWG 14-gauge leads without remote sensing
Figure 2: Using remote sensing to correct the lead-load problem
Tip
1
4.7 V
+S
5 V Load
–S
Power Supply
Programmed
for 5 V, 10 A
Load leads are
6 foot, AWG 14
0.015 Ω lead resistance
0.015 Ω lead resistance
+
–
5 V
+S
–S
Power Supply
Programmed
for 5 V, 10 A
+
–
0.015 Ω lead resistance
0.015 Ω lead resistance
5.3 V Load
Load leads are
6 foot, AWG 14