Specifications

II
1
TT
33
II
33
II
22
T
1
T
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 connect
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 output terminals (Figure 2).
The supply voltage shifts as necessary
to compensate for the resistance of
the load leads, relays, or connectors,
thereby keeping the voltage at the
load constant.
To implement remote sensing,
disconnect 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
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
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
Tip
1