Electronic switched-mode power supply for supplying power to an accumulator
AssigneeBraun GmbH
InventorGerhard Lang
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Abstract
The invention is directed to an electronic switched-mode power supply for supplying power to an accumulator (61), comprising a self-oscillating flyback converter having a transformer (50), a switching transistor (1) with an emitter resistor (22) and a feedback circuit (11, 27). A control circuit (St) inhibits conduction of the switching transistor (1) when the switching voltage at the accumulator (61) has reached a predetermined upper level (A). A switching arrangement (SE) lowers the upper switching voltage (A) to a lower switching voltage (B) when, with the switched-mode power supply in the pulsed mode, the ratio of the duration of oscillation pauses to the duration of oscillation bursts exceeds a specified magnitude.
Claims10
An electronic switched-mode power supply for supplying power to an accumulator from an input voltage source, the power supply comprising:
- (1) a self-oscillating flyback converter comprising
- (a) a switching transistor having a base and a collector-emitter circuit;
- (b) a first resistor;
- (c) a diode;
- (d) a feedback circuit;
- (e) a control circuit;
- and
- (f) a transformer with a primary winding and a secondary winding, wherein the primary winding, in a series arrangement with the collector-emitter circuit of the switching transistor and the first resistor, is connected in parallel with the input voltage source, and wherein the secondary winding is connected in series with the accumulator and the diode, with the base of the switching transistor being connected to the secondary winding through the feed back circuit in addition to being coupled to the control circuit, wherein the control circuit during operation inhibits conduction of the switching transistor when a voltage at the accumulator has increased to a switching voltage and renders the switching transistor conducting again when the voltage at the accumulator has dropped below this switching voltage;
- and
- (2) a switching arrangement which drives the control circuit such that the switching voltage is lowered to a lower switching voltage value when, with the switched-mode power supply in a pulsed mode, a ratio of a duration of oscillation pauses to a duration of oscillation bursts exceeds a specified magnitude, the switching arrangement comprising an evaluating circuit, connected to the flyback converter, for detecting the ratio of the duration of oscillation pauses to the duration of oscillation bursts, a trigger circuit connected to the evaluating circuit and the control circuit, the evaluating circuit causing the trigger circuit to pass to a different condition when the ratio of the duration of oscillation pauses to the duration of oscillation bursts exceeds the specified magnitude, wherein, when passed to a to a different condition, trigger circuit drives the control circuit such that the switching voltage of the control circuit is lowered to the lower switching voltage value, thereby terminating a high-current charging period.
Dependencies are inferred from the claim text.