Multiple-output switching power supply unit

Description: TECHNICAL FIELD [Detailed description of the invention]

【0001】

[Technical field to which the invention belongs]

The present invention belongs to a multi-output switching power supply device that obtains a plurality of constant voltage DC outputs by controlling the switching element on / off.

【0002】

[Conventional technology]

As a constant voltage control method for a multi-output switching power supply device, a chopper method or a mag amplifier (magnetic amplifier) method has been widely known. FIG. 7 shows an example of a chopper type multi-output switching power supply device, which serves as a main switching element constituting the primary winding (2a) of the transformer (2) connected to the DC power supply (1) and the main switching circuit. A MOS-FET (3), a secondary winding (2b) that is electromagnetically coupled to the primary winding (2a) of the transformer (2), and a DC output voltage V that is connected to the secondary winding (2b)._O1Is connected to the output terminal of the rectifying smoothing circuit (4) and the rectifying smoothing circuit (4), and the additional DC output voltage V_O2DC output voltage V of the rectifying smoothing circuit (4) by controlling the on / off time of the chopper circuit (10) and MOS-FET (3)_O1It is equipped with a main control circuit (9) that holds the above at a constant level. The rectifying smoothing circuit (4) is connected in series with the rectifying diode (5) and the freewheeling diode (6) connected to the secondary winding (2b) of the transformer (2) with respect to the freewheeling diode (6). It has a smoothing reactor (7) and a smoothing capacitor (8). The chopper circuit (10) was connected between a transistor (11) whose collector terminal was connected to one end of the smoothing capacitor (8) and between the other end of the smoothing capacitor (8) and the emitter terminal of the transistor (11). A smoothing diode (12), a smoothing reactor (13) and a smoothing capacitor (14) connected in series with the freewheeling diode (12), and a smoothing capacitor (14) by controlling the on / off time of the transistor (11). ) Voltage V_O2It has a chopper control circuit (15) that holds a constant level. The main control circuit (9) and the chopper control circuit (15) are the voltage V of the smoothing capacitors (8) and (14)._O1, V_O2Since it is a known PWM modulation circuit that outputs a PWM (pulse width modulation) signal whose duty ratio changes depending on the height with respect to the reference value of, detailed description of the configuration and operation will be omitted.

【0003】

In addition, FIG. 8 shows another example of a chopper type multi-output switching power supply device, in which the primary winding (2a) and MOS-FET of the transformer (2) connected in series with the DC power supply (1) are shown. For (3), the secondary winding (2b) and the additional secondary winding (2c) that are electromagnetically coupled to the primary winding (2a) of the transformer (2), and the secondary winding (2b). Connected and DC output voltage V_O1Rectification smoothing circuit (4a), additional rectification smoothing circuit (4b) connected to the additional secondary winding (2c), and additional rectification smoothing circuit (4b) connected to the output terminal of the additional rectification smoothing circuit (4b). DC output voltage V_O2DC output voltage V of the rectifying and smoothing circuit (4a) by controlling the on / off time of the chopper circuit (10) and MOS-FET (3)_O1It is equipped with a main control circuit (9) that holds the above at a constant level. The rectifying smoothing circuit (4a), the additional rectifying smoothing circuit (4b), and the chopper circuit (10) all have the same configuration as the rectifying smoothing circuit (4) and the chopper circuit (10) shown in FIG. The explanation will be omitted.

【0004】

Further, FIG. 9 shows an example of a mag-amp type multi-output switching power supply device, in which the primary winding (2a) and MOS-FET (3) of the transformer (2) connected in series with the DC power supply (1) are shown. ), A secondary winding (2b) and an additional secondary winding (2c) that are electromagnetically coupled to the primary winding (2a) of the transformer (2), and a secondary winding (2b). And DC output voltage V_O1Is connected to the rectifying smoothing circuit (4a) and the additional secondary winding (2c), and the additional DC output voltage V_O2Saturable reactor (16) connected between the additional secondary winding (2c) and the additional rectifying and smoothing circuit (4b), and the MOS-FET ( DC output voltage V of rectifying and smoothing circuit (4a) by controlling the on / off time of 3)_O1DC output voltage V of the additional rectifying and smoothing circuit (4b) by controlling the exciting current of the main control circuit (9) and the saturable reactor (16)._O2It is equipped with an exciting current control circuit (17) that holds the current at a constant level.

