JPS6166563A - Switching power supply apparatus - Google Patents

Abstract

PURPOSE:To improve cross regulation, by a method wherein a part of current route is formed in common with current of two loads and feedback voltage is taken out of the common route. CONSTITUTION:So far as a switching power supply apparatus of forward converter type is concerned, gate pulse for driving is given to the base of a transistor 16 of an inverter 14 from a pulse circuit 20 via a pulse transformer 18. Each output taken out of the secondary winding 22 for a transformer 10 including intermediate taps 22 is directed to the primary and secondary loads RL1, RL2 via a rectification-smoothing circuit. Then, a space between one end of the secondary winding 22 and the primary terminal 34 is served as current route in common with the both load current I1, I2, and the common current route is arranged to be a source for feedback 38. Then, voltage drop during the feedback is in common with the both output voltage, and the cross regulation can be improved.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a switching power supply, and particularly to a switching power supply of an on-on converter type or a forward converter type, for example.

(Prior Art) Conventionally, a switching power supply device has a plurality of, for example, two
When connecting two loads, connect the two loads in parallel to the secondary winding of the transformer (between the DC output terminals).

(Problems to be Solved by the Invention) In the conventional device, one of the two loads may not require much current. In this case, the unnecessary amount will be consumed on the load side. Therefore, not only the total energy loss increases, but also heat generation occurs on the load side due to the consumption of such unnecessary parts, which may require a separate cooling device on the load side.

Therefore, the main object of the present invention is to provide a switching power supply device that can reduce energy loss due to unnecessary current and prevent heat generation on the load side due to this.

(Means for Solving the Problems) Simply put, the present invention is a switching power supply device in which currents flowing through first and second loads partially flow through a common path.

Specifically, the present invention includes a first terminal connected to one end of a secondary winding of a transformer via a first diode, and a first terminal connected to the other end of the secondary winding via a second diode. a second terminal connected substantially to the intermediate tap of the secondary winding, the first load being connected between the first terminal and the third terminal; This is a switching power supply device in which a second load can be connected between a first terminal and a second terminal.

(Function) A current flows through the first load through a path from one end of the secondary winding of the transformer to the first diode to the first terminal to the first load to the third terminal to the intermediate tap. The second load has a current flowing through one end of the secondary winding - the first diode - the first terminal - the second load - the second terminal - the second diode - the other end of the secondary winding. flows.

(Effects of the Invention) In the present invention, in the current path between one end of the secondary winding and the first terminal, the current flowing to the first load and the current flowing to the second load are common. flows.

Therefore, the current flowing through the first load is, as far as the second terminal is concerned, an output current drawn into the power source from the current flowing through the common current path. Therefore, energy loss due to unnecessary current on the load side is minimized, and unnecessary energy is not consumed and heat is not generated on the load side. Therefore, since there is no need to provide a special cooling device on the load side, an overall compact switching power supply device can be obtained.

The above objects, other objects, features and advantages of the present invention will become more apparent from the following detailed description of embodiments with reference to the drawings.

(Embodiment) FIG. 1 is a circuit diagram showing an embodiment of the present invention. This embodiment is a forward converter type switching power supply device. One end of the primary winding of the transformer 10 is connected to a DC power supply (+V), and the other end is connected to the collector of the transistor 16 of the inverter 14. This inverter 14 is configured, for example, as a separately excited inverter, and a gate pulse or a switching pulse from a pulse circuit 20 is applied to the base of a transistor 16 via a pulse transformer 18.

Secondary winding 22 of transformer 10 includes an intermediate tap 22a. One end of the secondary winding 22 of the transformer 10 is connected to a first terminal 34 through a first diode 24 and a choke coil 28 . Another diode 26 is connected between the cathode of the first diode 24 and the intermediate tap 22a. A parallel circuit of a capacitor 30 and a leader resistor 32, which cooperate with the choke coil 28 to form a smoothing circuit, is connected between the output side of the choke coil 28 and a third terminal 36. The other end of the secondary winding 22 of the transformer 10 is connected to the second terminal 3 through a second diode 25 in the opposite direction.
Connected to 5. Another diode 27 is diode 25
The intermediate tap 22a is further connected to the third terminal 36 through the choke coil 29. This choke coil 2 is connected between the output side of the choke coil 29 and the third terminal 36.
A parallel circuit of a capacitor 31 and a leader resistor 33, which cooperate with the capacitor 9 to form a smoothing circuit, is connected.

A first load R is connected between the first terminal 34 and the third terminal 36.
LI is connected, and a second load RL2 is connected to the end between the first terminal 34 and the second terminal 35. This first load R
The LI and the second load RL2 may each be a single load or a plurality of loads connected in parallel.

The I-th terminal 34 is also connected to the pulse circuit 2o of the inverter 14 by a connecting line 3.

That is, this connection line 38 constitutes a feedback loop.

