JPS631030B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a self-oscillation type converter device.

The conventional converter device, as shown in Figure 1,
When the switching transistor Ts connected to the primary winding Np becomes conductive (turned on), its collector current Ic increases linearly. Note that if the transformer T is a step-up type and the leakage inductance and stray capacitance cannot be ignored, the voltage increases oscillatingly. Therefore, when the input voltage Vin is applied to the primary winding Np of the transformer T, a voltage proportional to the turns ratio is generated in the base winding N _B , and this voltage becomes the base voltage V _BE . The transistor Ts then continues to conduct. Then, when the collector current Ic reaches the maximum collector current Icpk= _hFE・_IB determined by the base current I and the current amplification factor _hFE of the transistor Ts, the rate of increase in the collector current Ic decreases, A back electromotive voltage is generated in the transformer T. Furthermore, the transistor Ts
The base of is reverse biased, the base current I _B becomes zero, and the transistor Ts becomes blocked (off).
At that moment, the diode D1 connected to the secondary winding Ns starts conducting, and the energy stored in the transformer T is supplied to the capacitor C1 and the load R _L.
Here, since the maximum collector current Icpk is determined by the base current I _B , the output voltage Vo
and the reference voltage Vr are compared by comparator 1, and the deviation is
The auxiliary transistor _TR for changing the equivalent base resistance according to Er is controlled by the feedback circuit 2, thereby stabilizing the output voltage Vo. However, such conventional converter devices have the disadvantage that the instantaneous loss when the transistor Ts becomes blocked is large, reducing the efficiency of the entire circuit. Furthermore, low efficiency and large heat loss lead to a decrease in reliability and are a major hindrance to miniaturization of the device. Then,
An object of the present invention is to provide a self-oscillating converter device that does not have the above-mentioned drawbacks.

This invention will be explained below.

FIG. 2 shows an embodiment of the present invention corresponding to FIG. 1, in which an input power supply Vin is converted into a stable output voltage Vo and output current Io.
Therefore, the transformer T has a primary winding Np and a secondary winding Ns.
and a base winding N _B , one end of the primary winding Np is connected to the input power supply Vin (+), and the other end is connected to the collector of the switching transistor Ts. Furthermore, the emitter of the transistor Ts is connected to the input power supply Vin (-), and the base winding N _B is increased by the increase in the primary current flowing through the primary winding Np when the transistor Ts is turned on. It is connected to the base of the transistor Ts via a current limiting resistor R1 so as to obtain positive feedback that increases the current. Furthermore, diode D1
and capacitor C1 form a rectifying and smoothing circuit, and when the transistor Ts transitions from the conductive state to the blocking state, the energy stored in the transformer T is generated as a reverse voltage in the secondary winding Ns, but the diode D1 absorbs this current. Connected to such a polarity that it conducts.

On the other hand, the collector of the shunt transistor _TN is connected to the base of the transistor Ts, the emitter is connected to the input power supply Vin(-), and the base is connected to the feedback circuit 10. Also,
An output voltage detection circuit 20 for detecting an output voltage Vo and an output current detection circuit 21 for detecting an output current Io are connected to the secondary winding Ns, and a comparator 22 is connected to the secondary winding Ns. The deviation Er is input to the feedback circuit 10. Therefore, the feedback circuit 10
As shown in the figure, a triangular wave generation circuit 11 that generates a triangular wave Rs synchronized with the oscillation frequency of the converter;
A comparator 1 that compares the deviation Er from the comparator 22 and the triangular wave Rs in terms of levels and outputs a control pulse Cs.
2, and an amplifier 1 which widens the control pulse Cs from this comparator 12 and sends it to the base of the transistor _TN .
3, and the base of the transistor Ts is momentarily grounded by the control pulse Css.

As described above, in this invention, the shunting transistor T _N is connected in parallel between the base and emitter of the switching transistor Ts, and the control pulse Css is applied to the base of the transistor T _N to control the switching transistor Ts. Since the base is momentarily grounded, the transistor
This makes it possible to eliminate the loss at the time when Ts transitions from conduction to blocking state.

