IEEE Power Electronics Magazine - March 2020 - 26

Drain Currents (A)

Drain-Source Voltages (V)

acid/lithium-ion battery applications. There
were several motivations behind this
LD3~70 nH
design. First, the conventional mechanical
contactors have a high profile, which
LD2~40 nH
requires allocation of a considerable
Q3
LD 1~10 nH
Q2
Q1
amount of space for them in the battery
LS1~10 nH
compartment, which in turn reduces the
LS2~40 nH
battery capacity. Next, the mechanical contactors are slower in comparison and
LS3~70 nH
require tens to hundreds of milliseconds to
open/close. In short circuit-sensitive applications, i.e., applications using lithium-ion
FIG 5 The designed PCB with three MOSFETs in parallel.
batteries, this time can be detrimental to
the safety of the system. Thanks to the fast
switching speeds of power semiconductor devices, the
70
solid-state relays can act in a few hundreds of nanoseconds,
V
which is significantly less in comparison and can provide
DS1
60
VDS2
better protection for battery/equipment. Finally, yet imporVDS3
50
tantly, the solid-state relay has a smaller driving power
40
requirement. Typically, several watts of power are needed to
activate the coil in mechanical contactors, whereas the volt30
age-controlled MOSFETs consume almost no power in
20
steady state. This helps improve the overall battery life and
10
system efficiency.
Figure 8 shows a solid-state switch implemented using
0
14 Si MOSFETs in parallel, intended to operate at currents
-10
up to 600-A dc and 1,000-A transient (under short circuit
0
2
4
6
8
×10-7
Time (s)
conditions, and so on). Selection of 14 MOSFETs in parallel
(a)
is because the MOSFETs are needed to operate in the linear
60
region at turn-off and absorb the energy of the significant
ID1
voltage spike due to the parasitic inductances of the large
50
ID2
cables in the system. Zener diode clamping is used to operID3
40
ate the devices in the linear region and dissipate the excess
amount of energy in the system [8]. Busbars are used in the
30
system to conduct the current, because the high rated current could not be handled using PCB traces. To achieve a
20
better form factor and avoid extreme parasitic inductances
10
in series with the devices, the 14 MOSFETs are divided into
two batches and placed in two rows.
0
The designed high-current solid-state switch of Figure 8
-10
was
tested under a variety of conditions including nomi0
2
4
6
8
×10-7
Time (s)
nal and short circuit currents and elevated temperatures.
(b)
The power-cycling test was also performed on more than
one prototype, and satisfactory results were obtained.
FIG 6 The experimental waveforms of (a) turn-on voltages
This product is still in its early design stages; thereand (b) turn-on currents of the parallel MOSFETs under 10-A
fore, no experimental test results are being reported
load current.
from its operation.
the proposed method can be used for much larger number
of MOSFETs in parallel than the three MOSFETs shown in
Figure 5. All that is needed for paralleling the MOSFETs
using this method is to simply place them in a linear layout.

High-Current Solid-State Relay
With the proof of concept for the proposed method, a highcurrent solid-state switch was designed to be used in lead-

IEEE POWER ELECTRONICS MAGAZINE

z March 2020

Conclusions
This article proposed a new method for paralleling power
semiconductor devices in solid-state switch application.
Although it can be applied to any other application that
requires low/medium switching frequencies, the proposed
technique adds inductances in series with the drain and
source terminals of semiconductor devices to equalize the
dynamic currents among them. The added inductances do

IEEE Power Electronics Magazine - March 2020

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