JPH0131332B2 - - Google Patents

Description

[Detailed Description of the Invention] (1) Technical Field of the Invention The present invention provides on/off control of a switching transistor via a drive transformer in a switching regulator used as a relatively large capacity stabilized power supply device. The invention relates to a drive circuit for switching transistors, and enables high-speed operation of switching transistors.

(2) Background of the technology In recent years, as electronic and communication devices have become smaller, there has been a demand for smaller switching regulators as stabilizing power supplies installed in these devices.

In switching regulators, relatively large components such as conversion transformers and smoothing coils can be made smaller by increasing the switching frequency; however, in switching transistors, increasing the switching frequency can reduce the number of switching cycles. As a result, losses will increase.

This switching loss includes loss due to collector-emitter saturation voltage during the transistor's on period, loss due to turn-on time and turn-off time, but loss due to turn-off time is due to accumulation time and fall time. By shortening these times, losses can be reduced.

Further, in a pulse width control type switching regulator, the control range of the pulse width is also limited due to the turn-on time and turn-off time of the switching transistor.

(3) Purpose of the Invention An object of the present invention is to provide a drive circuit that can shorten the turn-off time of a switching transistor in a switching regulator in order to operate the switching transistor at a higher speed than before. It's about doing.

(4) Prior art and its problems FIG. 1 shows a driving circuit for a switching transistor of a conventional switching regulator.

In this drive circuit, drive transistor 3
is turned on by a control pulse from a pulse width control circuit (not shown), the drive power supply voltage 15 is applied to the drive winding N1 of the drive transformer 1, and the black dot side of the output winding N2 (indicating the winding start end of each winding) is turned on. As a + voltage is induced, the current limiting resistor 5 and speed-up capacitor 7 are applied to the base of the switching transistor 2, limiting the current to the minimum to maintain the saturated state between the collector and emitter when turned on. The base current is supplied through a parallel circuit of resistor 6 for switching transistor 2.
is turned on.

Next, when the drive transistor 3 is turned off, the induced voltage in the output winding N2 disappears, and due to the charge accumulated in the capacitor 7 during the on period, the resistor 5 and the output winding N2 are
A current in the opposite direction to the base current flows through the switching transistor 2, extracting excess carriers between the base and emitter of the switching transistor 2, and the switching transistor 2 is turned off.

After that, the excitation energy stored in the drive transformer 1 during the ON period of the drive transistor 3 is
Due to the generation of back electromotive force, the current is returned to the drive power supply 15 through the current path from the end of the winding of the reset winding N3 to the drive power supply 15 → diode 4 → the winding start end of the reset winding N3 (black dot side), and the current is returned to the drive power supply 15. The magnetic flux is reset.

In such a drive circuit, the capacitor 7
The reverse bias current due to the charge on the capacitor 7 ensures that the switching transistor 2 is turned off, but the charging voltage on this capacitor 7 is typically about 2V.
Since the reverse bias current flows through the resistor 5, a delay time occurs, which is a factor in not being able to sufficiently shorten the turn-off time (storage time and fall time) of the switching transistor. There is.

Note that the load LD in Figure 1 is the load connected to the output circuit of the main transformer and its output winding.
17 is a DC input power source for this switching regulator.

(5) Embodiment of the Invention FIG. 2 shows an embodiment of the switching transistor drive circuit of the present invention, and FIG. 3 is an operation waveform diagram of each part of the drive circuit of FIG. 2.

The drive winding circuit includes a drive winding N of the drive transformer 8.
The winding start end (black dot) of No. 1 is connected to the + side of the drive power supply 15 via the resistor 14, the winding end end is connected to the collector of the drive transistor 10, and the emitter side is connected to the - side of the drive power supply 15. It is composed of

The output winding circuit is constructed by directly connecting the winding start end (black dot) of the output winding N2 to the base of the switching transistor 9, and connecting the winding end to the emitter side of the switching transistor 9.

In the reset winding circuit, the winding start end (black dot) of the reset winding N3 is connected to the collector of the transistor 11 and the cathode side of the diode 12, the winding end is connected to the capacitor 13, and the other end of the capacitor 13 is connected to the transistor 11 and connected to the anode side of the diode 12.

Further, a control pulse voltage V B10 as shown in FIG. 3 is applied to the base of the driving transistor 10 from a pulse width control circuit (not shown), and a control pulse voltage V B10 as shown in FIG. 3 is applied to the base of the transistor 11. By applying the inverted pulse voltage VB11 of the control pulse, the two transistors 10 and 11
is controlled to be turned on and off alternately.

First, when the transistor 11 is off and the drive transistor 10 is on, a drive voltage V N1 shown in FIG. 36 is applied to the drive winding N1 of the drive transformer 8.
is applied from the drive power supply 15 via the resistor 14 and is excited, and a voltage is induced in the output winding N2 with the winding start end (black dot) being +, and the switching transistor 9 is connected to the base shown in FIG. current I
It is forward biased by B9 and turns on, and the collector current I C9 shown in FIG. 3 flows.