【0005】

[Problems to be Solved by the Invention]

In the chopper type switching power supply shown in Fig. 7, the DC output voltage V of the rectifying and smoothing circuit (4)_O1When only is turned on or off by an external request, it is necessary to add a dedicated switching element on the output side of the rectifying smoothing circuit (4). Further, in the chopper type switching power supply device shown in FIG. 8, since the number of rectifying smoothing circuits (4a, 4b) required by adding one to the total number of chopper circuits (10), the number of parts increases and the circuit The configuration becomes complicated. In any of the chopper type switching power supply devices shown in FIGS. 7 or 8, the number of chopper circuits (10) is used to protect the switching elements such as the transistors (11) constituting the chopper circuit (10) from electrical stress. Only an output overvoltage protection circuit called an overcurrent protection circuit and a chopper circuit is required. In particular, when the switching frequency on the primary side of the transformer (2) and the oscillation frequency on the chopper circuit (10) are different, there is a problem that mutual interference occurs and the ripple of the output on the secondary side increases. On the other hand, in the mag-amp type switching power supply shown in FIG. 9, the DC output voltage V of the rectifying smoothing circuit (4a) is the same as in the case shown in FIG._O1When only is turned on or off by an external request, it is necessary to add a dedicated switching element on the output side of the rectifying smoothing circuit (4a). Further, since the saturable reactor (16) is a winding device, both its size and weight become large, which causes a problem that it hinders the miniaturization and weight reduction of the device.

【0006】

Therefore, an object of the present invention is to provide a multi-output switching power supply device having a simple circuit configuration and capable of independent on / off control and constant voltage control for each secondary output.

【0007】

[Means for solving problems]

The multi-output switching power supply according to the present invention includes a main switching circuit having a primary winding (2a) of a transformer (2) connected to a DC power supply (1) and at least one main switching element (3), and 1 A secondary winding (2b) that is electromagnetically coupled to the secondary winding (2a) and at least one additional secondary winding (2c) and a DC output (V) that is connected to the secondary winding (2b)._O1), And an additional DC output (V) connected to the additional secondary winding (2c)._O2) And the DC output (V) of the rectifying smoothing circuit (4a) by controlling the on / off time of the main switching element (3)._O1) Is provided with a main control circuit (9) that holds the voltage level at a constant voltage level, and an output control switching element (4b) connected between the additional secondary winding (2c) and the additional rectification smoothing circuit (4b). 21) and the additional DC output (V) of the additional rectifying and smoothing circuit (4b) by controlling the on / off time of the output control switching element (21)._O2) Is provided with an auxiliary control circuit (22) that holds the voltage level at a constant level.

【0008】

When the main switching element (3) on the primary side is turned on / off, the DC voltage of the DC power supply (1) is intermittently applied to the primary winding (2a) of the transformer (2), and the secondary winding A voltage proportional to each winding ratio is induced in (2b) and the additional secondary winding (2c). By controlling the on / off time of the main switching element (3) by the main control circuit (9), a constant voltage level is reached from the secondary winding (2b) of the transformer (2) via the rectifying smoothing circuit (4a). DC output (V_O1) Occurs. At the same time, by controlling the on / off time of the output control switching element (21) on the secondary side with the auxiliary control circuit (22), it is added from the additional secondary winding (2c) of the transformer (2). Additional DC output (V) at constant voltage level via rectifying and smoothing circuit (4b)_O2) Occurs. Therefore, a chopper circuit or a large and heavy saturable reactor is not required, and the number of parts can be reduced and the size and weight can be reduced. In addition, since the current waveform of the output control switching element (21) on the secondary side is similar to the current waveform of the main switching element (3) on the primary side, an overcurrent protection circuit is installed in the main control circuit (9). If provided, it is not necessary to provide an overcurrent protection circuit in the auxiliary control circuit (22). Therefore, it is possible to perform on / off control and constant voltage control independently for each secondary output with a simple circuit configuration.

