JPS63277471A - Multi-output switching power source device - Google Patents

Abstract

PURPOSE:To improve efficiency, by a method wherein feedback control is effected so that a first secondly coil output is kept at a predetermined value while feedback control is effected so that a second secondary coil output is kept at a predetermined value under no load condition of the output. CONSTITUTION:A multi-output switching power source device is constituted of a switching transformer 1, a MOSFET 12, a rectifying and smoothing circuit 3, a voltage detecting amplifier 4, a PWM control circuit 5, a voltage detecting amplifier 6 and a series control regulator 7. A control signal terminal 21, an inverter 22, transistors Tra, Trb, resistors R5, R6 and an output voltage detecting amplifier 24 are added to the control unit of the multi-output switching power source device. The output voltage Va of the rectifying and smoothing circuit 6 is detected and when the output voltage has exceeded a predetermined value, a photocoupler outputs. According to this constitution, feedback control is effected so that when said first rectifying output voltage V1 is under no load condition, a second rectifying output voltage V2 is kept at a predetermined value whereby a power consumption in the series control regulator 7 may be minimized.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a multi-output switching power supply device.

[Conventional technology]

As a conventional multi-output switching power supply device, Nikkei Electronics 198B, 12.1 (no, 409), I)
l) 146゜147 "There is a 3-output, 50III switching power supply that has been devised to reduce M noise and raised the operating frequency to 500 tlz. Among those described in the above literature, series control An example using a regulator is shown in FIG. 2, and an example using a magnetic amplifier is shown in FIG. 3, and these will be briefly explained.

In Fig. 2, the primary winding 1 of the switching transformer 1
When the 803 FET 2 connected in series with the winding turns on and off the current of a, a voltage is generated in the secondary winding 1b of the switching transformer 1, and the rectifying and smoothing circuit 3 of the diode D1 and capacitor C1 converts the current into a direct current. Output voltage V1
(+12V) is generated. Output voltage ■1 is resistor R1
and R2, and the divided voltage output is sent to the voltage detection amplifier 4
given to. The voltage detection amplifier 6 may be, for example, a variable shunt stabilized power supply circuit, such as a μ
PCI 093J can be used.

When the output voltage V1 becomes higher than +12V, the divided voltage output also increases accordingly, and the control terminal 4C of the voltage detection amplifier 4
, the input voltage of the main terminals 4a and 4b becomes higher than the predetermined value.
The current flows through the photodiode PCa of the photocoupler PC through the resistor R3, and the phototransistor PCt) is turned on. The PWM control circuit 5 composed of an IC (integrated circuit) controls the switching operation of the IQs FET 2, and includes a switching oscillation circuit and an 8
03 A circuit is provided to control the on/off time width ratio (duty) of the switching pulse applied to the FET 2.

When the phototransistor PCb of the photocoupler PC is turned on, the PWM control circuit 5 lowers the duty of the switching pulse applied to the FET 2).

As a result, the switching ON time of the primary winding 1a of the switching transformer 1 is reduced, the output voltage generation time of the secondary winding is also reduced, and as a result, the output voltage V1 is reduced.

On the other hand, when the output voltage ■1 falls below +12V, conversely, the main terminals 4a and 4b of the voltage detection amplifier 4 become non-conductive, and the photodiodes 7 of the photocoupler PCa4. The N current stops flowing, and the phototransistor PCb is turned off. As a result, the PWM control circuit 5 increases the duty of the switching pulse, and the output voltage (1) increases.

As described above, control is performed to maintain the output voltage v1 at +12V.

