Dc-to-dc converter

• US 6,519,165 B2
• Filed: 11/29/2001
• Issued: 02/11/2003
• 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
• Primary Examiner(s): BERHANE, ADOLF D
• Application Number:
  US09/996,841
• Publication Number:
  US 20020067629A1
• Time in Patent Office: 439 Days
• Field of Search: 363/20, 363/21.12, 363/21.13, 363/21.15, 363/21.18, 363/95, 363/97, 363/131
• US Class Current: 363/21.12
• 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. For intermittently operating the switch under light load, a sawtooth generator circuit is provided which provides a sawtooth voltage having a frequency less than that of the on-off operation of the switch. The sawtooth voltage is compared with a voltage indicative of the magnitude of a current flowing through the switch. The result of this comparison is utilized for modifying the delivery of switching pulses to the switch.

Claims

1. A d.c.-to-d.c. converter to be connected between a d.c. power supply and a load, 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 variable durations having a period (T_l);

(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 current detector circuit for putting out a voltage (V_c) indicative of the magnitude of a current (I_l) flowing through the switch;

(g) a periodic wave generator circuit for generating a periodic voltage (V_t) in the form of a series of alternations of a rise and a fall, with a period that is a plurality of times longer than the period (T_l) of the switching pulses, the periodic voltage (V_t) crossing the switch current detector output voltage (V_c) during its rises and falls;

(h) a comparator having an input connected to the switch current detector circuit, and another input connected to the periodic wave generator circuit, for providing an output (V₁₀) that changes from one state to another depending upon the relative magnitudes of the switch current detector output voltage (V_c) and the periodic voltage (V_t); and

(i) a switch control circuit having an output connected to the switch for delivering the switching pulses thereto, an input connected to the output voltage detector circuit for controlling the durations of the switching pulses according to the converter output voltage (V_o) so as to keep the same constant, and another input connected to the comparator for permitting or preventing the delivery of the switching pulses to the switch depending upon the binary output (V₁₀) from the comparator.

2. The d.c.-to-d.c. converter of claim 1 wherein the switch current detector circuit comprises:

(a) a current-detecting resistor having a first extremity connected to the switch, and a second extremity connected to one of the input terminals of the converter, the first extremity of the current-detecting resistor being grounded;

(b) a bias power supply; and

(c) a pair of voltage-dividing resistors connected in series with each other and, via the bias power supply, in parallel with the current-detecting resistor;

(d) whereby the voltage (V_c) indicative of the magnitude of the current flowing through the switch is obtained from between a junction between the pair of voltage-dividing resistors and the ground.

3. The d.c.-to-d.c. converter of claim 1 wherein the periodic wave generator circuit comprises:

(a) a capacitor;

(b) a charge/discharge circuit for causing the capacitor to be charged and discharged;

(c) a variable reference voltage source capable of selectively providing a first (V_th1) and a second (V_th2) reference voltage, the first reference voltage being less than the second reference voltage; and

(d) a second comparator having an input connected to the capacitor, another input connected to the variable reference voltage source, and an output connected to the variable reference voltage source, for causing the variable reference voltage source to switch from the first (V_th1) to the second (V_th2) reference voltage when a voltage across the capacitor drops to the first reference voltage, and from the second to the first reference voltage when the voltage across the capacitor rises to the second reference voltage, the output of the second comparator being additionally connected to the charge/discharge circuit for causing the same to charge the capacitor when the second comparator is in one state, and to discharge the capacitor when the second comparator is in another state.

4. The d.c.-to-d.c. converter of claim 3 further comprising:

(a) first circuit means connected to the periodic wave generator circuit for providing a signal indicative of the rises of the periodic voltage (V_t); and

(b) second circuit means connected between the first circuit means and the switch control circuit for permitting the delivery of the switching pulses to the switch during the rises of the periodic voltage (V_t).

5. The d.c.-to-d.c. converter of claim 4 wherein the first circuit means is connected to the output of the second comparator of the periodic wave generator circuit.

6. The d.c.-to-d.c. converter of claim 5 wherein the second circuit means comprises a gate circuit having inputs connected to the first recited comparator and the first circuit means.

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

(a) a pulse generator for providing a series of pulses at a repetition frequency for on-off control of the switch;

(b) a voltage feedback circuit coupled to the output voltage detector circuit for providing a voltage feedback signal (V_f) indicative of the converter output voltage (V_o);

(c) a second comparator having an input connected to the voltage feedback circuit, and another input connected to the switch current detector circuit, for providing an output that changes from one state to another when the switch current detector output voltage (V_c) agrees with the voltage feedback signal (V_f);

(d) a flip-flop having an input connected to the pulse generator, and another input connected to the second comparator of the switch control circuit, for providing an output that changes from a first to a second state in response to each output pulse of the pulse generator and that changes from the second to the first state upon agreement of the switch current detector output voltage (V_c) with the voltage feedback signal (V_f);

(e) a logic circuit having an input connected to the pulse generator, another input connected to the flip-flop, and an output connected to the switch, for delivering the switching pulses to the switch in order to cause conduction therethrough when the output from the flip-flop is in the second state and, at the same time, when no pulses are being put out by the pulse generator; and

(f) the first recited comparator being connected to the flip-flop for resetting the same.

