JPS6295968A - Switching control type power source circuit - Google Patents

Abstract

PURPOSE:To exactly turn a control transistor ON within a specified period, by detecting the fluctuation of DC voltage obtainable from the detecting winding of a converter transformer, with a detecting transistor. CONSTITUTION:In a power source circuit in self-exciting system with blocking oscillation, the input winding N1 of a converter transformer 3, a switching transistor (hereinafter, Tr)Q1, and a current detecting resistance R2 are connected in series to unstable DC voltage, and the TrQ1 is driven by a feedback winding N3 to take DC output voltage V0 via an output winding N2, a diode D3, and the like. Then, a capacitor C6 for bias is connected between the base and emitter of a control TrQ2, and the base of a detecting TrQ3 is connected to the voltage dividing resistance connected point C of a capacitor C2. Besides, to the collector of the control TrQ2, a capacitor C3 charged with the feedback winding N3 and its charging diode D3 are connected via a current limit resistance R4. Then, the fluctuation of DC voltage is exactly detected by the TrQ3, and according to the fluctuation, the control TrQ2 is exactly turned ON.

Description

DETAILED DESCRIPTION OF THE INVENTION A) Field of Industrial Application The present invention relates to an automatic switching control type power supply circuit used as a power supply for television receivers and the like.

(b) Conventional technology switching control type power supply circuits are classified into various types.
One such example is a self-excited type using blocking oscillation, as disclosed in Japanese Utility Model Application Publication No. 59-155884. Figure 3 shows an example of this, and this power supply circuit operates between the input winding (N1) of the converter transformer (3) and the switching transistor (Ql) in response to the unstable DC voltage supplied between terminals m (2j). Current detection resistor (R
2) in this order 1: The feedback winding of the transformer (3) is connected in series and one end is grounded via a positive feedback current limiting circuit consisting of a capacitor (CI), a diode (Dl), and a resistor (R3). The other end of the line (N5) is connected to the base of the switching transistor (Ql).

This constitutes a blocking oscillation circuit.

In addition, a detection winding (N4) is provided continuously with the feedback winding (N3) [the second is a capacitor (02) and its charging diode (D2) are connected in series, and the midpoint between these two connections ( A control transistor (Ql) is connected between Al and the grounding point via a current limiting resistor (R4), and
A Zener diode (D4) is connected between the base of this transistor (Ql) and the point A. A DC output voltage (vO) is taken out from the output winding (N2) of the transformer (3) by a diode (D3) and a capacitor (O5).

That is, in the power supply circuit shown in FIG. 3, when the switching transistor (Ql) is turned on by the propking oscillation operation, a current 1 flows.

Therefore, in this ON period, the potential of the above-mentioned 7 people at point A is:
The voltage VR generated in the resistor (R2) by the above-mentioned current IiC and the rising voltage v!!!+ between the base and emitter of the switching transistor (Q+).

During the previous OFF period of the switching transistor (Ql), the voltage C of the detection winding (N4) becomes the sum of the voltage Vt of the capacitor (C2) charged to the polarity shown. Then, this potential Vm increases as the electric current 1 increases,
When the sum of the Zener voltage VZ of the Zener diode (D4) and VBM2 of the control transistor (Ql) is exceeded, the control transistor (Ql) is turned on. Then, using the voltage yt of the capacitor (02) as a power source, the switching transistor (Q 1 ) (-reverse bias current 7.yBt flows through the illustrated path, thereby turning off this switching transistor (Ql) and turning on the transistor. The period C: ends.Here, when the above-mentioned DC output voltage (vO) rises above the set value,
Since the output winding (N2) and the detection winding (N4) are closely coupled, the voltage yt across the capacitor (Ct2) also increases.

Therefore, the turn-on timing of the control transistor (Ql) becomes earlier and the switching transistor (Ql)
The on-period of the output voltage (vO) is shortened, and the increase in the output voltage (vO) is suppressed and stabilized. The above output voltage (vO
) decreases to 9, the same is true.

Here, a diode (D6) and a resistor (R6) connected between the emitter of the switching transistor (Ql) and the base of the control transistor (Ql) are connected during the transient period immediately after turning on the power switch (SW) and the output line. (Lo) (
This is to limit the current 1 flowing through the switching transistor (Ql) from becoming excessive when two connected loads are short-circuited. That is, the current ri
Therefore, the voltage VR generated across the resistor (R2) is the same as that of the control transistor (Ql) and the upper diode (
C: when the sum of the rising voltages VD of D6) is exceeded.

