Matsushita Electric Works, Ltd.

Other

Kaoru Furukawa

Hideki Tamura

Hiromi Kakumoto

Hiroshi Sakamoto

Mikihiro Yamashita

Hironobu Sakaue

Satoshi Yamada

An inverter power supply operating at a high efficiency to provide an AC voltage to a load. The power source includes a DC voltage source and an output transformer with a primary winding, secondary winding, and a feedback winding. An FET is connected in series with the primary winding across the DC voltage source. The primary winding is connected to a capacitor to form a L-C resonant circuit which, in response to the switching of FET, provides across the primary winding an oscillation voltage to be applied through the secondary winding to drive a load, while inducing a feedback voltage across the feedback winding. The oscillation voltage is allowed to go negative at a point between FET and the primary winding. A biasing capacitor is connected to apply an offset voltage which is additive to the feedback voltage so as to give a bias voltage to FET. The power supply is characterized to include a level detector which issues a zero voltage signal when the oscillation voltage is detected to lower to at least zero level, and to include a pulse generator which, in response to the zero voltage signal, produces a pulse of a predetermined pulse-width which overrides the feedback voltage in such a manner as to enable FET to turn on for a ON-period determined by the pulse-width only after the oscillation voltage is lowered to at least zero level, whereby avoiding FET from flowing a current while the oscillation voltage is still positive and therefore reducing a switching loss.

Inverter power supply

An inverter power supply includes a DC supply providing a DC voltage from an AC mains, a transformer having primary, secondary, and feedback windings, and a self-excited oscillator energized by the DC supply to generate a high frequency voltage across the primary winding and induces across the secondary winding an output AC voltage for driving a load. The oscillator comprises an FET connected in series with the primary winding. A biasing capacitor is connected in series with the feedback winding across a source-gate path of FET for providing an offset voltage which is additive to a feedback voltage at the feedback winding to give a bias applied to a gate of FET so as to alternately turn on and off FET for self-excited oscillation. Also included is a bias stabilizing circuit which lowers the offset voltage by discharging the biasing capacitor through FET being turned on, thereby driving FET turned on only for substantially a constant ON-time period irrespective of an increase in the DC voltage within a limited range. The power supply is characterized to include a compensation circuit which produces a negative voltage to be superimposed to the offset voltage of the biasing capacitor, thereby enabling to lower the offset voltage negative even when the DC voltage increases over the limited range, thereby keeping the ON-time period of FET substantially constant over a wide range of variations in the DC voltage.

Inverter power source

An electronic detector for locating an object behind a wall surface has a metallic object detecting section and a general object detecting section which are energized by a common battery to be operative simultaneously. The metallic object detecting section includes a magnetic field sensor for detecting any change in a magnetic field developed therearound and providing a second electric signal indicative of that change. The general object detecting section includes a capacitor sensor for sensing any change in the capacitance of the wall and providing a first electric signal indicative of that change. The first and second electric signals are applied respectively to first and second control circuits where they are analyzed to provide first and second control outputs when their levels reach first and second reference levels, respectively. Upon receiving the first and second control output, first and second indicators turn on for indicating the detection results. Thus, both of the first and second indicators will turn on when there is detected a metallic object behind the wall surface and only the first indicator will turn on when there is deteced a non-metallic object behind the wall surface, whereby the user can easily distinguish the metallic object and the non-metallic object detected.

Electronic detector with capacitor sensor and magnetic field sensor for

A transformer employed in a power supply circuit of a ringing choke converter type comprises two feedback windings which share the current to be supplied to the base of a switching transistor for blocking oscillation. By virtue of the provision of the two feedback windings, a speedup capacitor for delivering a trigger current to the switching transistor is allowed to have less capacity, while the amount of heat generation of a resistor for regulating the trigger current can be restrained. These advantageous features of the present invention produces the effect that the bulk and weight of the capacitor and the resistor can be reduced, which leads to curtailing of the cost of the components as well as enhancing of the reliability of the circuit. The effect is more appreciable when a higher output is required.

Power supply circuit

A quick charging circuit comprises a charging current generating circuit including a rectifier connected to an A.C. power source and a high frequency inverter connected to the rectifier for supplying a charging current to a storage battery, a circuit for detecting a voltage across the battery, a timer circuit operated by an output of the battery voltage detecting circuit, and means for reducing the charging current in response to a time limit output of the timer circuit, wherein an integrating circuit is provided with respect to the battery voltage detecting circuit so that any influence of high frequency components in the battery voltage can be removed, whereby the timer circuit can be operated accurately with a set voltage to reduce the charging current and to reliably prevent the battery from being subjected to any overcharging and internal pressure rise.

Quick charging circuit

A charging circuit comprises a bypassing transistor connected at the collector and base respectively to the base and emitter of a switching transistor connected to the primary winding of a transformer for inducing a charging current in the secondary winding of the transformer forming a part of a secondary battery charging path, and a current detecting resistance and constant voltage element connected between the base and emitter of the bypassing transistor so that, when the peak of a collector current of the switching transistor exceeds a predetermined level, the bypassing transistor is conducted to bypass and reduce the base current of the switching transistor, the collector current of the switching transistor is thereby reduced, and the charging current substantially constant at the average value is generated regardless of the voltage of a selective one of different power sources.

Charging circuit

A battery charger includes a transistor inverter. The transistor inverter includes an oscillation transformer and a switching transistor for controlling a current flowing through a primary coil of the oscillation transformer. This current charges the battery when the transistor is on. While the switching transistor is in an off state, charging current is supplied to the battery from a secondary coil of the oscillation transformer. The period of time where the switching transistor is in an on state is controlled depending on the amplitude of a supply voltage. Accordingly, the average value of a charging current to the rechargeable battery is automatically kept substantially constant despite variations in the amplitude of the alternating current voltage supply.

Battery charging circuit for maintaining a substantially constant

A diode is disposed in the vicinity of a rechargeable battery. A current is applied to the diode from a current generating circuit. The current generating circuit comprises a thermistor which is responsive to the ambient temperature, so that a current associated with the ambient temperature is applied from the current generating circuit to the diode. The diode gives rise to a forward voltage drop, which is changeable as a function of the battery temperature. Accordingly, the forward voltage drop across the diode is changeable as a function of the ambient temperature and the battery temperature. The forward voltage drop across the diode is amplified to be used as a reference voltage. On the other hand, the rechargeable battery is supplied with a charging current from a power supply through a thyristor. The gate electrode of the thyristor is connected to receive the reference voltage and the cathode of the thyristor is connected to the battery. Accordingly, the thyristor is turned off if and when the difference between the reference voltage and the battery voltage becomes smaller than the switching voltage of the thyristor.

Growing community of inventors

Hikone, Japan

Kaoru Furukawa