【0009】

The auxiliary control circuit (22) in one embodiment of the present invention has a reference voltage (V)._R1) And the additional DC output (V) of the additional rectifying and smoothing circuit (4b)._O2) Voltage level and reference power supply (23) reference voltage (V)_R1) Level difference signal (V)_E1) Is output, and one main terminal is connected to one end of the additional secondary winding (2c) of the transformer (2) via the current limiting element (26) and the other main terminal. The output signal (V) of the error detecting means (24) in which the terminal is connected to the other end of the additional secondary winding (2c) and is applied to the control terminal._E1) To the current (I) flowing to one of the main terminals_C1), Which is connected between the main terminals of the current control element (25) and the current control element (25), and from the additional secondary winding (2c) of the transformer (2) via the current limiting element (26). Current flowing through (I_R1) And the current (I) flowing through one of the main terminals of the current control element (25)._C1On-time control capacitor (27) charged by the difference current from), reverse charge prevention means (28) connected in parallel with the on-time control capacitor (27), and on-time control capacitor (27). Voltage (V_COn / off control signal (V) of pulse width proportional to the rising speed of)_G2) Is output and the on-time (T) of the output control switching element (21)_ON2) With control signal generating means (29,30,31). In this case, since the switching frequencies of both the main switching element (3) and the output control switching element (21) are the same, mutual interference does not occur and each DC output (V) on the secondary side is not generated._O1, V_O2) Has the advantage of being able to reduce ripple.

【0010】

Further, when the auxiliary control circuit (22) is provided with a delay circuit (32) that delays the turn-off timing of the output control switching element (21), the current flowing through the output control switching element (21) becomes zero. After that, the output control switching element (21) is turned off. Therefore, switching loss does not occur at the time of turn-off of the output control switching element (21), and the conversion efficiency can be improved. Further, when the auxiliary control circuit (22) is provided with a switching means (33) for turning off the output control switching element (21) by an external input signal, the additional secondary winding of the transformer (2) is provided. Additional DC output (V) output from (2c) via the additional rectifying and smoothing circuit (4b)_O2) Can be turned on or off at the request of the outside.

【0011】

Another multi-output switching power supply according to the present invention includes a main switching circuit having a primary winding (2a) of a transformer (2) connected to a DC power supply (1) and at least one main switching element (3). , A secondary winding (2b) that is electromagnetically coupled to the primary winding (2a), and a DC output (V) that is connected to the secondary winding (2b)._O1), And at least one is connected in parallel to the secondary winding (2b) and has an additional DC output (V)._O2) And the DC output (V) of the rectifying smoothing circuit (4a) by controlling the on / off time of the main switching element (3)._O1) Is provided with a main control circuit (9) that holds the voltage level at a constant voltage level, and an output control switching element (21) connected between the secondary winding (2b) and the additional rectification smoothing circuit (4b). And the additional DC output (V) of the additional rectification smoothing circuit (4b) by controlling the on / off time of the output control switching element (21)._O2) Is provided with an auxiliary control circuit (22) that holds the voltage level at a constant level.

【0012】

When the main switching element (3) on the primary side is turned on / off, the DC voltage of the DC power supply (1) is intermittently applied to the primary winding (2a) of the transformer (2), and the secondary winding A voltage proportional to the winding ratio is induced in (2b). By controlling the on / off time of the main switching element (3) by the main control circuit (9), a constant voltage level is reached from the secondary winding (2b) of the transformer (2) via the rectifying smoothing circuit (4a). DC output (V_O1) Occurs. At the same time, by controlling the on / off time of the output control switching element (21) on the secondary side with the auxiliary control circuit (22), it is parallel to the secondary winding (2b) of the transformer (2). Additional DC output (V) with constant voltage level from the additional rectifying and smoothing circuit (4b) connected to_O2) Occurs. Therefore, since the current waveform of the output control switching element (21) on the secondary side is similar to the current waveform of the main switching element (3) on the primary side, an overcurrent protection circuit is installed in the main control circuit (9). If provided, it is not necessary to provide an overcurrent protection circuit in the auxiliary control circuit (22). Therefore, it is possible to perform on / off control and constant voltage control independently for each secondary output with a simple circuit configuration. Further, since only one secondary winding (2b) of the transformer (2) is required, there is an advantage that the winding structure of the transformer (2) is simplified.

