JPH0312067Y2 - - Google Patents

Description

[Detailed Description of the Invention] (Industrial Application Field) The present invention relates to a multi-output DC/DC converter capable of obtaining signals for overload protection.

(Prior Art) FIG. 3 is a connection diagram showing an example of a multi-output DC/DC converter. In the figure, V _io is the input DC voltage, T is a transformer with a primary winding n ₁ and secondary windings n ₂ and n ₃ , and D ₁ to D ₄ are voltages generated in each winding n ₂ and n ₃ . diodes that rectify the alternating current voltage, L ₁ and L ₂ are smoothing coils (chiyoke), and C ₁ and C ₂ are smoothing capacitors. Q is a switching transistor that turns on and off the input DC voltage V _io and applies it to the primary winding n ₁ of the transformer T, obtaining DC voltages V ₀₁ and V ₀₂ from each output terminal #1 and #2, respectively. .

CH ₁ is the first current transformer for current detection inserted and connected in series with the primary winding n ₁ of the transformer T;
CT ₂ and CT ₃ are second and third current transformers for current detection inserted and connected in series to the respective secondary windings n ₂ and n ₃ of the transformer T. 1 is a detection circuit that inputs signals from each of the first to third current transformers CT ₁ to CT ₃ and detects when any one of these becomes a predetermined value or more; 2 is a drive circuit for the transistor Q; For example, the on/off time of the transistor Q is controlled so that the output voltage V ₀₁ at the #1 output terminal becomes a constant value corresponding to the reference voltage. The drive circuit 2 also receives the signal from the detection circuit 1, and when the signals from the first to third current transformers exceed a predetermined value,
When it is determined that an overload condition exists, the transistor Q is turned off, for example, and the entire power supply is put into a protective operation.

(Problems to be solved by the invention) In a multi-output DC/DC converter with such a configuration, protection of the power supply due to overload is provided by (a) the primary side of the transformer T by the first current transformer CT ₁ ; monitor the total amount.

(b) Monitor each load current of each secondary side output terminal # ₁ , #2 of the transformer T by the second and third current transformers CT 2 and CT ₃ .

This is done by using in combination.

Here, the detection circuit 1 detects that the differential value di/dt of the current detected by each current transformer is larger than 0 (di/dt).
dt > 0), that is, the point where the signal waveform tends to rise to the right, the peak value of each load current is rectified and the maximum peak value is detected.

However, in the case of a multi-output DC/DC converter, the differential value of the current detected through the current transformer depends on the winding ratio of each transformer and chain.
There are cases where di/dt becomes smaller than 0 (di/dt<0).

In this case, a problem arises in that a change in load current cannot be accurately detected using normal detection, and a stable overload protection operation cannot be performed.

The present invention was devised in view of the problems in the prior art, and its purpose is to ensure that the differential value di/dt of the current detected through the current transformer is di/dt<
The aim is to realize a DC/DC converter that can perform stable overload protection even when the voltage is 0.

(Means for Solving the Problems) The present invention for solving the problems described above includes a transformer having a primary winding and a plurality of secondary windings, and an input DC voltage that is connected to the primary windings. In the multi-output DC/DC converter, the converter includes a switch circuit that turns the line on and off, and a rectifying and smoothing circuit that rectifies and smoothes the alternating current voltage obtained at each of the secondary windings. A current transformer for load current detection is inserted and connected in series with each current transformer, and if the differential value di/dt of the output of each current transformer is di/dt<0, the corresponding output is rectified by a diode, and a signal for overload protection is obtained via a resistor or inductance in series with the rectifier diode.

(Embodiment) FIG. 1 is a block diagram showing an example of a device according to the present invention. In this figure, parts corresponding to those in FIG. 3 are designated by the same reference numerals.

In this invention, the signals from each current transformer CT ₁ to _{CT 3} are connected to a resistor to unify the signal level.
A voltage signal is generated by R ₁ , R ₂ , and R ₃ , and is passed through capacitors C ₃ , C ₄ , and C ₅ to diodes D ₅ , D ₆ , D ₇ ,
It is rectified by D ₈ , D ₉ , and D ₁₀ .

Figure 2 A, B, and C represent current transformers CT ₁ , CT ₂ ,
3 is a waveform diagram of signals i ₀ , i ₁ , and i ₂ obtained through CT ₃ , respectively. FIG.

A signal i 0 corresponding to the total current on the primary side of the transformer T and varying as shown in A is obtained from the first current transformer CT ₁ , and a signal i ₀ corresponding to the total current on the primary side of the transformer T is obtained from the second current transformer CT ₂ . A signal _i1 corresponding to the load current of the load connected to the output terminal 1, which changes as shown in FIG. 1, is obtained. As shown in the figure, each of these signals i ₀ and i ₁ changes in an upward trend to the right.

