Cascode switch power supply

• US 7,345,894 B2
• Filed: 09/07/2006
• Issued: 03/18/2008
• Est. Priority Date: 09/27/2005
• Status: Active Grant

• Current Assignee: Dialog Semiconductor GmbH (Renesas Electronics Corporation)
• Original Assignee: Carl Sawtell
• Inventors: Sawtell, Carl K., Menegoli, Paolo
• Primary Examiner(s): Laxton; Gary L.
• Application Number:
  US11/516,484
• Publication Number:
  US 20070070659A1
• Time in Patent Office: 558 Days
• Field of Search: 363/16, 363/20, 363/21.01, 363/21.04, 363/21.07, 363/21.08, 363/21.1, 363/21.11, 363/21.12, 363/21.18, 363/97, 363/131, 323/224, 323/282, 323/351
• US Class Current: 363/21.11
• CPC Class Codes: H02M 1/0006 Arrangements for supplying an adequate voltage to the control circuit of converters
• CPC Class Codes: H02M 1/0009 Devices or circuits for detecting current in a converter
• CPC Class Codes: H02M 1/088 for the simultaneous control of series or parallel connected semiconductor devices
• CPC Class Codes: H02M 3/33523 with galvanic isolation between input and output of both the power stage and the feedback loop
• CPC Class Codes: H02M 3/33569 having several active switching elements H02M3/3353 takes precedence

Abstract

A switching power supply is disclosed for improving the no-load power drain of low-power mains operated supplies. The power converter utilizes a cascoded switch arrangement with a conventional high voltage power MOSFET and a low voltage, low gate charge MOSFET. Driving only the small low voltage device reduces the power required for gate drive. The disclosed configuration is also capable of generating a non-isolated auxiliary rail for powering its control circuitry utilizing the parasitic capacitance of the high voltage power devices as an element in a charge pump. The resulting power supply requires significantly fewer components.

Claims

1. A switching power supply comprising:

an input source of power;

an output terminal;

a feedback means providing an output responsive to the voltage at said output terminal of said power supply;

a coupled inductive element having multiple windings, each with a pair of terminals, a first terminal of a first winding being coupled to said input source of power;

a first transistor having a drain, a source and a gate, said drain coupled to a second terminal of said first winding of said coupled inductive element;

a reservoir capacitor coupled to said gate of said first transistor;

a control circuit being coupled to said reservoir capacitor as a source of power and producing a pulse modulated output in response to said feedback means, said control circuit having an undervoltage lockout function responsive to voltage on said reservoir capacitor with two hysteretic thresholds, a first higher threshold enabling operation of said control circuit when said voltage on said reservoir capacitor exceeds said first threshold, and a second lower threshold which disables said control circuit when said voltage on said reservoir capacitor falls below said second threshold;

a second transistor with a source, a gate and a drain, said source being coupled to a common node of said input source of power, said drain coupled to said source of said first transistor, and said gate being driven in response to said pulse modulated output of said control circuit;

a first rectifying means with an anode and a cathode, said anode connected to said drain of said second transistor and said cathode coupled to said reservoir capacitor; and

an output circuit comprising a second rectifying means with a rectifying input and a rectified output and a filtering means with a filtering input and a filtered output, said second rectifying means having said rectifying input coupled to a second winding of said coupled inductive element and having said rectified output coupled to said filtering input of said filtering means, said filtering means having said filtered output coupled to said output terminal of said switching power supply.

2. The switching power supply of claim 1 wherein said control circuit has a minimum pulse width.

3. The switching power supply of claim 1 wherein said second transistor is alternatively a bipolar transistor with an emitter, a base, and a collector, said emitter being tied to said common node of said input source of power, said collector coupled to said source of said first transistor and to said anode of said first rectifying means, and said base being driven in response to said pulse modulated output of said control circuit.

4. The switching power supply of claim 1 including a third capacitor with two terminals, a first terminal connected to said drain of said first transistor, and a second terminal connected to said source of said first transistor.

5. The switching power supply of claim 1 wherein said control circuit and said second transistor are contained in an integrated circuit.

6. The switching power supply of claim 1 wherein said control circuit, said second transistor and said first rectifying means are contained in an integrated circuit.

7. The switching power supply of claim 1 wherein said output circuit is configured as a flyback output.

8. The switching power supply of claim 1 wherein said output circuit is configured as a forward output.

9. A method for operating a switching power supply, comprising

switching a first transistor in response to a pulse modulated signal from a control circuit;

cascoding said first transistor with a second transistor having a gate terminal, a source terminal, and a drain terminal, said second transistor having capacitance between its respective terminals that result in capacitive charge flow during switching, and said second transistor being driven into and out of its conductive state in response to said switching of said first transistor;

recirculating a first capacitive charge flowing in said gate terminal of said second transistor during switching into a reservoir capacitor connected to said gate of said second transistor, said first capacitive charge flowing into and out of said reservoir capacitor in a substantially equal and opposite manner during turn-off and turn-on of said second transistor;

capturing a second capacitive charge coupled through said capacitance between said drain terminal and said source terminal of said second transistor following the switching off of said first and second transistors, and storing said second capacitive charge in said reservoir capacitor,

and utilizing said stored charge in said reservoir capacitor to power said control circuit.