Power supplying system with a delayed closing device for delayed closing of a heat-dissipating fan

A power supplying system includes a switching control circuit connected to a stand-by power source so as to receive electrical power therefrom. The switching control circuit is further connected to a power-supplying unit and is activated to control operation of the power-supplying unit in a selected one of an ON state, where the power-supplying unit supplies electrical power for operating a heat-dissipating fan, and an OFF state, where the power-supplying unit ceases to supply the electrical power to the heat-dissipating fan. A delayed closing device receives a power-OFF signal from the power-supplying unit at an instant the power-supplying unit is operated from the ON state to the OFF state, and connects the heat-dissipating fan to the stand-by power source upon receiving the power-OFF signal to enable the heat-dissipating fan to receive electrical power from the stand-by power source and permit continued operation of the heat-dissipating fan even after the heat-dissipating fan ceases to receive the electrical power from the power-supplying unit.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The invention relates to a power supplying system, more particularly to one 
with a delayed closing device for delayed closing of a heat-dissipating 
fan. 
2. Description of the Related Art 
Electronic equipment, such as a desktop computer or an uninterruptible 
power system (UPS), incorporates a power supplying system to provide 
electrical power needed to operate the equipment. FIG. 1 illustrates a 
conventional power supplying system installed in a desktop computer. When 
the user operates a power switch on the desktop computer to operate the 
latter, a power-supplying unit 1 is activated so that a 110-volt 
alternating current (AC) input from an electrical outlet is supplied to an 
input rectifying and filtering circuit 10 to obtain a rectified and 
filtered 300-volt direct current (DC) signal. A switching unit 11 converts 
the 300-volt DC signal into a .+-.150-volt square wave signal. An 
isolation power transformer 12 reduces the output of the switching unit 11 
to .+-.5 volts or .+-.12 volts. The output of the isolation power 
transformer 12 is filtered and rectified by an output rectifying and 
filtering circuit 13 before being supplied to a heat-dissipating fan 14 
and to other electronic components of the desktop computer. As such, when 
the power-supplying unit 1 is activated, electrical power is supplied to 
the various electronic components of the desktop computer to operate the 
latter, and the heat-dissipating fan 14 is turned on to dissipate the heat 
that is generated due to the operation of the power-supplying unit 1 and 
the desktop computer. The output rectifying and filtering circuit 13 is 
further connected to a pulse width modulation (PWM) control circuit 15 
that, in turn, is connected to the switching unit 11. The PWM control 
circuit 15 controls operation of the switching unit 11 to ensure that the 
power-supplying unit 1 will provide a stable output. When the user 
operates the power switch on the desktop computer to deactivate the 
latter, the AC input of the power-supplying unit 1 is cut-off, thereby 
disabling the power-supplying unit 1. The heat-dissipating fan 14 is also 
turned off at this time. 
The following drawback arises from the aforementioned design: When the 
power-supplying unit 1 is turned off abruptly after operating for a period 
of time, a continued rise in the ambient temperature of the electronic 
components of the power-supplying unit 1 and the desktop computer will be 
experienced. Because the heat-dissipating fan 14 is already turned off, 
heat cannot be dissipated immediately, thereby resulting in prolonged 
exposure of the electronic components of the power-supplying unit 1 and 
the desktop computer to high ambient temperature conditions. This can 
result in shorter service lives for the electronic components of the 
power-supplying unit 1 and the desktop computer and in lower reliability. 
FIG. 2 illustrates a conventional power supplying system for an ATX 
personal computer. Unlike the power supplying system of FIG. 1, the 
power-supplying unit 2 is further connected to a stand-by power source 23 
and a remote switching control circuit 24. The stand-by power source 23 
includes a switching and isolating circuit 230 and an output circuit 231. 