【0013】

The auxiliary control circuit (22) in another embodiment of the present invention is a reference voltage (V)._R1) And the additional DC output (V) of the additional rectifying and smoothing circuit (4b)._O2) Voltage level and reference power supply (23) reference voltage (V)_R1) Level difference signal (V)_E1) Is output, and one main terminal is connected to one end of the secondary winding (2b) of the transformer (2) via the current limiting element (26), and the other main terminal is connected. The output signal (V) of the error detecting means (24) connected to the other end of the secondary winding (2b) and applied to the control terminal._E1) To the current (I) flowing to one of the main terminals_C1), Which is connected between the main terminals of the current control element (25) and the current control element (25), and flows from the secondary winding (2b) of the transformer (2) via the current limiting element (26). Current (I_R1) And the current (I) flowing through one of the main terminals of the current control element (25)._C1On-time control capacitor (27) charged by the difference current from), reverse charge prevention means (28) connected in parallel with the on-time control capacitor (27), and on-time control capacitor (27). Voltage (V_COn / off control signal (V) of pulse width proportional to the rising speed of)_G2) Is output and the on-time (T) of the output control switching element (21)_ON2) With control signal generating means (29,30,31). In this case, since the switching frequencies of both the main switching element (3) and the output control switching element (21) are the same, mutual interference does not occur and each DC output (V) on the secondary side is not generated._O1, V_O2) Has the advantage of being able to reduce ripple.

【0014】

Further, when the auxiliary control circuit (22) is provided with a delay circuit (32) that delays the turn-off timing of the output control switching element (21), the switching loss at the time of turn-off of the output control switching element (21) is provided. Can be set to zero to improve conversion efficiency. If the auxiliary control circuit (22) is provided with a switch means (33) that turns off the output control switching element (21) by an external input signal, it is output from the additional rectification smoothing circuit (4b). Additional DC output (V)_O2) Can be turned on or off at the request of the outside.

【0015】

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, an embodiment in which the multi-output switching power supply device according to the present invention is applied to a forward converter will be described with reference to FIGS. 1 and 2. However, in FIG. 1, substantially the same parts as those in FIGS. 7 to 9 are designated by the same reference numerals, and the description thereof will be omitted. In the multi-output switching power supply device of the present embodiment, as shown in FIG. 1, the chopper circuit (10) of the multi-output switching power supply device of FIG. 8 is omitted, and an additional secondary winding (2c) is added. An output control MOS-FET (21) as an output control switching element is connected to the target rectification smoothing circuit (4b), and the on / off time of the output control MOS-FET (21) is controlled and added. Additional DC output voltage V of the rectifying and smoothing circuit (4b)_O2It is characterized by the provision of an auxiliary control circuit (22) that holds the power at a constant level. The auxiliary control circuit (22) has a first reference voltage V._R1The additional DC output voltage V of the first reference power supply (23) and the additional rectifying smoothing circuit (4b) that generates_O2Level and the first reference voltage V of the first reference power supply (23)_R1Difference signal V from the level of_E1The HOT side of the additional secondary winding (2c) of the transformer (2) via an error amplifier (24) as an error detection means to output the current and a current limiting resistor (26) whose collector terminal is a current limiting element. The output signal V of the error amplifier (24) that is connected to and the emitter terminal is connected to the GND side of the additional secondary winding (2c) and is applied to the base terminal._E1By collector current I_C1A current control transistor (25) as a current control element for controlling the current control, an on-time control capacitor (27) connected between the collector terminal and the emitter terminal of the current control transistor (25), and on-time control. A reverse charge prevention diode (28) as a reverse charge prevention means connected in parallel with the capacitor (27) and a second reference voltage V._R2The voltage V of the second reference power supply (29) and the on-time control capacitor (27) that generate_CLevel is the second reference voltage V_R2High (H) level voltage signal V when the level of_E2And the high (H) level or low (L) level voltage signal V output from the comparator (30)._E2The second on / off control signal V_G2It is equipped with a gate drive circuit (31) attached to the gate terminal of the output control MOS-FET (21). That is, the second reference power supply (29), the comparator (30) and the gate drive circuit (31) are the voltage V of the on-time control capacitor (27)._CSecond on / off control signal V with pulse width proportional to the rate of rise of_G2Output and output control MOS-FET (21) on-time T_ON2A control signal generating means for controlling the above is configured. Other configurations are the same as those of the conventional multi-output switching power supply device shown in FIG.

