JPH03272218A - Switching power supply circuit - Google Patents

Abstract

PURPOSE:To reduce the loss of a switching transistor(TR) by providing a charging circuit for a capacitor as a drive means for the switching TR and a resistor giving a reverse bias between a base and an emitter of the switching TR. CONSTITUTION:The circuit is provided with a capacitor 21 connected to a base limit resistor 22 and a switching TR 2, a discharge TR 23 to discharge the capacitor 21 and bias resistors 24, 25 for the discharge TR 23. When the switching TR 2 is turned on, a path charging the capacitor 21 is formed to accelerate turning on of the TR 2 and when the switching TR 2 is turned off, a path discharging the charge in the capacitor 21 is formed via the discharge TR 23 and the bias resistors 24, 25 to reverse-bias the base and emitter of the TR 2. Thus, the turn-on and turn-off time of the switching TR 2 are reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a switching power supply circuit having a chopper type transistor.

[Conventional technology]

Fig. 5 shows a conventional chopper-type switching power supply circuit. 3 is a switching control section, and 4 is a TR by a signal from the switching control section.

5 is a resistor for limiting the base current of TR (hereinafter referred to as R0); 6 is a resistor (hereinafter referred to as R0) for discharging the carriers accumulated in TR, 2; (hereinafter referred to as R2), 7 and 8
is a coil (hereinafter referred to as L1) and a capacitor (hereinafter referred to as C1) for smoothing the voltage switched by TR,2.
), 9 is a flywheel diode, 10.11
are voltage dividing resistors (hereinafter referred to as R3 and R4, respectively) for transmitting the output voltage VO12 to the switching control section 3.

Next, the operation will be explained using FIG. 5, FIG. 6, and FIG. 7. The input DC voltage Vi 1 is TR.

In this state, the control signal a from the switching control section 3 causes the TR, 4 emitter to be connected to the emitter of TR, 4.
turns on and off, and transmits the base of TR,2 through R+5'
control and turn TR12 on and off.

Further, R,6 is a resistor that discharges the accumulated carriers of TR,2 when it is off. Here, when TR,2 is on, Vl is supplied to coil L17 and capacitors C,8, and when TR,2 is off, the energy stored in coil L,7 is sent to the load via flywheel diode 9. Supplied. Here, the output power ■. 12 as voltage dividing resistor R310, R4
11 to divide the voltage, apply feedback to the switching control section 3,
The switching control unit 3 changes the duty cycle of the control signal a to obtain the output voltage ■. Keep 12 constant.

Next, paying attention to the operation of TR,2, the control signal a
The base current b of TR,2 and the collector-emitter voltage d of the collector current C5 are as shown in FIG. Furthermore, the waveform obtained by enlarging the transition period from OFF to ON and from ON to OFF of TR,2 is shown in FIG. From these figures, the loss of TR,2 is: (1) If the loss during the on period is Pon, then 1 ゛', -Vcl: (sat) (Ic+
+Icz) ・toNT. Ic4+IczHowever, I
It was set as c=.

Note that T is the switching period, and Vct (sat) is TR.
, Ic, is the collector saturation voltage of , Ic is the minimum and maximum value of the collector current of TR, and tON is the original on-period of TR.

(2) Turn-on loss P is the loss during the transition period from off to on.
Here, tr is the rise time of TR.

(3) Turn-off loss P is the loss during the transition period from on to off.
Assuming toff, where ts is the accumulation time of TR, and tf is TR.

is the fall time of

The total loss PTR of TR is P t++= P ON+ P tr+ P toff
becomes.

On the other hand, as a switching power supply, smoothing coil L17
, the switching frequency is increased in order to make the capacitor 0.8 as small as possible. Therefore, among the above PT and l, P tr and P toff, especially Ptoff, account for a large proportion of the loss, and TR.

Problems such as an increase in collector loss and a decrease in the efficiency of switching power supplies arise. In order to reduce this Ptoff, it is necessary to shorten the turn-off time toff (=ts+tf). However, the stored carrier discharge resistor R2 for shortening this toff needs to satisfy the following equation from the relationship of increase in reactive current when TR12 is on.

111+ However, VIIE is the base-emitter voltage of TR, 1
111 is the base current when on.

As can be seen from this equation, it is not possible to select a very small resistance value for R2, and therefore the turn-off time toff cannot be shortened.

[Problem to be solved by the invention]

Conventional switching power supplies have a tank bottom as described above, so the turn-on and turn-off times of the switching transistor are long, the loss of the switching transistor is large, the efficiency of the switching power supply is poor, and the switching frequency cannot be increased, making it difficult to downsize. There was a problem.

The present invention has been made in order to solve the above-mentioned problems, and provides a switching power supply circuit that can shorten the turn-on time and turn-off time of switching transistors, has high efficiency, and can be easily realized. The purpose is to

[Means to solve the problem]

The switching power supply circuit according to the present invention includes, as a driving means for the switching transistor, a charging circuit of a resistor and a capacitor that also serves to speed up when turning on, and a charging voltage of the capacitor that is reverse biased between the base and emitter of the switching transistor when turning off. It consists of a switch using a resistor and a transistor to add as much as possible.

