JPH11252908A - Voltage stabilizing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To fixedly hold a limit value of a current from a secondary side regardless of a level of primary side voltage by limiting a primary side current of a transformer so as to prevent it from exceeding a prescribed upper limit value, also changing the upper limit value of the primary side current in a manner such that it is almost inversely proportional to the primary side input voltage. SOLUTION: A primary side current Io carried in a power MOS transistor Qm by a current detection circuit 41 of an over-current protection circuit 4 is converted into a voltage by a shunt resistor Rs, to be detected, also a comparison reference voltage Vx is variably generated by a variable voltage generating circuit 51. Whether the counted voltage exceeds the generated comparison reference voltage or not is detected by current conversion detection voltage Vcs from a voltage comparison circuit 42, this detected output is inputted to an output limiting circuit 43, the power MOS transistor Qm is forcedly limited and is set to off. The comparison reference voltage Vx is changed in a manner wherein an upper limit value of a primary side current Io of a transformer is almost inversely proportional to a primary side input voltage VB thereof.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a voltage stabilizer,
Further, the present invention relates to a technology that is effective when applied to a switching control type voltage stabilizer having an overcurrent protection function, that is, a so-called switching regulator.

[0002]

2. Description of the Related Art In a voltage stabilizer (regulator) constituting a constant voltage power supply or a power supply voltage converter (DC-DC converter) for electronic equipment, a power element and a power element in the voltage stabilizer are usually used. In order to protect an external device or a circuit that receives a power supply voltage from the device, an overcurrent protection circuit that limits an output current that changes according to a load state or the like to a certain level or less is provided (for example, CQ).
Published by the publisher "Transistor Technology January 1998" 3
00, 301).

In a constant voltage power supply or a DC-DC converter of a switching control system, switching control of a primary current of a transformer controls stabilization of an output voltage obtained from a secondary side thereof. In such a voltage stabilizing device, overcurrent protection for limiting the primary current to a certain value or less is also performed. Thereby, the power element controlling the primary current of the transformer and the load connected to the secondary side can be protected from overcurrent.

[0004]

However, it has been clarified by the present inventors that the above-described technology has the following problems.

That is, in the overcurrent protection for limiting the secondary current by limiting the primary current of the transformer,
When the primary voltage of the transformer greatly changes, even if the primary current can be limited to a certain value or less, the secondary current may not be limited to a certain value or less. This is because the power generated in the secondary winding of the transformer is proportional to the power supplied to the primary winding. Therefore, even if the current of the primary winding is limited to a constant value, the current that can be extracted from the secondary winding increases in proportion to the voltage applied to the primary winding.

For this reason, the secondary side overcurrent protection by limiting the primary current of the transformer is based on the premise that the input voltage applied to the primary winding of the transformer is constant. This is because, when the primary voltage of the transformer changes, even if the primary current is limited to a certain value or less, the limited current on the secondary increases or decreases according to the primary voltage.

In a constant voltage power supply or the like, it is necessary to consider not only protection measures for a power element for controlling a primary current, but also safety measures for a load (equipment) to which a secondary current is supplied. For example, even when a failure such as a short circuit or an erroneous connection occurs on the load side, if the supply current to the load is limited to a certain level or less, damage to the load side due to the failure can be minimized. A so-called fail safe can be performed.

However, in the above-described voltage stabilizing device, the current limit value on the secondary side increases in accordance with the primary voltage of the transformer, which is a great obstacle in implementing safety measures (file safety). Had become.

An object of the present invention is to provide a voltage stabilizing device for controlling a primary current of a transformer to stabilize an output voltage obtained from a secondary side thereof, which can be taken out from the secondary side. It is an object of the present invention to provide a technique for keeping a current limit value constant irrespective of the level of a primary voltage.

The above and other objects and features of the present invention will become apparent from the description of the present specification and the accompanying drawings.

[0011]

SUMMARY OF THE INVENTION Among the inventions disclosed in the present application, the outline of a representative one will be briefly described.
It is as follows.