Since the base current I B9 of the switching transistor 9 at this time is limited by the resistor 14 of the drive winding circuit, there is no need to insert a limiting resistor on the base side of the switching transistor 9 as in the conventional case. Next, when the drive transistor 10 is turned off and the transistor 11 is turned on, the reset winding N3
Since it is connected to the capacitor 13, it has low impedance, and due to the charge in the capacitor 13, the capacitor 13 → reset winding N3 (winding end) → reset winding N3 (winding start end) →
A steep current I N3 shown in FIG. 3 and 5 flows in the closed circuit of the transistor 11 and the capacitor 13 in an extremely short period of time, and the discharge of the capacitor 13 is completed.

This current generates a voltage on the output winding N2 side with the end of the winding being positive, and a third reverse bias current from the base that pulls out the excess carrier between the base and emitter of the switching transistor 9 is generated.
As shown in FIG. 3, the current suddenly flows to the opposite polarity, rapidly turning off the switching transistor 9, and blocking the collector current I C9 as shown in FIG. 4.

After the switching transistor 9 is turned off, a voltage is generated in each winding of the drive transformer 8 due to a back electromotive force with the end of the winding being positive, and the reset winding N3 (end of winding) → capacitor 13
→ Diode 12 → A reset current with the opposite polarity to the steep current described above flows as shown in FIG. After being charged, the magnetic flux of the drive transformer 8 is reset.

At this time, since a positive voltage is also induced at the end of the winding of the output winding N2, a reverse voltage is applied between the base and emitter of the switching transistor 9, maintaining the off state.

By repeating the above-described operations, the drive circuit of the present invention can shorten the turn-off time of the switching transistor compared to the conventional one, and can perform high-speed driving.

In other words, the drive circuit of the present invention eliminates the delay element of the reverse bias current by eliminating the capacitor and resistor on the base side of the switching transistor in the conventional drive circuit, and also eliminates the delay element of the reverse bias current by using the low impedance reset winding circuit. Since the reverse bias current can be made extremely steep, the turn-off time consisting of the accumulation time and fall time can be shortened compared to conventional drive circuits.

FIG. 4 shows another embodiment of the present invention, which is applied to what is generally called a current feedback type switching transistor drive circuit.

In this drive circuit, the drive transformer 16 is provided with a feedback winding N4 for feeding back the collector current of the switching transistor 9 to the base side.
Since the base current during the period when is on is supplied from this feedback winding N4, the drive power of the switching transistor 9 to be supplied from the drive power supply 15 can be reduced.

Further, the operation of the present invention is exactly the same as that of the embodiment shown in FIG.

(6) Effects of the Invention According to the present invention, the turn-off time of the switching transistor can be shortened with an extremely simple circuit configuration, and the switching transistor can be operated at high speed, thereby reducing the switching loss of the switching transistor. This makes it possible to increase the switching frequency and contribute to miniaturization of the switching regulator, which is extremely useful in practice.

[Brief explanation of drawings]

FIG. 1 shows a switching transistor drive circuit of a conventional switching regulator, and FIG. 2 shows a switching transistor drive circuit of the present invention.
FIG. 3 is an operation waveform diagram of each part of the drive circuit shown in FIG. 2, and FIG. 4 is a circuit diagram of another embodiment of the present invention. In the figure, 1, 8 and 16 are drive transformers, 2 and 9 are switching transistors, 3 and 10 are drive transistors, 11 is a transistor, 4 and 12 are diodes, 5, 6 and 14 are resistors, and 7 and 13 are capacitors. , 15 indicates a DC drive power supply, and 17 indicates a DC input power supply.

Claims (1)

[Scope of Claims] 1. In a switching regulator that controls on/off of a switching transistor connected to a DC input power source via a drive circuit using control pulses to supply a stable output to a load, the switching transistor is turned on. , has a drive transformer that supplies a bias current for off-control, and a DC drive power supply, a resistor, a drive winding of the drive transformer, and a collector and emitter of a drive transistor that is switched by the control pulse are connected in series. a drive winding circuit; an output winding circuit in which the base and emitter of the switching transistor are respectively connected to both ends of the output winding of the drive transformer; and the collector and emitter of the transistor that performs switching operation by an inverted pulse of the control pulse. and a reset winding circuit in which a capacitor and a reset winding of the drive transformer are connected in series to the parallel circuit of the transistor and the diode, and when the drive transistor is turned from on to off. The base of the switching transistor is reverse biased and turned off by turning the transistor from off to on, discharging the charge in the capacitor through the reset winding of the drive transformer, and then turning the transistor off. A driving circuit for a switching transistor, characterized in that the capacitor is charged via the diode by a back electromotive force generated in the reset winding.