【0016】

In the above configuration, the first on / off control signal V output from the main control circuit (9)._G1When the MOS-FET (3) on the primary side is turned on / off by, the DC voltage E of the DC power supply (1) is intermittently applied to the primary winding (2a) of the transformer (2), and the first And the voltage V proportional to each winding ratio in the second secondary winding (2b, 2c)_N2, V_N3Is induced. Voltage V of smoothing capacitor (8a) of rectifying smoothing circuit (4a) in main control circuit (9)_O1The first on / off control signal V depending on the height of the reference value of_G1By changing the duty ratio of the transformer (3) and controlling the on / off time of the MOS-FET (3), a constant level of direct current is transmitted from the secondary winding (2b) of the transformer (2) through the rectifying smoothing circuit (4a). Output voltage V_O1Occurs. Here, the switching period of the MOS-FET (3) is set to T.₀[s], set the number of turns of the primary winding (2a) of the transformer (2) to N₁[Turn], the number of turns of the secondary winding (2b) and the additional secondary winding (2c) is N, respectively.₂, N₃[Turn], V forward voltage drop of rectifier diode (5a) of rectifier smoothing circuit (4a)_F1When [V] is set, the on-time T of MOS-FET (3)_ON1[s] is T_ON1= (N₁/ N₂) × (V_O1+ V_F1) × T₀It becomes / E. Also, during the ON period of the MOS-FET (3), V is applied to the secondary winding (2b) of the transformer (2)._N2= (N₂/ N₁) × E [V], V for additional secondary winding (2c)_N3= (N₃/ N₁) × E [V] voltages are generated respectively.

【0017】

On the other hand, in the auxiliary control circuit (22), the voltage V of the smoothing capacitor (8b) of the additional rectifying smoothing circuit (4b)._O2Second on / off control signal V depending on the height of the reference value of_G2By changing the duty ratio of the transformer (2) and controlling the on / off time of the output control MOS-FET (21) on the secondary side, additional rectification smoothing is performed from the additional secondary winding (2c) of the transformer (2). Constant level of additional DC output voltage V via circuit (4b)_O2Occurs. Here, the forward voltage drop of the rectifier diode (5b) of the additional rectification smoothing circuit (4b) is V._F2When [V] is set, the switching cycle of the output control MOS-FET (21) on the secondary side is the same as the switching cycle of the MOS-FET (3) on the primary side, so the additional DC output voltage V_O2On time T of the output control MOS-FET (21) in order to keep the_ON2[s] to T_ON2= (N₁/ N₃) × (V_O2+ V_F2) × T_OMust be / E.