That is, a voltage stabilizing device for stabilizing an output voltage obtained from a secondary side by controlling a primary side current of a transformer, wherein the primary side current exceeds a predetermined upper limit value. In addition to performing overcurrent protection to limit the primary current, the upper limit of the primary current is changed so as to be substantially inversely proportional to the primary input voltage.

According to the above-described means, even if the input voltage applied to the primary side of the transformer changes, the limit value of the primary side current changes in a form substantially inversely proportional to the change, so that the secondary side Can be kept almost constant.

This achieves the object of keeping the limit value of the current that can be extracted from the secondary side constant irrespective of the level of the primary side voltage.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows a first embodiment of a voltage stabilizer to which the technique of the present invention is applied.

The application example shown in FIG. 1 is a switching control type constant voltage power supply circuit, and includes a main circuit unit 1, an AC outlet 61, a full-wave rectifier 62, a transformer 63, a DC output circuit 7, etc. And AC1
A constant-voltage DC power supply is generated from a commercial AC power supply of 00V or 200V AC.

In FIG. 1, an AC input voltage (AC 100 V / AC 200
V) is rectified by the full-wave rectifier 62 to a DC voltage VB. This DC voltage VB is applied to primary winding L1 of transformer 63.

The main circuit section 1 includes a primary winding L of a transformer 63.
By controlling the switching of the current (primary current) Io flowing through the first winding, the voltage taken out from the secondary winding L2 is stably controlled.

The DC output circuit 7 rectifies and smoothes the secondary-side voltage generated in the secondary winding L2 of the transformer 63, and leads it to the DC output terminals 71, 71. Vdc is a DC stabilized output voltage taken out at its output terminals 71, 71, Id
c is a DC output current flowing from the output terminal 71 to the load side.

Here, the main circuit section 1 includes the transformer 63
MOS transistor Qm as a power element for switching control of primary current Io, pulse drive circuit 2 for turning on / off this power MOS transistor Qm with a pulse signal, and overcurrent protection circuit 4 for limiting the primary current Io Etc. The internal operating power supply Vcc of the main circuit 1 converts the secondary voltage taken out from the auxiliary secondary winding L21 of the transformer 63 into a rectifier 64 and a capacitor C2.
Generated by rectifying and smoothing at 1.

The pulse drive circuit 2 has a PWM (pulse width modulation) control function. The pulse drive circuit 2 drives the power MOS transistor Qm on / off at a constant cycle and varies the on / off time ratio (duty). Stabilization control of the DC output voltage Vdc is performed. This stabilization control
The DC output voltage Vdc of the DC output circuit 7 is
1, the error detection circuit 22 detects the error relative to a predetermined target set voltage Vst, amplifies the error, and feeds it back to the pulse drive circuit 2. The pulse drive circuit 2 variably controls the on / off time ratio of the power MOS transistor Qm in a direction that minimizes the error detected by the error detection circuit 22.

The overcurrent protection circuit 4 converts the primary side current Io supplied by the power MOS transistor Qm to a shunt resistance R
s, a current detection circuit 41 that converts the voltage into a voltage, and detects the voltage;
A voltage comparison circuit 42 for detecting whether the current conversion detection voltage Vcs exceeds the comparison reference voltage Vx, and an output limiting circuit for forcibly turning off the power MOS transistor Qm based on a detection output of the voltage comparison circuit 42 43
Formed by

The variable voltage generation circuit 51 includes the transformer 6
3 is configured to generate a voltage (Vx) that changes substantially in inverse proportion to a voltage k · VB (k is a voltage dividing ratio by R1 and R2) applied from the primary-side input voltage VB via the voltage dividing resistors R1 and R2. The voltage variably generated by the circuit 51 is supplied to the comparison circuit 42 by the comparison reference elastic pressure Vx.
Given as

The voltage Vx, which is inversely proportional to the input voltage k · VB, can be generated by using an analog divider circuit. As shown in FIG. 2, for example, a non-linear characteristic (non-linearity) of a transistor amplifier circuit is used. Can be generated approximately.

