JP3433799B2 - DC-DC converter - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a DC-DC converter, and more particularly to a DC-DC converter capable of improving power conversion efficiency under no load and light load.

[0002]

2. Description of the Related Art A DC power supply, a primary winding of a transformer, and a switching element are connected in series, and a switching signal is turned on / off by a drive signal from a drive circuit to rectify and smooth the secondary winding of the transformer. DC that extracts a DC output of a constant voltage different from the voltage of the DC power supply via a circuit
-The DC converter has been widely used in power supply circuits of electronic devices and the like. For example, Japanese Examined Patent Publication (Kokoku) No. 2-54029 discloses a self-excited DC-DC converter that extracts a predetermined DC output by controlling the off period of a switching element.

A conventional self-excited RCC (ringing choke converter) is, for example, as shown in FIG. 3, a DC power source (1) such as a capacitor input type rectifier circuit and a transformer (1) connected to the DC power source (1). 2) Primary winding (2a) and MOS-F
It is connected to the gate (control terminal) (3a) of the MOS-FET (3) through the series circuit of ET (3), the gate resistor (7) and the capacitor for oscillation (8) and the primary winding (2a). The drive winding (2c) of the transformer (2) magnetically coupled to the same polarity as the MOS-FE
A start-up resistor (6) connected between the gate (3a) of T (3) and the negative terminal of the DC power supply (1), and between the gate (3a) and the positive terminal of the DC power supply (1). The connected starting resistor (5) and the rectifying diode (9) connected to the secondary winding (2b) of the transformer (2).
And a smoothing capacitor (10) rectifying and smoothing circuit, and a control circuit (30) for applying a signal for controlling the on / off operation of the switching element (3) according to the DC output voltage supplied to the load (11). It has and.

Next, the operation of the self-excited RCC shown in FIG. 3 will be described. First, the gate (3a) and the source (3b) of the MOS-FET (3) are passed from the DC power source (1) through the starting resistor (5). ), And a current that charges the oscillation capacitor (8) flows,
-The FET (3) turns on and the primary winding of the transformer (2)
A current flows through (2a) and MOS-FET (3). At this time, since a voltage in the reverse bias direction of the rectifying diode (9) is induced in the secondary winding (2b) of the transformer (2), no current flows. The drive winding (2c) of the transformer (2) has a MOS-
Since a voltage that biases the FET (3) in the forward direction is induced, M is generated via the gate resistor (7) and the oscillation capacitor (8).
A drive signal is given to the gate (3a) of the OS-FET (3),
The on-state of the MOS-FET (3) is maintained. Primary winding
Since (2a) works as an inductance coil, MOS-
The current flowing through the FET (3) increases linearly. afterwards,
When the gate voltage of the MOS-FET (3) is lowered by the control circuit (30), the MOS-FET (3) begins to turn off, and the reverse voltage due to the drive winding (2c) is applied to the gate (3a) and source (3b). The voltage is applied between them and the MOS-FET (3) is turned off rapidly. The energy stored in the transformer (2) during the ON period is the MOS-F.
During the off period of ET (3), it is supplied to the load (11) from the secondary winding (2b) through the rectifying diode (9). Transformer (2)
After the end of the energy discharge of the drive winding (2c), a minute kick voltage is generated, and the drive signal is sent to the gate of the MOS-FET (3) through the gate resistor (7) and the oscillation capacitor (8).
Since it is applied to (3a), the MOS-FET (3) is turned on again. Such self-oscillation operation is controlled by the constant voltage correction operation of the control circuit (30). That is, the secondary winding (2b)
The control circuit (30) connected to the output side of the device adjusts the pulse width of the pulse signal applied from the drive circuit (4) to the gate (3a) so that the voltage applied to the load (11) becomes constant. To control.

[0005]

By the way, the DC-DC converter shown in FIG.
The oscillation frequency of T (3) is 20-40kHz, but the oscillation frequency of MOS-FET (3) is 3 when there is no load or light load.
It becomes as high as 00 to 400 kHz. As a result, the DC of FIG.
The -DC converter has a drawback that the number of times the MOS-FET (3) is switched increases and power loss due to switching loss and the like increases. Therefore, it is an object of the present invention to provide a DC-DC converter that reduces switching loss and improves power conversion efficiency under no load and light load.

