Hot-Plug Protection Circuit
Original Publication Date: 1990-Feb-01
Included in the Prior Art Database: 2005-Mar-15
Chung, CT: AUTHOR [+2]
This article describes a circuit to hot-plug (connect) and power-up a remote medium attachment unit (MAU) into a running computer system, and prevent high current surge and voltage dip on the system.
Hot-Plug Protection Circuit
describes a circuit to hot-plug (connect)
and power-up a remote medium attachment unit (MAU) into a running
computer system, and prevent high current surge and voltage dip on
New open architecture
requires systems to have the ability to
plug equipment that requires source voltage onto a running system and
not cause voltage transients that may cause system errors. The cir
cuit disclosed herein prevents high current surge and voltage dip,
allows slow current and voltage start, protects against short
circuit, and detects and indicates to the system a not-good signal
when a short circuit occurs in a MAU.
protection circuit is shown in the drawing.
the following description of the circuit Q designates a field-effect
transistor (FET), R a resistor, C a capacitor, and CR a zener diode.
A power FET Q1 is placed between the source voltage Vin and the
output voltage Vout to the MAU. Q1 is controlled in stages of
operation by the associated components to turn on slow, to be full-on
with minimum voltage drop, to be partially on, and to turn off. The
signal portion of the circuit switches to an up level when a short is
present on the output voltage Vout.
functions in the following modes of operation:
Mode 1. Start up and operate with MAU attached.
Mode 2. Start the system without the MAU attached, plug the
MAU onto a running system (hot plug), sequence the voltage to the MAU
in an orderly manner, and operate with the MAU attached.
Mode 3. In normal operation, whether a MAU is
attached or not,
detect a short circuit, turn off the Q1, signal the system that the
short is present, and recover only when the short is removed and the
MAU is unplugged.
Mode 4. Start up with MAU attached and with a short
in the MAU
circuit. Protect against the short and signal the system of the
short. Recover only when the short is removed and the MAU is
Start up and operate with a MAU attached. The MAU is attached to
Vout and Vout RTN. The source is applied to Vin and Vin RTN. Vin is
turned on. On initial Vin turn-on, Q1 is off since the
source-to-gate voltage is initially O volts. As the source voltage
increases, current flows through the parallel circuit, Q2 EB
(emmitter-base), R16 and C3 instead of Q1. This current flow turns
Q2 on and keeps the gate-to-source voltage of Q1 very low. Q1 is
of R8, CR7 and C4 will charge C4. The
of C4 through R8 and CR7 enables its voltage to be larger than the
voltage at the junction of R7 and R4, which is set by the divider net
work of Q2 EC (emitter-collector) in parallel with R5 in series with
R7 and R4. Therefore, CR6, which connects the junction of R7, R4 nd
C4, is back biased.
As the source
voltage reaches its value, C3 will charge and