JPS5918949B2 - Switching regulator - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a switching regulator including a start-up circuit and a shutdown control circuit.

The inventor of the present application proposed the starting circuit shown in Fig. 1 in the earlier filed application No. 13169/1983.A switching regulator connected to this starting circuit does not operate at low input voltage, and the switching transistor The power supply for the Qs drive circuit 1 is obtained from the input power supply E only at the time of startup, and is obtained from the auxiliary power supply 3 formed inside the circuit after startup.

SUMMARY OF THE INVENTION An object of the present invention is to provide a switching regulator in which a shutdown control circuit is added to the startup circuit.

That is, the present invention connects the input power supply, the primary winding of the transformer, and the main current path of the switching transistor in series to
In a switching regulator that configures a closed circuit and converts the voltage applied to the primary winding to the secondary winding by intermittent switching transistors, the switching transistor is driven and the voltage applied to the control terminal is determined by the presence or absence of the voltage applied to the control terminal. A drive circuit that can start and stop operation, a voltage dividing resistor that divides the input voltage, and a first and third resistor that are connected in series from the ground point.
A Zener diode is connected to the base, and the first transistor operates by comparing the potential at the voltage dividing point of the voltage dividing resistor with its base voltage, which is a reference voltage.The main current path of the first transistor is connected to the base. a starting circuit having a second transistor connected to the main current path and having a starting resistor connected to the main current path, and further having a connection point of the first and third Zener diodes connected to a control terminal of the drive circuit; From a third transistor whose base is connected to the main current path of the second transistor via a second Zener diode, and whose main current path is connected between the connection point of the first and third Zener diodes and ground. A shutdown control circuit short-circuits the third Zener diode terminal in response to the startup circuit output generated by the second transistor, changes the base voltage of the first transistor, and eliminates the voltage at the control terminal of the drive circuit to start operation. and the tertiary winding of the transformer, the first
A second closed circuit is formed by the diode and capacitor, and one end of the tertiary winding and the capacitor is grounded, and the first diode is connected to the power supply terminal of the drive circuit and a switching circuit consisting of the second diode. The second transistor is characterized by having an auxiliary power supply connected to the main current path of the second transistor and supplying power to the drive circuit after power supply from the startup circuit is stopped.

Next, one embodiment of the present invention is shown in FIG. 2, and will be described below based on the drawings.

In the embodiment shown in FIG. 2, the input power source E1, the primary winding Ll of the power conversion transformer T, and the collector and emitter of the switching transistor Qs are connected in series to form a closed circuit. Circuit 1 is connected.

Further, a switching circuit 5 is connected to the power supply terminal of the drive circuit 1, and a starting circuit 2 is connected between the switching circuit 5 and the input power source E.
and a shutdown control circuit 4 are connected. Further, an auxiliary power source 3 formed by providing a power conversion transformer T with a tertiary winding L is connected to the switching circuit 5. In the basic circuit configuration described above, the starting circuit 2 has voltage dividing resistors Rl and R2 connected between the input terminals A and b to which the input power source E is connected, and a transistor with a resistor R4 connected between the emitter and the base. Zener diode Dz at the base of Q1
l, Dz, are connected.

In addition, a starting resistor R, a transistor Q is connected between input terminals A and B.
, and a shutdown control circuit 4 are connected thereto.

In the shutdown control circuit 4, a Zener diode DZ2 and a resistor R are connected to the emitter of the transistor Q2.The base of the transistor Q3 is connected to the resistor R, and the collector and emitter of the transistor Q3 are connected to the Zener diode of the startup circuit 2. It is connected to both ends of a Zener diode DZ3 connected to Dz,. The connection point of Zener diodes DZl and Dz, and the voltage dividing resistor Rl,
A resistor R6 is connected between the voltage dividing point of R2 and the voltage dividing point. Further, the collector of the transistor Q is connected to the control terminal G of the drive circuit 1. Auxiliary power supply 3 is power conversion transformer T
One end of the tertiary winding L provided in the switching circuit 5 is grounded together with the emitter of the switching transistor Qs, and the other end is connected to the diode D of the switching circuit 5 via the diode D.
2 and is also grounded via a capacitor C1. FIG. 3 shows voltage waveforms at various parts of the circuit shown in FIG. 2, and the operation of the circuit shown in FIG. 2 will be described below.