8. The d.c.-to-d.c. converter of claim 1 further comprising a mode selector circuit for providing a signal indicative of whether the converter is under normal or light load, the mode selector circuit being connected to the periodic wave generator circuit for permitting the same to generate the periodic voltage (V_t) only when the converter is lightly loaded.

9. The d.c.-to-d.c. converter of claim 1 wherein the inductance means comprises a transformer having a primary winding connected to the switch, and a secondary winding connected to the rectifying and smoothing circuit.

10. A d.c.-to-d.c. converter to be connected between a d.c. power supply and a load, 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 variable durations having a period (T_l);

(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 providing a voltage feedback signal (Vf) indicative of the output voltage (V_o) of the converter;

(f) a switch current detector circuit for putting out a voltage (V_c) indicative of the magnitude of a current (I_l) flowing through the switch;

(g) a periodic wave generator circuit for generating a periodic voltage (V_t) in the form of a series of alternations of a first and a second ramp which are oriented in opposite directions, with a period that is a plurality of times longer than the period (T_l) of the switching pulses, the periodic voltage (V_t) being of such magnitude that the first ramp thereof is partly traversed by the switch current detector output voltage (V_c) when the switch is turned on;

(h) a comparator having an input connected to the switch current detector circuit, and another input connected to the periodic wave generator circuit, for producing pulses (V₁₀) for limiting the conducting periods of the switch depending upon the relative magnitudes of the switch current detector output voltage (V_c) and the periodic voltage (V_t);

(i) binary circuit means for providing a binary output having either of two possible states indicative of the first and the second ramps of the periodic voltage (V_t); and

(j) a switch control circuit connected between the output voltage detector circuit and the switch for delivering to the latter the switching pulses of durations controlled according to the converter output voltage (V₀), in order to keep constant the converter output voltage, the switch control circuit having inputs connected to the comparator and the binary circuit means for preventing the delivery of the switching pulses to the switch both when the binary output is in a prescribed one of the two possible states and when the comparator is producing the pulses (V₁₀).

11. The d.c.-to-d.c. converter of claim 10 wherein the periodic wave generator circuit comprises:

(a) a capacitor;

(b) a charge/discharge circuit for causing the capacitor to be charged and discharged;

(c) a variable reference voltage source capable of selectively providing a first (V_th1) and a second (V_th2) reference voltage, the first reference voltage being less than the second reference voltage; and

(d) a second comparator having an input connected to the capacitor, another input connected to the variable reference voltage source, and an output connected to the variable reference voltage source, for causing the variable reference voltage source to switch from the first (V_th1) to the second (V_th2) reference voltage when a voltage across the capacitor drops to the first reference voltage, and from the second to the first reference voltage when the voltage across the capacitor rises to the second reference voltage, the output of the second comparator being additionally connected to the charge/discharge circuit for causing the same to charge the capacitor when the second comparator is in one state, and to discharge the capacitor when the second comparator is in another state.

12. The d.c.-to-d.c. converter of claim 11 wherein the binary circuit means is connected to the second comparator of the periodic wave generator circuit for providing the binary output.

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

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

(b) a first pair of output terminals to be connected to a first load;

(c) a second pair of output terminals to be connected to a second load;

(d) a transformer having a primary winding connected between the pair of input terminals, a secondary winding connected between the first pair of output terminals, and a tertiary winding connected between the second pair of output terminals;

(e) a switch connected between the pair of input terminals and in series with the transformer primary in order to be repeatedly turned on and off by a series of switching pulses of variable durations having a period (T_l);

(f) a first rectifying and smoothing circuit connected between the transformer secondary and the first pair of output terminals for providing a first output voltage (V_o) to be applied to the first load;

(g) a second rectifying and smoothing circuit connected between the transformer tertiary and the second pair of output terminals for providing a second output voltage to be applied to the second load;

(h) an output voltage detector circuit connected to the first rectifying and smoothing circuit for detecting the first output voltage (V_o);

(i) a switch current detector circuit for putting out a voltage (V_c) indicative of the magnitude of a current (I_l) flowing through the switch;

(j) a periodic wave generator circuit for generating a periodic voltage (V_t) in the form a series of alternations of a rise and a fall, with a period that is a plurality of times longer than the period (T_l) of the switching pulses, the periodic voltage (V_t) crossing the switch current detector output voltage (V_c) during its rises and falls;

(k) a comparator having an input connected to the switch current detector circuit, and another input connected to the periodic wave generator circuit, for providing an output (V₁₀) that changes from one state to another depending upon the relative magnitudes of the switch current detector output voltage (V_c) and the periodic voltage (V_t); and

(l) a switch control circuit having an output connected to the switch for delivering the switching pulses thereto, an input connected to the output voltage detector circuit for controlling the durations of the switching pulses according to the first output voltage (V_o) so as to keep the same constant, and another input connected to the comparator for permitting or preventing the delivery of the switching pulses to the switch depending upon the binary output (V₁₀) from the comparator.

14. The d.c.-to-d.c. converter of claim 13 further comprising:

(a) a quaternary winding of the transformer; and

(b) a third rectifying and smoothing circuit connected to the transformer quaternary for powering the periodic wave generator circuit and the switch control circuit.