# US 2017/0288558 A1 · Voltage discharge circuit > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 2017/0288558 A1 - Document ID: US20170288558A1 - Status: Published application - Kind: A1 - Application number: 15/477,342 - Filed: 2017-04-03 - Published: 2017-10-05 - Earliest claimed: 2016-04-04 - Assignees: Microsoft Technology Licensing, LLC - Applicants: Microsoft Technology Licensing, LLC - Inventors: David Perchlik; Monty Ross - Web page: https://patentgrep.com/patent/US20170288558A1 ## CPC - H02M 3/33592: {having a synchronous rectifier circuit or a synchronous freewheeling circuit at the secondary side of an isolation transformer} - H02M 1/08: Circuits specially adapted for the generation of control voltages for semiconductor devices incorporated in static converters - H02M 1/0012: {Control circuits using digital or numerical techniques (in DC/DC converters H02M3/157, H02M3/33515; in DC-AC converters H02M7/53873)} - H02M 1/0025: {Arrangements for modifying reference values, feedback values or error values in the control loop of a converter} - H02M 1/322: {Means for rapidly discharging a capacitor of the converter for protecting electrical components or for preventing electrical shock} - Y02B 70/10: Technologies improving the efficiency by using switched-mode power supplies [SMPS], i.e. efficient power electronics conversion e.g. power factor correction or reduction of losses in power supplies or efficient standby modes - H02M: APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF (transformers H01F; dynamo-electric converters H02K47/00; controlling transformers, reactors or choke coils, control or regulation of electric motors, generators or dynamo-electric converters H02P) - Y02B: CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO BUILDINGS, e.g. HOUSING, HOUSE APPLIANCES OR RELATED END-USER APPLICATIONS ## Abstract Technologies are described for an adaptable power supply that can switch between two or more output voltages. The power supply includes discharge circuitry that utilizes the secondary windings of a transformer as a discharge path when the power supply switches from a high voltage level to a low voltage level. In some embodiments, the discharge circuitry is included within a synchronous rectifier. In other embodiments, the discharge circuitry is separate from the synchronous rectifier. In still other embodiments, the power supply does not include a synchronous rectifier. Whichever embodiment is used, an output capacitor can be discharged through the secondary windings of a transformer and the transformer can store that energy for future use. ## Claims ### Claim 1 A method changing voltage levels in a power supply, comprising: detecting a control signal to change a voltage level on an output node of the power supply from a first voltage level to a second voltage level; and in response to detecting the control signal, transmitting an activation signal to a switch between the output node and a transformer so that energy on the output node is discharged through a secondary winding of a transformer within the power supply. ### Claim 2 (depends on 1) The method of claim 1, wherein the detecting occurs when the first voltage level is higher than the second voltage level, otherwise the activation of the switch does not occur. ### Claim 3 (depends on 1) The method of claim 1, further including logically combining the activation signal with a flyback control signal from a synchronous rectifier control circuit so as to ensure that the output node is discharged through the secondary winding. ### Claim 4 (depends on 1) The method of claim 1, further including monitoring a voltage level on the output node to generate a monitoring signal and inputting the monitoring signal and the control signal into a comparator so as to generate the activation signal. ### Claim 5 (depends on 1) The method of claim 1, further including storing the energy in a primary storage capacitor after the energy passes through the transformer from the secondary winding to the primary winding. ### Claim 6 (depends on 1) The method of claim 1, further including monitoring a voltage level across the secondary winding and only transmitting the activation signal if there is a 0V crossing in the secondary winding. ### Claim 7 (depends on 1) The method of claim 1, further including monitoring the output node and when a voltage level drops below a threshold, switching the activation signal to a deactivation signal. ### Claim 8 A power supply that can switch between two or more output voltage levels, comprising: a transformer having primary and secondary windings; an output voltage capacitor coupled in parallel with the secondary windings and coupled to an output node for supplying an output voltage of the power supply; a switch coupled between the secondary windings and the output voltage capacitor; and control circuitry coupled to the switch having an input signal node for receiving an input signal indicating that the output voltage of the power supply is switching voltage levels and for controlling the switch so that the output voltage capacitor discharges through the secondary windings of the transformer. ### Claim 9 (depends on 8) The power supply of claim 8, wherein the control circuitry includes zero-crossing circuitry that detects when the secondary windings have a threshold voltage and wherein the controlling of the switch is dependent on whether the secondary windings are at or below the threshold voltage. ### Claim 10 (depends on 8) The power supply of claim 8, further including output-voltage detection circuitry that determines whether the output voltage of the power supply is above a threshold level. ### Claim 11 (depends on 8) The power supply of claim 8, further including a synchronous rectifier control circuit coupled to the switch for deactivating the switch when a fly-back mode is detected wherein current flows back through the secondary winding from the output node. ### Claim 12 (depends on 8) The power supply of claim 8, further including a primary storage capacitor coupled across the primary windings, wherein the primary storage capacitor is charged by the output voltage capacitor discharging. ### Claim 13 (depends on 8) The power supply of claim 8, wherein the control circuitry switches a state of the switch when the output voltage drops below a threshold level. ### Claim 14 A method of discharging an output capacitor in a power supply, comprising: powering an output voltage at a first voltage level using a power supply having primary and secondary windings, wherein current flows through the secondary windings in a first direction; receiving a control signal to change the output voltage from the first voltage level to a second, lower voltage level; detecting a change in voltage level of the secondary windings sufficient to initiate a current flow in a second direction, opposite the first direction, through the secondary windings; and activating a switch using a discharge signal to allow the current to continue to flow in the second direction through the secondary windings to discharge the output voltage through the secondary windings. ### Claim 15 (depends on 14) The method of claim 14, wherein a primary storage capacitor associated with the primary winding is charged using energy from discharging the output voltage. ### Claim 16 (depends on 14) The method of claim 14, further including initiating a fly-back control signal using a synchronous rectifier control circuit to deactivate the switch, contrary to the discharge signal. ### Claim 17 (depends on 14) The method of claim 14, wherein the primary and secondary windings are within a transformer and wherein the discharging of the output voltage through the secondary windings stores energy within the transformer using magnetizing inductance. ### Claim 18 (depends on 14) The method of claim 14, wherein the detecting of the change in voltage level includes comparing a voltage across the secondary windings to a reference voltage level. ### Claim 19 (depends on 14) The method of claim 14, further including deactivating the switch after the output voltage drops to a threshold level so as to prevent further current to pass through the secondary windings. ### Claim 20 (depends on 14) The method of claim 14, further including detecting that the output voltage is at the first voltage level and only activating the switch if the output voltage is transitioning from the first voltage level to the second, lower voltage level and not activating the switch if the output voltage is transitioning from the second, lower voltage level to the first voltage level.