【0018】

Next, the operation of the auxiliary control circuit (22) will be described with reference to FIGS. 2 (A) to 2 (E). Time t₁The MOS-FET (3) on the primary side is turned on at, and as shown in FIGS. 2 (A) and 2 (B), the secondary winding (2b) and the additional secondary winding (2b) of the transformer (2) are turned on. 2c) Voltage V_N2, V_N3Is positive, the current I flows from the additional secondary winding (2c) through the current limiting resistor (26)._R1And the current I flowing through the collector terminal of the current control transistor (25)_C1The on-time control capacitor (27) is charged by the difference current with. As a result, the voltage V between both terminals of the on-time control capacitor (27)_CRise as shown in Fig. 2 (C). Also, the voltage V of the smoothing capacitor (8b) of the additional rectifying smoothing circuit (4b)._O2Level and the first reference voltage V of the first reference power supply (23)_R1Signal V that amplifies the difference from the level of_E1Is output from the error amplifier (24) and applied to the base terminal of the current control transistor (25) to collect the collector current I._C1Is controlled. Therefore, the voltage V of the smoothing capacitor (8b) of the additional rectifying smoothing circuit (4b)_O2Level is the first reference voltage V of the first reference power supply (23)_R1If it is much higher than the level of, the collector current I of the current control transistor (25)_C1Increases and the charging current flowing through the on-time control capacitor (27) decreases, so the voltage V of the on-time control capacitor (27)_CGradient of rising with respect to time, that is, voltage V_CThe ascending speed of Conversely, the voltage V of the smoothing capacitor (8b) of the additional rectifying smoothing circuit (4b)._O2Level is the first reference voltage V of the first reference power supply (23)_R1If it is slightly higher than the level of, the collector current I of the current control transistor (25)_C1Decreases and the charging current flowing through the on-time control capacitor (27) increases, so the voltage V of the on-time control capacitor (27)_CAscends faster.

【0019】

As shown in Figure 2 (C), time t₂On-time control capacitor (27) voltage V_CLevel is the second reference voltage V of the second reference power supply (29)_R2When the level of is reached, a high (H) level voltage signal is output from the comparator (30), and as shown in Fig. 2 (D), the output control MOS-FET (21) is output from the gate drive circuit (31). High voltage (H) level second on / off control signal V applied to the gate terminal_G2The output control MOS-FET (21) is turned on. After that, the on-time control capacitor (27) is set to the time t as shown in Fig. 2 (C).₃In the voltage V of the additional secondary winding (2c) of the transformer (2)_N3Voltage value V obtained by subtracting the voltage drop of the current limiting resistor (26) from_CMAXTime t when the MOS-FET (3) on the primary side is turned off after being charged until it reaches [V]₄Hold that value until. Time t₂From t₄Until, that is, during the ON period of the output control MOS-FET (21), the drain current I flowing through the output control MOS-FET (21) as shown in FIG. 2 (E)._D2Rise linearly.

【0020】

And time t₄When the MOS-FET (3) on the primary side changes from the on state to the off state at, the current I that flows from the additional secondary winding (2c) of the transformer (2) to the current limiting resistor (26)._R1Is approximately 0, and the on-time control capacitor (27) is discharged via the current limiting resistor (26), so that the secondary winding (2b) and additional secondary winding (2c) of the transformer (2) ) Voltage V_N2, V_N3Is negative as shown in FIGS. 2 (A) and 2 (B), and then gradually decreases to 0 [V]. As a result, the voltage V of the on-time control capacitor (27)_CIs promptly the maximum value V as shown in Fig. 2 (C)._CMAXIt descends from [V] to 0 [V]. At this time, the voltage signal output from the comparator (30) changes from a high (H) level to a low (L) level, and is applied from the gate drive circuit (31) to the gate terminal of the output control MOS-FET (21). Second on / off control signal V_G2Changes from a high voltage (H) level to a low voltage (L) level as shown in Fig. 2 (D). As a result, the output control MOS-FET (21) changes from the on state to the off state, and the drain current I flowing through the output control MOS-FET (21) as shown in FIG. 2 (E)._D2Becomes 0.