The other secondary winding 1c of the switching transformer 1 generates a voltage somewhat higher than the DC output voltage V2 (+5V) by a rectifying and smoothing circuit 6 consisting of a diode D2 and a capacitor C2. This varies depending on the load fluctuation of the output voltage ■2 and the load fluctuation of the output voltage ■1, so it is always +5■
The winding ratio is determined to generate a higher voltage, and the series control regulator 7 lowers the voltage to +5V, and the output voltage v
2 to maintain a stable voltage of +5V. The output voltage v2 tends to decrease when the load of the output voltage 2 is large, and increases when the load is small. Furthermore, when the load on the output voltage ■1 increases, the duty of the switching pulse output by the PWM control circuit 5 increases, so the output voltage ■2 also increases, and conversely, when the load on the output voltage ■1 decreases, the output voltage ■ 2 tends to be lower. Note that the resistor R4 is a dummy load for reducing fluctuations in the output voltage (2) due to load fluctuations in the output voltage V1.

In addition, control using a series control regulator generally consumes more power than feedback control, so
In order to reduce overall power consumption, the output voltage with the highest rated load current (+12V in Figure 4) is feedback-controlled, and a series control regulator is installed in the other circuits with output voltages (+5V) with smaller rated load currents. It is inserted.

In another conventional example shown in FIG. 3, 11 is a switching transformer, 12 is an 803 FET, and 13 is an IC. IJ 111 circuit, Dlo is a diode, MAI, MA'2 is a magnetic amplifier, D11 ~
D14 is a diode, C11-012 is a capacitor,
14 and 15 are output voltage detection amplifier circuits.

pH) 1 control circuit 13 is the switching transformer 11 2
The voltage of the tertiary winding 11d, which changes in accordance with the load condition of the secondary windings 11b and 11C and changes in the input voltage, is detected via the diode 10, and the voltage of the secondary windings 11b and 11c is detected.
The output voltage V3 is generated by a current smoothing circuit 17 consisting of a diode D12 and a capacitor C11.

As shown in FIG. 4, when the voltage Vi of the secondary winding 11b is negative, the output voltage VC is applied to the magnetic amplifier MA via the output voltage detection amplifier circuit 14, the resistor R11, and the diode D11.
Since the reverse voltage is applied to the magnetic amplifier MA11, the magnetic flux φ decreases and the magnetic amplifier MA11 changes from a saturated state to a non-saturated state. Next, when the secondary winding voltage Vi becomes positive, the magnetic flux φ of the magnetic amplifier MAII gradually increases until it reaches a saturated state, and the current Im flows through the magnetic amplifier MA11, passing through the diode DI2 and flowing into the capacitor C11. Charging current flows.

This charging current continues until the secondary winding voltage Vi reverses to negative again.

When the output voltage v3 is high, the variation width of the magnetic flux φ of the magnetic amplifier MA11 becomes large, so the time td from when the secondary winding voltage Vi is positively reversed until the current starts flowing to the capacitor C11 becomes longer, and as a result, The time tc during which current flows through the capacitor C11 becomes shorter, and the output voltage v3 decreases. Control is performed in this way.

Conversely, when the output voltage V3 is low, the width of the magnetic flux change becomes small, so the time tc during which current flows through the capacitor C11 becomes longer, and the output voltage V3 is controlled to increase. In this way, the output voltage v3 is maintained at +5V by the output voltage amplification circuit 14 and the magnetic amplifier MA1'l. Output voltage V4 (
+12V) is also stabilized at +12V similarly to the output voltage V3.

[Problem that the invention seeks to solve]

The methods described above each have the following problems.

(a) As shown in Figure 2, when using a series control regulator, if the load current of the feedback-controlled output voltage V1 is set to 0, the voltages of other output circuits will decrease, so the value of the dummy resistor R4 should be changed. It is necessary to make the power supply smaller or to set the voltage of the secondary winding 1b of another output circuit higher, but in either case, the efficiency of the power supply decreases and heat countermeasures are required.

(b) As shown in Figure 3, when a magnetic amplifier is used, it stabilizes the voltage of each output circuit, so it is efficient, but it requires a large number of parts and is expensive, so it is not suitable for small output power supplies. It's fleeting.

The purpose of this invention is to provide a power supply for a small output power supply as described above, which requires a small number of parts, is inexpensive, and has high efficiency even when the load current of the feedback-controlled output voltage becomes O. do.

