JPH04251565A - Switching power supply circuit - Google Patents

Abstract

PURPOSE:To prevent the discharge current from the capacitor of a snubber circuit from concentrating on one switching transistor even if the snubber circuit is shared. CONSTITUTION:The emitters of switching transistors Q1 and Q2 are connected to the negative terminal of a DC power source severally through individual resistors R1 and R2, and one end of the snubber circuit consisting of the series circuit of a resistor R11 and a capacitor C11 is connected to the collectors of the switching transistors Q1 and Q2, and the other end of the said snubber circuit is connected to the junction between a balance resistor R1 and the negative pole terminal of the DC power source 1. Hereby, the other end of the snubber circuit is connected to the emitters of the switching transistors Q1 and Q2 through individual balance resistors R1 and R2, so even if the snubber circuit is shared, the discharge current from the capacitor can be prevented from concentrating on one switching transistor.

Description

[Detailed description of the invention]

[Object of the invention]

0002

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a switching power supply circuit for electrical equipment such as a television receiver, and more particularly to a switching power supply circuit in which the number of snubber circuits of switching elements can be reduced.

0003

[Prior Art] Conventionally, in switching power supply circuits in electrical equipment such as television receivers and personal computers, DC voltage obtained by rectifying and smoothing AC input voltage or DC voltage from a battery is switched to AC once, and then the DC voltage is changed again. It was converted to . Among such switching power supply circuits, there are those in which a plurality of switching elements (switching transistors) are operated by a drive circuit. A feature of this circuit is that it is extremely easy to increase the power of the device.

FIG. 4 shows an example of a switching power supply circuit including such a plurality of switching transistors.

[0005] In FIG. 4, reference numeral 1 denotes a DC power source consisting of two batteries connected in series. The DC voltage from the positive terminal of the DC power supply 1 is applied to the input winding Lp of the converter transformer 2.
through the first and second switching transistors Q1
, Q2. The emitters of the first and second switching transistors Q1 and Q2 are connected to the negative terminal of the DC power supply 1 via balance resistors R1 and R2, respectively. First switching transistor Q1
A series circuit (snubber circuit) of a capacitor C1 and a resistor R3 is connected in parallel to the collector-emitter path of the transistor Q1 to prevent an abnormal voltage rise in the input winding Lp when the switching transistor Q1 is turned off. A snubber circuit consisting of a similar capacitor C2 and a resistor R4 is connected in parallel to the collector-emitter path of the second switching transistor Q2. A base drive circuit 3 is connected to the bases of the switching transistors Q1 and Q2, and a base drive signal from the base drive circuit 3 is supplied to the bases of the switching transistors Q1 and Q2.

One end of the output winding Ls of the converter transformer 2 is connected to the other end of the output winding Ls via a diode D1 and a capacitor C3. A connection point between the diode D1 and the capacitor C3 is connected to one input terminal of the load 4. A connection point between the capacitor C3 and the output winding Ls is connected to the other input terminal of the load 4. Thereby, the output winding Ls of the converter transformer 2 supplies a DC voltage to the load 4 via the rectifier circuit consisting of the diode D1 and the capacitor C3.

To explain the operation of such a conventional circuit, a DC voltage Ei from the DC power supply 1 is applied to the input winding Lp.
is applied and the terminal voltage v1 of the input winding Lp increases,
The switching transistor Q1 is controlled by the base drive circuit 3.
, Q2, and the switching transistors Q1 and Q2 become conductive. This makes the input winding L
A current flows through p, and the switching power supply circuit starts self-oscillation.