By the way _, a specific configuration example of the triangular wave generation circuit 11 is as shown in FIG _. In addition to the base of the transistor T2 via the resistor R5, the collector output of the transistor T2 is applied to the base of the transistor T1. On the other hand, the input power
A current limiting resistor R2 and a constant voltage diode Z1 are connected in parallel to Vin, and a constant voltage diode Z
1, a resistor R3 and a capacitor C2 are connected in parallel. Therefore, resistor R3 and capacitor C
The collector of transistor T1 is connected to the connection point with 2, and the triangular wave Rs is generated only when the voltage of the base winding N _B is positive, that is, during the period when the transistor Ts is conductive.
is starting to occur. Transistor T1
When conductive, the connection point between resistor R3 and capacitor C2 is grounded and becomes zero potential, and transistor T1
When is blocked, capacitor C2 starts charging with the time constant of R3 and C2. Here, an example of this operation is shown in time charts as shown in FIGS. 5A to 5E. That is, FIG. 5A shows the collector-emitter voltage V _CE of the transistor Ts, and the output voltage of the base winding N _B at this time has a waveform as shown in FIG. 5B. Since only a positive pulse is applied to the base of the transistor T2 by the diode D2, the base-emitter voltage V _BE is as shown in Figure 5C, and the base-emitter voltage V _BE of the transistor T1 is The opposite is true, as shown in figure D, and thus the collector-emitter voltage V _CE of transistor T1, that is, the charging voltage of capacitor C2, becomes a triangular wave R5 as shown in figure E.

The triangular wave Rs obtained in this way from the triangular wave generating circuit 11 has a function as a measuring circuit for detecting the conduction point of the transistor Ts, and the comparator 1
2 and is compared with the deviation Er from the comparator 22. In other words, as shown in Figure 6, the triangular wave
Time t1, t2 when Rs reaches the level of deviation Er from comparator 22 and voltage V1, V of deviation Er at that time
Therefore, if the deviation Er of the comparator 22 is lowered when the output voltage Vo or output voltage Io increases, the load
Output to R _L can be stably controlled.
However, in the case of a ringing choke converter, the energy stored in the coil during the conduction period of the switching transistor is supplied to the load from the secondary winding when the switching transistor is blocked, so switching is necessary to control the output power. What is necessary is to control the conduction period of the transistor. Furthermore, since the feedback circuit 10 of the present invention is synchronized with the oscillation frequency of the self-excited oscillation type converter, even if the inverter transformer is used for high voltage generation, which is a problem in the case of a separately excited oscillation type converter, leakage inductance and stray Disorders that occur due to the influence of capacitance are less likely to occur.

Based on the above premise, the operation of the apparatus shown in FIG. 2 will be explained with reference to FIGS. 7A to 7G.

When the output current Io or the output voltage Vo gradually decreases as shown in FIG. 7A, the deviation Er from the reference voltage Vr from the comparator 22 gradually increases as shown in FIG. 7B. Therefore, the comparator 12 is the comparator 22
The deviation Er from the triangle wave generation circuit 11 is compared in level with the triangular wave Rs from the triangular wave generating circuit 11 (see Fig. 7C), and when the triangular wave Rs becomes larger than the level of the deviation Er, the control pulse Cs as shown in Fig. 7D is generated. Output
It is applied to the base of transistor T _N via amplifier 13 to drive transistor T _S. However,
The control pulse Cs generation interval t1, t2 is the output current
It changes in relation to the magnitude of Io (or output voltage Vo), and when this control pulse Cs is applied, the transistor _T
The base of Ts is grounded (Fig. 7 E, F). Here, the collector current Ic of the transistor Ts increases during its conduction period as shown in FIG. 7G, and is stopped and becomes zero when the base is grounded by the control pulse Cs. Also, the energy stored in the coil inductance L _P is expressed as 1/2 · Lp · Icpk ² if the maximum collector current is Icpk, so if the collector current Ic is made zero at an appropriate position, the desired energy ( output power). Note that this embodiment uses a constant current circuit and a constant voltage circuit, so when the output decreases, it is necessary to increase it, and the maximum collector current Icpk also increases.

Next, the operation of the present invention will be explained in comparison with a conventional device.

