Switched mode power supply responsive to current derived from voltage across energy transfer element input

• US 20060098460A1
• Filed: 12/19/2005
• Published: 05/11/2006
• Est. Priority Date: 03/02/2000
• Status: Active Grant

• Current Assignee: Balu Balakrishnan, David Michael Hugh Matthews
• Original Assignee: Balu Balakrishnan, David Michael Hugh Matthews
• Inventors: Matthews, David Michael Hugh, Balakrishnan, Balu
• Granted Patent: US 7,193,865 B2
• Time in Patent Office: Days
• US Class Current: 363/16
• CPC Class Codes: H02M 1/0009 Devices or circuits for detecting current in a converter
• CPC Class Codes: H02M 3/335 using semiconductor devices only
• CPC Class Codes: H02M 3/33507 with automatic control of the output voltage or current, e.g. flyback converters H02M3/33561, H02M3/33569 take precedence

Abstract

A switched mode power supply having a regulated reflected voltage. In one circuit, a power switch is coupled between first and second electrical terminals. An energy transfer element is coupled to the first electrical terminal of the power switch. A power supply rail is coupled to the second electrical terminal. A control circuit is coupled to the energy transfer element and to the power switch. The control circuit is to switch the power switch in response to a signal derived from a voltage at the energy transfer element to regulate an output of the circuit.

Claims

1. A circuit, comprising:

a power switch coupled between first and second electrical terminals;

an energy transfer element coupled to the first electrical terminal of the power switch;

a power supply rail coupled to the second electrical terminal;

a control circuit coupled to the energy transfer element and to the power switch, the control circuit to switch the power switch in response to a signal derived from a voltage at the energy transfer element to regulate an output of the circuit.

2. The circuit of claim 1 further comprising an optocoupler including:

an input light emitting diode (LED) coupled to the energy transfer element and the output of the circuit; and

an output transistor coupled to the control circuit.

3. The circuit of claim 2 wherein a current through the output transistor is coupled to be received by the control circuit and is responsive to the signal derived from the voltage at the energy transfer element.

4. The circuit of claim 1 wherein the energy transfer element comprises a transformer having a primary winding and a secondary winding.

5. The circuit of claim 4 wherein the voltage at the energy transfer element comprises a reflected voltage across the primary winding.

6. The circuit of claim 1 wherein the power switch comprises a metal oxide semiconductor field effect transistor (MOSFET).

7. The circuit of claim 6 wherein the MOSFET is an n-channel MOSFET having a source terminal coupled to the energy transfer element, a drain terminal coupled to the power supply rail and a gate terminal coupled to the control circuit.

8. The circuit of claim 4 further comprising a first capacitor coupled in parallel with the primary winding during an off cycle of the power switch, the first capacitor decoupled from the primary winding during an on cycle of the power switch, the control circuit coupled to the first capacitor, wherein a signal derived from the voltage at the primary winding is responsive to a voltage across the secondary winding.

9. The circuit of claim 1 wherein the control circuit comprises a pulse width modulator coupled to the power switch, the pulse width modulator to pulse width modulate the power switch in response to the signal derived from the voltage at the energy transfer element.

10. The circuit of claim 1 wherein the control circuit comprises a on/off control circuitry coupled to the power switch, the on/off control circuitry to adjust cycles of a control signal coupled to be received by the power switch in response to the signal derived from the voltage at the energy transfer element.

11. The circuit of claim 1 wherein the control circuit disables switching of the power switch in response to the signal derived from the voltage at the energy transfer element exceeding a threshold amount.

12. The circuit of claim 1 wherein the control circuit and the power switch are included on a single monolithic chip having as few as three electrical terminals.

13. The circuit of claim 1 wherein the control the signal derived from the voltage at the energy transfer element to regulate an output of the circuit comprises a current derived from the voltage at an input of the energy transfer element.