JPS5947974A - Multioutput switching power source - Google Patents

Abstract

PURPOSE:To enable to decrease the overcurrent detecting level without additional circuit for detection by dividing a plurality of output channels into two groups, and respectively detecting the current flowed through a rectifying diode by one group and the current flowed through a free wheel diode by the other group. CONSTITUTION:The primary coil 411 of a current transformer (CT) 41 is connected in series with the V1 output side rectifying diode 12, while the primary coil 412 is connected in series with the V2 output side free wheel diode 17. A resistor 42 is connected in parallel with the secondary coil 413 of the CT41, and the AC voltage generated across the resistor 42 is rectified by full-wave rectifying bridge circuit 43. A reference voltage generator is contained, the output voltage of the bridge circuit 43 is compared by a comparator 44 with the reference voltage generated from the generator, thereby detecting that the output voltage of the bridge circuit 43 exceeds the reference voltage and notifying it to a CNT circuit 20.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a multi-output switching power supply device having a plurality of output channels and equipped with an overcurrent detection circuit.

[Technical background of the invention and its problems]

In a general multi-output switching power supply device that utilizes the cross regulation of a Nitrans, a means for detecting overcurrent using a current transformer is applied. As this means, there are known methods that detect the primary current of the converter transformer and methods that detect the sum of the secondary currents of the converter transformers. FIG. 1 shows a two-output switching power supply to which the former means is applied, and FIG. 2 shows a two-output switching power supply to which the latter means is applied.

First, general operations related to DC voltage output in these switching power supply devices will be explained.

In FIGS. 1 and 2, 10 is a converter transformer for transmitting primary side energy to the secondary side. A switching transistor 11 is connected to the primary winding 101 of the converter transformer 10.
Converter transformer 1 by turning on/on
An alternating current waveform voltage is generated in each secondary winding 10Z+1'3 of 0. The AC waveform voltage generated in the secondary winding 102 is rectified by a rectifying diode 12, and further smoothed by a filter circuit consisting of a choke coil 13 and a capacitor 14, and the output voltage V! is output as Incidentally, the current flowing through the choke coil 13 via the rectifying diode 12 while the transistor 11 is on is the same as the energy stored in the choke coil 13 even if the transistor 11 is turned off and the rectifying diode 12 is turned off. It tries to flow continuously. Therefore, the freewheeling diode 15 maintains the continuity of the current flowing through the choke coil 13 even while the transistor 11 is off. The above operation is performed by the secondary winding l
A rectifier diode 16, a freewheel diode 17, a choke coil 18, and a capacitor 1 on the ag side.
The same applies to the output channel with the filter circuit consisting of 9. In addition, in the switching power supply devices shown in FIGS. 1 and 2, the control circuit (hereinafter referred to as a CNT circuit) 201g, more particularly, the
The on time of the transistor 11 or the switching frequency is controlled so that the output voltage Vl on the side of the next winding 102 is constant.

Next, overcurrent detection in the switching power supply device shown in FIG. 1 will be explained. In the example shown in FIG. 1, in order to detect the primary current of the converter transformer 10, the transistor 1
A current transformer 21 having a primary winding 211 connected to the current transformer 1 and a secondary winding 21g is provided. Accordingly, a voltage is generated in the resistor 22 connected in parallel to the secondary winding 212 of the current transformer 21 in accordance with the primary side current of the converter transformer 10. The voltage generated across this resistor 22 is compared with a reference voltage by a comparison circuit 23. As described above, the voltage generated across the resistor 22 depends on the primary current of the converter transformer 100. 1, this primary current corresponds to the sum of the secondary currents of the converter transformer 10. Therefore, the reference voltage value should be detected as an overcurrent (of the converter transformer 10).
An overcurrent is detected by the comparator circuit 23 by setting the value of the voltage across the resistor 220 when a primary current corresponding to the sum of the secondary currents flows. When the comparator circuit 22 detects that the voltage across the resistor 22 has become higher than the reference voltage, this is notified to the CNT circuit 20, and the CNT circuit 20 is notified of this fact.
The operation of the transistor 11 is stopped by the NT circuit 20.

On the other hand, in the switching power supply device shown in FIG. 2, in order to detect the sum of the secondary current of the converter transformer 10, one
Next winding 311.