In the control method of the conventional circuit shown in Figure 1, as mentioned above, the output voltage detected on the output side is used as the reference voltage.
It is compared with Vr, and the fluctuation of the difference Er is converted into an inverted signal by the feedback circuit 2 to control the transistor _TR . However, since the transistor _TR is connected in series to the base of the transistor Ts, the control of the transistor _TR is controlled by the transistor Ts.
By controlling the base current _IB of the transistor Ts, it is possible to control the collector current Ic of the transistor Ts and stabilize the output voltage Vo. The operation of the transistor Ts in this case is continuous, and its operating point is shown in FIG. 8, and the collector-emitter voltage Vc _E and collector current Ic of the transistor Ts at this time are shown in FIG. It will look like B. In other words, the operating point at which the transistor Ts conducts moves from O to P, and if the current amplification factor of the base current I _B is h _FE , the collector current Ic becomes h _FE・I _B
It continues to rise until it reaches point P. Since the rate of increase of current Ic decreases at point P, this decreasing effect generates a back electromotive force in the primary winding N _P , causing a rapid switch-off. At this time, the operating point quickly moves from P to Q. Also, the collector-emitter voltage
Vc _E increases, and in return the voltage across the primary winding Np decreases, causing the base current I _B to decrease. As a result, the collector current Ic decreases, the voltage across the base winding N _B induced by the collector current Ic is reversed, and the transistor Ts is blocked. During the time when the operating point is at point Q, the inductance of the coil sends the stored energy to the output side, and when this ends, it returns to point O along the Ic _B o curve and the transistor becomes conductive again.
The operating point continues to move in the direction of the arrow in FIG. 8 through such repeated operations.

For this reason, in the device shown in Fig. 1, it is necessary to use the decreasing characteristic of the rate of increase of the current before point P as the operating point, so that the voltage Vc _EOFF at point P increases and it is impossible to reduce it. I couldn't do it. Also, at this P point, the collector current Ic is the maximum value (Icpk)
Since the product of the voltage Vc _EOFF and the current Icpk is the maximum loss of the transistor Ts, Fig. 9 A and B
There was a strong desire to make the shaded area as small as possible.

In contrast, in the device of the present invention shown in FIG. 2, the voltage detected by the output voltage detection circuit 20 and output current detection circuit 21 provided on the output side (the current is converted to voltage) is compared with the reference voltage Vr. Then, the fluctuation of the difference Er is converted into a pulse signal by the feedback circuit 10,
This pulse signal Css is applied to the base of a transistor _TN connected in parallel to the base of the transistor Ts. However, the transistor
T _N is made conductive when the control pulse Css is supplied, thereby blocking the transistor Ts. If this operating point is illustrated, it is the 10th point.
As shown in the figure, the collector-emitter voltage Vc _E and collector current Ic of the transistor Ts at this time
is as shown in FIG. 11A and B. In other words, when the transistor Ts conducts, its operating point moves from O to P on the Ic-Vc _E curve, and the base current I _B is set so that the desired maximum current Ic is obtained.
The collector current Ic increases according to the saturation voltage characteristic when the transistor Ts is turned on, with its base current Ib as a parameter. At the same time as the desired point P is reached, a control pulse Css is input to the transistor _TR , causing the transistor T _N to conduct, thereby grounding the base of the transistor Ts. In this way, the base current I _B that had previously flowed from the base winding N _B to the base of the transistor Ts becomes zero, so
Transistor Ts is blocked. At this time, the operating point moves quickly from P→R→Q, and while the operating point is at point Q, the inductance of the coil sends out the stored energy to the output side, and when this ends, it returns to point O along the Ic _BO curve. Returning to , transistor Ts becomes conductive again,
Repeat the following operations. From the above, in the converter device of the present invention, even if the operating point reaches the desired point P, the rate of increase of the current Ic is on a straight line, so the voltage Vc _EOFF is as shown in the shaded area in FIG. (See FIG. 9A) It is much smaller than that. Thus, even if the collector current Ic is at its maximum value Icpk, the voltage
Since _VcEOFF is small, the loss is small, which reduces heat generation and increases efficiency.

Here, a specific example of the configuration of the converter device shown in FIG. 2 is shown in FIG. 12, in which 23 and 24 are comparison amplifiers;
5 is an amplifier.

Note that it is also possible to use a feedback circuit 30 as shown in FIG. 13 instead of the feedback circuit 10 described above. That is, in this example, a triangular wave Rp whose slope changes in accordance with a change in the deviation Er from the comparator 22 is used.
is generated by the triangular wave generation circuit 31 only during the conduction period of the transistor Ts, and the triangular wave Rp is inputted to the level detection circuit 32 to obtain the same control pulse Cs as described above at a predetermined level.
Here, a specific example of the configuration of the triangular wave generation circuit 31 and the level detection circuit 32 is shown in FIG. 14, and the operation thereof will be explained with reference to the time charts of FIGS. 15A to 15G.