The third current transformer CT ₃ outputs a signal i 2 corresponding to the load current of the load connected to the #2 output terminal, which changes as shown by the solid line C, that is, a signal i ₂ , that is, a downward slope (di ₂ /
A signal that changes as dt<0) is obtained. signal here
The reason why i ₂ tends to fall to the right is due to the relationship between the turns ratio of the chains L ₁ and L ₂ .

The signal waveform shown in Fig. 2 is for each current transformer CT1,
It is obtained by passing the signals obtained from CT2 and CT3 through a differentiating circuit and observing them with, for example, an oscilloscope. From the observation of the signal waveforms from each current transformer CT1, CT2, CT3, which output signal of each current transformer changes upward to the right like A and B (di/
dt > 0) or the current transformer output changes downward to the right (di/dt<0) as shown in C. The characteristic configuration of the present invention is applied to this.

That is, in this example, the current transformer CT
Since the output of No. 3 changes downward to the right, the characteristic configuration of the present invention is applied to this output.

In FIG. 1, R ₀ is a resistance, and among the outputs i ₀ , i ₁ , i ₂ from each current transformer CT ₁ , CT ₂ , CT ₃ ,
The output of the current transformer CT ₃ , which changes in a downward trend (di/dt<0), is connected in series to the rectifier diode D ₉ .

_C0 is a capacitor that smoothes the rectified output from each current transformer _CT1 , _CT2 , _CT3 , and 1 is this capacitor.
This is a detection circuit that receives signals smoothed by C ₀ and detects whether any of the signals exceeds a predetermined level, and outputs an overload signal to the drive circuit 2 from here.

According to this configuration, the output from the current transformer _CT3 , which changes in a downward trend to the right, is caused by the first-order lag circuit consisting of the resistor _R0 and the capacitor _C0 , as shown by the broken line in Fig. 2C. It signals an upward trend. resistance
By adjusting the value of R ₀ , a signal with a waveform equivalent to the output with di/dt>0 can be obtained. Note that an inductance may be used instead of the resistance R ₀ .

Therefore, the detection circuit 1 can detect the output of each current transformer under the same conditions, and can perform an operation for overload protection accurately and stably.

Note that although Figure 1 shows the case where an ON/ON type DC/DC converter is used, the ON/OFF type
It is also possible to apply it to a DC/DC converter. Also, if you increase the number of secondary windings of the transformer,
You can also get a lot of output.

(Effect of the invention) As explained above, the present invention has two
In a DC/DC converter that has multiple secondary windings and rectifies and smooths them to obtain multiple DC outputs, the output of multiple current transformers is used to detect the current flowing through each secondary winding. Even if either of them changes downward to the right (di/dt < 0), the effect of the resistance or inductance connected between the rectifier circuit that rectifies the output of the current transformer and the smoothing capacitor causes it to change downward to the right. It can be converted into a signal that changes upward.

Therefore, it is possible to realize a DC/DC converter in which overload protection can be performed accurately and stably.

[Brief explanation of the drawing]

Fig. 1 is a configuration block diagram showing an example of the device according to the present invention, Fig. 2 is a waveform diagram of signals obtained through each current transformer in Fig. 1, and Fig. 3 is a known multi-output DC/DC. FIG. 2 is a connection diagram showing an example of a converter. T...Transformer, _n1 ...Primary winding, _n2 , _n3 ...
Secondary winding, CT ₁ to CT ₃ ... Current transformer, D ₅ to _{D 9} ...
Diode, R ₀ ... Resistor, 1 ... Detection circuit, 2
...Drive circuit, Q...Switching transistor.

Claims (1)

[Claims for Utility Model Registration] A transformer having a primary winding and a plurality of secondary windings, a switch circuit that turns on and off an input DC voltage to the primary winding, and each of the two A plurality of rectification and smoothing circuits that rectify and smooth the AC voltage obtained in the next winding, and a switch circuit that receives a signal regarding the output voltage of at least one of the plurality of rectification and smoothing circuits and controls the output voltage to a constant value. In a multi-output DC/DC converter equipped with a drive circuit for controlling on/off of each rectifier circuit D7, D8, D9, D10 that rectifies the output from the current transformer, a smoothing capacitor _C0 that smoothes the rectified output from each rectifier circuit, and at least one of the plurality of rectifier circuits that rectifies the output of the current transformer. A resistor or inductor R ₀ connected between one rectifier circuit and one end of the capacitor
and a detection circuit 1 that inputs the signal smoothed by the smoothing capacitor, detects when the value of the signal exceeds a predetermined value, and outputs a detection signal for overload protection to the drive circuit. , a resistor or inductor R connected between the at least one rectifier circuit and one end of the capacitor is a current transformer whose output waveform changes downward to the right by observing each output from a plurality of current transformers. A multi-output DC/DC converter, characterized in that the output of the CT3 is connected between a rectifier circuit that rectifies the output and one end of a smoothing capacitor _C0 .