Specifications

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Tip
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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 out-
put at the load terminals, rather
than at its own output terminals
(Figure 2). The supply voltage
shifts as necessary to compensate
for the resistance of the load
leads, relays, or connectors, there-
by keeping the voltage at the load
constant.
To implement remote sensing, dis-
connect the local sense leads from
the output terminals. Use twisted
two-wire shielded cable to con-
nect the power supply sensing ter-
minals 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 tempera-
ture coefficient (usually stated in
mV/°C). This is easy to achieve
with readily available 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.
Power Supply
Programmed
for 5 V, 10 A
S
S
0.015 Ω lead resistance
Load
0.015 Ω lead resistance
load leads are
6 foot, AWG 14
4.7 V
5 V
Power Supply
Programmed
for 5 V, 10 A
S
S
0.015 Ω lead resistance
Load
0.015 Ω lead resistance
load leads are
6 foot, AWG 14
5 V
5.3 V
2
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