Dc-to-dc converter

• US 6,515,876 B2
• Filed: 11/29/2001
• Issued: 02/04/2003
• Est. Priority Date: 12/04/2000
• Status: Expired due to Fees

• Current Assignee: Sanken Electric Company Limited
• Original Assignee: Sanken Electric Company Limited
• Inventors: Koike, Kengo, Okada, Kei
• Primary Examiner(s): NGUYEN, MATTHEW VAN
• Application Number:
  US09/996,835
• Publication Number:
  US 20020067626A1
• Time in Patent Office: 432 Days
• Field of Search: 363/16, 363/20, 363/21.01, 363/21.12, 363/21.15, 363/21.16, 363/95, 363/97, 363/131
• US Class Current: 363/21.16
• CPC Class Codes: H02M 1/0032 Control circuits allowing low power mode operation, e.g. in standby mode
• CPC Class Codes: H02M 3/33523 with galvanic isolation between input and output of both the power stage and the feedback loop
• CPC Class Codes: Y02B 70/10 Technologies improving the efficiency by using switched-mode power supplies [SMPS], i.e. efficient power electronics conversion e.g. power factor correction or reduction of losses in power supplies or efficient standby modes

Abstract

A transformer has a primary winding connected between a pair of d.c. input terminals via an on-off switch, and a secondary winding connected between a pair of d.c. output terminals via a rectifying and smoothing circuit. The output voltage applied from the rectifying and smoothing circuit to the load is held constant by switching the input voltage through feedback control. The switch is driven in either of two different prescribed modes depending upon whether the converter is under normal or light load. In order to ascertain the load magnitude a flyback period determination circuit is connected to a tertiary winding of the transformer for providing a signal indicative of a flyback period during which a flyback voltage exists across the transformer tertiary after the switch is turned off each time. Each flyback period is compared with two different reference periods of time for hysteretic determination of whether the converter is under normal or light load. Several other embodiments are disclosed.

Claims

1. A d.c.-to-d.c. converter to be connected between a d.c. power supply and a load to be powered, comprising:

(a) a pair of input terminals to be connected to a d.c. power supply for inputting a unidirectional voltage;

(b) a switch connected between the pair of input terminals in order to be repeatedly turned on and off by a series of switching pulses (V_G) for switching the d.c. power supply;

(c) inductance means connected in series with the switch;

(d) a rectifying and smoothing circuit connected to the inductance means for providing an output voltage (V_o) to be applied to the load;

(e) an output voltage detector circuit for detecting the output voltage (V_o) of the converter;

(f) a switch control circuit connected between the output voltage detector circuit and the switch for delivering to the latter the series of switching pulses (V_G) which are modulated according to the converter output voltage (V_o) in order to keep the converter output voltage constant;

(g) a flyback period determination circuit for providing a flyback period signal (V_f) indicative of a flyback period (T_f) during which a flyback voltage exists across the inductance means after the switch has been turned off each time;

(h) a reference period generator circuit for providing at least one reference period of time (T_A, T_B); and

(i) a load magnitude discriminator circuit having inputs connected to the flyback period determination circuit and to the reference period generator circuit in order to provide a load magnitude discrimination signal indicative of whether the converter is under normal or light load by comparing the flyback period (T_f) and the reference period (T_A, T_B), the load magnitude discrimination signal being delivered to the switch control circuit for causing the same to make on-off control of the switch in either of two different prescribed modes depending upon whether the converter is under normal or light load.

2. The d.c.-to-d.c. converter of claim 1 wherein the reference period generator circuit comprises:

(a) a first reference period generator for providing a signal indicative of a first reference period of time (T_A) following the beginning of each flyback period (T_f); and

(b) a second reference period generator for providing a signal indicative of a second reference period of time (T_B) following the beginning of each flyback period (T_f), the second reference period being longer than the first reference period.