FIG. 2 shows a configuration example of the variable voltage generation circuit 51 and its characteristics.

The variable voltage generation circuit 51 shown in FIG.
Comprises an MOS transistor Qn1, resistors R3 to R6, and an operational amplifier 511.

MOS transistor Qn1 and resistors R3, R
4 forms a source-grounded type voltage amplifying circuit,
The input voltage k · VB divided by R2 is inverted and amplified. After the inverted amplified output is gain-adjusted by the resistors R5 and R6,
The signal is buffer-amplified and output by the operational amplifier 511, and the buffer output voltage is used as the comparison reference voltage Vx.

Here, in a common-source voltage amplification circuit for general use used for an audio amplifier or the like, a complete change rate of an output voltage with respect to an input voltage, that is, a voltage amplification rate is constant at any operating point (bias point). Although the linear characteristic (linearity) is ideal, the characteristic actually obtained is quite different from the ideal characteristic, and exhibits a non-linear characteristic in which the voltage amplification factor greatly changes depending on the operating point.

In the circuit of FIG. 2A, the voltage Vx which is substantially inversely proportional to the input voltage k · VB is approximated as shown in FIG. To be generated.

Next, the operation will be described.

In FIG. 1 and FIG.
The current Idc that can be extracted from the voltage output terminals 71, 71 is limited by the upper limit of the primary current Io of the transformer 63. This upper limit is set by the comparison reference voltage Vx. The comparison reference voltage Vx is changed almost in inverse proportion to the primary-side input voltage VB of the transformer 63. For example, when the primary-side input voltage VB of the transformer 63 increases twice, the comparison reference voltage V
When x decreases to １ ／, and conversely, when VB decreases to １ ／, Vx increases twice.

As a result, even if the input voltage VB applied to the primary side of the transformer 63 changes, the limit value of the primary side current Io changes in a form substantially inversely proportional to the change, and the limit value is generated on the secondary side. The power limit value to be maintained is kept substantially constant. Therefore, while controlling the DC output voltage Vdc obtained from the secondary side via the DC output circuit 7 to a constant target value, the limit value of the current that can be extracted from the DC output terminals 71, ie, the protection set current value Is the primary side voltage V
It can be kept constant regardless of the level of B.

FIG. 3 shows a second embodiment of the voltage stabilizer to which the technique of the present invention is applied. The application example shown in the figure is a switching control type constant voltage power supply device, and its basic configuration is almost the same as that shown in FIG. 1, but the power MOS transistor Qm is turned on / off by the pulse signal Pg.
The pulse drive circuit 2 for driving off and the overcurrent protection circuit 4 for limiting the primary current Io of the transformer 63 are integrated. In other words, both the operation of stabilizing the DC output voltage Vdc to a constant target voltage (Vst) and the operation of limiting the upper limit of the primary current Io are both performed by varying the on / off time ratio (duty) of the power MOS transistor Qm. This is done by control.

In FIG. 1, reference numeral 1 denotes a main circuit unit formed as a semiconductor integrated circuit, and 11 denotes a reference voltage generation circuit for generating a reference voltage Vref in the main circuit unit 1 from an operating power supply voltage Vcc supplied to the main circuit unit 1. , 12 are low voltage detection circuits for forcibly stopping the operation of the main circuit unit 1 when the operation power supply voltage Vcc becomes lower than the minimum operation voltage of the main circuit unit 1.

In the main circuit section 1, reference numeral 201 denotes a pulse oscillation circuit for generating a pulse signal (clock signal) Ps having a constant period, and 202 denotes a DC output voltage Vdc and a target voltage (Vs
t), an error detection amplifier for detecting an error during t), 203 a voltage comparison circuit, 204 an RS (set / reset) flip-flop, 205 a buffer amplifier, and 41 a power M
Reference numeral 52 denotes a variable voltage clamp circuit which converts a primary current Io supplied by the OS transistor Qm into a voltage and detects the voltage.

