JPH0644313Y2 - Ringing choke converter - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial field of application> The present invention relates to a ringing choke converter which is a kind of switching power supply device, and more particularly to improvement of controllability when a plurality of main transistors are operated in parallel.

<Prior Art> A ringing choke converter is disclosed, for example, in Japanese Utility Model Application Laid-Open No. 62-117,788 proposed by the present applicant. FIG. 3 is a circuit diagram of a conventional device. In the figure, a DC voltage Vin is applied to the primary winding n1, and the main transistor Q1
Switching signal is generated by turning it on and off. Then, since a switching signal is induced in the secondary winding n2,
DC output voltage Vout is supplied to the load after being rectified by diode D2 and smoothed by capacitor C2. The reset circuit is connected in parallel with the primary winding n1 and includes a capacitor C1 and a resistor.
It is composed of R1 and diode D1, and resets the energy stored in the primary winding n1 accompanying switching.

Since the switching signal of the primary winding n1 is induced in the feedback winding n3, this is rectified by the diode D3, applied to the base terminal of the main transistor Q1, and the on / off duty ratio is adjusted by the control transistor Q3. . The starting resistor Rg is inserted between the primary winding n1 and the base terminal of the main transistor Q1, and supplies the energy required for starting switching.

The voltage detection winding n4 indirectly detects the voltage Vout output from the secondary winding n2 by using the switching signal of the primary winding n1, and the output voltage detection signal is rectified and smoothed by the diode D4 and the capacitor C4. Is getting The output voltage detection circuit controls the control transistor Q3, and uses, for example, a Zener diode to detect the output voltage detection signal and the reference voltage Vr.
ef is compared and a control signal is supplied in the direction in which the error is reduced to stabilize the output voltage Vout. The voltage detection winding n4 is provided, for example, in Japanese Patent Application Laid-Open No. 61-351 proposed by the present applicant.
This is to reduce the dependency of the output voltage Vout on the load current Iout, as disclosed in Japanese Patent Laid-Open No. 63.

The main transistor Q1 has a sense resistor R on the emitter terminal side.
_When the output current Iout is excessive, the overcurrent control circuit is based on the potential V _s1 generated in the sense resistor R _s1.
OLP operates and stops switching operation.

FIG. 4 is a circuit diagram of a device in which a plurality of main transistors are connected in parallel. If the load current Iout is increased, the current capacity of the single main transistor may be insufficient, so multiple capacitors are connected in parallel. In FIG. 4 below,
Components having the same functions as those in FIG. The cathodes of the primary windings n1 are connected to the collector terminals of the main transistors Q1 and Q2, respectively. The feedback winding n3, the control transistor Q3, and the starting resistor Rg are commonly connected to the base terminal, and the corresponding overvoltage control circuit OVP is also connected. Sense resistors R _s1 , R _s2 are connected to the emitter terminal side, and when the output current Iout is excessive, the potential V _s1 , V s generated in the sense resistors R _s1 , R _s2.
The overcurrent control circuit OLP operates based on _s2 to stop the switching operation.

The cathode side of the voltage detection winding n4 is connected to the emitter terminal of the main transistor Q2 via the diode D4 and is grounded via the sense resistor R _s2 . Through the sense resistor R _s2 is the shift current (I _sft ) from the voltage sensing winding n4.
This is for more reliably stabilizing the output voltage Vout by supplying. The reason for not connecting to the main transistor Q1 is that the ON resistance of the transistors varies, so that the current flows through the side with the lower ON resistance among the transistors connected in parallel. This is because the temperature rises when a current flows and the temperature coefficient of the on-resistance of the transistor is negative, so the on-resistance further decreases and the current flows exclusively to one of the main transistors. In addition, the switching element is MO
When using SFET, the temperature coefficient of on-resistance is positive,
Can be connected in parallel as it is.

<Problems to be Solved by the Invention> However, in the conventional device, the main transistors Q1 and Q2 cannot be connected in parallel completely for the above reason, and the wiring for controlling the output voltage is integrated in one main transistor Q2. Therefore, a difference occurs between the base-emitter voltage V _BE of the main transistors Q1 and Q2, and the collector currents I _c1 and I _c2 of the main transistor Q1 are larger than that of the main transistor Q1, causing imbalance. However, the sense resistor that detects the overcurrent
The electric potentials V _s1 and V _s2 generated in R _s1 and R _s2 are equal as in the following equation.