The control transistor (Ql) turns on and supplies the aforementioned reverse bias current t, turning off the switching transistor (Ql).

Note that when the switching transistor (Ql) is turned on after a certain off period has passed, the output winding (N2) is turned on when the flowing current f becomes approximately zero, and the input winding (N1) is turned on.
This operation is performed by resonance operation due to inductance and distributed capacitance, and this operation is the same as the blocking oscillation operation of conventional M.

Also, the resistor (R1) is turned on when the power switch (SW) is turned on!
- It is for starting to supply base current to the switching transistor (Ql).

(c) Problems to be Solved by the Invention Now, in the circuit of FIG. 3, since the resistor (R2) is provided for the above-mentioned overcurrent protection, the control transistor (Q
l) is on, yz-t-yB l 2==V
'C-)-VB m 1 +VR and VBK2=v
You can think of it as B1i1, so in the end, 't7't+vR
=yz. That is, the control transistor (Ql
The on-period length of the switching transistor (Ql) is controlled by the turn-on operation of the transistor (Ql), and the current generator 1 that generates the voltage VR changes depending on input voltage, load fluctuations, and the like. Therefore, the DC output voltage (
The voltage yt proportional to vO) cannot be detected accurately (2);
Therefore, there was a problem that the stability of the output voltage (vO) was poor.

One object of the present invention is to accurately detect the voltage obtained from the detection winding of the converter transformer in a blocking oscillation type switching control power supply circuit equipped with a control transistor for turn-off control of the switching transistor. The purpose is to stabilize the output voltage with high precision.

B)) Means for Solving the Problems The present invention provides a blocking oscillation type switching control power supply circuit including a control transistor as described above.
A bias capacitor is connected between the base and emitter of the control transistor, and a detection transistor is provided in which the DC voltage obtained from the detection winding of the converter transformer is applied between the emitter and the base via a constant voltage diode for reference voltage. The collector of this detection transistor was connected to the base of the control transistor so that the control transistor was turned on when the bias capacitor was charged to a predetermined level.

According to the above configuration, fluctuations in the DC voltage obtained from the detection winding of the converter transformer are accurately detected by the detection transistor (2), and the on-period of the switching transistor is changed according to the detected voltage to control the control transistor. It can be turned on reliably at the timing within.

(F) Example Hereinafter, an example of the present invention shown in FIG. 1 will be described. In this embodiment, the parts with the same numbers as those in the conventional circuit of FIG. 3 are the same, but instead of these points, this embodiment is characterized by the following points.

That is, it connects a bias capacitor (C6) between the base and emitter of the control transistor (C2), and connects the two ends of the capacitor (C2) (Al , its connection midpoint (C1
A Zener diode for reference voltage (
D7) and the emitter-base of the detection transistor (C5) are connected in series, and the collector of the detection transistor (C3) is connected to the base of the control transistor (C2).

In addition, in this embodiment, a switching transistor (Q
This capacitor (C
3) and its charging diode (D5) as shown in the figure, and by connecting the collector of the control transistor (C2) via the connection midpoint (OIC current limiting resistor (R4)), the capacitor ( (Separately provided with capacitor (C2) for exclusive use of 351 turn-off.

In such an embodiment, a switching transistor (Ql
), a current Xi (see FIG. 2) flows, the voltage 'VR (see FIG. 2) across the resistor (R2) increases, and the emitter potential of the control transistor (C2) rises. At this time, the capacitor (C4) is almost discharged, and the voltage VC across this capacitor is extremely small. Therefore, the control transistor (C2) is reverse biased between its base and emitter and is turned off.

Next, this switching transistor (Ql).

During the ON period, the voltage yb of the feedback winding (N3) has the polarity C: shown in Figure 2, so the sum of this voltage yb and the voltage yt of the capacitor (C2) is used as a power source to connect the capacitor along the path shown in the diagram. A charging current IC flows to (04) because in steady state.

The voltage between point 01 is the Zener voltage yz of the Zener diode (D7) and the base of the detection transistor (C3).
Emitter voltage VB! This is because they are set to be slightly larger than the sum of lis, and both (1), 7), and (C2) are electrically connected. In this way, the base potential (VC in FIG. 2) of the control transistor (C2) rises due to the current IC.

At the point in time, the base potential becomes VB1 higher than the emitter potential.
When the voltage increases by 12, the control transistor (C2) turns on and the reverse bias current t, which serves as the capacitor (Olt-power supply), flows through the path shown, thereby causing the C nitswitching to rise as in the previous conventional example. Transistor (
Ql) turns off.

