Switched mode power supply with a simplified start-up supply

Patent metadata

Field	Value
Publication number	US-9444347-B2
Application number	US-201114112032-A
Country	US
Kind code	B2
Filing date	Apr 15, 2011
Priority date	Apr 15, 2011
Publication date	Sep 13, 2016
Grant date	Sep 13, 2016

Abstract

A switched mode power supply (SMPS) is disclosed in which a simple primary side controller is used to send a single pulse of energy to the secondary side to switch on an output voltage controller. The pulse is sent across the main power train and a filtering arrangement is provided on the secondary side to minimize the energy at the output of the SMPS while maximizing the energy supplied to the output voltage controller. Advantageously, the SMPS is configured such that the maximum amount of energy transferred from the primary side to the secondary side during a start-up operation is inherently limited. Protection against short circuit conditions and malfunctions is therefore provided without requiring complicated circuitry.

First claim

The invention claimed is:

1. A switched mode power supply comprising:
a transformer having a primary side and a secondary side;
an input to the switched mode power supply arranged on the primary side;
a main output of the switched mode power supply arranged on the secondary side;
an output voltage controller arranged on the secondary side and operable to control an output voltage at the main output of the switched mode power supply;
a power supply circuit arranged to provide a power supply on the secondary side, wherein the power supply circuit is operable to receive power from the primary side via the transformer and to output power to the main output and also to the output voltage controller, the power supply circuit including a filter arrangement to output power;
an energy storage unit arranged on the primary side and operable to receive and store a finite amount of energy from the input to the switched mode power supply and to output a finite energy pulse to the primary side of the transformer during a start-up operation; and
a control module arranged on the primary side and operable to switch on the output voltage controller during the start-up operation by releasing stored energy from the energy storage unit in the finite energy pulse to switch on the output voltage controller, wherein the control module controls a duration of the finite energy pulse to limit an amount of stored energy transferred across the transformer to the power supply circuit to switch on the output voltage controller and wherein the filter arrangement of the power supply circuit responds faster in providing the power to the output voltage controller than providing the power to the main output to ensure that the output voltage controller is functional prior to providing the output voltage at the main output.

2. The switched mode power supply according to claim 1 , wherein the control module is operable to monitor an amount of energy stored in the energy storage unit and to control a start of a release of stored energy from the energy storage unit as the finite energy pulse in dependence upon the amount of energy stored in the energy storage unit.

3. The switched mode power supply according to claim 2 , wherein the control module is operable to monitor an amount of energy released from the energy storage unit and to stop the release of energy from the energy storage unit as a finite energy pulse in dependence upon the amount of energy released from the energy storage unit.

4. The switched mode power supply according to claim 3 , further comprising a switching module controllable by the control module to start and stop the release of energy from the energy storage unit for transfer from the primary side to the secondary side.

5. The switched mode power supply according to claim 4 , wherein the switching module is controllable to provide a switching of a main power train of the switched mode power supply when the switched mode power supply is operating.

6. The switched mode power supply according to claim 5 , wherein:
the switching module comprises a first switch coupled to a first terminal of the input to the switched mode power supply, and a second switch coupled to a second terminal of the input to the switched mode power supply;
the first switch and second switch are arranged in series between terminals of the input to the switched mode power supply; and
a position within a series connection of the first switch and second switch is coupled to a second terminal of a primary side coil of the transformer;
wherein:
the second terminal of the input to the switched mode power supply is a ground reference; and
the control module is operable to:
start the release of energy from the energy storage unit by switching on the second switch; and
stop the release of energy from the energy storage unit by switching off the second switch.

7. The switched mode power supply according to claim 6 , wherein the energy storage unit comprises at least one capacitor.

8. The switched mode power supply according to claim 7 , wherein:
the energy storage unit comprises a series connection of at least two capacitors;
the series connection of at least two capacitors is arranged between terminals of the input to the switched mode power supply; and
a first terminal of the primary side coil of the transformer is connected to a position within the series connection of at least two capacitors.

9. The switched mode power supply according to claim 8 , further comprising:
a series connection of bleeder resistors arranged in series with the primary side coil of the transformer;
wherein:
the series connection of bleeder resistors and the primary side coil of the transformer are arranged between terminals of the input to the switched mode power supply; and
the control module is operable to detect a voltage level at a position within the series connection of bleeder resistors and primary side coil of the transformer to recharge the energy storage unit to repeat the start-up operation to switch on the output voltage controller when a first attempt to switch on the output voltage controller fails.

10. The switched mode power supply according to claim 9 , wherein the control module is operable to stop the release of energy from the energy storage unit by switching off the second switch when the detected voltage level reaches a predetermined threshold level or after a predetermined time from when the second switch was switched on.

11. The switched mode power supply according to claim 10 , further comprising:
a series connection of at least first and second input resistors arranged between terminals of the input to the switched mode power supply;
wherein:
the control module is operable to detect a voltage level at a position within the series connection of at least first and second input resistors to determine an input voltage level to the switched mode power supply; and
the control module is operable to determine when the start-up operation is to be performed in dependence upon the determined input voltage level and the detected voltage level at the position within said series connection of bleeder resistors and primary side coil of the transformer.

12. The switched mode power supply according to claim 11 , further comprising a third switch operable to switch the first switch off when both the first switch and the second switch are on.

13. The switched mode power supply according to claim 12 , further comprising a coupling device for transmitting control signals for the switching module from the secondary side to the primary side;
and wherein the output voltage controller comprises a voltage regulator and a pulse width modulator (PWM) controller for controlling the switching module on the primary side.

14. The switched mode power supply according to claim 13 , wherein the control module is operable to monitor a drive signal of the switching module to determine when the output voltage controller is operating.

15. A method of operating a switched mode power supply having a transformer with a primary side and a secondary side, an input to the switched mode power supply arranged on the primary side, an energy storage unit arranged on the primary side, a main output of the switched mode power supply arranged on the secondary side, and an output voltage controller arranged on the secondary side to receive power from the primary side and to control an output voltage at the main output of the switched mode power supply, the method being performed to switch on the output voltage controller during a start-up operation comprising:
receiving energy at the input of th

Assignees

• Persson Oscar
• Appelberg Mikael
• Leskovec Marko
• ERICSSON TELEFON AB L M (publ)

Inventors

• Persson Oscar
• Appelberg Mikael
• Leskovec Marko

Classifications

• H02M3/33507

  with automatic control of the output voltage or current, e.g. flyback converters (H02M3/33561, H02M3/33569 take precedence) · CPC title

• H02M3/335 Primary

  using semiconductor devices only · CPC title

• H02M1/36 Primary

  Means for starting or stopping converters · CPC title

• H02M3/33523

  with galvanic isolation between input and output of both the power stage and the feedback loop · CPC title