JP3058304B2 - Converter overcurrent protection circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an overcurrent protection circuit for a converter. Here, the converter refers to a device that converts a certain DC voltage to another DC voltage, and is often called a switching regulator or a DC-DC converter. When a converter is used as a power supply device, a constant voltage operation is normally performed by feedback connection between an input DC voltage terminal and a load, and an overcurrent protection circuit is connected to protect the converter from overload.

However, the protection ability is not sufficient for a severe overload such as a load short circuit, and the converter is often damaged.

[0003]

2. Description of the Related Art A conventional technique will be described below. FIG. 6 shows the input voltage Vi versus output voltage Vo characteristic of the constant voltage circuit connected to the converter circuit. As shown, Vi
Within the specified range, that is, from Vi _L to Vi _H Vo is constant Vo _C.

FIG. 7 shows the output current Io versus output voltage Vo characteristic of the overcurrent protection circuit also connected to the converter circuit. As shown, Io increases and the standard maximum value Io _H
Is maintained at a constant value Vo _C until the voltage reaches Io _H
When it exceeds, the descent starts rapidly. This voltage drop characteristic is called an overcurrent drooping characteristic or simply a drooping characteristic. The converter is protected from overload by reducing the supply voltage due to the drooping characteristic.

There are roughly three types of drooping characteristics.
FIG. 7 schematically shows three types of molds. That is, the drooping characteristic A shown by a solid line is a constrained type (a person skilled in the art calls it a "F" shape), and the drooping characteristic B shown by a dotted line is a constant current type and is shown by a broken line. The drooping characteristic C is what is referred to as a current decreasing type (referred to by those skilled in the art as a "F" shape).

As is apparent from the figure, the constant current drooping characteristic B and the current decreasing drooping characteristic C are considered to be the most preferable because the load current decreases when overloaded or at least maintains a constant value. However, in order to realize these characteristics, a high level of technology is required, and the circuit is very complicated, which is disadvantageous in terms of economy.

The point constraint type drooping characteristic A is widely used because it can be realized by a relatively simple technique and is economical. FIG. 8 is a circuit diagram showing an example of a converter including an overcurrent protection circuit according to the related art. Note that the part of the constant voltage circuit that normally performs the constant voltage of the output voltage together with the overcurrent protection circuit is omitted in FIG.

Referring to FIG. 1, main components and devices will be described. Ci is an input capacitor, T is a main transformer,
Q is a switching element such as a (bipolar) transistor or MOSFET (field effect transistor), D is a low forward voltage drop diode such as a Schottky barrier diode, L is a choke coil for smoothing, and Co is an output capacitor. Form the body part of the converter.

As shown in the figure, as a more general term, the switching element Q is a variable conduction time width DC interrupting means, which is numbered and appended with 1, and the main transformer T, in descending order. The directional voltage drop diode D, the smoothing choke coil L, and the output capacitor Co are voltage-rectifying and smoothing means, and are numbered as 2 and appended.

On the other hand, R _S is a current detection resistor, D _S and C
_S is a diode and a capacitor for smoothing, and R is
₁ and R ₂ are current detecting dividing resistor, E is a voltage amplifier, F is the pulse width modulation voltage comparator to one input and the output of the sawtooth generator OSC to a reference voltage V _R, P is the switching In the drive circuit for driving the element Q, up to the comparison voltage amplifier forms a part of the overcurrent protection circuit.

[0011] Again, as a more general call it, and a current detecting resistor R _S, a diode and a capacitor, respectively D _S and C _S for smoothing and the current detection voltage dividing resistors R ₁ and overcurrent detecting means for R ₂ The voltage amplifier E, the saw-tooth wave generator OSC, the pulse width modulation comparator F, and the drive circuit P are energization time width control means and are numbered as 4. It is appended.