A current transformer 31 having a secondary winding 312 and a secondary winding 313 is provided. Therefore, due to the ON operation of the transistor 11, a voltage is applied to the resistor 32 connected in parallel to the secondary winding 313 of the current transformer 31 in accordance with the current flowing through each rectifying guide 5-ode 12, 16, that is, the sum of the secondary current. occurs. This resistance 3
The voltage generated across the terminal 2 is compared with a reference voltage by a comparator circuit 33, and overcurrent detection is performed.

As is clear from the above explanation, even in the method shown in Fig. 1 in which overcurrent is detected on the primary side, the secondary output current of each output channel is
Overcurrent detection is performed based on the sum of the current (corresponding to the voltage conversion value) converted to the primary side by the ratio to the next winding. That is, the method shown in FIG. 1 for detecting the primary current for overcurrent detection and the method shown in FIG. 2 for detecting the sum of the secondary currents are essentially the same.

In the conventional multi-output switching power supply device in which overcurrent detection is performed based on the sum of the secondary currents,
1) If only one output channel is overloaded and the remaining output channels are unloaded, the output current of the one output channel will not exceed the maximum value unless the output current reaches an extremely large value. There was a drawback that current could not be detected. Therefore, when one output channel is overloaded due to a short circuit or the like, there is a problem in that the overcurrent detection is not activated and each component of the channel is destroyed. In addition, in order to prevent such destruction, a circuit design that can withstand excessive current is required, which requires the use of components with large rated current capacities, which increases the cost and size of the device. There was a drawback.

For reference, the above-mentioned problem in the case where there is an unloaded output channel will be specifically explained using the case of FIG. 1 as an example. Rated output V1 of one output channel (secondary winding 102 side) in the switching power supply shown in FIG.
+11, and the rated output V2+I2 of the other output channel (secondary winding 103 side). Also converter transformer 1
The current (peak value) on the primary side of 0 is zp, primary winding 10
The number of turns of the secondary winding 1021103 is Np, and the number of turns of the secondary winding 1021103 is Nsl and Ns□, respectively. First, assuming that both channels are at rated load, Npi, = NsII,
Ten Ns! I2, i, is z p ; (Ns) /
Np ) I r + (Ns□Kishi, )I2. By the way, the overcurrent detection condition is generally 110% of the rated output, and if the primary current at the time of detection is Z p d, then R d
is Zpd =1. I Zpsuwachi d=(NslA
h) xl, 1r, + (Ns2/IV,) X 1. I
I, becomes. Therefore, if the channel on the output voltage v2 side (v2 output side) is unloaded, the overcurrent Z
The output current 1 of the channel on the output voltage Vl side (V1 output side) when p d is detected is (Ns t /Np
) Since I t' = z p d, I+' =
1.1 h + (NB, ha,, ) X 1. I I
It becomes 2. Therefore, for example, Vl'' V2 + I
In the case of a 2-output switching power supply device where 1 = I 2, Ns□ = N, □, so ■ If the 2 output side is no load, I+': 2.2I2 appears ■ The output side of the 1 output side channel If an output current of 2.2 times the rated current does not flow, an overcurrent will be detected and the output will be interrupted.

In order to eliminate these drawbacks of conventional multi-output switching power supplies, we have developed multiple current transformers that independently detect the secondary current corresponding to each output channel, and comparison circuits for the number of current transformers. Although it is conceivable to provide a 100% rated capacity, it would be expensive due to the increase in the number of component parts, and is not much different from the conventional case where components with large rated capacities are used.

[Purpose of the invention]

The present invention has been made in view of the above circumstances, and its purpose is to:
It is an object of the present invention to provide a multi-output switching power supply device capable of lowering an overcurrent detection level without adding a circuit for overcurrent detection.

[Summary of the invention]

The present invention focuses on the fact that in a multi-output switching power supply device, almost the same current flows through the rectifying diode during one operation period of the on/off operation of the switching transistor and flows through the freewheeling diode during the other operation period. , the plurality of output channels are divided into two groups, and for the output channels of one group, the current flowing through the rectifying diode is detected, and for the output channels of the other group, the current flowing through the freewheeling diode is detected. I'm trying to detect it. Therefore, in the present invention, a current transformer having a plurality of secondary windings is provided, and for the output channels of one group, the secondary windings are connected in series with a rectifying diode, and for the output channels of the other group, the secondary windings are connected in series with a rectifying diode. By connecting the secondary winding in series with the freewheeling diode, the sum of the secondary currents of the output channels of one group during the on/off operation period of the switching transistor is On the other hand, during the other operation period, the sum of the secondary currents of the output channels of the other group is detected on the primary winding side of the current transformer.