[Effect]

In the switching transistor drive circuit of the present invention, when the switching transistor is turned on, the turn-on time is shortened by the charging current of the capacitor, and when the switching transistor is turned off, the charging voltage of the capacitor is applied to the resistor, and a switch by the transistor forms a release route for the accumulated carriers of the switching transistor. At the same time, it accelerates switching, reduces turn-off time, reduces losses in switching transistors, and improves efficiency of switching power supplies.

〔Example〕

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a circuit diagram showing the bottom of a main part of a switching power supply circuit according to an embodiment of the present invention, and FIG. 2 is a circuit diagram of the entire circuit. In the figure, the same or equivalent parts as those of the conventional example explained in FIG. 5 are given the same reference numerals, and detailed explanation thereof will be omitted.

21 is a capacitor C2 for speeding up TR, 2,
22 is TR, 2 base current limiting resistor R5, 23 is TR
, 22 is off, the switch transistor TRff creates a discharge path for the capacitor C221, 24.25 is TR
323 bias resistors R6 and R7.

In the above configuration, the input power supply voltage V,1 is switched by the switching transistor TR,2, and the coil L including the flywheel diode 9, 7 capacitors C,
Smooth the output voltage with 8■. Get 12. Further, the output voltage V012 is fed back to the switching control unit 3 via the voltage dividing resistors R310 and R411 to generate a control signal, and this control signal causes the switching transistors TR and 2 to be connected via the driver transistor TR24.
control the on/off duty cycle of the output voltage V
The operation for measuring the stability of 012 is the same as that described in the conventional example.

Hereinafter, the switching transistor TR,2 will be turned on based on FIGS. 1, 2, 3, and 4, which is an enlarged view of the turn-on and turn-off parts of FIG.

The explanation will focus on the off operation.

When the TR 24 is turned on by the control signal m, (shown as r in FIG. 4) from the switching control section 3,
TR via R522, R+5.

A base current 1s+n (shown as S in FIG. 4) is applied to turn on the transistor. On the other hand, capacitor C221 is R522,
Charged via R725, TR+2. At this time, the charging current of the capacitor C221 is changed to the above I□ as shown in A in FIG.
This contributes to speeding up the turn-on time of TR,2. When TR is turned on, the following relationship is required.

0 ■ R+ +Rs ”= (Vi VEE+
) / In+However, Vllll! 1 is the base-emitter voltage of the TR during saturation operation, and 2 is the base current necessary to make the collector-emitter saturation voltage sufficiently small with respect to the collector current flowing through the TR.

■, R,, R5O ratio is the reverse breakdown voltage VE between base and ξ ivy of TR, 23, which is the potential due to the partial voltage ratio including R7! It is necessary to set it to a value lower than +03, which can be expressed as the following formula.

VEIIO+> R4・R7 R4・R, + R, · R5+ R7・R5 Next, when TR, 4 is turned off by the control signal m from the switching control section 3, R, 5, R624, R? Bias is applied to TR 323 via 25, turning TR 23 on. As a result, the voltage of C221 is changed to R322.
via TR.

It is added to the base eco-vine of 2 as a reverse bias, and T
A current is applied as IB□ with a base current of 5 to accelerate the release of accumulated carriers in R,2, and TR.

Shorten the turn-off mission of 2.

〔Effect of the invention〕

As described above, according to the switching power supply circuit according to the present invention, when the switching transistor is turned on, the charging current of the capacitor flows to speed up the turn-on, and when the switching transistor is turned off, the charging voltage of the capacitor is switched through another transistor. Since a reverse bias is applied between the base and emitter of the transistor to rapidly release accumulated carriers and speed up the turn-off time, it has the effect of reducing loss in switching transistors and improving efficiency of switching power supplies.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram of a main part of a switching power supply circuit according to an embodiment of the present invention, FIG. 2 is an overall circuit diagram of FIG. 1, and FIGS. 2. Operating waveform diagram, Figure 5 is a conventional switching power supply circuit diagram,
6 and 7 are operation waveform diagrams of FIG. 5. In the figure, 1 is a human power supply voltage, 2 is a switching transistor, 3 is a switching control section, 4 is a driver transistor, 5, 22, 24, 25 are resistors, 21 is a capacitor, and 23 is a transistor. Note that the same reference numerals in the figures indicate the same or equivalent parts.

Claims (1)

[Claims] (1) A switching power supply that includes a switching transistor that switches voltage from a DC power supply to supply power to a load, a driver transistor that turns on and off this switching transistor, and a switching control section that controls this driver transistor. The circuit includes a capacitor connected by dividing the base limiting resistance of the switching transistor, a discharging transistor for discharging the capacitor, and a bias resistor for the discharging transistor, and when the switching transistor is turned on, the above-mentioned forming a path for charging the capacitor to accelerate turn-on of the transistor; forming a path for discharging the charge in the capacitor via the discharging transistor and the bias resistor when the switching transistor is turned off;・Switching power supply circuit characterized by reverse bias between emitters.