SWITCHED-MODE POWER SUPPLY

• US 20140098579A1
• Filed: 10/01/2013
• Published: 04/10/2014
• Est. Priority Date: 10/05/2012
• Status: Active Grant

• Current Assignee: NXP B.V. (NXP Semiconductors NV)
• Original Assignee: NXP B.V. (NXP Semiconductors NV)
• Inventors: KLEINPENNING, Jeroen
• Granted Patent: US 8,749,994 B2
• Time in Patent Office: Days
• US Class Current: 363/21.17
• CPC Class Codes: H02M 3/33523 with galvanic isolation between input and output of both the power stage and the feedback loop

Abstract

Consistent with example embodiments disclosed, there are switched-mode power supplies (SMPS) in which a signaling capacitor transmits information across a transformer of the power supply. Such embodiments can avoid drawing power from the output capacitor in order to provide communication signals and so do not cause a drop in the output voltage when signaling to the primary side. Further, the switched mode power supply can send signals from the secondary side of the transformer to the primary side via the transformer itself and so may not require the incorporation of an opto-coupler. Such embodiments may reduce production costs, the printed circuit board (PCB) footprint and reduce the no-load power consumption of the SMPS.

Claims

1. A switched-mode power supply comprising:

a transformer with a primary winding and a secondary winding, the secondary winding having a first terminal and a second terminal;

a rectifier with an input and an output, the input coupled to the first terminal of the secondary winding;

an output capacitor with a first plate and a second plate, the first plate coupled to the output of the rectifier and the second plate coupled to the second terminal of the secondary winding;

a power switch coupled in series with the primary winding, configured to be coupled between an output of a rectifier and ground;

a signalling unit provided in parallel with the secondary winding, the signalling unit comprising a signalling capacitor and a signalling switch coupled in series with each other;

a secondary controller configured to;

detect a secondary side variable at the secondary winding, and

control the signalling switch in accordance with the secondary variable, wherein closing the signalling switch is configured to generate a transformer signal by connecting the signalling capacitor to the secondary winding;

a primary controller configured to;

receive the transformer signal from the primary winding or a primary side auxiliary winding of the transformer, and

control the power switch in accordance with the transformer signal.

2. The switched-mode power supply of claim 1, wherein closing the signalling switch is configured to generate the transformer signal by discharging the signalling capacitor into the secondary winding.

3. The switched-mode power supply of claim 2, wherein the secondary side variable is indicative of one of:

a voltage, a power, or a current at the secondary side of the transformer.

4. The switched-mode power supply of claim 1, wherein the primary controller is configured to set the switching frequency of the power switch and the peak value of the primary stroke current or the on-time of the power switch in accordance with the transformer signal.

5. The switched-mode power supply of claim 1, wherein the secondary controller is configured to connect the signalling capacitor to the secondary winding in a single pulse during a ringing stroke between a secondary stroke of a first cycle and a primary stroke of a next cycle of the switched-mode power supply.

6. The switched-mode power supply of claim 1, wherein the secondary controller is configured to connect the signalling capacitor to the secondary winding in a plurality of pulses during a ringing stroke between a secondary stroke of a first cycle and a primary stroke of a next cycle of the switched-mode power supply.

7. The switched-mode power supply of claim 5, wherein the transformer signal comprises at least one of:

a rate of change of voltage across a winding of the transformer that is greater than or less than a threshold value, a change of voltage below or above a threshold of a winding of the transformer and a change in ringing frequency.

8. The switched-mode power supply of claim 1, further comprising a diode coupled across terminals of the signalling switch.

9. The switched-mode power supply of claim 1, wherein the signalling capacitor is configured to be charged during a secondary stroke of the switched-mode power supply cycle.

10. The switched-mode power supply of claim 9, wherein the signalling switch is a first signalling switch and the signalling capacitor is a first signalling capacitor, further comprising a second signalling unit having a second signalling capacitor and a second signalling switch, wherein a terminal of the second signalling capacitor is coupled directly to the input of the rectifier, a terminal of the first signalling switch coupled directly to the input of the rectifier, and wherein the secondary controller is further configured to control the second signalling switch in accordance with the secondary variable.

11. The switched-mode power supply of claim 10, wherein a first polarity transformer signal resulting from a connection of the first signalling capacitor to the secondary side winding is of an opposite polarity to a second polarity transformer signal resulting from a connection of the second signalling capacitor to the secondary side winding, and wherein the primary controller is configured to increase the power delivered to the primary winding if the first polarity transformer signal is received and to decrease the power delivered to the primary winding if the second polarity transformer signal is received.

12. The switched-mode power supply of claim 9, wherein the primary controller is configured to alter the power level within a cycle of the power supply in a step size, wherein the step size is one of:

a constant step size;

a steps that scales with the absolute power level for a constant ripple voltage; and

a step size determined by an algorithm that enlarges the step size if consecutive power-up or power-down transformer signals are received.

13. The switched-mode power supply of claim 10, wherein the secondary controller is configured to part-discharge the first signalling capacitor and to part-discharge a second signalling capacitor by providing respective pulsed signalling switch control signals in order to provide a plurality of transformer signals.

14. The switched-mode power supply of claim 1, wherein the secondary controller is configured to part-discharge the signalling capacitor by providing a pulsed signalling switch control signal in order to provide a plurality of transformer signals.

15. The switched-mode power supply of claim 1, wherein the signalling capacitor has a first plate coupled to the first terminal of the secondary winding, and a second plate coupled to the signalling switch, the switched mode power supply further comprising:

a charging switch having a first terminal coupled to the first plate of the output capacitor and a second terminal coupled to the second plate of the signalling capacitor;

wherein the secondary controller is configured to operate the charging switch in accordance with the secondary variable.