When the switching transistors Q1 and Q2 are turned on by the positive voltage of the base drive circuit 3, the current ip flowing through the input winding Lp is equal to the DC voltage Ei and the input winding L.
The current ip increases with a slope Ei/L1 determined by the inductance L1 of p, and after a predetermined time ti (ti that maintains the output voltage at a constant prescribed voltage under certain conditions), the current ip becomes i1=
(Ei/L1)×ti. As a result, magnetic energy is accumulated in the converter transformer 2. Thereafter, when the switching transistors Q1 and Q2 are cut off, the terminal voltage v2 of the output winding Ls is inverted as the terminal voltage v1 of the input winding Lp is inverted, and the rectifying diode D2 becomes conductive. As a result, the magnetic energy accumulated in the converter transformer 2 is released to the secondary side of the converter transformer 2. On the other hand, the switching transistor Q1,
Due to the interruption of Q2, the inductance L1 of the input winding Lp
The abnormal voltage rise caused by this is absorbed by the capacitors C1 and C2 of the snubber circuit. In this case, resistor R3
, R4 are inductance L1 and capacitors C1, C2
This prevents resonance with the Thereafter, when switching transistors Q1 and Q2 are turned on, resistors R3 and R4 consume the energy stored in capacitors C1 and C2.

[0009] In such a circuit, one snubber circuit is used for one switching transistor, so there is a disadvantage that the number of parts is large and it is disadvantageous in terms of cost. Correspondingly, capacitor C2 and resistor R4
It is also possible to share the snubber circuit consisting of the capacitor C1 and the resistor R3 with the switching transistor Q1 and the switching transistor Q2 by connecting the collector of the switching transistor Q2 and the collector of the switching transistor Q1. Now, when the switching transistor Q1 and the switching transistor Q2 are turned on, the resistance Ra between the collector and emitter of the switching transistor Q1 and the resistance R between the collector and emitter of the switching transistor Q2 are
The ratio Ra/Rb of b may greatly differ from 1 due to a shift in on-timing, and in this case, the discharge current from the capacitor C1 will concentrate on one switching transistor, which is disadvantageous.

0010

[Problem to be solved by the invention] In such a circuit,
In order to prevent the discharge current from the capacitor from concentrating on one switching transistor, one snubber circuit is required for each switching transistor, which has the disadvantage of requiring a large number of parts and being disadvantageous in terms of cost. .

[0011] Therefore, the present invention eliminates the above problems and
An object of the present invention is to provide a switching power supply circuit that can prevent discharge current from a capacitor of a snubber circuit from concentrating on one switching transistor even if the snubber circuit is shared.

[Configuration of the invention]

[0013]

[Means for Solving the Problems] The switching power supply circuit according to claim 1 connects the emitters of a plurality of switching transistors to the negative terminal of a DC power supply through individual balance resistors, and connects the resistors and capacitors in series. A switching power supply circuit characterized in that one end of a snubber circuit consisting of a circuit is connected to the collectors of the plurality of switching transistors, and the other end of the snubber circuit is connected to a connection point between a balance resistor and a negative terminal of a DC power supply.

A switching power supply circuit according to a second aspect of the present invention is characterized in that a diode is connected in parallel to the resistor of the snubber circuit according to a first aspect of the present invention such that an anode thereof faces toward the input winding side of the converter transformer.

[0015] In the switching power supply circuit according to the third aspect, the emitters of the plurality of switching transistors are connected to the negative terminal of the DC power supply through individual balance resistors, and one end of the capacitor is connected to the collector of the plurality of switching transistors. A switching power supply circuit characterized in that the other end of the capacitor is connected to a connection point between a balance resistor and a negative terminal of a DC power supply.

[0016]

[Operation] According to this configuration, the other end of the capacitor is
Since it is connected to the emitters of multiple switching transistors via individual balance resistors, even if the snubber circuit is shared by multiple switching transistors, the discharge current from the capacitor will not be concentrated in one switching transistor. can be prevented.

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be explained in detail below with reference to the drawings. FIG. 1 is a circuit diagram showing an embodiment of a power supply circuit according to the present invention. Components in FIG. 1 that are the same as those in FIG. 4 are designated by the same reference numerals and their explanations will be omitted.

That is, a DC power supply 1, a converter transformer 2
, base drive circuit 3, load 4, input winding Lp, output winding Ls, switching transistors Q1, Q2, balance resistors R1, R2, capacitor C3, and diode D1 are the same as in the conventional example shown in FIG.