Time T. When the input power supply E is turned on and the input voltage Vi shown in Fig. 3A is applied between the input terminals A and B, the potential at the voltage dividing point of the voltage dividing resistors R, R2 becomes equal to the input voltage Vi. It increases in proportion to the partial pressure ratio. At this time, from the input power supply E to the resistor Rl
, R6, a voltage is applied to the control terminal G of the drive circuit 1,
The drive circuit 1 stops operating (shuts down). Time t
1, and when the input voltage Vil)5Vi1 is reached, the voltage across the resistor R2 exceeds the Zener voltage of the Zener diodes Dz, Dz, as shown at the beginning of Figure 3, and the input power supply E
A current flows from the resistor R4 to the Zener diodes Dzl and Dz.

Further, when the voltage across the resistor R4 exceeds the base-emitter voltage of the transistor Q1, the transistor Q1 becomes conductive, and as a result, the base current of the transistor Q2 flows, and the transistor Q2 becomes conductive. Furthermore, current flows from the input power supply E to the starting resistor R3, the collector/emitter of the transistor Q, and the diode D, and the emitter voltage VB of the transistor Q2 charges the capacitor C, as shown in Fig. 3C. to rise like that. Furthermore, the voltage c across the capacitor C1 rises as shown in FIG. 3, and at time T2
When the Zener voltage of the Zener diode Dz, is exceeded, a current flows from the emitter of the transistor Q2 in the direction of the Zener diode Dz, and the resistor R. This results in
When a voltage is generated across the resistor R, the transistor Q becomes conductive and the collector potential of the transistor Q becomes zero, and the Zener diode DZ3 is shot, so the resistor R
The voltage across the line 2 shows a voltage drop as shown at the top of FIG. Further, since the voltage supplied from the input power supply E to the control terminal G of the drive circuit 1 via the resistors R, R6 decreases, the drive circuit 1 releases the shutdown, drives the switching transistor Qs, and switches the switching leg. Yurator starts working. While the switching regulator is operating, when the input voltage Vil:)5Vi2 is reached at time T3, the resistance R
The voltage across the zener diode DZl becomes lower than the zener voltage of the zener diode DZl, and the transistor Q is cut off.

As a result, from the input power supply E to the resistor R3 and the transistor Q2
, Zener diode DZ2, and resistor R7 stop, the base current of transistor Q3 is cut off, and the collector potential of transistor Q3 rises. As a result, the base potential of the transistor Q1 rises, and the reference voltage of the starting circuit 2 is switched from the Zener voltage of the Zener diode Dz, to the Zener voltage of the Zener diodes DZl, DZ3, which is input to the control terminal G of the drive circuit 1. Power supply E
A current is supplied from the resistors R1 and R6, and the switching regulator stops operating. Along with this, the operation of the auxiliary power supply 3 also stops, so the voltage Vc across the capacitor C1 decreases as shown in 2 of FIG. FIG. 4 shows the input/output voltage characteristics of the embodiment of FIG. 2 which operates as described above. When the operation of the switching regulator is stopped, the input voltage i increases and the zener voltages DZl, DZ3
After the Zener voltage exceeds the Zener voltage and transistors Ql and Q2 become conductive, the transistor Q3 is made conductive, the Zener diode DZ3 is shot, and the switching regulator is activated.