[0006]

DC-DC according to the present invention
The converter turns on / off the switching element (3) connected in series with the primary winding (2a) of the transformer (2) by the drive signal of the drive circuit (4) to turn the secondary winding of the transformer (2). Extract the constant voltage DC output from (2b). DC-DC according to the present invention
In the converter, the voltage of the primary winding (2a) or secondary winding (2b) of the transformer (2) or the primary winding (2a) and secondary winding (2b)
Differentiation circuit (21) for differentiating the voltage of the tertiary winding electromagnetically coupled to, and integration for accumulating electric charge corresponding to the output of the differentiating circuit (21) and discharging the electric charge with a time constant A circuit (22), a comparison circuit (23) that generates an output when the voltage value of the integration circuit (22) exceeds a reference voltage value, and a switching element (3) when the output of the comparison circuit (23) occurs And a drive signal cutoff circuit (24) for cutting off the drive signal of the drive circuit (4). Drive circuit
(4) is an oscillation capacitor connected in series between the drive winding (2c) of the transformer (2) and one end of the drive winding (2c) and the control terminal (3a) of the switching element (3). (8) and gate resistance (7)
And the drive signal interruption circuit (24) is a switching element.
A short-circuit switching element (15) is connected between the control terminal (3a) of (3) and the main terminal.

The drive winding (2c) is a switching element for switching the drive signal through the gate resistor (7) and the oscillation capacitor (8).
Since it is given to the control terminal (3a) of (3),
When the voltage of the control terminal (3a) of the switching element (3) is lowered by the control circuit (30) after the (3) is turned on, the switching element (3) is turned off and the self-excited oscillation operation is performed. Primary winding (2a) or secondary winding (2) of transformer (2)
Integrate corresponding to the voltage of b) or the differential output obtained through the differentiating circuit (21) from the output of the tertiary winding electromagnetically coupled to the primary winding (2a) and the secondary winding (2b) The electric charge is accumulated in the circuit (22). If the voltage value of the integrating circuit (22) does not exceed the reference voltage value, the drive signal interruption circuit (24) is not activated and the short-circuit switching element (15) is not turned on. When the number of differential pulses per unit time increases when the oscillation frequency is high and when there is no load, the voltage value of the integration circuit (22) exceeds the reference voltage value, and the drive signal is generated by the output generated from the comparison circuit (23). Since the short-circuit switching element (15) of the cutoff circuit (24) is turned on, the drive signal of the drive circuit (4) to the switching element (3) is cut off. Therefore, when the oscillation frequency is high, that is, when the load is light, the drive signal cutoff circuit (24) operates to cut off the drive signal of the drive circuit (4) to the switching element (3) for a certain period of time. As a result, the secondary winding (2b) with intermittent oscillation
Output can be controlled to a constant voltage, and the number of times of switching can be reduced to reduce switching loss and improve power conversion efficiency.

In the embodiment of the present invention, the short-circuit switching element (15) is turned on when the output of the comparison circuit (23) is generated.

The control terminal (15a) of the short-circuit switching element (15) is connected to one end of the drive winding (2c) via the control switching element (16b) and the rectifying element (18) connected in series. Connected, control switching element (16b) is a comparison circuit
It turns on when the output of (23) occurs. Drive circuit (4)
Is powered by the drive winding (2c) of the transformer (2),
The output is given to the control terminal (3a) of the switching element (3),
Drive signal cutoff circuit when the output of the comparison circuit (23) occurs
Drive circuit (4) to switching element (3) by operation of (24)
Drive signal is cut off.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment of a DC-DC converter according to the present invention will be described below with reference to FIGS. However, in FIGS. 1 and 2, the portions substantially the same as the portions shown in FIG. 3 are denoted by the same reference numerals, and the description thereof will be omitted.

As shown in FIG. 1, the DC-DC converter according to this embodiment corresponds to a differentiating circuit (21) for differentiating the output of the secondary winding (2b) and an output of the differentiating circuit (21). When the output of the comparison circuit (23) is generated, and the output of the comparison circuit (23) is generated when the voltage value of the integration circuit (22) exceeds the reference voltage value. The point is that an intermittent oscillation control circuit (20) composed of a drive signal cutoff circuit (24) for cutting off the drive signal of the drive circuit (4) to the MOS-FET (3) as a switching element is provided. There are features. Other configurations are the same as those of the DC-DC converter in FIG.

As shown in FIG. 2, the differentiating circuit (21) includes a differentiating capacitor (31) and a limiting resistor (32) connected in series.
Through the limiting resistor (32) and the differentiating capacitor (31)
Base and secondary winding (2b) connected to one end of secondary winding (2b)
Transistor having an emitter connected to the other end of (35)
And a differentiating resistor (33) connected between the base and emitter of the transistor (35), and a protective diode connected in parallel to the differentiating resistor (33) and with the cathode connected to the limiting resistor (32).
(34) and the voltage divider resistor (3) connected in series between the cathode of the rectifying diode (9) and the collector of the transistor (35).
6) (37) and a transistor (38) having a base connected between the voltage dividing resistors (36) and (37) and an emitter connected to the cathode of the rectifying diode (9).

