Switched-mode power supply and method for driving a switch in a switch-mode power supply for improved switch-on after a waiting period or disconnection from the network

• US 6,239,990 B1
• Filed: 04/19/2000
• Issued: 05/29/2001
• Est. Priority Date: 04/21/1999
• Status: Expired due to Term

• Current Assignee: Infineon Technologies AG
• Original Assignee: Infineon Technologies AG
• Inventors: Feldtkeller, Martin
• Primary Examiner(s): Riley, Shawn
• Application Number:
  US09/552,496
• Time in Patent Office: 405 Days
• Field of Search: 363/21.1, 363/20, 363/131, 363/97
• US Class Current: 363/21.1
• CPC Class Codes: H02M 1/32 Means for protecting converters other than automatic disconnection
• CPC Class Codes: H02M 1/40 Means for preventing magnetic saturation
• CPC Class Codes: H02M 3/33523 with galvanic isolation between input and output of both the power stage and the feedback loop

Abstract

A switched-mode power supply with a switch for applying a supply voltage to a primary coil of a transformer based on the criterion of a drive signal. A pulse-width modulator has supplied a first regulating signal that is dependent on an output voltage and a first current signal that is dependent on a voltage through the primary coil for providing the drive signal. A second regulating signal that is variable in dependency on the current through the primary coil is also supplied to the pulse-width modulator in addition to the first regulating signal and first voltage signal. A method is provided for driving the switch in a switched-mode power supply.

Claims

1. A switched-mode power supply, comprising:

a switch for applying a supply voltage to a primary coil of a transformer based on a criterion of a drive signal;

a pulse-width modulator for providing a drive signal to the switch and having supplied thereto a first regulating signal dependent on an output voltage and a first first voltage signal which is dependent on a current through the primary coil; and

a second regulating signal which is variable in dependency on the current through the primary coil also being supplied to the pulse-width modulator in addition to the first regulating signal and the first drive signal.

2. The switched-mode power supply according to claim 1 wherein a signal generation arrangement is connected to the pulse-width modulator with an output terminal at which the second regulating signal is picked off and with an input terminal to which is supplied said first voltage signal dependent on the current through the primary coil.

3. The switched-mode power supply according to claim 2 wherein the second regulating signal which is variable is based on the second voltage signal different than the first voltage signal which is fed to the pulse width modulator, said second voltage signal also being dependent on and representative of the current through the primary coil.

4. The switched-mode power supply according to claim 2 wherein the signal generation arrangement comprises a series connection of a current source and a capacitance connected between a supply potential and a reference potential, whereby the second regulating signal is picked off as a voltage across the capacitance.

5. The switched-mode power supply according to claim 4 wherein a second switch is connected parallel to the capacitance, which second switch is driven based on a criterion of a second drive signal dependent on the first voltage signal.

6. The switched-mode power supply according to claim 5 wherein the signal generation arrangement comprises a comparing arrangement for generating the second drive signal by means of comparing the first voltage signal to a reference signal.

7. The switched-mode power supply according to claim 6 wherein the comparing arrangement is designed as a trans-conductance amplifier and the second switch is designed as a bipolar transistor.

8. The switched-mode power supply according to claim 6 wherein the comparing arrangement is designed as a difference amplifier and the second switch is designed as a field-effect transistor.

9. A method for driving a switch connected in series to a primary coil in a switched-mode power supply, comprising the steps of:

generating a drive signal for driving the switch based on a criterion of a first regulating signal dependent on an output voltage and on a criterion of a voltage signal dependent on a current through the primary coil; and

the generation of the drive signal also being based on a criterion of a second regulating signal in addition to the first regulating signal and the voltage signal, which is adjusted according to the current through the primary coil.

10. A method according to claim 9 wherein the adjustment of the second regulating signal comprises the following method steps:

comparing the voltage signal to a reference signal; and

reducing the second regulating signal when the voltage signal exceeds the reference signal.

11. The method according to claim 10 wherein the second regulating signal is reduced in dependency on a difference between the first voltage signal and the reference signal.

12. The method according to claim 9 wherein the generation of the drive signal comprises the method steps of:

generating a chronological sequence of drive input pulses that respectively start based on a criterion of an oscillator cycle and that respectively end when the first voltage signal reaches a value of the first regulating signal or of the second regulating signal.

13. A switched-mode power supply, comprising:

a switch for applying a supply voltage to a primary coil of a transformer based on a drive signal;

a pulse-Width modulator for providing a drive signal to the switch and having supplied thereto a first regulating signal dependent on an output voltage and a voltage signal dependent on a current through the primary coil; and

a second regulating signal also supplied to the pulse-width modulator and developed by comparison to a reference and which is variable in dependency on the current through the primary coil.

14. A method for driving a switch connected in series to a primary coil in a switched-mode power supply, comprising the steps of:

generating a drive signal for driving the switch based on a first regulating signal dependent on an output voltage and on a voltage signal dependent on a current through the primary coil; and

the generation of the drive signal also being based on a second regulating signal developed by comparison to a reference and which is adjusted according to the current through the primary coil.