Patent ID: 6445598
Filing Date: 2002-09-03
Classification: H02M,Y02B

Abstract:
A dc-to-dc converter for delivering direct-current power to a load (26) characterized by comprising:a dc power supply (1) for providing a unidirectional voltage; a switching device (3) connected between terminals (18) and (19) of said power supply (1) and having a first and a second main terminal and a control terminal; inductance means (2 or 2a) connected in series with said switching device (3) and adapted to store energy during the conducting periods of said switching device and to release the energy during the nonconducting periods of said switching device; a rectifying and smoothing circuit (6) connected to said inductance means (2 or 2a); output voltage detector means (8, 10) for detecting a signal indicative of the output voltage of said rectifying and smoothing circuit (6); switch voltage detector means (11, 11a or 11b) for providing a signal indicative of a voltage between said first and said second main terminal of said switching device (3); and switch control means (13) connected to said output voltage detector means (8, 10) and said switch voltage detector means (11, 11a or 11b) and said switching device (3) for producing a switch control signal for on-off control of said switching device and for applying the switch control signal to said control terminal of said switching device, said switch control means having a function of determining the conducting periods (Ton) of said switching device so as to keep constant the output voltage in response to the output of said output voltage detector means (8, 10), a function of forming a signal indicative of a first minimum nonconducting period (T1) to which the nonconducting periods (Toff) of said switching device are to be limited, a function of forming a signal indicative of a second minimum nonconducting period (T2) which is longer than the first minimum nonconducting period (T1), a function of selectively providing the first and the second minimum nonconducting period signals, a function of detecting the duration (T0) of the flyback voltage of said inductance means (2 or 2a), a function of judging whether the flyback voltage duration (T0) is shorter than the first minimum nonconducting period (T1) or not, a function of judging whether the flyback voltage duration (T0) is longer than the second minimum nonconducting period (T2) or not, a function of limiting the nonconducting periods (Toff) of said switching device (3) under the second minimum nonconducting period (T2) when the flyback voltage duration (T0) proves to be shorter than the first minimum nonconducting period (T1), a function of limiting the nonconducting periods (Toff) of said switching device (3) under the first minimum nonconducting period (T1) when the flyback voltage duration (T0) proves to be longer than the second minimum nonconducting period (T2), and a function of terminating the nonconducting periods (Toff) of said switching device (3) when the signal indicative of the voltage of said switching device, obtained by said switch voltage detector means (11, 11a or 11b) upon termination of the first (T1) or second (T2) minimum nonconducting period, grows equal to or less than a predetermined reference value (Vr1 or Vr2â€²).