By doing so, the overcurrent detection level can be lowered compared to the conventional method which detects the sum of the secondary side currents of all output channels.

[Embodiments of the invention]

Hereinafter, one embodiment of the present invention will be explained with reference to the drawings. Note that the same parts as in FIGS. 1 and 2 are given the same reference numerals and detailed explanations will be omitted. FIG. 3 shows a circuit configuration of a pulse width modulation type two-output switching power supply device similar to, for example, FIGS. 1 and 2. In FIG. In the figure, 41 is a current transformer having a primary winding "l +412" and a secondary winding 413. This primary winding 411 is connected in series with the rectifier diode 12 on the v1 output side, whereas the The secondary winding 412 is connected in series to the freewheel diode 17 on the v2 output side. 42 is a resistor connected in parallel to the secondary winding 413 of the current transformer 41; 43
is a double-wave rectification bridge circuit that rectifies the alternating current voltage generated across the resistor 420. 44 has a built-in reference voltage generation circuit (not shown), and compares the reference voltage generated from this circuit with the output voltage of the bridge circuit 43 (the first
This is a comparator circuit (similar to comparator circuit 23, 33 in FIG. 2).

When the comparison circuit 44 detects that the output voltage of the bridge circuit 43 exceeds the reference voltage, it notifies the CNT circuit 20 of this fact.

Next, the operation of the configuration shown in FIG. 3 will be explained with reference to the signal waveform diagram shown in FIG. 4. Now ■! It is assumed that both the output side and the v2 output side are operating at a rated load of 11+I2. vl
On the output side, the current flowing through the choke coil 13 is a DC current containing a Rizzoll component, as shown in FIG.
The average value is the output current ■1. The current flowing through this choke coil 13 is a continuous current, and when the transistor 11 is on, the rectifying diode 12 is on and the current flows through the diode 12. On the other hand, when the transistor 11 is off, the rectifying diode 12 is off and the freewheeling diode 15 is on, and the continuity of the current flowing through the choke coil 13 is maintained by the current path between the diode 15 and the choke coil 13. . Therefore, as shown in FIG. 4, the currents flowing through the diodes 12 and 15 are the same in magnitude, although the timing and conduction time are different. This indicates that in order to measure the output current, it is possible to detect the current flowing through the freewheeling diode 15 as well as detecting the current flowing through the rectifying diode 12 as in the conventional method. . This is the same on the v2 output side, and as shown in FIG.
When the transistor 11 is on, current flows through the choke coil 18 through the rectifying diode PI3, and when the transistor 11 is off, current flows through the choke coil 18 through the freewheeling diode 17.

In this embodiment, the rectifier diode 12 is connected in series with the primary winding 411 of the current transformer 41.
Therefore, when the transistor 11 is on, the current flowing through the rectifying diode 12, that is, the output current on the v1 output side, is detected by the primary winding 411 as shown in FIG. In addition, in FIG. 4, after time t1, v1
It shows that the output side is in an overcurrent condition.

On the other hand, the primary winding 412 of the current transformer 41 is connected in series to the freewheeling diode 13-12, and therefore the current flowing through the freewheeling diode 17 when the transistor 1 is off, that is, the v2 output. The side output current is detected by the primary winding 412 as shown in FIG. Then, when the transistor 11 is on, the current transformer 41
Next winding 41. According to the current flowing through the transformer 41, a fourth resistor 42 is connected in parallel to the secondary winding 412 of the transformer 41.
A voltage is generated as shown in the figure. In addition, depending on the current flowing through the primary winding 412 of the current transformer 41 when the transistor 1 is off, a fourth transistor is connected across the resistor 42.
As shown in the figure, a voltage is generated in the opposite direction to that when the transistor 11 is on. The voltage across the resistor 420 (AC waveform voltage) is rectified by a double-wave rectifier bridge circuit 43 (see FIG. 4). The rectified output of this bridge circuit 43 is supplied to a comparison circuit 44. Comparison circuit 44 is bridge circuit 43
The rectified output and the reference voltage are compared to perform overcurrent detection 14-. As is clear, the comparator circuit 44 detects an overcurrent only on the v1 output side when the transistor 11 is on, and detects an overcurrent only on the v2 output side when the transistor 11 is off.