[Means for solving problems]

A multi-output switching power supply device of the present invention includes a transformer having a primary winding and first and second secondary windings;
a switching element connected in series to the next winding;
a first rectifying and smoothing circuit that rectifies and smoothes the output of the secondary winding of the second secondary winding; a second rectifying and smoothing circuit that rectifies and smoothes the output of the second secondary winding; and the second rectifying and smoothing circuit that rectifies and smoothes the output of the second secondary winding. a series control regulator provided on the output side of the smoothing circuit; and the switching element so that the output of the first rectifying and smoothing circuit is maintained at a predetermined value when the output of the first rectifying and smoothing circuit is in a loaded state. and a control circuit that feedback-controls the switching element so that the output of the second rectification and smoothing circuit is maintained at a predetermined value when the output of the first rectification and smoothing circuit is in a no-load state. It is prepared.

[For production]

With the above configuration, when there is a load on the output of the first rectifying and smoothing circuit, feedback control is performed so that the output voltage of the first rectifying and smoothing circuit is maintained at a predetermined value. At this time, the output voltage of the second rectifying and smoothing circuit may be a lower value than the conventional one, that is, it can be set to a voltage that substantially minimizes the power consumption of the series control regulator. A series control regulator supplied with such a relatively low voltage operates with low power consumption and maintains its output voltage at a predetermined value.

When the output of the first rectifying and smoothing circuit is in a no-load state, the output of the second rectifying and smoothing circuit is
Feedback control is performed so that the output voltage of the rectifying and smoothing circuit is maintained at a predetermined value. In other words, if feedback control is performed to maintain the output voltage of the first rectifying and smoothing circuit at a predetermined value even when there is no load, the output voltage of the second rectifying and smoothing circuit tends to become too low. By performing feedback control to maintain the output voltage of the second rectifying and smoothing circuit at a predetermined value as in the present invention, power consumption in the series control regulator can be minimized at this time as well.

At this time, the output voltage of the first rectifying and smoothing circuit tends to be higher than a predetermined value, but even if it becomes higher, there is no adverse effect because it is in a no-load state.

〔Example〕

FIG. 5 is a block diagram showing a power supply device according to an embodiment of the present invention together with its load, and FIG. 1 is a circuit diagram showing the power supply device PS of FIG. 5 in detail. In these figures, the same reference numerals as in FIG. 2 refer to circuit members having similar configurations and functions. Description of these similar members will be omitted. PS is a power supply device,
CD is the control device, R1-Rn is the load and +12V power supply V
1 is supplied. Tr 1 to Tr n are loads R1 to Rn
A transistor connected in series with the transistor is turned on or off by a control device CD.

The control device CD receives a +5V power source 2 for the control circuit from the power supply device PS, and provides control signals TC1 to TCn to the transistors Tr1 to Trn, and control signal C0NT to the power supply device 1, respectively.

In addition to the components shown in FIG. 2, the control section 20 of the power supply device PS shown in FIG. 1 includes a control terminal 21 that receives a control signal C0NT.
, inverter 22, and transistor Tra.

The difference is that Trb, resistors R5 and R6, and an output voltage detection amplifier 24 are added.

Of these, the output voltage detection amplifier 24 and the resistors R5 and R6 detect the output voltage ya of the rectifying and smoothing circuit 6 consisting of the diode D2 and the capacitor C2, and detect the output voltage ya.
When exceeds a predetermined value, conduction occurs between the main terminals 24a and 24b of the output voltage detection amplifier 24, causing the photodiode PCa of the photocoupler PC to emit light. Transistor Tra
and T'b lower the voltage at the control input terminals 4C124c of the output voltage sense amplifiers 4 and 24 when they conduct, respectively, to prevent conduction between the main terminals of the respective output voltage sense amplifiers 4 and 24. The control unit @C0NT is directly input to the base, and the control signal C0NT is input to the base of the transistor Trb via the inverter 22.

