Electricity: power supply or regulation systems – In shunt with source or load – Using choke and switch across source
Reexamination Certificate
2000-07-21
2001-08-14
Sterrett, Jeffrey (Department: 2838)
Electricity: power supply or regulation systems
In shunt with source or load
Using choke and switch across source
C323S231000, C323S266000
Reexamination Certificate
active
06275013
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a switching power supply which switches current flowing through an inductor by using a switching element thereby to obtain a boosted DC output.
A tuner provided in a television etc. employs an arrangement wherein a tuning frequency is changed by changing a tuning voltage. The tuning voltage is generally a voltage slightly exceeding 30 volt at the maximum. Thus, the tuning voltage cannot be generated from the operation power supply in a vehicle-mounted television having the operation power supply of 12 volt. Accordingly, in this case, a booster circuit is provided in order to obtain the DC voltage slightly exceeding 30 volt used for generating the tuning voltage.
FIG. 2
shows the prior art of the booster circuit which is generally configured by the known arrangement of a chopper type booster circuit. That is, a transistor Q
7
performing the switching operation in accordance with the output of an oscillation circuit
53
is provided on the output side of an inductor L
7
. The oscillation of the oscillation circuit
53
is controlled by the output of an error detection circuit
54
for detecting error voltage of the DC output, whereby the voltage of the DC output is stabilized (this technique is hereinafter called a the first prior art).
One of the prior arts for generating the tuning voltage is proposed in the Unexamined Japanese Utility Model No. Sho 62-178619.
FIG. 3
is a block diagram showing this technique. This technique will be explained with reference to the figure. In this technique, a positive power supply +B is introduced to a zener diode D
7
through a serial resistor R
21
for voltage drop, thereby obtaining DC output necessary for generating the tuning voltage from the cathode of the zener diode D
7
. A tuning voltage limiting circuit
51
for limiting the voltage to a predetermined voltage is provided between the cathode of the zener diode D
7
and a PWM circuit
52
for generating the tuning voltage. When receiving a particular band, the voltage of the DC output supplied to the PWM circuit
52
is limited to the predetermined voltage, whilst when receiving other bands, the voltage supplied to the PWM circuit
52
is made equal to the cathode voltage of the zener diode D
7
(this technique is hereinafter called as the second prior art).
However, according to the first prior art, since the error detection circuit
54
for detecting the error voltage of the DC output is required in order to stabilize the voltage of the DC output, there arises a problem that the circuit configuration becomes complicated. According to the second prior art, the serial resistor R
21
and the zener diode D
7
are employed in order to stabilize the voltage supplied to the tuning voltage limiting circuit
51
. Thus, since the two elements are required for stabilizing the voltage, the number of the elements is increased. In this case, since the serial resistor R
21
serves as an element for causing the voltage drop for absorbing the voltage variation, there arises a problem that the serial resistor R
21
can not be eliminated.
SUMMARY OF THE INVENTION
Accordingly, the present invention has been made in view of the aforesaid problems of the prior arts, and an object of the present invention recited in claim
1
is to provide a switching power supply which can stabilize the output voltage by using only a zener diode without using a serial resistor for voltage drop, in the arrangement that unstable voltage is generated by using a switching element and the unstable voltage is stabilized by using a zener diode and the arrangement that an internal resistance of a switching circuit for generating the unstable voltage is used as a serial resistor for generating voltage drop for absorbing voltage variation thereby to eliminate an error detection circuit.
In addition to the aforesaid object, another object of the invention is to provide a switching power supply which can simplify the circuit arrangement of a block for switching a switching element in a manner that the output of an auxiliary coil magnetically coupled to an inductor is introduced to the switching element thereby to switch the switching element.
In addition to the aforesaid object, still another object of the invention is to provide a switching power supply which can reduce the ripple component of the DC output sufficiently by providing a n type smoothing circuit.
In addition to the aforesaid object, still another object of the invention is to provide a switching power supply which can simplify the arrangement of a block for generating tuning voltage by using an operation power supply for a tuning voltage generation circuit.
In addition to the aforesaid object, still another object of the invention is to provide a switching power supply which can suppress dissipation power to a lower value when viewed from a switching side.
In order to attain the aforesaid object, the switching power supply according to the invention is applied to such a switching power supply which includes an inductor whose one terminal is coupled to a primary side DC power supply and a switching element coupled to the other terminal of the inductor, wherein current flowing through the inductor is switched by using the switching element to obtain a boosted DC output, and the switching element is arranged to further include a rectifying and smoothing circuit coupled to the other terminal of the inductor, and a zener diode coupled to an output of the rectifying and smoothing circuit, wherein an internal resistance on the inductor side viewed through the rectifying smoothing circuit is employed as a serial resistor for generating a voltage drop which is required for the zener diode to absorb voltage fluctuation, thereby to stabilize a voltage of the DC output.
That is, when the voltage of the DC output decreases, the zener diode acts to decrease an amount of the voltage drop generated by the internal resistance on the inductor side viewed through the rectifying and smoothing circuit thereby to prevent the decrease of the voltage of the DC output. Further, when the voltage of the DC output increases, the zener diode acts to increase an amount of the voltage drop generated by the internal resistance thereby to prevent the increase of the voltage of the DC output.
In addition to the aforesaid arrangement, the switching power supply is arranged to further comprise an auxiliary coil magnetically coupled to the inductor, wherein an output of the auxiliary coil is introduced to the switching element thereby to perform a switching operation in the switching element. That is, the inductor, the auxiliary coil and the switching element form a blocking oscillation circuit which performs self-oscillation.
In addition to the aforesaid arrangement, the switching power supply is arranged in a manner that the rectifying smoothing circuit is provided with a n type smoothing circuit. Thus, the ripple component can be removed more efficiently.
In addition to the aforesaid arrangement, the switching power supply is arranged in a manner that the DC output is introduced to a tuning voltage generation circuit for generating a tuning voltage to be supplied to a tuner. That is, the switching power supply provided as a constituent element for a block for generating the tuning voltage can be configured with a simple arrangement wherein the error detection circuit and the serial resistor for the zener diode are eliminated.
In addition to the aforesaid arrangement, the switching power supply is arranged in a manner that a current value flowing through the zener diode is set to be smaller than twice a maximum value of a current flowing through the tuning voltage generation circuit when a load of the DC output is no load, and a current value flowing through the zener diode is set to be larger than 0 also when a current flowing through the tuning voltage generation circuit is maximum. Thus, even if the variance of the elements are expected, merely a small current flows through the zener diode in such a range that the DC output can be
Crowell & Moring , L.L.P.
Funai Electric Co. Ltd.
Sterrett Jeffrey
LandOfFree
Switching power supply employing an internal resistance in... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Switching power supply employing an internal resistance in..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Switching power supply employing an internal resistance in... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2510533