The difference in this embodiment is that instead of separately connecting snubber circuits in parallel to the collector-emitter paths of switching transistors Q1 and Q2, a capacitor is connected between the collector of switching transistor Q1 and the negative terminal of power supply 1. A snubber circuit consisting of C11 and resistor R11 is connected so that switching transistors Q1 and Q2 can share this snubber circuit.

To explain in more detail, capacitor C1
1, one end is connected to the collectors of switching transistors Q1 and Q2, and the other end is connected to the connection point between power supply 1 and balance resistor R1 (power supply 1 and balance resistor R1) through resistor R11.
2 connection point).

According to this embodiment, when the switching transistors Q1 and Q2 are cut off, the input winding Lp
The abnormal voltage rise caused by the inductance L1 is
It is absorbed by the capacitor C11 that constitutes the snubber circuit. In this case, the resistor R11 prevents resonance between the input winding Lp and the capacitor C2. When switching transistors Q1 and Q2 are turned on, balance resistors R1 and
R2 and resistor R11 consume the energy stored in capacitor C2.

On the other hand, switching transistors Q1, Q
When switching transistors Q1 and Q2 are turned on, switching transistors Q1 and
Even if the resistances between the respective collectors and emitters of Q2 are significantly different, the switching transistors Q1,
Q2 is connected to the snubber circuit through individual balance resistors, so the ratio Ra of the resistor Ra1 of the series connection of the switching transistor Q1 and the resistor R1 to the resistor Rb1 of the series connection of the switching transistor Q2 and the resistor R2 is
1/Rb1 does not differ much from 1 even if the on-timing shifts, and the discharge current from the capacitor C11 will not concentrate on one switching transistor.

In this way, in this embodiment, the snubber circuit of the switching transistors Q1 and Q2 can be shared, making it possible to reduce the number of parts and manufacturing costs.

FIG. 2 is a circuit diagram showing another embodiment of the power supply circuit according to the present invention. In FIG. 2, the same components as in FIG. 1 are denoted by the same reference numerals, and the description thereof will be omitted.

That is, a DC power supply 1, a converter transformer 2
, base drive circuit 3, load 4, input winding Lp, output winding Ls, switching transistors Q1, Q2, balance resistors R1, R2, capacitor C3, and diode D1 are the same as in the embodiment of FIG.

The difference in this embodiment is that the collectors of the switching transistors Q1 and Q2 are connected to the connection point between the balance resistor R1 and the power supply 1 via a parallel circuit of a resistor R21 and a diode D11, and a snubber circuit consisting of a capacitor C21. That's true.

More specifically, the collectors of the switching transistors Q1 and Q2 are connected to one end of a capacitor C21 via a resistor R21, and also to the anode of a diode D11. Diode D1
The cathode of No. 1 is connected to one end of the capacitor C21. The other end of the capacitor C11 is the connection point between the power supply 1 and the balance resistor R1 (the connection point between the power supply 1 and the balance resistor R2)
is connected to.

According to this embodiment, the abnormal voltage rise generated from the input winding Lp due to the interruption of the switching transistors Q1 and Q2 is absorbed by the capacitor C21 forming the snubber circuit via the diode D11. On the other hand, when discharging the charge absorbed by the capacitor C11, the current due to this charge flows through the resistor R11 without passing through the diode D11, so the input winding L
Resonance between p and capacitor C21 is prevented by resistor R21. Thereafter, when the switching transistor Q1 is turned on, the balance resistors R1, R2 and the resistor R11 consume the energy stored in the capacitor C2.

According to this embodiment, there is an effect similar to that of the embodiment of FIG. 1, and the abnormal voltage rise generated by the inductance L1 of the input winding Lp is absorbed by the capacitor C21 without going through the resistor R21. Therefore, it is possible to absorb abnormal voltage increases with higher efficiency.