The integrating circuit (22) has a transistor (38) at one end.
And an integrating capacitor (40) connected in series between the collector and the other end of the secondary winding (2b). The comparator circuit (23) includes a discharging resistor (48) connected between the connecting point of the integrating resistor (39) and the integrating capacitor (40) and the other end of the secondary winding (2b), and a discharging resistor (48). Between the series circuit of the comparative Zener diode (43) and the resistor (41) connected in parallel with the resistor (48), the cathode of the rectifying diode (9) and the other end of the secondary winding (2b). LEDs connected in series to
(16a), resistor (46), diode (47) and transistor (4
5) A series circuit and a transistor (44) having a base and a collector connected to the collector and the base of the transistor (45), respectively. The base of the transistor (45) is also connected between the comparative Zener diode (43) and the resistor (41), and the emitter of the transistor (45) is connected to the other end of the secondary winding (2b). The emitter of the transistor (44) is connected to the cathode of the comparison Zener diode (43) via the resistor (42).

Further, the drive signal cutoff circuit (24) includes a short circuit transistor (15) having a collector and an emitter connected in parallel with the starting resistor (6), a drive winding (2c) and a gate resistor (7). ), A diode (18), a resistor (17), and a light receiving transistor (16b) connected in series between the base of the short-circuiting transistor (15). The base of the light receiving transistor (16b) is the light emitting diode (16a) of the comparison circuit.
The light is received to form a photocoupler (16).

Next, in the present embodiment, during operation of the DC-DC converter, a part of the output of the secondary winding (2b) is connected to one end of the secondary winding (2b) for the differentiation circuit ( 21) forms a derivative pulse which turns on the transistor (35). When the base current flows through the transistor (38) in synchronism with this, the transistor (38) turns on, so that it corresponds to the differential pulse of the differentiating circuit (21) and is integrated via the integrating resistor (39). A charge is stored in the capacitor (40). The amount of charge accumulated in the integrating capacitor (40) set by the time constant of the integrating resistor (39) and the integrating capacitor (40) is
The higher the oscillation frequency of the current flowing through the secondary winding (2b), the larger the oscillation frequency, and the lower the oscillation frequency, the smaller the oscillation frequency.

When the load becomes no load or light load, sufficient charge is accumulated in the integrating capacitor (40) of the integrating circuit (22), and the voltage value is the Zener diode for comparison of the comparing circuit (23).
When the reference voltage value of (43) is exceeded, the base current flows through the transistor (45), and the transistor (45) and transistor (44)
Turns on and discharges the capacitor (40) through the resistor (42). A current flows through the light emitting diode (16a) during discharging. As a result, the light emitting diode (16a) emits light, and the base current flows through the light receiving transistor (16b) of the drive signal cutoff circuit (24), so that the base current also flows through the short-circuiting transistor (15) and turns on. , The drive signal of the drive winding (2c) is not applied to the gate (3a).
FET (3) turns off. When the discharge of the capacitor (40) through the resistor (42) is completed, no light signal is applied from the light emitting diode (16a) to the light receiving transistor (16b), and the short circuit transistor (15) is turned off. After that, the MOS-FET (3) is turned off for the starting time determined by the starting resistor (5). As a result, from the intermittent oscillation control circuit (20), the signal that cuts off the drive signal of the drive winding (2c) to stop the ON operation of the MOS-FET (3) is the voltage value of the integration circuit (22). It is not applied until the reference voltage value of the comparison circuit (23) is exceeded, and the control circuit
The on / off operation of the MOS-FET (3) is controlled by the (30) so that the voltage applied to the load (11) becomes constant. The intermittent oscillation in which the oscillation stop state and the oscillation state are repeated for a certain period operates when the load is no load or light load. The oscillation interval of the MOS-FET (3) at this time can be arbitrarily set by adjusting the time constants of the integrating resistor (39) and the integrating capacitor (40) and the resistance values of the discharge resistor (48). Further, the oscillation and stop periods can be arbitrarily set by the discharge time constant of the capacitor (40) and the resistor (42) and the starting time by the starting resistor (5).

As described above, in this embodiment, the transformer is
The electric charge is accumulated in the integrating capacitor (40) corresponding to the differential output obtained from the output of the secondary winding (2b) of (2) through the differentiating circuit (21), and the voltage value is compared with the Zener diode (43). ), The drive signal cutoff circuit (24) is activated by a signal generated from the light emitting diode (16a). Therefore, the drive signal of the drive winding (2c) is supplied to the MOS-F at no load and when the load becomes high because of the constant voltage control.
Since it is applied intermittently to the gate (3a) of ET (3), it reduces switching loss that occurs at no load and at light load,
The power conversion efficiency can be improved.

