High speed power supply circuit with circuit with positive feedback

• US 5,101,334 A
• Filed: 05/21/1990
• Issued: 03/31/1992
• Est. Priority Date: 02/14/1989
• Status: Expired due to Fees

• Current Assignee: US Philips Corporation (Koninklijke Philips N.V.)
• Original Assignee: US Philips Corporation (Koninklijke Philips N.V.)
• Inventors: Algra, Johannes E., Plagge, Joseph A. M.
• Primary Examiner(s): Skudy, R.
• Assistant Examiner(s): Sterrett, Jeffrey L.
• Application Number:
  US07/515,998
• Time in Patent Office: 680 Days
• Field of Search: 363/18, 363/19, 363/20, 363/21, 363/97, 363/131
• US Class Current: 363/19
• CPC Class Codes: H02J 2207/20 Charging or discharging characterised by the power electronics converter
• CPC Class Codes: H02J 7/02 for charging batteries from ac mains by converters
• CPC Class Codes: H02M 1/10 Arrangements incorporating converting means for enabling loads to be operated at will from different kinds of power supplies, e.g. from ac or dc
• CPC Class Codes: H02M 3/3385 with automatic control of output voltage or current H02M3/33561 takes precedence

Abstract

A self-oscillating power supply circuit comprises a series arrangement of the primary winding (N₁) of a transformer (TR), the main current path of a first semiconductor switch (T₁) and a current measuring resistor (R₁). The first semiconductor switch is driven by a second semiconductor switch (T₂) which in turn is controlled by a comparator (CP). The voltage across the current measuring resistor is applied to the non-inverting input (6) of the comparator and, a reference voltage obtained from a reference voltage source (RS) is applied to the comparator inverting input (5). By arranging a capacitor (C₂) between the output of the second semiconductor switch and the inverting input (5) of the comparator, the first semiconductor switch rapidly turns-off at the end of the forward phase at an accurately determined current through the primary winding. By applying a lower reference voltage to the comparator at a higher mains voltage, an output current is obtained from the transformer secondary winding (N₂) for the load L, which is substantially independent of the mains voltage.

Claims

1. A power supply circuit for supplying a load from input voltages of different magnitude, comprising:

a pair of input terminals for connection to a source of unidirectional input voltage, means connecting a first series arrangement including a primary winding of a transformer and a first semiconductor switch to said input terminals, a second series arrangement including a secondary winding of the transformer and a rectifier diode, said second series arrangement having terminals for connection to the load, a second semiconductor switch coupled to a control electrode of the first semiconductor switch for switching the first semiconductor switch off a comparator having a first input connected to a source of reference voltage, a second input and an output coupled to a control input of the second semiconductor switch, means for supplying to said second input of the comparator a signal proportional to the current in said primary winding, and a positive feedback circuit coupling an output terminal of the second semiconductor switch to said first input of the comparator.

2. A power supply circuit as claimed in claim 1, wherein said positive feedback circuit comprises a capacitor, and said source of reference voltage includes a control input for receiving a signal proportional to the input voltage and means responsive thereto for supplying to said first input of the comparator a reference voltage which varies inversely with the input voltage.