FIG. 3 is a circuit diagram showing another embodiment of the power supply circuit according to the present invention, which is adapted to simplify the circuit. In FIG. 2, the same components as in FIG. 1 are denoted by the same reference numerals, and the description thereof will be omitted.

In FIG. 3, the snubber circuit is connected to a capacitor C.
31, switching transistors Q1, Q
2 is connected to the connection point between the power supply 1 and the balance resistor R1 via the capacitor C31.

According to this embodiment, the abnormal voltage rise caused by the inductance L1 of the input winding Lp due to the interruption of the switching transistors Q1 and Q2 is absorbed by the capacitor C31. Thereafter, when switching transistors Q1 and Q2 are turned on, balance resistors R1 and R2 and resistor R11 consume the energy stored in capacitor C31.

Here, the inductance L of the input winding Lp
1 and capacitor C31 is also considered, but the inductance L1 and capacitance Cx of capacitor C31 should be set to appropriate values.
That is, if the switching frequency is w, then

[0034]

Resonance can be suppressed by setting as follows.

According to this new configuration, the resistance of the snubber circuit can be reduced, and the number of parts can be reduced more than in the embodiment of FIG.

In the embodiment shown in FIG. 1, the resistor R11
The positions of the capacitor C11 and the capacitor C11 may be interchanged. In addition, in the embodiment of FIG. 2, the resistor R11 and the diode D
The positions of the parallel circuit with C11 and the capacitor C11 may be exchanged. Furthermore, the snubber circuits of the embodiments shown in FIGS. 1 to 3 can also be applied to switch circuits for turning on and off solenoids, such as snubber circuits for electromagnetic relays.

[0038]

As described above, according to the present invention, the snubber circuit can be shared, the number of parts can be reduced, and the cost can be reduced.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing an embodiment of a switching power supply circuit according to the present invention.

FIG. 2 is a circuit diagram showing another embodiment of the switching power supply circuit according to the present invention.

FIG. 3 is a circuit diagram showing another embodiment of the switching power supply circuit according to the present invention.

FIG. 4 is a circuit diagram showing a conventional switching power supply circuit.

[Explanation of symbols]

1 DC power supply 12 Converter transformer 3 Base drive circuit Lp Input winding Ls Output winding Q1, Q2 Switching transistor R1, R2
Balance resistor C11 Capacitor R11 Resistor

Claims (3)

[Claims] Claim 1: A positive terminal of a DC power source is connected to one end of the input winding of a converter transformer having an input winding and an output winding, and collectors of a plurality of switching transistors are connected to the other end of the input winding. , a base drive circuit is connected to the bases of the plurality of switching transistors, the emitters of the plurality of switching transistors are connected to the negative terminal of the DC power supply through individual balance resistors, and the DC power supply is connected to the input winding. In a switching power supply circuit that obtains an output voltage from the output winding by supplying an input voltage from the output winding, one end of a snubber circuit consisting of a series circuit of a resistor and a capacitor is connected to the collector of the plurality of switching transistors, and the series circuit is connected to the collector of the plurality of switching transistors. A switching power supply circuit characterized in that the other end is connected to a connection point between the balance resistor and the negative terminal of the DC power supply. 2. The switching power supply circuit according to claim 1, further comprising a diode connected in parallel to the resistor of the snubber circuit according to claim 1, with an anode facing toward the input winding of the converter transformer. 3. A positive terminal of a DC power source is connected to one end of the input winding of a converter transformer having an input winding and an output winding, and collectors of a plurality of switching transistors are connected to the other end of the input winding. , a base drive circuit is connected to the bases of the plurality of switching transistors, the emitters of the plurality of switching transistors are connected to the negative terminal of the DC power supply through individual balance resistors, and the DC power supply is connected to the input winding. In a switching power supply circuit that obtains an output voltage from the output winding by supplying an input voltage from the output winding, one end of the capacitor is connected to the collector of the plurality of switching transistors, and the other end of the capacitor is connected to the balance resistor and the collector of the DC power supply. A switching power supply circuit characterized in that it is connected to a connection point with a negative terminal.