In other words, according to this embodiment, although only one current transformer and one comparison circuit are provided for overcurrent detection as in the conventional example, the output current of the two output channels is not calculated as the sum of the output currents of the two output channels. Each output current of each output channel can be detected independently. By the way, the output current 11 on the V output side and the output current 2 on the V2 output side are generally not equal. Therefore, in order for the comparison circuit 44 to perform voltage comparison based on the same reference voltage whether the transistor 1 is on or off, the absolute value of the output voltage of the current transformer 41, that is, the voltage across the resistor 42 The primary winding 411 of the current transformer 41 is arranged so that the values are approximately equal at the rated output.

412 turns NCT1. You need to choose NCT2.

For this, I, -Nc T1 = I2・Nc T2
It is sufficient if the turns ratio satisfies the following. Note that two types of reference voltages may be prepared and the reference voltages may be switched depending on whether the transistor 11 is turned on or off. In this case, it is not necessary to set the turns ratio so as to satisfy the above formula. do not have.

When the comparison circuit 44 detects that the rectified output of the bridge circuit 43 exceeds the reference voltage, the comparison circuit 44 sends a signal to that effect to the CNT circuit 20.
to notify. As a result, the CNT circuit 20 stops driving the transistor 11. As a result, the switching operation of the transistor 11 is stopped, the power is turned off, and the components of the corresponding output channel (in this example, V, the output side) and furthermore the transistor 11 are prevented from being destroyed. In this embodiment, since the output currents of the two output channels can be detected independently as described above, the overcurrent detection level of each output channel is not affected by the presence or absence of an unloaded output channel. Therefore, there is no need to reduce the overcurrent detection sensitivity or use components with large rated current capacities to withstand excessive currents, which is required in the past, making it possible to create low-cost, compact, and highly reliable power supplies. can be realized.

The comparator circuit 44 is not limited to the one using the peak value detection method described above, but may be an overcurrent circuit using a drooping characteristic method, for example. Further, in the above embodiment, the case of a switching power supply device with two outputs has been described, but the present invention can be similarly implemented in a switching power supply device with three or more outputs. However, the current transformer must have at least as many primary windings as the number of output channels. Then, the multiple output channels are divided into two groups, and for the output channels of one group, the corresponding primary winding of the current transformer is connected in series with each rectifier diode, and for the output channels of the other group, each By connecting the corresponding primary windings of the current transformer in series with the 7 Lee wheel diodes, the current transformer's 2
On the next side, the sum of the output currents of each output channel of one group and the sum of the output currents of each output channel of the other 17 groups are independently detected. In this case, although the overcurrent detection level is high in both the above embodiments, the overcurrent detection level is sufficiently lower than in the conventional example in which the sum of output currents of all output channels is detected.

Further, the present invention can be implemented in various control methods such as a constant switching frequency control method (duty cycle control method), a variable frequency type, a constant on-time type, and a constant off-time type, a self-excited switching power supply device, and the like.

〔Effect of the invention〕

As detailed above, according to the present invention, it is possible to lower the overcurrent detection level without adding an additional circuit for overcurrent detection, resulting in lower cost and smaller size, and improved reliability. .

[Brief explanation of drawings]

1 and 2 are circuit configuration diagrams of a conventional multi-output switching power supply device, FIG. 3 is a circuit configuration diagram showing an embodiment of the multi-output switching power supply device of the present invention, and FIG. 4 is a circuit diagram showing the operation. FIG. 3 is a signal waveform diagram for explaining. 10... Converter transformer, 11... Switching transistor, 12.16... Rectifier diode, 15.17... Freewheel diode, 41
...Current transformer, 411 t 412...1
Next winding, 43... Bridge circuit for double wave rectification. Applicant's agent Patent attorney Takehiko Suzue 19- Figure 1 Figure 2

Claims (1)

[Claims] In a multi-output switching power supply device having a plurality of output channels each having a rectifying diode and a freewheeling diode on the secondary side of a converter transformer, a first , a second primary winding connected in series with the freewheeling diode on the side of the output channel different from any of the output channels, and the eleventh second primary winding. A current transformer having a secondary winding for detecting current, a double-wave rectifier circuit that double-wave rectifies the voltage induced on the secondary winding side of the current transformer, and an output from the double-wave rectifier circuit. A multi-output switch and tingling source device characterized by comprising means for detecting overcurrent based on DC voltage.