[0012] Note that V _CC is the power supply voltage for supplying power to auxiliary circuits such as constant voltage circuit and the overcurrent protection circuit is provided separately from the voltage Vi and Vo, etc. of the main power supply. The current flowing into the primary winding of the main transformer T based on the input DC voltage Vi is intermittently switched by the switching element Q, and is taken out from the secondary winding as an AC voltage. This AC voltage is rectified by the low forward voltage drop diode D, smoothed by the smoothing choke coil L and the output capacitor Co, and supplied to the load as the output DC voltage Vo. In this case, the value of Vo is determined by the conduction time width of the switching element Q. That is, the width increases when the energization time width increases, and decreases when the width decreases.

Now, the primary winding of the main transformer T of the converter
The current sensing resistor R_SIntermittent
Voltage drop occurs, but this intermittent voltage drop
Diode D_SAnd capacitor C_SRectification and smoothing with
Moreover, after smoothing C _STerminal voltage V_STo R₁/
(R₁+ R_Two) Current detection voltage dividing resistor R₁Terminal
Voltage V_S1Is applied to the + input of the voltage amplifier E.

A reference voltage V is applied to the negative input of the voltage amplifier E._R
Is applied, the above V_S1Is V_RAs long as it does not reach
The voltage amplifier E does not generate a positive output. However,
V_S1Is V_RExceeds, the voltage amplifier E generates a positive output
And the output voltage level is (V _S1-V_R) Is almost proportional to
Rise. V_RIs the maximum value Io described above for the load.
_HV when the flow_S1= V_S・ R₁/ (R₁+ R_Two)The value of the
Is set in advance to be equal to

The output voltage of the voltage amplifier E is applied to a first input of a comparator F for pulse width modulation at the next stage. The output of the triangular waveform pulse oscillator OSC is applied to a second input of the pulse width modulation comparator F.

The pulse width modulation comparator F corresponds to a voltage discrimination circuit from the viewpoint of the operation principle, and discriminates the voltage of the second input signal using the first input voltage as a threshold value. That is, a pulse train whose pulse width is the time width during which the amplitude of the second input signal exceeds the first input voltage is obtained from the output.

Since the first input voltage is not constant and changes according to the terminal voltage V _S1 of the current detection voltage dividing resistor R ₁ as described above, while the second input signal is a triangular waveform pulse,
When the first input voltage is low, a pulse train having a wide pulse width is output. When the first input voltage is high, a pulse train having a narrow pulse width is output.

As described above, the pulse width modulation comparator F
Is a pulse width modulation circuit from the viewpoint of application. The pulse width modulation signal output from the pulse width modulation comparator F drives the switching element Q via the drive circuit P.

[0019] That is, the output current Io exceeds the maximum value Io _H above standards, in accordance with further increases, the output pulse width of the pulse width modulation comparator F is gradually narrowed.
For this reason, the output DC voltage Vo obtained by rectifying and smoothing the AC voltage derived from the output pulse drops, and the drooping characteristic suppresses the overload.

[0020]

However, since the overcurrent protection circuit according to the prior art described above has a restrained drooping characteristic, the output voltage drops when an overload occurs, and the output current also decreases based on this. Despite suppression, it continues to increase. Therefore, if the overload is light, the converter is sufficiently protected, but if the overload is severe such as a short circuit, it cannot be completely protected and the converter is often damaged.

Accordingly, an object of the present invention is to provide an overcurrent protection circuit for a converter in which the overcurrent suppression property in the drooping characteristic is improved, excluding the above-mentioned disadvantages of the prior art.

[0022]

FIG. 1 is a block diagram showing the principle of the present invention. In the figure, 1 is an energization time width variable DC intermittent means, 2 is a transformer rectifying and smoothing means, 3 is an overcurrent detecting means,
Reference numeral 4 denotes an energization time width control means, and reference numeral 5 denotes a drooping characteristic control block according to the present invention. The drooping characteristic control block 5 includes:
It includes a voltage drop detection means 6 and an overcurrent detection sensitivity control means 7.