As a result, the base voltage of the transistor Q1, which is compared with the voltage across the resistor R2, decreases, and as a result, the reference voltage of the starting circuit 2 becomes the Zener voltage of the Zener diode DZl. When the input voltage i falls and the voltage across the resistor R2 becomes the Zener voltage of the Zener diode DZl, the transistors Ql, Q2, and Q3 are cut off, stopping the operation of the switching regulator. Furthermore, since transistor Q3 is cut off, the base voltage of transistor Q1, which is compared with the voltage across resistor R2, increases. Therefore, as shown in the input/output voltage characteristics of FIG. 4, the drive circuit 1 stops operating at an input voltage I2 lower than the input voltage 11 at which the drive circuit 1 starts operating. That is, the present invention can have hysteresis in the input/output voltage characteristics. t According to the present invention, the switching regulator starts when a sufficient power supply voltage for the drive circuit 1 is obtained, and even if the switching regulator is in operation, when the input voltage Vi decreases, Since the switching regulator can be stopped, the power supply voltage of the drive circuit 1 is always ensured while the switching regulator is operating, and the switching regulator operates safely.

In addition, since the present invention has hysteresis in the input/output voltage characteristics, if the input voltage Vi includes ripples, it will not repeatedly start and shut down in ripple synchronization, and the input power supply E has an internal resistance. Therefore, even when a voltage drop occurs due to the load current, it is possible to provide a switching regulator that is shut off due to the voltage drop after startup and does not repeat startup and shutoff thereafter. In the above embodiments, a separately excited type switching regulator has been described, but it goes without saying that the present invention can also be applied to a self-excited type switching regulator.

Further, as in the embodiment shown in FIG. 5, the connections between the Zener diode DZ2 and the resistor R7 of the shutdown control circuit 4 are led out of the housing 6 of the switching regulator to form external terminals E and f, respectively. Mode switch SW. at both ends of terminals E and f. When connecting mode switch SW. is turned on, the base current of transistor Q3 disappears, shutdown is activated, and mode switch SW. When the transistor Q3 is turned off, the transistor Q3 becomes conductive and the shutdown is canceled.

Therefore, the mode switch SW. By turning on and off the output voltage o obtained between output terminals C and d.
can be taken out or extinguished, and the constant voltage output can be easily controlled remotely.

[Brief explanation of the drawing]

Figure 1: A circuit diagram showing a conventional switching regulator, Figure 2: A circuit diagram showing an embodiment of the present invention, Figure 3: A diagram showing operating voltage waveforms of various parts of the circuit in Figure 2. Figure 4: 2nd
FIG. 5 is a circuit diagram showing another embodiment of the present invention. 1...Drive circuit, 2...Start circuit, 3
...Auxiliary 4...Shutdown control circuit, T...Electric transformer (L1: primary winding, L2
: Secondary winding, Q8...Switching transformer: J
power supply.

Claims (1)

[Claims] 1 The input power supply, the primary winding of the transformer, and the main current path of the switching transistor are connected in series to form a first closed circuit, and the voltage applied to the primary winding is connected to the secondary winding by switching on and off the switching transistor. In a switching regulator that converts power to a line, there is a drive circuit that drives the switching transistor and can stop and start operation depending on the presence or absence of voltage applied to the control terminal, a voltage dividing resistor that divides the input voltage, and a circuit connected in series from the ground point. The first transistor has first and third Zener diodes connected to its base, and operates by comparing the potential at the voltage dividing point of the voltage dividing resistor with its base voltage, which is a reference voltage, and the main current of the first transistor. a starting circuit having a second transistor having a base connected to the main current path and a starting resistor connected to the main current path, and further having a connection point of the first and third Zener diodes connected to a control terminal of the driving circuit; and a third transistor whose base is connected to the main current path of the second transistor via a second Zener diode, and whose main current path is connected between the connection point of the first and third Zener diodes and ground. Shutdown, which consists of a transistor, shorts the terminal of the third Zener diode in response to the startup circuit output generated by the second transistor, changes the base voltage of the first transistor, and eliminates the voltage at the control terminal of the drive circuit to start operation. A second closed circuit is formed by the control circuit, the tertiary winding of the transformer, the first diode, and the capacitor, one end of the tertiary winding and the capacitor is grounded, and the first diode is connected to the power supply of the drive circuit. connected to the main current path of the second transistor via a switching circuit consisting of a terminal and a second diode;
A switching regulator comprising: an auxiliary power source that supplies power to a drive circuit after power supply from the startup circuit has stopped.