JPS5918860Y2 - Switching regulator - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to an improvement in a switching regulator of a type called series switching.

Conventionally, a series switching type switching regulator is configured as shown in FIG. 1, for example.

In FIG. 1, reference numeral 1 indicates a power supply with poor stability, and its supply voltage is designated as El.

The positive terminal of the power supply 1 is connected to a first output terminal 4a through a main switch element, for example, the collector-emitter of an NPN transistor 2, and a voltage conversion choke coil 3 in series.

The negative pole of the power supply 1 is directly connected to the second output terminal 4b.

Reference numeral 5 denotes a main switch element driving element, for example a PNP type transistor, whose emitter is connected to the collector of transistor 2, whose collector is connected to the base of transistor 2, and whose base is connected to switching amplifier 6.

Switching amplifier 6 is here a general term for components not shown in FIG. 1 that are necessary for a switching regulator, including error amplifiers, voltage comparators, pulse width converters, and the like.

A flywheel diode 7 is used to bypass the current flowing through the choke coil 3 when the transistor 2 is turned from on to off.

Reference numeral 8 indicates a voltage conversion capacitor, and reference numerals 9 and 10 indicate resistors for obtaining the required stabilized output voltage between the output terminals 4a and 4b.

The output voltage E2 is generally expressed by the following equation, where the resistance values of the resistors 9 and 10 are R9 and Rlo, respectively, and the voltage of the reference power supply 11 for voltage comparison of the switching amplifier 6 is R3.

R2-Jukuseimo 3 lO 12 is a resistor for speeding up the discharge of the base capacitor of the switching transistor 2.

As is well known, in order to reduce the switching loss of the main switch element 2, a drive current sufficient for the current is required.

On the other hand, it is necessary that the time relationship between the decrease in collector current and the increase in collector-emitter voltage when the main switch element 2 is turned off changes quickly.

That is, the collector current Ic and the collector-emitter voltage EcE of the switching transistor 2 change as shown in FIG. 2 as the transistor 2 turns on and off, and the product of the current and voltage that occurs at time t shown in FIG. This results in switching loss.

Therefore, when transistor 2 is turned off, its collector current Ic and collector-emitter voltage E decrease as quickly as possible.

E needs to decrease and increase.

In the circuit configuration shown in FIG. 1, when the output of the switching amplifier 6 cuts off the drive transistor 5,
The base drive current of switching transistor 2 will no longer flow in from transistor 5, and the collector current of transistor 2 will therefore be cut off, but due to the carrier accumulation effect in the base, it will not be cut off instantaneously, but after a certain time delay. It slowly passes through the active region and is blocked.

The time in FIG. 2 corresponds to the passage through this active region.

In order to reduce this time t, in the circuit of FIG.
2 is placed between the base and emitter of transistor 2 to speed up the release of base carriers.

However, in order to reduce the time t, the value of the resistor 12 must be reduced, and therefore the current handled by the drive transistor 5 becomes large.

However, since speeding up the release of pace carriers is a so-called spontaneous discharge type processing method, there is a limit, and there is a drawback that the time t cannot be reduced very much.

In order to further reduce the time t, it is necessary to apply a reverse bias between the base and emitter of the transistor 2, and this method is used for high-speed, high-efficiency switching.

However, the series switching method
A reverse bias system with a simple circuit configuration that can be applied to regulators has not yet been proposed.

The present invention was developed in view of the above points, and uses a simple circuit configuration to apply a reverse bias to the main switch element when the main switch element drive element is turned off, further improving switching efficiency. It provides a switching regulator.

An embodiment of the present invention will be described below with reference to FIGS. 3 and 4.

FIG. 3 is a circuit connection diagram showing an embodiment of the switching regulator according to the present invention. In FIG. 3, 1 is an unstable power source, 2 is a main switch element such as an NPN transistor, and 4a and 4b are output terminals. , 5 is a main switch element driving element such as a PNP transistor, 6 is a switching amplifier, 7 is a flywheel diode, 8 is a voltage conversion capacitor, 9 and 10 are resistors,
Reference numeral 11 indicates a reference power supply for voltage comparison of the switching amplifier 6, and these circuit elements are the same as those in FIG. 1 and are connected in the same manner.

In the present invention, the voltage conversion choke coil 14 is
A bias winding n2 between bc is provided in the winding n1 between ab and bc, and the connection point between these windings n1 and n2 is connected to the emitter of the switching transistor 2, and the bias winding n
The other end C of the switching transistor 2 is connected to the base of the switching transistor 2 via a diode 13 having the polarity shown.