The induced electromotive force (Fig. 15B) in the base winding N _B by the primary winding Np is half-wave rectified by the diode D2,
In addition to the base of transistor T2 via resistor R5 (FIG. 15C), the collector output of transistor T2 is applied to the base of transistor T1 (FIG. 15D). On the other hand, a resistor R2 and a constant voltage diode Z1 are connected to the input power supply Vin, and a transistor T3, a resistor R9, and a capacitor C2 are connected in parallel to the constant voltage diode Z1. In addition, a transistor T1 is connected in parallel to the capacitor C2.
is connected, and as shown in FIG. 15E, the collector voltage V _E of this transistor T1 is equal to the equivalent resistance value of the transistor T3 and resistor R9 plus the capacitor C2 during the conduction period of the transistor Ts (0 period in FIG. 15A). The triangular wave rises with a time constant based on
Rp is output. However, transistor T3
Since the deviation Er from the comparator 22 is input to the base of , the slope of the triangular wave Rp changes as the equivalent resistance of the transistor T3 changes. Thus, the obtained triangular wave Rp (transistor T1
Vc _E ) is diode D2 and voltage regulator diode Z
2 is input to the level detection circuit 32 consisting of
Get Cs. The interval between such control pulses Cs changes according to the deviation Er of the comparator 22, and this pulse interval controls the conduction time of the transistor Ts.

Here, a specific example of the configuration of a converter device using the feedback circuit 30 shown in FIGS. 13 and 14 is shown in FIG. 16. In FIG. 16, 34 is a comparison amplifier, and 35 is an amplifier.

Although the present invention has been variously explained above with reference to preferred embodiments, the present invention is not limited to these embodiments, and it goes without saying that many modifications can be made without departing from the spirit of the invention. That's true.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram showing an example of a conventional converter device, Fig. 2 is a circuit diagram showing an embodiment of the present invention, Fig. 3 is a block diagram showing a part of the converter in detail, and Fig. 4 is a circuit diagram showing an example of a conventional converter device. FIG. 3 is a circuit diagram showing a specific example of the triangular wave generation circuit, FIGS. 5A to 5E are time charts showing an example of its operation, FIG. 〜G is a time chart showing the operation example of FIG. 2, FIG. 8 is a diagram showing the operating point of the device of FIG. 1, and FIGS. 9A and B are the collector-emitter voltage Vc _E and collector current.
Ic waveform diagram, Figure 10 is a diagram showing the operating point of the device in Figure 2, and Figures 11A and B are the collector and
Waveform diagram of emitter voltage Vc _E and collector current Ic,
12 is a circuit diagram showing a specific example of the configuration shown in FIG. 2, FIG. 13 is a block diagram showing another example of the feedback circuit used in the present invention, and FIG. 14 is a specific example of the triangular wave generating circuit shown in FIG. 13. The circuit diagram shown in Fig. 15A~
G is a time chart showing an example of its operation, and FIG. 16 is a circuit diagram showing a specific configuration example of a converter device using the feedback circuit of FIG. 13. 1... Comparator, 2... Feedback circuit, 10... Feedback circuit, 11... Triangle wave generation circuit, 12... Comparator, 13... Amplifier, 20... Output voltage detection circuit, 21... Output current detection Circuit, 22...Comparator, 23, 24...Comparison amplifier, 25...Amplifier, 30...Feedback circuit, 31...Triangle wave generation circuit, 32...Level detection circuit, 33...Amplifier.

Claims (1)

[Claims] 1. A switching transistor connected to the primary winding of the converter, a shunt transistor connected to the base of the switching transistor, and a triangular wave synchronized with the oscillation frequency of the converter. A triangular wave generation circuit that generates a triangular wave, a comparison detection circuit that detects the output current or output voltage of the converter and outputs a deviation signal from a reference voltage, and a comparison circuit that compares the levels of the triangular wave and the deviation signal and outputs a control pulse. 1. A self-oscillation type converter comprising: a circuit for controlling on/off of said shunt transistor by said control pulse to reduce loss when said switching transistor is blocked. 2. A switching transistor connected to the primary winding of the converter, a shunt transistor connected to the base of this switching transistor, and a shunt transistor connected to the base of the switching transistor, detecting the output current or output voltage of the converter and comparing it with the reference voltage. a comparison detection circuit that outputs a deviation signal; a triangular wave generation circuit that generates a triangular wave synchronized with the oscillation frequency of the converter with a slope corresponding to the deviation signal; and a level that cuts the triangular wave at a predetermined level and outputs a control pulse. A self-oscillation type converter device comprising: a detection circuit, the shunt transistor is controlled on and off by the control pulse to reduce loss when the switching transistor is blocked.