Now, in order to achieve the above-mentioned object, the present invention has the following configuration as shown in FIG. That is, a variable current-duration variable DC interrupting means 1 for interrupting a current by an input direct-current voltage and having a controllable current-duration width, transforms and rectifies an AC voltage induced by the variable current-duration width DC interrupting means 1, and smoothing the transformer rectifier smoothing means 2 for supplying an output DC voltage to a load, in relative configured converter circuit, detecting measures the overcurrent flowing into the conduction time width variable DC disconnecting means 1 for overcurrent protection Overcurrent detection means 3
Controlling the energization time width of the energization time width variable DC interrupting means 1 in accordance with the current value detected by the overcurrent detection means 3, so that the output DC voltage of the transformer rectification smoothing means 2 is controlled. Is controlled by the overcurrent detection means 3
As the value increases, the energization time width to be controlled decreases.
Output DC voltage droop due to overcurrent
Achieved a constrained drooping characteristic as
An overcurrent protection circuit for a converter comprising: an energization time width control means for gradually decreasing a current voltage ; a drooping characteristic control block connected between the transformer rectification smoothing means and the overcurrent detection means; The drooping characteristic control block 5
The voltage drop rectifying / smoothing means 2 includes a voltage drop detecting means 6 for detecting the output DC voltage when it falls to a specific value or a plurality of specific values each time. In response, the overcurrent detecting means 3
An overcurrent detection sensitivity control means 7 for controlling the detection sensitivity of the current value applied to the power supply time width control means 4 .

[0024]

FIG. 2 is a droop characteristic diagram of the overcurrent protection circuit of the converter according to the present invention. In the figure, the output current Io
Until but reached increased by standard maximum value Io _H, Vo is maintaining a constant value Vo _C, to the point of showing the a drooping characteristic exceeds Io _H are the same as described in FIG.

The operation of the present invention will be described below with reference to FIGS. 1 and 2 showing the principle blocks of the present invention. Upon detecting that the output DC voltage Vo _C of the transformer rectifying / smoothing means 2 has dropped to a _first specific value Vo ₁ due to the drooping characteristic, the drop voltage detecting means 6 in the drooping characteristic control block 5 detects the first drop voltage. Outputs a detection signal. Incidentally, at this time, the output current has increased to _I1H .

When the voltage drop detection signal is added, the overcurrent detection sensitivity control means 7 outputs a detection sensitivity increase signal and applies it to the overcurrent detection means 3, thereby dramatically increasing the overcurrent detection sensitivity. Let it.

That is, while the conventional object of detection and measurement is only the smoothed voltage V _S of the DC intermittent current as described above, the present invention also detects the output voltage Vo. Therefore, both of these are added. since set at a voltage level of the voltage drop detection signal combined output from the overcurrent detection means 3, equivalently, smoothing the voltage V _S of the DC intermittent current in the prior art equivalent to that dramatically increased Result.

The drastically increased voltage drop detection signal output from the overcurrent detecting means 3 controls the energizing time width of the energizing time width variable DC interrupting means 1 via the energizing time width controlling means 4 and makes the jump. Therefore, the output current decreases drastically from I _1H to I _1L at the output voltage Vo ₁ .

Next, when detecting that the output DC voltage Vo _C has further dropped and dropped to the second specific value Vo ₂ , the drop voltage detecting means 6 outputs the next drop voltage detection signal. At this time, the output current has increased to _I2H .

When the voltage drop detection signal is added, the overcurrent detection sensitivity control means 7 outputs a detection sensitivity increase signal again and applies the signal to the overcurrent detection means 3, thereby dramatically increasing the overcurrent detection sensitivity again. To increase.

The overcurrent detection means 3 outputs a drastically increased voltage drop detection signal again, and controls the power supply time width of the power supply time width variable DC interrupting means 1 via the power supply time width control means 4. Since the output current is drastically reduced, the output current is drastically reduced again from I _2H to I _2L at the output voltage Vo ₁ .

Similarly, when Vo _C falls to the minimum n-th specific value V On, the output current _changes from In _n to I _n.
It drastically decreases to _nL and the drooping characteristics are completed. As is clear from FIG. 2, the realization of a plurality of stages of drooping characteristics according to the present invention makes it possible to obtain an overcurrent suppression characteristic equivalent to that of a constant current type or a current step-down type, while being of a constrained type.