When the power-supplying unit 2 is activated, aside from processing the AC 
input for supplying the electrical power needed to operate the 
heat-dissipating fan 22 and the various electronic components of the ATX 
personal computer, the power-supplying unit 2 further provides the AC 
input to the stand-by power source 23. The stand-by power source 23 
provides electrical power needed to operate the remote switching control 
circuit 24, and is connected to the motherboard (not shown) of the ATX 
personal computer. The motherboard is connected to a remote switch (not 
shown), such as a keyboard or a modem. When the remote switch input is at 
a high logic state, the remote switching control circuit 24 will control 
the PWM control circuit 210 of the power-supplying unit 2 to a remote OFF 
state, whereby the power-supplying unit 2 ceases to supply electrical 
power to the various electronic components of the ATX personal computer, 
and the heat-dissipating fan 22 is turned off. The stand-by power source 
23 continues to operate at this time to supply the electrical power needed 
by the remote switching control circuit 24. When the remote switch input 
changes to a low logic state, the remote switching control circuit 24 will 
control the PWM control circuit 210 of the power-supplying unit 2 to a 
remote ON state, whereby the power-supplying unit 2 resumes the supply of 
electrical power to the various electronic components of the ATX personal 
computer, and the heat-dissipating fan 22 is once again turned on. The 
conventional power-supplying system of FIG. 2 has the following drawback 
during use: When the remote switch is activated to operate the 
power-supplying unit 2 in the remote OFF state, the power-supplying unit 2 
ceases to generate electrical power for activating the heat-dissipating 
fan 22. Thus, a continued rise in the ambient temperature of the 
electronic components of the power-supplying unit 2 and the ATX personal 
computer will be experienced at the instant of operating the 
power-supplying unit 2 in the remote OFF state. This situation is 
aggravated due to the continued operation of the stand-by power source 23. 
Because the heat-dissipating fan 22 is already turned off, heat cannot be 
dissipated immediately, thereby resulting in prolonged exposure of the 
electronic components of the power-supplying unit 2 and the ATX personal 
computer to high ambient temperature conditions that can lead to shorter 
service lives for the electronic components of the power-supplying unit 2 
and the ATX personal computer and lower reliability. 
SUMMARY OF THE INVENTION 
Therefore, the main object of the present invention is to provide a power 
supplying system with a delayed closing device for delayed closing of a 
heat-dissipating fan to prolong the service lives and increase the 
reliability of electronic components within the vicinity of the 
heat-dissipating fan. 
According to this invention, a power supplying system comprises a 
power-supplying unit, a heat-dissipating fan connected to the 
power-supplying unit, a stand-by power source, and a switching control 
circuit connected to the stand-by power source so as to receive electrical 
power therefrom. The switching control circuit is further connected to the 
power-supplying unit and is adapted to be activated to control operation 
of the power-supplying unit in a selected one of an ON state, where the 
power-supplying unit supplies electrical power for operating the 
heat-dissipating fan, and an OFF state, where the power-supplying unit 
ceases to supply the electrical power to the heat-dissipating fan. A 
delayed closing device is connected to the power-supplying unit, the 
heat-dissipating fan and the stand-by power source. The delayed closing 
device receives a power-OFF signal from the power-supplying unit at an 
instant the power-supplying unit is operated from the ON state to the OFF 
state. The delayed closing device connects the heat-dissipating fan to the 
stand-by power source upon receiving the power-OFF signal to enable the 
heat-dissipating fan to receive electrical power from the stand-by power 
source and permit continued operation of the heat-dissipating fan even 
after the heat-dissipating fan ceases to receive the electrical power from 
the power-supplying unit.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring to FIG. 3, the preferred embodiment of a power supplying system 
according to the present invention is adapted for use with an ATX personal 
computer and is shown to include a power-supplying unit 30, a stand-by 
power source 31, a remote switching control circuit 32, a heat-dissipating 
fan 33 and a delayed closing device 34. The power-supplying unit 30 is 
connected to the stand-by power source 31, the remote switching control 
circuit 32 and the heat-dissipating fan 33. The stand-by power source 31 
includes a switching and isolating circuit 310 and an output circuit 311. 