The loads R1 to Rn are, for example, heating resistors of a thermal head, and when a device including the thermal head, for example a printer, is in operation, that is, transistors Tr1 to Trn
In a state where is selectively turned on, the control unit @
When C0NT is at a low level "0" and in a non-operating state, that is, when all transistors Tr1 to Trn are kept off, the control signal C0NT is at a high level "1".

When the control signal C0NT is at a low level, the transistor Tra of the control signal 20 of the power supply PS is off, and the transistor Tr b is on. Therefore, the control unit 20
The output of the rectifying and smoothing circuit 3, that is, the first output voltage 1 is detected and fed back to control the PWM control circuit 5, thereby) 103
Feedback control of FET 2 is performed.

As a result, voltage (1) is maintained at a predetermined value.

The secondary winding 1C minimizes power consumption in the series control regulator 7 when the output voltage V1 of the rectifier and smoothing circuit 3 is maintained at a predetermined value by feedback control of the output voltage of the rectifier and smoothing circuit 3. The turns ratio etc. are determined so as to generate the DC voltage ■a.

When the control signal C0NT is at a high level, the transistor Tra of the control section 20 of the power supply PS is on, and the transistor Trb is off. Therefore, the control unit 20 detects and feeds back the output voltage Va of the rectifying and smoothing circuit 6 to control the PWM control circuit 5, thereby controlling the MOS FET 2 in feedback. As a result, voltage Va is maintained at a predetermined value.

In other words, if feedback control is performed using the output voltage ■1 even after the load of the output voltage v1 becomes zero as in the past, the voltage ■a decreases and it becomes impossible to maintain the output voltage V2 at a predetermined value. Conventionally, to avoid this, the winding ratio etc. of the secondary winding 1C is determined so that it always generates a sufficiently high voltage, but in the present invention, instead of doing so, the output When the load of voltage (1) is zero, feedback control is performed using voltage ya. Therefore, even when the load on the output voltage (1) is zero (non-operating state or idle state), the output voltage (2) is maintained at a predetermined value. Further, unlike the conventional case, it is not necessary for the secondary winding 1C to always generate a sufficiently high voltage (even when the load of the output voltage V1 becomes zero). Therefore, power consumption in the series control regulator can be reduced.

Note that when the voltage va is feedback-controlled, the voltage V1 may become higher than a predetermined value, but since it is a no-load state, it does not adversely affect the load.

FIG. 6 shows a part of another embodiment of the present invention, and the parts not shown are the same as those in FIG. 1. The power supply device of this embodiment is provided with a third secondary winding 1d in addition to the secondary windings 1b and 1c similar to those shown in FIG. Through a rectifying and smoothing circuit 31 and a series control regulator 32,
The third output voltage becomes V5 (for example, +80V).

When the first output voltage ■1 is under no load, two output circuits are provided with a second series control regulator, a series control regulator 7 that generates an output voltage V2, and a series control regulator that generates a third output voltage ■5. The input side voltage of one of the regulators 32 (in the illustrated example, the input side voltage of the series control regulator 7>Va is detected, and based on this, the input side voltage of one of the regulators 32 is
03 Perform feedback control of FET2 (Fig. 1) to reduce voltage V
a is maintained at a predetermined value.

FIG. 7 roughly shows a part of another embodiment of the present invention, and the parts not shown are the same as those in FIG. 1. The control unit 40 of this embodiment detects the output voltage V1 both when the output voltage V1 is in a loaded state and in an unloaded state, but the voltage dividing ratio of the voltage dividing circuit that transmits the detected voltage to the output voltage detection amplifier 4 is The above voltage (1) differs between the loaded state and the no-load state. That is,
A resistor R7 is roughly connected in series with resistors R1 and R2,
A transistor TrC is provided so as to bypass the resistor R7 when conductive. The base of the transistor TrC is connected via an inverter 41 to a control terminal 21 that receives a control signal C0NT.