In the above description, the specific voltage drop is V
o _1, Vo _2, ~, the description has been given of the plurality and Vo _n, for example by Vo _1, or a like and singular only Vo _n is of course that may be.

[0034]

FIG. 3 is a circuit diagram showing a first embodiment of the present invention. The parts and devices shown in FIG.
There are many things that are exactly the same, so here we will explain only the major new ones.

First, PI (abbreviation of Photocoupled Insulator) and pi are a light-emitting element (for example, a GaAs light-emitting diode) and a light-receiving element (for example, a transistor or a PIN photodiode) of a photocoupler.
Is a voltage comparison circuit using V _Rm as a reference voltage.

The operation of the main body of the converter and the operation of the overcurrent protection circuit according to the prior art has already been described in the section of [Prior Art], so that the description will not be repeated. The correspondence between this embodiment and FIG. 1 showing the principle block of the present invention is as follows.

That is, the photocouplers PI and pi in FIG. 3 correspond to the overcurrent detection sensitivity control means 7 in FIG. 1, and the comparison circuit G including the reference voltage _VRm corresponds to the drop voltage detection means 6.

FIG. 4 is a drooping characteristic diagram of the overcurrent protection circuit of this embodiment. Hereinafter, description will be made with reference to FIGS. 3 and 4. In this embodiment, by connecting the respective collector and emitter of the transistor as a light receiving element pi of photocoupler to both ends of the current detection voltage dividing resistors R _2, is compared with the reference voltage V _Rm added output voltage Vo to the comparison circuit G. Then, since the output of the comparison circuit G is connected to the light emitting element PI of the photocoupler, when the output voltage Vo drops to the specific value _VRm , an output current is generated in the comparison circuit G, which flows through the light emitting element PI to emit light. As a result, the collector and the emitter of the light receiving element pi become conductive, and the current detection voltage dividing resistor R
₂ will be short-circuited.

As described in the section of [Prior Art], the terminal voltage V _S1 of the current detection voltage dividing resistor R ₁ is equalized with the smoothing capacitor C 1.
_It is equal to the value obtained by multiplying the terminal voltage V _S of _S by R ₁ / (R ₁ + R ₂ ). In the present embodiment, R ₂ is short-circuited, so that R ₂ =
0, that is, V _S1 = V _S , which is a remarkably large value as compared with the related art, is applied to the pulse width modulation comparator F via the voltage amplifier E. Therefore, the switching element Q
Is driven by a pulse train having a drastically narrow pulse width via the driving circuit P, so that the output current is I at the output voltage V _Rm .
It drastically decreases from _mH to I _ml , and a one-stage drooping characteristic is realized. Io is exceeded standards maximum value Io _H described above, according to further increases, the output pulse width of the pulse width modulation comparator F is gradually narrowed. For this reason, the output DC voltage Vo obtained by rectifying and smoothing the AC voltage derived from the output pulse drops, and the drooping characteristic suppresses the overload.

As is apparent from FIG. 4, the single-stage drooping characteristic is much more excellent in overcurrent suppression performance than the conventional stepless drooping characteristic, and a severe overload such as a short circuit occurs. From the converter.

FIG. 5 is a circuit diagram showing a main part of a second embodiment of the present invention. In FIG, R ₃ is the application of the third current detection voltage dividing resistors, PI ₁ and pi ₁ a first photocoupler, PI ₂ and pi ₂ are second photo coupler, G ₁ is a first reference voltage V _R1 In the first comparison circuit, G ₂ is a comparison circuit to which the second reference voltage V _R2 is applied. The other parts are exactly the same as FIG. 3 showing the first embodiment.

As shown in the figure, in this embodiment, three current detection voltage dividing resistors are newly provided, two photocouplers and two comparison circuits are used, and different reference voltages V _R1 and V _R2 are respectively used.
_{(Here, V R2 <V R1 <Vo} c) are applied.

