Switched-mode power supply and method for determining the supply voltage in a switched-mode power supply

• US 6,411,119 B1
• Filed: 04/14/2000
• Issued: 06/25/2002
• Est. Priority Date: 04/14/1999
• Status: Expired due to Term

• Current Assignee: Siemens AG
• Original Assignee: Infineon Technologies AG
• Inventors: Feldtkeller, Martin
• Primary Examiner(s): Karlsen, Ernest
• Assistant Examiner(s): TANG, MINH NHUT
• Application Number:
  US09/549,277
• Time in Patent Office: 802 Days
• Field of Search: 324/118, 324/119, 324/120, 324/123.R, 324/123.C, 324/771, 363/15, 363/18, 363/19, 363/20, 363/21.1, 363/26, 363/56, 363/97, 363/131
• US Class Current: 324/750.3
• 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 has a switch for a pulsed application of a variable supply voltage to a primary coil of a transformer. The power supply has a first current measuring configuration for providing a current measurement signal that is dependent on a current through the primary coil. An evaluation circuit, which is connected to the first current measuring configuration, evaluates a time characteristic of the current and/or of the current measurement signal and is provided for the purpose of determining a value of the supply voltage. A method for determining the value of the supply voltage in the switched-mode power supply by evaluating the time characteristic of the current through the primary coil is also disclosed.

Claims

1. A switched-mode power supply, comprising:

a transformer having a primary coil;

a switch for providing a pulsed application of a variable supply voltage to said primary coil of said transformer;

a current measuring configuration providing a current measurement signal dependent on a current through said primary coil; and

an evaluation circuit connected to said current measuring configuration, said evaluation circuit determining a value of the variable supply voltage by evaluating a time characteristic of at least one of the current through said primary coil and the current measurement signal.

2. The switched-mode power supply according to claim 1, wherein said evaluation circuit has an output terminal at which a signal dependent on the variable supply voltage can be tapped off.

3. The switched-mode power supply according to claim 1, wherein said evaluation circuit has a switching unit for providing a signal dependent on a gradient of the current measurement signal.

4. The switched-mode power supply according to claim 1, wherein said evaluation circuit has a switching unit with a comparator for providing a signal dependent on a gradient of the current measurement signal and for comparing the signal with a reference signal.

5. The switched-mode power supply according to claim 1, wherein said evaluation circuit has a series circuit formed by a further current measuring configuration and a capacitance element, said series circuit being connected to said current measuring configuration.

6. The switched-mode power supply according to claim 5, including a current source connected to a node that is common to said further current measuring configuration and said capacitance element.

7. The switched-mode power supply according to claim 6, wherein said further current-measuring configuration has a resistor with connecting terminals.

8. The switched-mode power supply according to claim 7, including a comparator connected to said connecting terminals of said resistor.

9. The switched-mode power supply according to claim 7, including:

a comparator having connecting terminals and an output terminal, one of said connecting terminals of said comparator receiving a reference voltage source; and

an operational amplifier connected to said connecting terminals of said resistor and having an output terminal connected to another of said connecting terminals of said comparator.

10. The switched-mode power supply according to claim 1, wherein said evaluation circuit has a capacitive element and a switch connected in parallel with said capacitance element, said switch of said evaluation circuit receiving and being driven by drive pulses.

11. The switched-mode power supply according to claim 9, including a storage element connected downstream of said comparator, said storage element storing a signal present at said output terminal of said comparator and said storage element receiving and driven by drive pulses.

12. The switched-mode power supply according to claim 1, wherein said current measuring configuration has a resistor connected in series with said primary coil.

13. A method for assessing a variable supply voltage of a switched-mode power supply having a semiconductor switch for providing a pulsed application of the variable supply voltage to a primary coil of a transformer and a current measuring configuration for measuring a current through the primary coil, which comprises:

determining a value of the variable supply voltage by evaluating a time characteristic of at least one of the current through the primary coil and a current measurement signal provided by the current measuring configuration.

14. The method according to claim 13, which comprises determining a gradient of at least one of the current and the current measurement signal during the evaluating step.

15. The method according to claim 14, which comprises comparing the gradient with a reference signal.