V _s1 = R _s1 · I _c1 = V _s2 = R _s2 · (I _c2 + I _sft ) (1) Then, the main transistor Q2 is the main transistor Q1
Entering the overcurrent protection state with the collector current I _c2 being smaller than that in. In this way, when a large amount of output current is drawn, the main transistor Q1 side is always burdened, which may have an unfavorable influence on reliability and the like.

The present invention solves such a problem, and a ringing choke that shifts to the overcurrent protection state with the collector current sufficiently drawn while keeping the overcurrent protection circuit of the main transistors Q1 and Q2 in parallel in common. The purpose is to provide a converter.

<Means for Solving the Problems> FIG. 1 is a block diagram of the configuration of the present invention for achieving the above object. In the figure, as in a general ringing choke converter, a primary winding (n1) to which a DC voltage is applied,
Input terminals are connected in parallel to the primary winding and first and second switching elements (Q1, Q
2), a secondary side circuit that rectifies and smoothes the switching signal induced in the secondary winding (n2) and outputs a DC voltage, one end of which is connected to the control terminal of the switching element via the rectification circuit, It is provided with an output voltage detecting means to which a switching signal induced by the winding is input.

First and second sense resistors respectively connected to the output terminals of the switching elements for the purpose of preventing overcurrent,
When the voltage generated in the sense resistor is excessive, first and second overcurrent protection circuits (OLP) that send a control signal for suppressing the ON state to the control terminal of the switching element are provided.

For the purpose of preventing overvoltage, a switching signal induced by the primary winding is input, the control signal is sent to the control terminals of the first and second switching elements in a direction that matches a predetermined reference voltage, and the second signal is transmitted. It is provided with an output voltage stabilizing means for supplying a shift current (I _sft ) to the sense resistor of.

And, in order to extract the maximum load current among the plurality of switching elements, trim voltage generating means for correcting the voltage input to the first or second overcurrent prevention circuit is provided, and the trim voltage is the first voltage. With respect to the current flowing between the input and output terminals of the second switching element, the currents that operate the first and second overcurrent prevention circuits are set to be equal values.

<Operation> Each component of the present invention has the following operation. The primary winding, the secondary winding, and the output voltage detecting means are main windings constituting the ringing choke converter. Here, a plurality of main transistors are provided to increase the load current Iout. The output voltage stabilizing means sends a control signal to the control terminal of the main transistor so that the output voltage is maintained at a predetermined voltage, and a shift current is supplied to the sense resistor to further increase the stability. Since the shift current is supplied only to the sense resistor of one of the main transistors, the operating point of the overcurrent protection circuit is deviated. Therefore, the trim voltage generating circuit corrects this deviation so that the overcurrent preventing circuit operates when both main transistors have the same load current.

<Example> The present invention will be described below with reference to the drawings.

FIG. 2 is a circuit diagram showing an embodiment of the present invention. The second
In the figure, the elements having the same functions as those in FIG. 3 and FIG. In the figure, as the DC input voltage source Vin, a circuit that rectifies a commercial AC power supply AC by a diode bridge DB and smoothes it by a capacitor C0 is used. The triac TA is inserted between the diode bridge DB and the feedback winding n3, and is controlled by the voltage of the voltage detection winding n4 to prevent the generation of inrush current when the power is turned on.

The first overcurrent protection circuit is a transistor Q11, which has an input / output terminal (referred to as a collector terminal and an emitter terminal) connected to the main transistor Q1 and a primary side common, and a control terminal (referred to as a base terminal). It is connected to the feedback winding n3 via the resistor R11, to the primary side common via the resistor R12, and to the sense resistor R _s1 via the resistor R13. The second overcurrent protection circuit is the transistor Q12, the input / output terminal of which is connected to the main transistor Q2 and the primary side common, and the control terminal of which is the feedback winding n3 via the resistor R21.
Further, it is connected to the primary side common via the resistor R22 and to the sense resistor R _s2 via the resistor R23.

