U.S. Philips Corporation

Abraham L Melse

Johan Christiaan Halberstadt

Hendrikus Johannes Janssen

A power supply circuit, particularly a flyback converter, comprises a transformer having a secondary winding that powers a load device and/or a rechargeable battery via a rectifier diode. The secondary winding is short circuited by means of a switch connected in series with a diode. The short-circuit is detected by a measurement circuit comprising a measurement winding and a comparator which compares the amplitude variation of the voltage across the measurement winding with a threshold voltage. When a short-circuit is detected a control circuit for the control of the switching transistor of the flyback converter is changed over to a mode in which a given small current is supplied, which flows almost exclusively through the switch. As soon as the short-circuit ends the flyback converter resumes its normal mode of operation. If desired, the load device can control the desired current and/or voltage for powering the load device and charging the battery by turning on and turning off the switch.

Power-supply circuit with a transformer and an on/off switch at the

A reference voltage source comprises a first current branch (16, 36) and a second current branch (30, 34, 12). The voltage on a first terminal (6) in the first current branch (16, 26) is one junction voltage higher than the voltage on a second terminal (8) in the second current branch (30, 34, 12) owing to the presence of a transistor (80). The ratio between the current I.sub.1 through the first current branch (16, 36) and the current I.sub.2 through the second current branch (30, 34, 12) is thus determined by two non-linear characteristics having opposite temperature coefficients. A reference voltage (v.sub.z) with a small temperature coefficient and with a value which can be chosen freely can be generated by an appropriate choice of the resistance values for the resistors (58, 30, 16, 12) and by scaling the emitter areas of the transistors (34, 36, 70, 80).

Temperature compensated reference voltage source

A reference voltage source for driving a constant-current source. The reference voltage source comprises a first common terminal, a second common terminal, a first connection terminal, and a second connection terminal. A first semiconductor junction device and a first resistor are connected in series between the first connection terminal and the second common terminal. A second resistor is connected between the first common terminal and the second connection terminal and a second semiconductor junction device is connected between the second connection terminal and the second common terminal. A third semiconductor junction device is connected between the first common terminal and the first connection terminal. A differential amplifier has an output and an inverting input and a non-inverting input. One input is coupled to the first connection terminal and the other input is coupled to the second connection terminal and one of the first and second common terminals is coupled to the output of the differential amplifier. The temperature coefficient of the sum current (I.sub.1 +I.sub.2) can be made zero. The sum current is mirrored to current source transistors which supply a temperature stable current.

Reference voltage source for biassing a plurality of current source

An oscillator circuit having a 50% duty cycle comprises an oscillating stage and an output stage. The output stage comprises a series arrangement of first and second output transistors of complementary conductivity types. The oscillating stage applies a combination of an oscillating signal and a first DC bias to the gate of the first output transistor. The first DC bias is dependent on the amplitude of the oscillating signal. The oscillator circuit also includes a bias-generating circuit for generating a second DC bias at the gate of the second transistor, so as to adjust the input switching level to the median level of the input signal dependent upon the amplitude of the oscillating signal.

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Nijmegen, Netherlands

Abraham L Melse