In the figure, an output voltage Vo is applied to first and second comparison circuits G ₁ and G ₂ and compared with first and second reference voltages V _R1 and V _R2 , respectively. First, the output current is generated when the output voltage Vo drops to the first specified value V _R1 to the first comparison circuit G _1, which is the first light-emitting element P
To emit light flows through the I _1. For this reason, the collector and the emitter of the light receiving element pi ₁ are brought into conduction, and the current detection voltage dividing resistor R ₃ is short-circuited.

[0044] In this embodiment, Vo> terminal voltage V _S1 of the current detection voltage dividing resistors R ₁ in a section of the V _R1 to the terminal voltage V _S of the smoothing capacitor _{C S R 1 / (R 1} + R 2 + R 3 )
, But when V _R1 >Vo> V _R2 , R ₃
= 0, that is, R ₃ = 0, that is, V _S1 = V _S · R ₁
/ (R ₁ + R ₂ ), which is applied to the pulse width modulation comparator F via the voltage amplifier E. Therefore, since the switching element Q is driven by a pulse train with a narrow pulse width via the drive circuit P, the output current is drastically reduced at the output voltage _VR1 , and the first stage drooping characteristic is realized.

Next, the output voltage Vo becomes the second specific value V_R2
When the voltage drops to _TwoAlso R_ThreeShort circuit following
And V_S1= V_SAnd further increase
Force current is output voltage V_R2In the second stage
The drooping characteristic of is realized. That is, according to the second embodiment,
Then, a two-stage drooping characteristic can be realized.

It will be apparent that the same technique can be used to realize an arbitrary multi-stage hanging characteristic.

[0047]

As described above, according to the present invention,
An overcurrent protection circuit for a converter that can be easily manufactured technically, is economical, and safely protects the converter from severe overload such as a short circuit can be realized.

[Brief description of the drawings]

FIG. 1 is a principle block diagram of the present invention.

FIG. 2 is a drooping characteristic diagram of the overcurrent protection circuit of the present invention.

FIG. 3 is a circuit diagram of a first embodiment of the present invention.

FIG. 4 is a drooping characteristic diagram of the overcurrent protection circuit according to the first embodiment.

FIG. 5 is a circuit diagram of a main part of a second embodiment of the present invention.

FIG. 6 is a characteristic diagram of a constant voltage circuit connected to a converter circuit.

FIG. 7 is a characteristic diagram of the overcurrent protection circuit connected to the converter circuit.

FIG. 8 is a circuit diagram of a conventional overcurrent protection circuit.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 conduction time width variable DC intermittent means 2 transformer rectification smoothing means 3 overcurrent detection means 4 conduction time width control means 5 drooping characteristic control block 6 drop voltage detection means 7 overcurrent detection sensitivity control means

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) G05F 1 / 445,1 / 56 G05F 1 / 613,1 / 618 H02M 3/00-3/44

Claims (1)

(57) [Claims] 1. An intermittent current duration variable DC intermittent means for intermittently interrupting a current caused by an input direct current voltage and having a controllable energization time width, and transforms and rectifies an AC voltage induced by the energization time duration variable DC intermittent means. And a transforming rectifying / smoothing means for smoothing and supplying an output DC voltage to the load. Overcurrent detection means, and a current value detected by the overcurrent detection means.
When controlling the output DC voltage of said transformer rectifier smoothing means by controlling the energization duration of the energization time width variable DC interrupting means depending, electrodeposition said overcurrent detecting means detects
As the flow value increases, the energization time width to be controlled increases.
Perform the operation to narrow the output DC voltage
Realizes a restrained drooping characteristic as the lower characteristic and outputs when overcurrent occurs
An overcurrent protection circuit for a converter, comprising: an energization time width control unit for gradually decreasing a DC voltage . A droop characteristic control block is connected between the transformer rectification smoothing unit and the overcurrent detection unit. The block includes a voltage drop detecting means for detecting the output DC voltage of the transformer rectifying / smoothing means each time the voltage drops to a specific value or a plurality of values, and responds to each detection signal of the output of the voltage drop detecting means. Said
The current which the overcurrent detecting means gives to the energizing time width controlling means
An overcurrent protection circuit for a converter, comprising: an overcurrent detection sensitivity control means for controlling a value detection sensitivity.