Here, when the output voltage (■0) increases.

Because the voltage Vt of the capacitor fc02) increases.

As the forward bias of the detection transistor (C5) becomes deeper and its collector current, that is, the charging current IC to the capacitor (C6) increases, the base potential vO of the control transistor (C2) rises faster, and its turn-on or The switching transistor (Ql) is turned off earlier, and the increase in the output voltage (vO) is suppressed and stabilized.

In addition, Fig. 2 (2 is the switching transistor (Q+)
The current If in the base current (of N2) and the output winding (N2) are also shown. Further, VR is a voltage generated by the current detection resistor (R2).

Here, when the detection transistor (C5) is on, vZ +VB I SWV E ・R6/(R
6+R7), the control transistor (C2) is set so that the DC voltage yt of the capacitor (C2) satisfies this equation.
The turn-on operation described above controls the on-period length of the switching transistor (Ql). Therefore,
It is not affected by the current flow rate 1, which changes due to fluctuations in input voltage and load.

A constant voltage control operation is achieved in response only to the voltage vt that is proportional to the output voltage (VO).

By the way, if you just want to supply the detection output obtained by detecting the voltage fluctuation between the base and emitter of the control transistor (C2) (not including the voltage VR across the resistor (R2)) using the detection transistor (C2), then The capacitor (C6) is unnecessary, but this capacitor (C6) connects the control transistor (C2) to the switching transistor (Ql) as described above.
) is required in order to turn it on in the latter half of the on-period circle.
) is not connected, the control transistor (C2
Since the voltage applied between the base and emitter of ) remains constant during the on period of the switching transistor (Ql),
To perform constant voltage control, the control transistor (C
2) must be operated in an active state throughout the ON period of the switching transistor (Ql). That is, in this case, the control transistor (C2) is connected to the feedback winding (N5).
It is used to shunt the positive feedback current supplied to the base of the switching transistor (Ql).

The corresponding flow rate is varied according to the collector output of the detection transistor (C5), and the switching transistor (Ql
) is configured to control the length of the on period. However, with this configuration, a sufficient forward base current (positive feedback current) cannot be supplied to the switching transistor (Ql) during its on-period C, and a reverse bias current is supplied at turn-off, causing a rapid cut-off. This is because there is a drawback that switching loss is large because it is not possible.

In the above embodiment, the turn-off condenser + (05
) is provided separately from the capacitor (02) for voltage change detection, and the former (05) is connected to the latter (05) as in the conventional example shown in Fig. 3.
It is also possible to use C2).

(G) Effects of the Invention According to the switching control type power supply circuit of the present invention, the DC voltage obtained from the detection winding of the converter transformer is not affected by the current in the input winding that changes due to fluctuations in input voltage or load. It is possible to detect only changes in . Moreover, since the temperature change in vBM of the detection transistor can be compensated for by the temperature characteristics of the constant voltage diode on the emitter side, the above detection can be performed more accurately. Therefore, since the switching transistor can be accurately controlled according to the DC voltage, there are advantages that the stability of the DC output voltage is high and the switching loss is low.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing an embodiment of the present invention, FIG. 2 is a waveform diagram showing voltage and current waveforms of the main parts, and FIG. 3 is a circuit diagram showing an example of a conventional switching control type source circuit. be. (Ql); switching transistor, (C2) two control transistors, CQ3): hl output transistor, (05
): Turn-off capacitor, (C6): Bias capacitor, (N5): Feedback winding, (N4): Detection winding.

Claims (1)

[Claims] (1) A switching transistor whose emitter is connected in series with a current detection resistor, an input winding and a feedback winding of a converter transformer are connected to form a blocking oscillation circuit, and the base side of the feedback winding is A detection winding commonly connected to one end of the turn-off capacitor connected to the detection winding or the feedback winding and charged during the off period of the switching transistor is provided between one end of the turn-off capacitor and the emitter of the switching transistor. A bias capacitor is connected between the collector and emitter of the control transistor, and a bias capacitor is connected between the base and emitter of the control transistor. A detection transistor is provided between which a voltage is applied, and the collector of the detection transistor is connected to the base of a control transistor, and when the bias capacitor is charged to a predetermined level, the control transistor is turned on and the voltage of the turn-off capacitor is turned on. A switching control type power supply circuit in which a reverse bias is applied to a switching transistor.