3. The d.c.-to-d.c. converter of claim 2 wherein the load magnitude discriminator circuit comprises:

(a) first circuit means for comparing each flyback period (T_f) with the first reference period (T_A);

(b) second circuit means for comparing each flyback period (T_f) with the second reference period (T_B); and

(c) third circuit means connected between the first and second circuit means of the load magnitude discriminator circuit and the switch control circuit for supplying to the latter the load magnitude discrimination signal indicative of normal loading when each flyback period (T_f) is longer than the second reference period (T_B), and of light loading when each flyback period is not longer than the first reference period (T_A).

4. The d.c.-to-d.c. converter of claim 2 wherein the load magnitude discriminator circuit comprises:

(a) a first D flip-flop having a data input connected to the flyback period determination circuit for inputting the flyback period signal (V_f), and a clock input connected to the first reference period generator in order to be clocked at the end of the first reference period (T_A);

(b) a second D flip-flop having a data input connected to the flyback period determination circuit for inputting the flyback period signal (V_f), and a clock input connected to the second reference period generator in order to be clocked at the end of the second reference period (T_B); and

(c) an RS flip-flop having a set input connected to the first D flip-flop in order to be thereby triggered when the first D flip-flop is reset, a reset input connected to the second D flip-flop in order to be thereby triggered when the second D flip-flop is set, and an output for providing the load magnitude discrimination signal which indicates normal loading when the RS flip-flop is set, and light loading when the RS flip-flop is reset.

5. The d.c.-to-d.c. converter of claim 1 wherein the switch control circuit comprises:

(a) first circuit means for making on-off control of the switch at a first repetition frequency when the load magnitude discrimination signal from the load magnitude discriminator circuit indicates normal loading; and

(b) second circuit means for making on-off control of the switch at a second repetition frequency, which is less than the first repetition frequency, when the load magnitude discrimination signal indicates light loading.

6. The d.c.-to-d.c. converter of claim 1 wherein the switch control circuit comprises:

(a) first circuit means for making on-off control of the switch at a repetition frequency that is in inverse proportion to the load magnitude when the load magnitude discrimination signal from the load magnitude discriminator circuit indicates normal loading; and

(c) second circuit means for making on-off control of the switch at a fixed repetition frequency, which is less than a minimum of the repetition frequencies during normal loading, when the load magnitude discrimination signal indicates light loading.

7. The d.c.-to-d.c. converter of claim 1 wherein the switch control circuit comprises:

(a) first circuit means for making on-off control of the switch at a prescribed repetition frequency when the load magnitude discrimination signal from the load magnitude discriminator circuit indicates normal loading; and

(b) second circuit means for making on-off control of the switch at intervals at the prescribed repetition frequency when the load magnitude discrimination signal indicates light loading.

8. The d.c.-to-d.c. converter of claim 1 wherein the switch control circuit comprises:

(a) first circuit means for making on-off control of the switch at a repetition frequency that is in inverse proportion to the load magnitude when the load magnitude discrimination signal from the load magnitude discriminator circuit indicates normal loading; and

(b) second circuit means for making on-off control of the switch at intervals, and at a repetition frequency less than a minimum of the repetition frequencies during normal loading, when the load magnitude discrimination signal indicates light loading.

9. A d.c.-to-d.c. converter to be connected between a d.c. power supply and a load to be powered, comprising:

(a) a pair of input terminals to be connected to a d.c. power supply for inputting a unidirectional voltage;

(b) a switch connected between the pair of input terminals in order to be repeatedly turned on and off by a series of switching pulses of (V_G) for switching the d.c. power supply;

(c) inductance means connected in series with the switch;

(d) a rectifying and smoothing circuit connected to the inductance means for providing an output voltage (V_o) to be applied to the load;

(e) an output voltage detector circuit for detecting the output voltage (V_o) of the converter;

(f) a switch control circuit connected between the output voltage detector circuit and the switch for delivering to the latter the series of switching pulses (V_G) which are modulated according to the converter output voltage (V_o) in order to keep the converter output voltage constant;

(g) means for ascertaining the conducting periods (T_on) of the switch;

(h) a reference period generator circuit for providing at least one reference period of time (T_A, T_B); and

(i) a load magnitude discriminator circuit having inputs connected to the ascertaining means and to the reference period generator circuit in order to provide a load magnitude discrimination signal indicative of whether the converter is under normal or light load by comparing the conducting periods (T_on) of the switch and the reference period (T_A, T_B), the load magnitude discrimination signal being delivered to the switch control circuit for causing the same to make on-off control of the switch in either of two different prescribed modes depending upon whether the converter is under normal or light load.