Since the present invention is configured in this way, when the drive transistor 5 is turned on, the potential at point C of the choke coil 0...14 rises by n2 from point b, but the diode 13 with the polarity shown Therefore, no current flows.

Therefore, the base drive of the switching transistor 2 is performed only by the collector current of the drive transistor 5.

Next, when the drive transistor 5 is turned off, the collector current Ic of the switching transistor 2 decreases.

Therefore, a back electromotive force is generated in the choke coil 14, and the flywheel and diode 7 are forward biased and conductive.

As a result, the potential at point C is lower than the potential at point C by 1-n2, ignoring the forward voltage drop of the switching transistor 2 and the flywheel diode.

FIG. 4 explains such state 1. FIG. 4A shows the on/off state of the drive transistor 5, the solid line in the figure shows the potential at point b, and the dotted line shows the potential at point C.

As is clear from the circuit configuration of FIG. 3, the emitter of the switching transistor 2 is connected to a point B, and the base thereof is connected to a point C via a diode 13.

Therefore, when the drive transistor 5 is turned off, the diode 13 is forward biased and conductive, thereby reverse biasing the base of the switching transistor 2.

As a result, the switching transistor 2 is instantly cut off when the drive transistor 5 is turned off, so that the collector current instantly decreases and the collector-emitter voltage instantly increases, so that the switching loss is drastically reduced. Switching efficiency increases significantly.

As an example, when the present invention was applied to a switching regulator with an output of 12 VIA, the power consumption was reduced by 2W.

FIG. 5 is a circuit connection diagram showing another embodiment of the switching regulator according to the present invention. The difference from the circuit in FIG. 3 is that the flywheel diode 7 is removed and a new flywheel diode 15 is added. choke coil 1
This is the point connected between the 0 point of 4 and the ground.

According to such a circuit configuration, when the drive transistor 5 is turned off, if the voltage drop due to the switching transistor 2 and the flywheel diode 7 is ignored in the same manner as described above, the potential at point b of the choke coil 14 is - - from the potential at point 0. When the potential of the choke coil 14 at point 0 increases by 1 drop' (nt+n2) from the potential at point b, when the drive transistor 5 turns on.

That is, when the drive transistor 5 is turned off, a reverse bias voltage of n1+n2.n2 is applied between the base and emitter of the switching transistor 2, and the switching transistor 2 is rapidly cut off, producing the same effect as described above.

As described above, according to the present invention, one end of the bias winding is connected to one end of the choke coil, and the connection point between the choke coil and the bias winding is directly connected to one electrode of the main switch element. The other end is connected to the base of the main switch element through a diode in series, and the circuit configuration is such that a reverse bias voltage is applied to the base of the main switch element when the drive element is off. It is extremely simple, and therefore has the remarkable effect of being easy to manufacture, inexpensive, and capable of reducing the switching loss of the switching regulator.

In addition, in the above embodiment, an NPN type transistor was used as the main switch element, but a PNP type transistor may also be used.

However, in this case, it is necessary to change the polarity of the semiconductor accordingly.

Furthermore, it goes without saying that the circuit configuration can be changed as necessary.

[Brief explanation of the drawing]

Fig. 1 is a circuit connection diagram showing an example of a conventional switching regulator, Fig. 2 is a waveform diagram for explaining the operation of the main switch element, and Fig. 3 is a switching regulator according to the present invention.
A circuit connection diagram showing one embodiment of the regulator, FIG. 4 is a waveform diagram for explaining its operation, FIG. 5 is a circuit connection diagram showing another embodiment of the switching regulator according to the present invention, and FIG. FIG. 3 is a waveform diagram for explaining the operation. 2 in the figure is the main switch element (NPN type transistor),
3 and 14 are choke coils, 5 is a main switch element drive element (PNP type transistor), 6 is a switching amplifier, 7 and 15 are flywheel diodes, 13
is a reverse bias diode.

Claims (1)

[Scope of utility model registration request] A power supply, a main switch element that controls the power supplied from the power supply, a voltage conversion choke coil and a voltage conversion capacitor that convert the power from the power supply supplied through the element into voltage, and a voltage conversion capacitor that responds to fluctuations in the output voltage. a switching amplifier that operates when the main switch element is turned off; a drive element that operates the main switch element with a signal supplied from the amplifier; In a switching regulator comprising a bypass diode that bypasses the current flowing through a choke coil, one end of a bias winding is connected to one end of the choke coil, and the connection point between the choke coil and the bias winding is connected to the main The bias winding is connected directly to one electrode of the switch element, and the other end of the bias winding is connected to the base of the main switch element through a diode in series, so that when the drive element is off, the base of the main switch element A switching regulator configured to apply a reverse bias voltage to.