The error detection amplifier 202 is connected to the DC output circuit 7
And detects and amplifies an error between the DC output voltage Vdc fed back via the photocoupler 21 and the predetermined target set voltage Vst. This detection output voltage is input as a comparison reference voltage Ve to the voltage comparison circuit 203 through a voltage dividing circuit including the resistors R7 and R8.

The voltage comparison circuit 203 includes a current detection circuit 41
Is equal to the comparison reference voltage Ve.
Is detected, and the RS flip-flop 204 is reset with the detection output Pr.

The RS flip-flop 204 is periodically set (S) by a pulse signal Ps having a constant period, and is reset (R) by the detection output Pr of the voltage comparison circuit 203. The set output (Q) of the RS flip-flop 204 is applied to the gate of the power MOS transistor Qm via the buffer amplifier 205.

The variable voltage clamp circuit 52 clamps (limits) the upper limit value of the comparison reference voltage Ve input to the voltage comparison circuit 203 to a predetermined voltage Vx, and converts the clamp voltage Vx to the primary side input voltage VB of the transformer 63. Is changed almost in inverse proportion to.

FIG. 4 shows a configuration example of the voltage clamp circuit 52 and its characteristics.

The voltage clamp circuit 52 shown in FIG.
Is such that, similarly to the variable voltage generating circuit 51 shown in FIG. 2, an inverse proportional characteristic curve is approximately realized by using the non-linear characteristic of the common-source amplifier circuit.
S transistor Qn1, resistors R3 to R6, operational amplifier 5
21 and a MOS transistor Qn2 for current absorption, and realizes variable characteristics as shown in FIG.

FIG. 5 shows an operation waveform chart of a main part of the circuit shown in FIGS. First, FIG. 3A shows that the DC output voltage Vdc is reduced to a predetermined target voltage (Vs
The switching regulator operation for stabilizing control is shown in t).

In FIG. 5A, the power MOS transistor Qm is set / set by the RS flip-flop 204.
ON / OFF by pulse signal Pg generated by reset
The primary current Io is switched off by being driven off. The RS flip-flop 204 is set periodically by a pulse signal Ps having a fixed period,
It is reset each time the detection voltage Vcs of the primary current Io supplied by the transistor Qm reaches the comparison reference voltage Ve.

As described above, the comparison reference voltage Ve is a voltage generated based on the error between the DC output voltage Vdc and the target voltage (Vst).
It decreases when c is lower than the target voltage (Vst), and increases when the opposite is true. As a result, the comparison reference voltage Ve is feedback-controlled to a value that minimizes the error between the DC output voltage Vdc and the target voltage (Vst). Accordingly, the set / reset time ratio of the RS flip-flop 204, that is, the power ON / OFF of MOS transistor Qm
The off-time ratio is also feedback-controlled so that the error is minimized. That is, the on / off time ratio of the power MOS transistor Qm is feedback (negative feedback) so that the DC output voltage Vdc becomes the predetermined target voltage (Vst).
Controlled.

The comparison reference voltage Ve is equal to the DC output voltage V
The feedback operation for maintaining dc at a predetermined target voltage (Vst) increases or decreases according to the state of the load. The upper limit value is set to the clamp voltage of the variable voltage clamp circuit 52 as shown in FIG. Vx. As a result, the peak value of the primary current Io becomes equal to the clamp voltage Vx
Is limited to the upper limit or less. By limiting the upper limit of the primary current Io in this way,
Overcurrent protection is performed to prevent the DC output current Idc from flowing beyond a certain level.

Further, the primary-side input voltage V of the transformer 63
When B increases, the clamp voltage Ve decreases in a manner inversely proportional to the increase in the primary-side input voltage VB, as shown in FIG. It is reduced in inverse proportion to voltage VB. Thus, the limit value of the DC output current Idc can be kept constant irrespective of the change in the primary-side input voltage VB.

