Semiconductor device for controlling switching power supply

• US 20050218942A1
• Filed: 03/25/2005
• Published: 10/06/2005
• Est. Priority Date: 03/31/2004
• Status: Active Grant

• Current Assignee: Collabo Innovations, Inc. (Wi-LAN Inc.)
• Original Assignee: Matsushita Electric Industrial Company Limited (Panasonic Holdings Corporation)
• Inventors: Yamashita, Tetsuji
• Granted Patent: US 7,208,985 B2
• Time in Patent Office: Days
• US Class Current: 327/108
• 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
• CPC Class Codes: H02M 3/33523 with galvanic isolation between input and output of both the power stage and the feedback loop

Abstract

In a semiconductor device for controlling switching power supply of this invention, having a switching element and switching operation control circuit, after receiving a current detection signal when switching is turned off, a fixed delay time is applied to the current detection signal by a delay circuit so that switching turn-on control by a transformer reset pulse signal obtained based on a signal from the tertiary windings of the transformer is not accepted within a blanking time corresponding to the delay time. Thus, the switching by the switching element is halted.

Claims

1. A semiconductor device for controlling switching power supply, in a switching power supply in which a DC input voltage is applied to a switching element through the primary windings of a transformer, and the switching operation of said switching element controls the DC voltage obtained by rectifying and smoothing the alternating current appearing across the secondary windings of said transformer, to supply power to a load, said semiconductor device for controlling switching power supply comprising a control circuit,

said control circuit, comprising:

a transformer reset detection circuit for detecting the reset state of said transformer occurring due to switching operation of said switching element from the AC voltage occurring across tertiary windings of said transformer, and outputting a transformer reset detection signal indicating the reset state;

an I-V converter for converting into a voltage the current value of a control current indicating the change in said DC voltage based on the alternating current appearing across the secondary windings of said transformer; and

,

current detection signal output device for detecting a current flowing in said switching element based on the output voltage from said I-V converter, and outputting a current detection signal to control switching turn-on action of said switching element according to the detected value, wherein

the control electrode of said switching element is driven by said control circuit based on the transformer reset detection signal from said transformer reset detection circuit and the current detection signal from said current detection signal output device, to control switching operation of said switching element,

said semiconductor device for controlling switching power supply further comprising a delay circuit for applying a prescribed delay time to the current detection signal from said current detection signal output device, and configured so that the transformer reset detection signal from said transformer reset detection circuit is masked until output of said current detection signal with prescribed time delay applied by said delay circuit, thereby to halt switching operation of said switching element.

2. The semiconductor device for controlling switching power supply according to claim 1, wherein a component to determine said delay time of said delay circuit is connected externally, and said delay circuit is configured such that said delay time is determined according to a constant of the externally connected component.

3. The semiconductor device for controlling switching power supply according to claim 1, wherein said delay circuit is configured such that said delay time is determined automatically according to the current value of said control current which changes according to fluctuations in said loading state.

4. The semiconductor device for controlling switching power supply according to claim 1, further comprising a light loading detection circuit which, upon detecting light loading as a load state indicating the power supplied to said load based on a change in output voltage from said I-V converter, outputs a control signal to control intermittent operation of switching by said switching element, wherein

said light loading detection circuit is configured so as to output a control signal to control said intermittent operation such that switching operation of said switching element is halted when the output voltage from said I-V converter falls below the light loading detection lower limit voltage for detection of said light loading, and such that the switching operation of said switching element is resumed when the output voltage from said I-V converter rises above the light loading detection upper limit voltage for detection of said light loading, and

the control electrode of said switching element is driven, by means of said control circuit, to control said intermittent operation based on the transformer reset detection signal from said transformer reset detection circuit and the control signal from said light loading detection circuit.

5. The semiconductor device for controlling switching power supply according to claim 1, wherein said switching element and said control circuit are integrated on the same semiconductor substrate, and comprises on said semiconductor substrate as external connection terminals, at least, a switching element input terminal for inputting said input voltage to said switching element through the primary windings of said transformer, a switching element output terminal for outputting the switching current obtained by switching operation of said switching element, a power supply terminal for supplying to said control circuit a DC voltage based on the current appearing across the tertiary windings of said transformer through switching operation of said switching element, a control terminal for inputting a control signal to control switching operation of said switching element based on the DC voltage across the secondary windings of said transformer which changes according to said load state, and a transformer reset detection terminal for supplying said transformer reset detection signal to said transformer reset detection circuit.

6. The semiconductor device for controlling switching power supply according to claim 4, wherein said switching element and said control circuit are integrated on the same semiconductor substrate, and comprises on said semiconductor substrate as external connection terminals are, at least, a switching element input terminal for inputting said input voltage to said switching element through the primary windings of said transformer, a switching element output terminal for outputting the switching current obtained by switching operation of said switching element, a power supply terminal for supplying to said control circuit a DC voltage based on the current appearing across the tertiary windings of said transformer through switching operation of said switching element, a control terminal for inputting a control signal to control switching operation of said switching element based on the DC voltage across the secondary windings of said transformer which changes according to said load state, and a transformer reset detection terminal for supplying said transformer reset detection signal to said transformer reset detection circuit.