Electricity: electrical systems and devices – Safety and protection of systems and devices – With specific voltage responsive fault sensor
Reexamination Certificate
1999-03-08
2001-05-08
Jackson, Stephen W. (Department: 2836)
Electricity: electrical systems and devices
Safety and protection of systems and devices
With specific voltage responsive fault sensor
C361S018000, C361S115000
Reexamination Certificate
active
06229681
ABSTRACT:
CLAIM OF PRIORITY
This application makes reference to, incorporates the same herein, and claims all benefits accruing under 35 U.S.C. §119 from an application for SWITCHING MODE POWER SUPPLY APPARATUS HAVING A LOW VOLTAGE PROTECTION CIRCUIT earlier filed in the Korean Industrial Property Office on the Mar. 7, 1998 and there duly assigned Serial No. 7650/1998.
BACKGROUND OF THE INVENTION
1. Technical Field
The present invention relates, in general, to a switching mode power supply (SMPS) unit having a protection circuit for a brown-out condition and, more particulary, to a switching mode power supply apparatus having a protection circuit for a brown-out condition in which, if an input alternating voltage is below a predetermined value, it is detected so that a switching mode power supply apparatus cannot be actuated or, if actuated, its operation is stopped. As a result, the switching mode power supply apparatus and a load circuit connected to an output terminal of the switching mode power supply apparatus are protected from the influx of excessive current.
2. Related Art
Generally, electric or electronic equipment need a direct current power supply apparatus which converts an alternating current (AC) power source to a predetermined DC power source so as to enable the system therein to be operated, for which a switching mode power supply apparatus of small size and light weight is mainly employed as a DC power supply apparatus.
U.S. Pat. No. 4,999,730 presents a solution to this problem but with disadvantages in that a power control device is necessary to directly control the alternating input, the control circuit is complicated, and an auxiliary power source is necessary for the control circuit.
As described in more detail below, prior switching mode power supply apparatus have several disadvantages. A primary disadvantage occurs when an input alternating voltage is less than a normal value, that is, when a brown-out condition occurs. Under such circumstances, the feedback controller of the apparatus applies a control signal to a pulse width modulation (PWM) controller of the apparatus. As explained in more detail below, this causes current accumulating in a secondary coil of the transformer of the apparatus to increase by an amount corresponding to the enlarged duty cycle of the PWM pulse generated by the PWM controller. As a result, circuitry of the apparatus or the load circuit connected to the apparatus can malfunction or be damaged due to overcurrent. As a further result, equipment employing the apparatus can also be damaged or break down.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a switching mode power supply apparatus having a low voltage protection circuit of simple construction in which, when an input alternating current power becomes lower than a predetermined value, a switching mode power supply apparatus is not actuated, or its operation is stopped after the switching mode power supply apparatus is normally actuated, the purpose being to attain reliability in electric and electronic equipment employing the switching mode power supply apparatus, even in a brown-out condition.
To achieve the above objects, there is provided a switching mode power supply apparatus having a low voltage protection circuit including: a first rectifying and smoothing circuit for rectifying and smoothing an input alternating current voltage to output a direct voltage; an actuating power supply unit for receiving the output voltage from the first rectifying and smoothing circuit, and for converting it to a predetermined DC voltage; a PWM controller for being actuated upon receipt of output voltage from the actuating power supply unit, and outputting a predetermined pulse width modulation waveform, said PWM controller having an overvoltage protection circuit; a switching transistor which is switched by the output waveform of the PWM controller; a switching transformer for accumulating the output power of the first rectifying and smoothing circuit, applied to a first coil in accordance with the switching of the switching transistor, at a second coil and a third coil; a second rectifying and smoothing circuit for rectifying and smoothing the voltage accumulated at the second coil, and for outputting a predetermined DC voltage supplied to a load circuit; a third rectifying and smoothing circuit for rectifying and smoothing a voltage accumulated at the third coil of the switching transformer, and for outputting another predetermined DC voltage; a constant-voltage circuit for receiving the output voltage from the third rectifying and smoothing circuit, and for outputting the driving voltage of the PWM controller; a first protection circuit for receiving the output voltage from the first rectifying and smoothing circuit, and for controlling in such a way that an actuating power supply unit is not driven if the value of the output voltage of the first rectifying and smoothing circuit becomes lower than a predetermined value; and a second protection circuit for controlling in such a way that, when an input alternating current voltage becomes lower than a predetermined value, the output voltage of the constant-voltage circuit becomes higher, so that a driving voltage sufficient to operate an overvoltage protection circuit of the PWM controller is supplied to the PWM controller, thereby to stop the operation of the PWM controller.
Additional advantages, objects and other features of the invention will be set forth in part in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from practice of the invention. The object and advantages of the invention may be realized and attained as particularly pointed out in the appended claims.
REFERENCES:
patent: 4999730 (1991-03-01), Pickard
patent: 5818670 (1998-10-01), Ahn
Bushnell , Esq. Robert E.
Jackson Stephen W.
Samsung Electronics Co,. Ltd.
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