In operation, the switching transistor 16 included in the inverter 14 is turned on/off in response to a switching pulse or a gate pulse from the pulse circuit 2o. When the switching transistor 16 is turned on, a current flows through the primary winding 12 of the transformer 1o, and accordingly the 2
A voltage is induced in the secondary winding 22. The magnitude of the output voltage is the power supply voltage (+■), the primary winding 12 and the secondary winding 22.
It is determined by the turns ratio. The output voltage from the secondary winding 22 is rectified by the first diode 24, smoothed by a smoothing circuit including a choke coil 28, etc., and appears at the first output terminal 34.

At this time, the thickness of the voltage generated at the first terminal 34 is applied to the pulse circuit 2o through the connection line 38. In the pulse cycle 1/320, the magnitude of this output voltage is compared with an appropriate reference voltage, and if the voltage at the terminal 34 is larger than a predetermined value, the ON period of the transistor E 6 is shortened.
Furthermore, if the output voltage is small, the duty ratio of each switching pulse is controlled so that the on period of the transistor 16 is lengthened.

The first load RLI connected between the first terminal 34 and the third terminal 36 includes one end of the secondary winding 22 - the first diode 24 - the choke coil 28 - the first terminal 34 −
A current flows through the path of load RLI - third terminal 36 - choke coil 29 - intermediate tap 22a. On the other hand, a load RL connected between the first terminal 34 and the second terminal 35
2 D is one end of the secondary winding and the first diode 24
- Choke coil 28 - First terminal 34 - Load RL2 -
A current flows through the path from the second terminal 35 to the diode 25 to the other end of the secondary winding.

In this embodiment, as shown in FIG. 2A, the voltage ■1 to be applied to the second load RL2 is output between the first terminal 34 and the second terminal 35, and the voltage and third
A voltage 2 to be applied to the first load RLI appears between the terminal 36 and the terminal 36 of the first load RLI. In contrast, in the conventional circuit, a common voltage Vl is applied in parallel to the two loads RLI and RL2, as shown in FIG. 2B. As is clear from the circuit of FIG. 1, the voltage 2 in this embodiment is the voltage V1
It will definitely become smaller. and FIGS. 2A and 2B.
Considering the amount of energy in each circuit in the figure, the case of FIG. 2A is expressed by the following equation (1), and the case of FIG. 2B is expressed by the following equation (2).

... (1) It is assumed that V2=(1/n)Vl.

From equations (1) and (2), it will be understood that according to the embodiment of FIG. 1, the total energy can be reduced.

Furthermore, according to the embodiment shown in FIG.
It is formed as a common current path for current 2 flowing through load RL2 and load RL2. Therefore, the voltage drop between one end of the secondary winding 22 and the first terminal 34 is common to voltages 1 and V2. For this reason, the cross regulation between voltages 1 and V2 is improved.

That is, when the load RLI changes, a voltage drop of, for example, ΔVl occurs between one end of the secondary winding 22 and the first terminal 34. At this time, the first terminal 34 and the second terminal 3
The voltage 1 between 5 and 5 is controlled to be constant by the original feedback loop. On the other hand, regarding V2 between the first terminal 34 and the third terminal 36, this voltage V2 is given by the following equation (3).

V2=(V2-ΔVl)+ΔVl-... (3) From this equation (3), it can be seen that the voltage V2 is also maintained substantially constant. Because rV2−ΔVIJ is fL(q
This is the voltage drop due to changes in Rt and t, and is [+ΔVIJ
is the voltage compensated by the feedback control via the connection line 38. In this way, a part of the current path is configured in common for the currents of the two loads, and the feedback voltage is taken out from that common path, so even if load fluctuations occur, the voltages V1 and ■2 will remain the same. , respectively, are kept approximately constant and the cross regulation is significantly improved.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing one embodiment of the present invention. 2A and 2B show equivalent circuits, respectively, with FIG. 2A corresponding to the embodiment shown in FIG. 1, and FIG. 2B corresponding to the conventional circuit. In the figure, IO is a transformer, 14 is an inverter, 34
is the first terminal, 35 is the second terminal, 36 is the third terminal,
RLI is a first load, RL2 is a second load, and 38 is a connection line.

Claims (1)

[Scope of Claims] 1. A switching power supply device including a transformer whose primary winding receives an output from an oscillation circuit and has a secondary winding, wherein the secondary winding of the transformer has an intermediate tap. an output voltage is induced at one end of the secondary winding, and a first terminal connected to the one end of the secondary winding via a first diode; the other end of the secondary winding. a second terminal connected to via a second diode, and a third terminal substantially connected to the center tap, and a third terminal connected between the first terminal and the third terminal. 1 load is connected, and a second load is connected between the first terminal and the second terminal, such that the current flowing through the first load and the second load is equal to or less than the first load. A switching power supply that has a common path that includes terminals. 2. The switching power supply device according to claim 1, further comprising a feedback loop for feeding back a voltage drop occurring on the common path to the oscillation circuit.