10. The d.c.-to-d.c. converter of claim 9 wherein the reference period generator circuit comprises:

(a) a first reference period generator for providing a signal indicative of a first reference period of time (T_A) following the beginning of each conducting period (T_on) of the switch; and

(b) a second reference period generator for providing a signal indicative of a second reference period of time (T_B) following the beginning of each conducting period (T_on) of the switch, the second reference period being longer than the first reference period.

11. The d.c.-to-d.c. converter of claim 10 wherein the load magnitude discriminator circuit comprises:

(a) first circuit means for comparing each conducting period (T_on) of the switch with the first reference period (T_A);

(b) second circuit means for comparing each conducting period (T_on) of the switch with the second reference period (T_B); and

(c) third circuit means connected between the first and second circuit means of the load magnitude discriminator circuit and the switch control circuit for supplying to the latter the load magnitude discrimination signal indicative of normal loading when each switch conducting period (T_on) is longer than the second reference period (T_B), and of light loading when each switch conducting period is not longer than the first reference period (T_A).

12. The d.c.-to-d.c. converter of claim 10 wherein the load magnitude discriminator circuit comprises:

(a) a first D flip-flop having a data input connected to the ascertaining means for inputting the switching pulses (V_G), and a clock input connected to the first reference period generator in order to be clocked at the end of the first reference period (T_A);

(b) a second D flip-flop having a data input connected to the ascertaining means for inputting the switching pulses (V_G), and a clock input connected to the second reference period generator in order to be clocked at the end of the second reference period (T_B); and

(c) an RS flip-flop having a set input connected to the first D flip-flop in order to be thereby triggered when the first D flip-flop is reset, a reset input connected to the second D flip-flop in order to be thereby triggered when the second D flip-flop is set, and an output for providing the load magnitude discrimination signal which indicates normal loading when the RS flip-flop is set, and light loading when the RS flip-flop is reset.

13. The d.c.-to-d.c. converter of claim 9 wherein the switch control circuit comprises:

(a) first circuit means for making on-off control of the switch at a first repetition frequency when the load magnitude discrimination signal from the load magnitude discriminator circuit indicates normal loading; and

(b) second circuit means for making on-off control of the switch at a second repetition frequency, which is less than the first repetition frequency, when the load magnitude discrimination signal indicates light loading.

14. The d.c.-to-d.c. converter of claim 10 wherein the switch control circuit comprises:

(a) first circuit means for making on-off control of the switch at a repetition frequency that is in inverse proportion to the load magnitude when the load magnitude discrimination signal from the load magnitude discriminator circuit indicates normal loading; and

(b) second circuit means for making on-off control of the switch at a fixed repetition frequency, which is less than a minimum of the repetition frequencies during normal loading, when the load magnitude discrimination signal indicates light loading.

15. The d.c.-to-d.c. converter of claim 10 wherein the switch control circuit comprises:

(a) first circuit means for making on-off control of the switch at a prescribed repetition frequency when the load magnitude discrimination signal from the load magnitude discriminator circuit indicates normal loading; and

(b) second circuit means for making on-off control of the switch at intervals at the prescribed repetition frequency when the load magnitude discrimination signal indicates light loading.

16. The d.c.-to-d.c. converter of claim 10 wherein the switch control circuit comprises:

(a) first circuit means for making on-off control of the switch at a repetition frequency that is in inverse proportion to the load magnitude when the load magnitude discrimination signal from the load magnitude discriminator circuit indicates normal loading; and

(b) second circuit means for making on-off control of the switch at intervals, and at a repetition frequency less than a minimum of the repetition frequencies during normal loading, when the load magnitude discrimination signal indicates light loading.