The stand-by power source 31 provides electrical power needed to operate 
the remote switching control circuit 32, and is connected to the 
motherboard (not shown) of the ATX personal computer. The motherboard is 
connected to a remote switch (not shown). The remote switch can be a 
keyboard or a modem, and is operable to activate the remote switching 
control circuit 32 to control operation of the power-supplying unit 30 in 
a selected one of a remote OFF state or a remote ON state. When the 
power-supplying unit 30 is in the remote OFF state, the power-supplying 
unit 30 cuts off its supply of electrical power to the heat-dissipating 
fan 33. However, the stand-by power source 31 continues to operate at this 
time to supply the electrical power needed by the remote switching control 
circuit 32 to permit activation of the remote switching control circuit 32 
for resuming operation of the power-supplying unit 30 in the remote ON 
state. Referring to FIG. 4, the delayed closing device 34 is connected to 
the heat-dissipating fan 33, the stand-by power source 31 and the 
power-supplying unit 30. A first protective isolating component (D1) 
interconnects the power-supplying unit 30 and the heat-dissipating fan 33. 
A second protective isolating component (D2) interconnects the delayed 
closing device 34 and the heat-dissipating fan 33. In this embodiment, the 
first and second protective isolating components (D1, D2) are diodes. In 
use, when the power-supplying unit 30 supplies electrical power to the 
heat-dissipating fan 33, the second protective isolating component (D2) 
prevents electrical current from the heat-dissipating fan 33 from flowing 
into the delayed closing device 34. When the power-supplying unit 30 
ceases to supply electrical power to the heat-dissipating fan 33, the 
first protective isolating component (D1) prevents electrical current 
supplied to the heat-dissipating fan 33 by the delayed closing device 34 
from flowing into the power-supplying unit 30. 
The delayed closing device 34 of the preferred embodiment includes a 
temperature sensing circuit 4, a timer 5, a controller 6 and a fan driving 
circuit 7. 
The temperature sensing circuit 4 includes a temperature sensor 40 and a 
comparator 41. In this embodiment, the temperature sensor 40 is a thermal 
resistor but is not limited thereto. The temperature sensor 40 generates a 
sensor output that varies according to the ambient temperature (T). The 
comparator 41 receives the sensor output of the temperature sensor 40, and 
compares the same with an internal reference voltage (Vref) thereof that 
corresponds to a predetermined reference temperature (To). When the sensor 
output is greater than the reference voltage (Vref), indicating a 
condition in that the ambient temperature is greater than the reference 
temperature (T&gt;To), the comparator 41 generates an overheating detect 
signal. 
The timer 5 includes an oscillator (OSC) 50. In this embodiment, the 
oscillator 50 is a 555 integrated circuit but is not limited thereto. At 
the instant the power-supplying unit 30 is deactivated, the 
power-supplying unit 30 generates a power-off signal to the oscillator 50. 
At this time, the oscillator 50 starts executing a timing operation during 
which the oscillator 50 generates a timing signal. After a predetermined 
time period has elapsed, the oscillator 50 will terminate generation of 
the timing signal. 
The controller 6 includes two transistors (Q1, Q2) having base terminals 
that are connected to the oscillator 50 and the comparator 41, 
respectively. The emitter terminals of the transistors (Q1, Q2) are 
connected to the output circuit 311 of the stand-by power source 31 to 
receive an operating voltage therefrom. The collector terminals of the 
transistors (Q1, Q2) are coupled to each other. The controller 6 generates 
a driver enable signal at the collector terminals of the transistors (Q1, 
Q2) upon receiving the timing signal from the oscillator 50 and the 
overheating detect signal from the comparator 41 at the same time. The 
controller 6 does not generate the driver enable signal when it fails to 
receive the timing signal and the overheating detect signal 
simultaneously. 