The output voltage stabilizing means is the voltage detection winding n4 and the diode.
D4, a capacitor C4, an output voltage control circuit and a control transistor Q3. In addition, diode D4 and sense resistor R
The main transistor Q2 of _s2 is connected to the emitter terminal side of the main transistor Q2 and supplies the shift current I _sft to the sense resistor R _s2 .

Here, the trim voltage generating means is the trim resistor R _trim and the voltage detection winding n4, one end of the trim resistor R _trim is connected to the transistor Q12 side of the resistor R23, and the other end is connected to the anode side of the voltage detection winding n4. ing. The value of the trim resistor R _trim is commensurate with the shift current I _sft supplied to the sense resistor R _s2 , and the collector currents I _c1 and I _{c2 of} the transistors Q11 and Q12 are set to be equal. .

The operation of the apparatus thus configured will be described below. The ringing choke converter starts operating and the load current Io
ut is supplied. Then, the collector currents I _c1 and I _{c2 of the} main transistors Q1 and Q2 increase. At this time, since the following equation is established, the collector current I _c1 is larger than the collector current I _c2 (I _c1 > I _c2 ).

V _BE2 = V _BE1 + I _sft · R _s2 (2) Then, the potentials V _s1 and V _{s2 of the} sense resistors R _s1 and R _s2 increase. Here, the resistance values of the sense resistors R _s1 and R _s2 are equal.
When the potentials V _s1 and V _s2 reach the potential set by the overcurrent protection circuit, the transistors Q11 and Q12 turn to the main transistors Q1 and Q2.
Absorbs the base current of and turns off the main transistors Q1 and Q2. Trim resistor R on the base terminal of transistor Q12
_{Since the trim} is connected, the operating potential V _s2 of the transistor Q12 is made lower than in the conventional case, so that the main transistor Q1 can be prevented from precedingly entering the overcurrent protection operation. However, when the main transistor Q2 reaches the set current, the main transistor Q1 can be synchronized to start the overcurrent prevention operation.

Although the trim voltage generating means is provided on the main transistor Q2 side in the above embodiment, the present invention is not limited to this, and it is provided on the main transistor Q1 side to start the overcurrent prevention operation of the main transistor Q1. The potential may be increased by an amount commensurate with the shift current.

Further, although the output voltage is detected by using the feedback winding n3 in the above embodiment, it may be detected by other means such as a photocoupler.

<Effect of Device> As described above, according to the present invention, the imbalance between the two main transistors caused by the shift current is canceled by the trim voltage generating means, so that each of the two main transistors has a sufficient capacity. Collector current can be subtracted,
There is a practical effect in that only one of the main transistors will not be overloaded near the overcurrent region.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram illustrating the outline of the present invention, and FIG.
FIG. 3 is a circuit diagram showing an embodiment of the present invention, and FIGS. 3 and 4 are circuit diagrams of a conventional device. Q1, Q2 …… Main transistor, Q3 …… Justice transistor, OLP …… Overcurrent prevention circuit, R _trim …… Trim resistor.

Claims (1)

[Scope of utility model registration request] 1. A primary winding (n1) to which a DC voltage is applied, first and second switching elements (Q1, Q1) having input terminals connected in parallel to the primary winding to generate a switching signal.
2), a secondary side circuit that rectifies and smoothes the switching signal induced in the secondary winding (n2) and outputs a DC voltage, one end of which is connected to the control terminal of the switching element via the rectifier circuit Output voltage detection means to which a switching signal induced by the winding is input, first and second sense resistors respectively connected to the output terminals of the switching element, and when the voltage generated in the sense resistor is excessive. , 1st and 2nd overcurrent prevention circuit (OLP) which sends the control signal which suppresses the ON state to the control terminal of the switching element, inputs the switching signal induced by the primary winding, and matches the predetermined reference voltage Output voltage stabilization that sends a control signal to the control terminals of the first and second switching elements in the direction to turn on and supplies a shift current (I _sft ) to the second sense resistor. Means and trim voltage generating means for correcting the voltage input to the first or second overcurrent prevention circuit, wherein the trim voltage is a current flowing between the input and output terminals of the first and second switching elements. With respect to, the ringing choke converter is characterized in that the operating currents of the first and second overcurrent protection circuits are equal.