The embodiment of the present invention is not limited to the above-mentioned embodiment, and various modifications can be made. For example, in the above-described embodiment, an example in which the voltage of the secondary winding (2b) is differentiated by the differentiating circuit (21) is shown, but the differentiating circuit (21) differentiates the primary winding (2b).
The voltage of a) may be differentiated or the voltage of a tertiary winding electromagnetically coupled to the primary winding (2a) and the secondary winding (2b) may be differentiated.
The tertiary winding is composed of a winding (not shown) or a drive winding (2c). In the above-mentioned embodiment, the case of the self-excitation type using the drive winding (2c) as the drive signal of the MOS-FET (3) is shown, but the separately excited type using the control IC which is the RCC type control system is shown. Even in this case, the same effect as described above can be obtained. Further, in the above embodiment, the MOS-F is used as the switching element.
Although ET (3) (MOS type field effect transistor) is shown, other types of transistors such as J-FET (junction type field effect transistor), bipolar transistor or IGBT (insulated gate type transistor) can be used.

[0019]

According to the present invention, the standby power loss of an electronic device is reduced by reducing the switching loss under no load and light load and improving the power conversion efficiency of the device.
Energy saving can be realized.

[Brief description of drawings]

FIG. 1 is an electric circuit diagram showing a DC-DC converter of the present invention.

FIG. 2 is an electric circuit diagram of a DC-DC converter showing an embodiment of the present invention.

FIG. 3 is an electric circuit diagram showing a conventional DC-DC converter.

[Explanation of symbols]

(1) ・ ・ DC power supply, (2) ・ ・ Transformer, (2a) ・ ・ Primary winding, (2b) ・ ・ Secondary winding, (2c) ・ ・ Drive winding,
(3) ・ ・ Switching element (MOS-FET), (3a) ・
・ Control terminal (gate), (4) ・ ・ Drive circuit, (5) ・ ・
Starting resistance, (6) ・ ・ Starting resistance, (7) ・ ・ Gate resistance, (8) ・ ・ Oscillating capacitor, (9) ・ ・ Rectifying diode, (10) ・ ・ Smoothing capacitor, (11 ) ・ ・ Load, (15) ・ ・ Short-circuit switching element (short-circuit transistor), (15a) ・ ・ Control terminal (base), (16b) ・
・ Control switching element (light receiving transistor), (1
8) ・ ・ Rectifying element (diode), (20) ・ ・ Intermittent oscillation control circuit, (21) ・ ・ Differentiation circuit, (22) ・ ・ Integration circuit,
(23) ・ ・ Comparison circuit, (24) ・ ・ Drive signal interruption circuit,

─────────────────────────────────────────────────── ─── Continuation of front page (56) References JP-A-11-235037 (JP, A) JP-A-8-255025 (JP, A) JP-A-10-98879 (JP, A) JP-A-8- 84466 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) H02M 3/28

Claims (4)

(57) [Claims] 1. A DC-DC converter for extracting a constant-voltage DC output from a secondary winding of the transformer by turning on / off a switching element connected in series with a primary winding of the transformer in response to a drive signal from a drive circuit. A differential circuit for differentiating the voltage of the primary winding or the secondary winding or the voltage of the tertiary winding electromagnetically coupled to the primary winding and the secondary winding, and the output of the differentiating circuit Integrating circuit for accumulating electric charge corresponding to the above and discharging electric charge with a time constant, a comparing circuit for generating an output when the voltage value of the integrating circuit exceeds a reference voltage value, and an output of the comparing circuit A drive signal cutoff circuit that cuts off a drive signal of the drive circuit to the switching element when occurs, the drive circuit includes a drive winding of the transformer, one end of the drive winding, and the switching element. With control terminal of An oscillating capacitor and a gate resistor connected in series to the drive signal interrupting circuit, wherein the drive signal cutoff circuit includes a short-circuit switching element connected between the control terminal and the main terminal of the switching element. DC-DC converter. 2. The DC-DC converter according to claim 1, wherein the switching element for short circuit is turned on when an output of the comparison circuit is generated. 3. The control terminal of the short-circuit switching element is connected to one end of the drive winding through a control switching element and a rectifying element connected in series, and the control switching element is connected to the comparison circuit. The DC-DC converter according to claim 2, which is turned on when an output is generated. 4. The drive circuit is supplied with power from the drive winding of the transformer to give an output to a control terminal of the switching element, and when the output of the comparison circuit occurs, The DC-DC according to claim 1, wherein the drive signal of the drive circuit to the switching element is cut off by the operation.
converter.