In the load state, the control signal C0NT is "Oop", so the transistor Trc is on, and the detected voltage V1 divided by the resistor 1 and R2 is input to the output voltage detection amplifier.As a result, the voltage 1 is set to a specified value. On the other hand, in the no-load state, the control signal C0NT is kept at “1”.
'', so the transistor TrC is off and the detection voltage ■
1 divided by resistor R1 and resistors R2 and R7 is input to output voltage detection amplifier 4. As a result, control is performed to maintain the voltage Va at a predetermined value. That is, when the output voltage V1 is in a no-load state, if feedback control is performed using the output voltage V1, the voltage Va tends to decrease, but if the voltage division ratio is changed as in the above embodiment, the control section 41 ■Control is performed to keep V1 at a value higher than a predetermined value (for example, 12■) in the load state, and as a result, the voltage V
a is maintained at a predetermined value.

〔Effect of the invention〕

As described above, according to the present invention, when the output of the first secondary winding is in a loaded state, feedback control is performed to maintain the output of the first secondary winding at a predetermined value, and In the no-load state of the output of the secondary winding, feedback control is performed to keep the output of the second secondary winding at a predetermined value, so the output of the second secondary winding is always kept at the optimal value. can be kept. Therefore,
When the first secondary winding is loaded, the output voltage of the second secondary winding can be lower than in the conventional case, and the power consumption of the series control regulator can be reduced. Therefore,
Increases power supply efficiency.

Further, as a result of the power consumption within the power supply device being reduced, the heat generation of the power supply device is also reduced, which facilitates the thermal design of the power supply device. This feature is particularly important in the case of natural cooling. Furthermore, the reliability of the device is increased because the temperature rise is reduced.

[Brief explanation of drawings]

1 is a circuit diagram showing a power supply device according to an embodiment of the present invention; FIGS. 2 and 3 are circuit diagrams showing a conventional power supply device; FIG. 4 is a waveform diagram showing the operation of the device shown in FIG. 3; FIG. 5 is a schematic diagram showing the power supply device and load of FIG. 1, and FIGS. 6 and 7 are circuit diagrams showing other embodiments of the present invention. 109. Switching transformer, 1a - primary winding, 1b, 1G, 1d - secondary winding,
2...803 FET, 3.5... Rectifier and smoothing circuit, 4,24... Output voltage detection amplifier, 5... PWM
Control circuit, 7゜32...Series control regulator, l
ra, Trb, Trc...transistor. Patent Applicant: Oki Electric Industry Co., Ltd. HeoL Co., Ltd. II Fig. 2. Oki Co., Ltd. Example No. 3 Minyang 3λ Responsibility! 7e”〉 4 p.m.? Island 11. Zusou power supply bag i'r-'A load contact 1st motor 9th fan power voltage Keishi to Xianxang Lane' Departure 2/l Shuang & I row tea 6 section l: Switch Nanku ° transformer 3 large Giving (certain 7 times)

Claims (1)

[Claims] 1. A transformer having a primary winding and first and second secondary windings, a switching element connected in series to the primary winding, and the first secondary winding. a first rectifying and smoothing circuit that rectifies and smoothes the output of the wire; a second rectifying and smoothing circuit that rectifies and smoothing the output of the second secondary winding; and an output of the second rectifying and smoothing circuit. a series control regulator provided on the side; and feedback control of the switching element so that the output of the first rectification and smoothing circuit is maintained at a predetermined value when the output of the first rectification and smoothing circuit is in a loaded state. , a control circuit that feedback-controls the switching element so that the output of the second rectification and smoothing circuit is maintained at a predetermined value when the output of the first rectification and smoothing circuit is in a no-load state. Switching power supply. 2. The control circuit detects the output voltage of the first rectifying and smoothing circuit when the output of the first rectifying and smoothing circuit is in a loaded state, and feedback-controls the switching element based on this, and A patent characterized in that when the output of the first rectifying and smoothing circuit is in a no-load state, the output voltage of the second rectifying and smoothing circuit is detected, and the switching element is feedback-controlled based on this. A multi-output switching power supply device according to claim 1.