The fan driving circuit 7 includes a transistor (Q3) having an emitter 
terminal connected to the output circuit 311 of the stand-by power source 
31, a base terminal connected to the controller 6, and a collector 
terminal connected to the heat-dissipating fan 33 via the second 
protective isolating component (D2). Upon receipt of the driver enable 
signal from the controller 6, the transistor (Q3) conducts, thereby 
connecting the output circuit 311 of the stand-by power source 31 to the 
heat-dissipating fan 33. As such, the heat-dissipating fan 33 can continue 
to operate even after the power-supplying unit 30 ceases to supply 
electrical power thereto. Thus, residual heat in the vicinity of the 
heat-dissipating fan 33 can be dissipated quickly to lower the ambient 
temperature of the power-supplying unit 30 and the ATX personal computer. 
The heat-dissipating fan 33 will be turned off when the oscillator 50 ends 
its timing operation, or when the comparator 41 stops generating the 
overheating detect signal. 
Referring once again to FIGS. 3 and 4, at the instant the remote switch is 
operated to activate the remote switching control circuit 32 and operate 
the power-supplying unit 30 in the remote OFF state, the power-supplying 
unit 30 generates a power-off signal to the oscillator 50, thereby 
enabling the latter to initiate a timing operation during which the 
oscillator 50 generates the timing signal. At this time, if the ambient 
temperature (T) is higher than the reference temperature (To), the 
comparator 41 will generate the overheating detect signal. Since the 
controller 6 receives the timing signal and the overheating detect signal 
simultaneously, the controller 6 will generate the driver enable signal to 
enable the fan driving circuit 7 to interconnect the output circuit 311 of 
the stand-by power source 31 and the heat-dissipating fan 33. Thus, the 
heat-dissipating fan 33 continues to operate even after the 
power-supplying unit 30 ceases to supply electrical power thereto, as long 
as the ambient temperature (T) is higher than the reference temperature 
(To) and the oscillator 50 continues to generate the timing signal. 
Therefore, residual heat in the vicinity of the heat-dissipating fan 33 
can be quickly dissipated to lower the ambient temperature of the 
power-supplying unit 30 and the ATX personal computer. As such, the 
objective of prolonging the service lives and increasing the reliability 
of electronic components within the vicinity of the heat-dissipating fan 
33 can be achieved with the provision of the delayed closing device 34 of 
this invention. 
When the ambient temperature (T) becomes lower than the reference 
temperature (To), or when the oscillator 50 terminates generation of the 
timing signal after the predetermined time period has elapsed, the 
controller 6 ceases to generate the driver enable signal, thereby 
disabling the fan driving circuit 7 to break electrical connection between 
the output circuit 311 of the stand-by power source 31 and the 
heat-dissipating fan 33. The heat-dissipating fan 33 ceases to operate at 
this time. 
In the preferred embodiment, both of the conditions that the ambient 
temperature (T) is higher than the reference temperature (To) and the 
oscillator 50 continues to generate the timing signal must be satisfied 
for continued operation of the heat-dissipating fan 33 when the 
power-supplying unit 30 is operated in the remote OFF state. It should be 
noted that the objective of the present invention can still be met even if 
continued operation of the heat-dissipating fan 33 occurs when only one of 
the conditions, i.e. the ambient temperature (T) is higher than the 
reference temperature (To) or the oscillator 50 generates the timing 
signal, is satisfied. Thus, only one of the temperature sensor 4 and the 
oscillator 5 is present in other embodiments of the delayed closing device 
of this invention. 
While the present invention has been described in connection with what is 
considered the most practical and preferred embodiment, it is understood 
that this invention is not limited to the disclosed embodiment but is 
intended to cover various arrangements included within the spirit and 
scope of the broadest interpretation so as to encompass all such 
modifications and equivalent arrangements.