【0021】

Due to the operation described above, the voltage V of the on-time control capacitor (27)_CSecond on / off control signal V in proportion to the rising speed of_G2Since the pulse width of is changed, the on-time T of the output control MOS-FET (21)_ON2Can be controlled. Therefore, the additional DC output voltage V is due to a change in impedance of a load (not shown) connected to the output terminal of the additional rectification / smoothing circuit (4b)._O2Even if the current fluctuates, the collector current I of the current control transistor (25)_C1The voltage V of the on-time control capacitor (27)_COn-time T of the output control MOS-FET (21) by adjusting the ascending speed of_O_N2Is controlled and the additional DC output voltage V_O2Is held at a certain level.

【0022】

In the present embodiment, an output control MOS-FET (21) is connected between the additional secondary winding (2c) of the transformer (2) and the additional rectification smoothing circuit (4b), and the output control MOS. -DC output voltage V of the additional rectification smoothing circuit (4b) by controlling the on / off time of FET (21)._O2On / off control and constant voltage control for each secondary output are possible with a simple circuit change such as providing an auxiliary control circuit (22) that holds the power at a constant level. The shape and heavy saturable reactor are not required, the number of parts can be reduced, the circuit configuration can be simplified, and the size and weight can be reduced. In addition, the drain current I of the output control MOS-FET (21) on the secondary side_D2The waveform of is the drain current I of the MOS-FET (3) on the primary side._D1If an overcurrent protection circuit is provided in the main control circuit (9), it is not necessary to provide an overcurrent protection circuit in the auxiliary control circuit (22) because the waveform is similar to that of. Therefore, it is possible to perform on / off control and constant voltage control independently for each secondary output with a simple circuit configuration. Furthermore, since the switching frequencies of both the primary side MOS-FET (3) and the secondary side output control MOS-FET (21) are the same, mutual interference does not occur and each direct current on the secondary side does not occur. Output V₀₁, V₀₂Ripple can be reduced.

【0023】

The embodiment shown in FIG. 1 can be changed. For example, in the multi-output switching power supply device of the embodiment shown in FIG. 3, an output control MOS is provided between the comparator (30) and the gate drive circuit (31) in the auxiliary control circuit (22) shown in FIG. -A delay circuit (32) is provided to delay the turn-off timing of FET (21). As a result, as shown in FIGS. 4 (E) and 4 (D), the time t₄Drain current I flowing through the output control MOS-FET (21)_D2After becoming 0, the delay time t_DOnly delayed by the second on / off control signal V_G2Changes from the high (H) level to the low (L) level, and the output control MOS-FET (21) changes from the on state to the off state. Therefore, since zero current switching (ZCS) occurs at the turn-off of the output control MOS-FET (21), no switching loss occurs at the turn-off of the output control MOS-FET (21), which is shown in FIG. There is an advantage that the conversion efficiency can be improved as compared with the case.

【0024】

Further, the multi-output switching power supply device of the embodiment shown in FIG. 5 is for output control by an external input signal in parallel with the on-time control capacitor (27) in the auxiliary control circuit (22) shown in FIG. A transistor (33) is connected as a switching means for turning off the MOS-FET (21). In the multi-output switching power supply shown in FIG. 5, a high (H) level voltage signal V is transmitted from the outside to the base terminal of the transistor (33)._EXTBy inputting, the transistor (33) is turned on, so the voltage V of the on-time control capacitor (27)_CDoes not rise, and the output control MOS-FET (21) can be kept off. Therefore, the additional DC output voltage V output from the additional secondary winding (2c) via the additional rectifying smoothing circuit (4b)._O2There is an advantage that only can be turned on or off at the request of the outside.

【0025】

Further, FIG. 6 shows an embodiment of the present invention in the case where the transformer (2) has one secondary winding (2b). That is, in the multi-output switching power supply device of the embodiment shown in FIG. 6, an additional rectifying and smoothing circuit (4b) is connected in parallel to the secondary winding (2b) of the transformer (2), and the secondary winding The embodiment differs from the embodiment shown in FIG. 1 in that the output control MOS-FET (21) is connected between the wire (2b) and the additional rectifying and smoothing circuit (4b). Since the other configurations are substantially the same as those of the embodiment shown in FIG. 1, the same effects as those of the embodiment shown in FIG. 1 can be obtained in the embodiment shown in FIG. Further, in the embodiment shown in FIG. 6, since the transformer (2) has only one secondary winding (2b), the winding structure of the transformer (2) is simplified and the weight of the transformer (2) is reduced. There are advantages that can be done. Of course, the same changes as those of the embodiments shown in FIGS. 3 and 5 can be implemented in the multi-output switching power supply device of the embodiment shown in FIG.

