Power-supply circuit with a transformer and an on/off switch at the secondary side of the transformer
First Claim
1. A power supply circuit comprising:
- a transformer having a primary winding connected to receive a primary voltage and having a secondary winding for generating a secondary voltage;
a load device and a rectifier diode connected in series across the secondary winding to supply a current to the load device;
an on/off switch for interrupting the current from the secondary winding to the load device, wherein the on/off switch is coupled in parallel with the load device to provide a current conduction path in addition to the current conduction path of the load device, measurement means for the comparison of a voltage proportional to the voltage of the secondary winding with a reference voltage (UR); and
means coupled to a circuit including the primary winding for changing over the current intensity of the current to a predetermined comparatively small value in response to the comparison, wherein the circuit forms a part of a flyback converter comprising a switching transistor having a main current path connected in series with the primary winding and having a control electrode connected to receive control pulses from a control circuit having a control input for receiving a change-over signal for changing over the current intensity;
the transformer further comprises a third winding for supplying a measurement voltage which is proportional to the secondary voltage; and
the measurement means further comprises;
a detector for determining an amplitude of the measurement voltage and for supplying an amplitude signal;
a reference source for supplying the reference voltage (UR);
a comparator for comparing the amplitude signal with the reference voltage and for generating the change-over signal in response to the comparison.
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Accused Products
Abstract
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.
22 Citations
13 Claims
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1. A power supply circuit comprising:
- a transformer having a primary winding connected to receive a primary voltage and having a secondary winding for generating a secondary voltage;
a load device and a rectifier diode connected in series across the secondary winding to supply a current to the load device;
an on/off switch for interrupting the current from the secondary winding to the load device, wherein the on/off switch is coupled in parallel with the load device to provide a current conduction path in addition to the current conduction path of the load device, measurement means for the comparison of a voltage proportional to the voltage of the secondary winding with a reference voltage (UR); and
means coupled to a circuit including the primary winding for changing over the current intensity of the current to a predetermined comparatively small value in response to the comparison, wherein the circuit forms a part of a flyback converter comprising a switching transistor having a main current path connected in series with the primary winding and having a control electrode connected to receive control pulses from a control circuit having a control input for receiving a change-over signal for changing over the current intensity;
the transformer further comprises a third winding for supplying a measurement voltage which is proportional to the secondary voltage; and
the measurement means further comprises;
a detector for determining an amplitude of the measurement voltage and for supplying an amplitude signal;
a reference source for supplying the reference voltage (UR);
a comparator for comparing the amplitude signal with the reference voltage and for generating the change-over signal in response to the comparison. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13)
- a transformer having a primary winding connected to receive a primary voltage and having a secondary winding for generating a secondary voltage;
Specification