As described above, in the present invention, by controlling the primary current (Io) of the transformer (63),
A voltage stabilizing device for stabilizing an output voltage (Vdc) obtained from the secondary side, wherein the primary side current (I
Overcurrent protection for limiting o) so as not to exceed a predetermined upper limit value is performed, and the upper limit value of the primary current (Io) is changed so as to be substantially inversely proportional to the primary input voltage (VB). By providing the variable setting circuits (51, 52), the limit value of the output current (Idc) can be set to the primary side voltage (V
It can be kept constant regardless of the level of B).

The primary current (I) of the transformer (63)
o) A switching control method for performing stabilization control of a DC output voltage (Vdc) obtained from a secondary side of the power element (Qm) via a rectifier circuit by varying an on / off time ratio of a power element (Qm) for switching control of o). In the voltage stabilizing device, the overcurrent protection for limiting the peak value of the primary current (Io) so as not to exceed a predetermined upper limit value is performed, and the upper limit value of the primary current (Io) is set. Of the DC output voltage (Vdc) by the switching control of the primary side current (Io) by providing the variable setting circuits (51, 52) for changing the output voltage in a manner substantially inversely proportional to the primary side input voltage (VB). With the operation, the DC output current (Id
An overcurrent protection operation for keeping the limit value c) constant regardless of the level of the primary voltage (VB) can be performed.

A current detecting circuit (41) for converting the current (Io) of the power element (Qm) for controlling the switching of the primary current (Io) of the transformer (63) into a voltage (Vcs) for detection, A comparison circuit (42) for detecting whether or not the current conversion detection voltage (Vcs) of the circuit (41) exceeds the reference voltage (Vx); and the comparison circuit (42) detects a voltage higher than the reference voltage (Vx). An output limiting circuit (43) that forcibly sets the power element (Qm) to an off state when detected, and a voltage that changes in a form substantially inversely proportional to the primary-side input voltage (VB) of the transformer (63). By providing a variable voltage generation circuit (51) for generating and providing the comparison circuit (42) as a reference voltage (Vx),
The DC output current (Idc) when the power element (Qm) is forcibly set to the off state is changed to the primary side voltage (VB).
It can be kept constant regardless of the height of the vehicle.

A current detection circuit (4) for converting the current (Io) of the power element (Qm) for controlling the switching of the primary current (Io) of the transformer (63) into a voltage and detecting the voltage.
1), a comparison circuit (203) for comparing a current conversion detection voltage (Vcs) of the detection circuit with a reference voltage (Ve), and the power element () based on a comparison output (Pr) of the comparison circuit (203). Switching control means (2) for performing negative feedback control of the on / off time ratio of Qm);
Output feedback means (2) variably controlling the reference voltage (Ve) of the comparison circuit (203) so that the output voltage (Vdc) obtained from the secondary side of (3) becomes a predetermined target value.
1, 202) and this output feedback means (21,
202), the upper limit (Vx) of the reference voltage (Ve) variably controlled by the primary input voltage (V
B), a variable voltage clamp means (52) for changing the voltage in a form substantially inversely proportional to B) allows the DC output voltage (V
Both the operation of stabilizing dc) to a constant target voltage (Vst) and the operation of limiting the upper limit of the primary current (Io) are performed by variable control of the on / off time ratio (duty) of the power MOS transistor Qm. And the DC output current (Id
The limit value of c) can be kept constant regardless of the level of the primary side voltage (VB).

As described above, the invention made by the inventor has been specifically described based on the embodiments. However, the present invention is not limited to the above embodiments, and can be variously modified without departing from the gist thereof. Needless to say. For example, a configuration using a bipolar transistor as the power element is also possible.

In the above description, the case where the invention made by the present inventor is applied to a constant voltage power supply device, which is the application field of the background, has been mainly described. However, the present invention is not limited to this case. The present invention can also be applied to a power circuit that drives a heater or the like at a constant voltage.

[0054]

The effects obtained by typical ones of the inventions disclosed in the present application will be briefly described as follows.