【0026】

The embodiment of the present invention is not limited to each of the above-described embodiments, and various modifications can be made. For example, in each of the above embodiments, a MOS-FET (MOS field effect transistor) is used as the primary side main switching element and the secondary side output control switching element, but a large-capacity bipolar transistor is used. Other switching elements such as transistors, IGBTs (Insulated Gate Bipolar Transistors) or psyllistas can also be used. Further, in each of the above embodiments, the embodiment in which the present invention is applied to a multi-output switching power supply device that generates two DC outputs is shown, but the present invention is applied to a multi-output switching power supply device that generates three or more DC outputs. The present invention can also be applied, and in this case, the effect of the present invention is remarkably exhibited. Further, in each of the above embodiments, the embodiment in which the present invention is applied to the forward converter is shown, but the present invention can also be applied to the flyback converter (RCC). Further, the main switching circuit on the primary side may have any configuration, for example, a multi-stone converter having a plurality of main switching elements such as a bridge type or a push-pull type, or a current resonance type converter having a reactor for current resonance. The present invention can be applied.

【0027】

[Effect of the invention]

According to the present invention, on / off for each secondary output by a simple circuit change such as connecting an output control switching element between the secondary winding of the transformer and at least one additional rectifying and smoothing circuit. Since control and constant voltage control are possible, the number of parts can be reduced, the size and weight can be reduced, and the circuit configuration of the multi-output switching power supply can be simplified and the manufacturing cost can be reduced. can get.

[Simple explanation of drawings]

[Figure 1]

An electric circuit diagram showing an embodiment of a multi-output switching power supply device according to the present invention. [Figure 2]

Waveform diagram showing voltage and current of each part in FIG. [Fig. 3]

An electric circuit diagram showing a modified embodiment of FIG. [Fig. 4]

Waveform diagram showing voltage and current of each part in Fig. 3 [Fig. 5]

An electrical circuit diagram showing another modified embodiment of FIG. [Fig. 6]

An electric circuit diagram showing another embodiment of the multi-output switching power supply device according to the present invention. [Fig. 7]

An electric circuit diagram showing an example of a conventional chopper type multi-output switching power supply device. [Fig. 8]

Electrical circuit diagram showing other examples of conventional chopper type multi-output switching power supply [Fig. 9]

Electric circuit diagram showing a conventional mag-amp type multi-output switching power supply [Explanation of symbols]

(1) DC power supply, (2) Transistor, (2a) Primary winding, (2b) Secondary winding, (2c) Additional secondary winding, (3) MOS-FET (main switching element), (4), (4a) Rectification smoothing circuit, (4b) Additional rectification smoothing circuit, (5), (5a), (5b) Rectification diode , (6), (6a), (6b) ... Reflux diode, (7), (7a), (7b) ... Smoothing transistor, (8), (8a), (8b) ... Smoothing capacitor, ( 9) Main control circuit, (10) Chopper circuit, (11) Transistor, (12) Reflux diode, (13) Smoothing reactor, (14) Smoothing capacitor, (15) Chopper control circuit, (16) Saturable reactor, (17) Excitation current control circuit, (21) MOS-FET for output control (switching element for output control), (22) Auxiliary Control circuit, (23) ... 1st reference power supply, (24) ... Error amplifier (error detection means), (25) ... Current control diode (current control element), (26) Current limiting resistor (current limiting element), (27) On-time control capacitor, (28) Reverse charge prevention diode (reverse charge prevention means), (29) 2nd Reference power supply, (30) ... comparator, (31) ... gate drive circuit, (32) ... delay circuit, (33) ... transistor (switch means)