IEEE Electrification - December 2020 - 15

where these two are interfaced through the overcurrent
protection circuit and a heater switch. The overcurrent
protection circuit is the same interfacing either the battery converter or the main bus depending on the adopted
configuration. The heater switch is controlled through a
microcontroller unit (MCU), which is programmed for the
battery's housekeeping and heater control. This MCU is
also fed by the battery itself through a 3.3-V low-dropout
voltage regulator, as displayed in Figure 9.

whether the current level has exceeded the predefined
limit as a consequence of an overload or fault, or by the
reading of the differential voltage across the switch [(as
shown in Figure 10(a)].

LCL
In the case of an overload or a fault in the load, when the
current of the latter goes higher than a predetermined
threshold, the LCL changes its mode of operation into
current limitation. At the beginning of this event, the
timer displayed in Figure 10(a) is activated. This timer
counts for a duration called the trip-off time as long as
the current absorbed by the load is still higher than its
predefined threshold. During this mode of operation,
switch S 1 is forced to operate in a linear mode instead of
operating in the ohmic " on " mode. This mode change at
the level of switch S 1 should be quick to decrease the
surge current. The current sensor is responsible for controlling the load current in this mode at a lower and fixed
level, as shown in Figure 10(b), which is achieved by
modulating switch S 1\s gate voltage. The accuracy of this
latter is dependent upon the voltage reference used in
the design and current sensing circuit. Note that the

EPS Protection on the CubeSat
A typical diagram of a latch-up current limiter (LCL),
together with the undervoltage protection (UVP), is
shown in Figure 10(a). The combination of the LCL with
the UVP is referred to as the protection unit hereafter. As
detailed in Volpi 2007, the protection unit is usually
placed between the load and voltage regulator. It consists
of a switch with its driver, current sensor, trip-off trigger,
undervoltage detector, and a memory cell. The protection
unit can be on or off, and this is usually determined by
the memory cell.
The protection unit switch may be triggered by either a
signal coming from the current sensor, which identifies

VBus
Rs

Trip-Off Trigger

Differential
Amplifier

Current
Sensor

R
Off
On

S1
Current Sensor,
Driver, and Switch
Memory Cell

Timer

UVP
Undervoltage
Detection

(a)
Current Overshoot Decay Time
Current
Overshoot

Time to Current Overshoot

Excess
Current

10% of
Excess
Current

Max
Current Limit
Limitation Min
Nominal LCL
Current

Bus Voltage
LCL Enabled
On Threshold

UVP Switch
Off Threshold

LCL Is On
Max Overshoot
Recovery Time

LCL Is Off

500-µs
UVP Noise Immunity

Trip-Off Time

LCL Is On

500-µs
Switch On Response Time
(c)

(b)

Figure 10. An LCL diagram including UVP. (a) A typical diagram, (b) the overcurrent event, and (c) the undervoltage event. Max: m
- aximum; Min:
minimum.

IEEE Elec trific ation Magazine / D EC EM BE R 2 0 2 0

IEEE Electrification - December 2020

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