That is, in the voltage stabilizing device for controlling the primary current of the transformer to perform the stabilization control of the output voltage obtained from the secondary side thereof, the limit value of the current that can be taken out from the secondary side Can be maintained constant regardless of the level of the primary side voltage.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing a first embodiment of a voltage stabilizer to which the technique of the present invention is applied;

FIG. 2 is a circuit diagram showing a configuration example of a variable voltage generation circuit used in the device of FIG. 1 and its characteristics;

FIG. 3 is a circuit diagram showing a second embodiment of the voltage stabilizer to which the technique of the present invention is applied;

FIG. 4 is a circuit diagram showing a configuration example and characteristics of a voltage clamp circuit used in the device of FIG. 3;

FIG. 5 is an operation waveform chart of a main part of the circuit shown in FIG. 3;

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 main circuit unit integrated into a semiconductor integrated circuit 11 reference voltage generation circuit 12 low voltage detection circuit 2 pulse drive circuit 201 pulse oscillation circuit 202 error detection amplifier 203 voltage comparison circuit 204 RS (set / reset) flip-flop 205 buffer amplifier 4 Overcurrent protection circuit 41 Current detection circuit 52 Variable voltage clamp circuit 61 AC outlet 62 Full-wave rectifier 63 Transformer 64 Rectifier 7 DC output circuit 71 DC power terminal VB Primary input voltage Io Primary current Qm Power MOS transistor Vdc DC stabilized output Voltage Idc DC output current Ve Comparison reference voltage (error detection voltage) Vcc Operating power supply voltage of main circuit unit 1

──────────────────────────────────────────────────続 き Continued on front page (51) Int.Cl. ⁶ Identification code FI H02M 3/335 H02M 3/335 B

Claims (4)

[Claims] 1. A voltage stabilizing device for controlling a primary current of a transformer to stabilize an output voltage obtained from a secondary side of the transformer, wherein the primary current exceeds a predetermined upper limit. A voltage stabilizing device comprising: a variable setting circuit for performing overcurrent protection for limiting the primary current so as not to be limited and changing the upper limit value of the primary current in a form substantially inversely proportional to the primary input voltage. . 2. A switching device for performing a stabilization control of a DC output voltage obtained from a secondary side of the transformer via a rectifier circuit by varying an on / off time ratio of a power element for switching-controlling a primary current of a transformer. A voltage stabilizing device of a control method, which performs overcurrent protection for limiting a peak value of the primary current so as not to exceed a predetermined upper limit, and sets an upper limit value of the primary current to the primary input. 2. The voltage stabilizing device according to claim 1, further comprising a variable setting circuit that changes the voltage substantially in inverse proportion to the voltage. 3. A current detection circuit for converting a current supplied to a power element for controlling switching of a primary current of a transformer into a voltage and detecting the voltage, and detecting whether a current conversion detection voltage of the detection circuit exceeds a reference voltage. A comparison circuit, an output limiting circuit for forcibly setting the power element to an off state when the comparison circuit detects a voltage equal to or higher than the reference voltage, and an output limiting circuit substantially in inverse proportion to the primary side input voltage of the transformer. 3. The voltage stabilizing device according to claim 1, further comprising: a variable voltage generating circuit that generates a changing voltage and supplies the changing voltage as a reference voltage to the comparing circuit. 4. A current detection circuit for converting an energizing current of a power element for switching-controlling a primary current of a transformer into a voltage and detecting the voltage, a comparison circuit for comparing a current conversion detection voltage of the detection circuit with a reference voltage, Switching control means for performing negative feedback control on the on / off time ratio of the power element based on a comparison output of the comparison circuit; and a switching control means for controlling an output voltage obtained from a secondary side of the transformer to a predetermined target value. Output feedback means for variably controlling the reference voltage of the circuit; and variable voltage clamp means for changing the upper limit of the reference voltage variably controlled by the output feedback means in a manner substantially in inverse proportion to the primary input voltage of the transformer. The voltage stabilizing device according to any one of claims 1 to 3, wherein: