JPS6264267A - Switching regulator - Google Patents

Abstract

PURPOSE:To obtain stable output voltage, by connecting a control coil between the base and the emitter of a main transistor, and by enabling a control circuit to be not influenced by a current detection resistance. CONSTITUTION:The both ends of a control coil 2b of a transformer 2 are connected between the base and the emitter of a main transistor 10 via a resistance 12, and the action of a control circuit 4 is arranged to be not influenced by a current detection resistance 11. The voltage of a condenser 13 which should be always monitored to be constant to be set a value obtained by deducting blocking-layer voltage between the base and the emitter of the main transistor 10, from the voltage of a Zener diode 15, and the both voltage is kept constant, and so output voltage can be stabilized.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of the Invention] The present invention relates to a switching regulator that controls opening and closing of a main transistor to transmit power at a constant voltage from a primary coil of a transformer to an output coil.

[Prior art and its problems]

Switching regulators, which use a transistor to pass intermittent DC current through the primary coil of a transformer and utilize the constant voltage obtained at the output coil of the transformer, are often used as stabilized power sources for electronic devices. A conventional example of such a switching regulator is shown in FIG. Here, the main parts of the circuit include a first current power supply 1, a transformer 2) a main current circuit 3, a control circuit 4, a control transistor 5, an output circuit 6, etc. The DC power supply 1 has an AC power supply 7 rectified by a full-wave rectifier 8 and smoothed by a smoothing capacitor 9. The transformer 2 has a primary coil 2'a1 and a control coil 2b.

a main transistor 10 having an output coil 2C and having a collector connected to the secondary coil 2a and the primary coil 2a;
1! A series circuit of current detection resistors 11 forms a main current circuit 3, a second coil 2a1 is connected to a DC power supply terminal, and a resistor 11 is connected to one terminal.

One end of the control coil 2b is connected to the base of the main transistor IO via a resistor 12, and the other end is connected to one terminal f of the power supply 1.

The control circuit 4 includes one capacitor 13 at both ends of the control coil 2b.
A Zener diode 15 is connected between the connection point of the capacitor 13 and the diode 14 and the base of the main transistor 10.

Further, the base of the main transistor 10 is connected to the ten terminal of a power source 1 via a starting resistor 1G. The control transistor 5 has its collector connected to the base of the main transistor 10, its emitter connected to one terminal of the source 1, and its base connected to the connection point between the main transistor 10 and the resistor 11. The output circuit 6 is a series circuit of a diode 17 and an output capacitor 18 connected to the output coil 2c.
A load 19 is connected to both ends of the capacitor 18 . Note-
An ordinary snubber circuit 20 is connected to both ends of the secondary coil 2a.

When the power supply l is applied, a base current flows to the transistor 10 via the starting resistor 16, and the transistor 10 begins to conduct. Then, '1!' is applied to the primary coil 2a of the transformer 2! The current begins to flow, the control coil 2b voltage rises, and the base current increases through the resistor 12, so that the main transistor lO momentarily slows down to a saturated conduction state. Therefore, the current of the secondary coil 2a increases linearly, and the resistance 11
is a voltage drop vTL proportional to the current I in the primary coil 2a.
is obtained. When this voltage drop V exceeds the emitter layer voltage between the base and emitter of the control transistor 5, the transistor 5 becomes conductive, and the transistor 5 shunts the base current of the main transistor 10 that was flowing through both resistors 12 and 16. The main transistor 10 then goes into a non-saturated state. As a result, since ti flowing through the secondary coil 2aJ decreases, the voltage of the control coil 2b also decreases, the current flowing through the resistor 12 decreases, and the current of the main transistor 10 is instantaneously cut off. Subsequently, the base current begins to flow into the main transistor 10 via the resistor 16 again, and the above-described operation is repeated. In this way, the current I in the coil 2a is intermittent in a sawtooth pattern, and the voltage V across the current detection resistor 11 has a waveform as shown in FIG. That is, the voltage vR increases from 0 as the iTI of MIRr increases linearly, and when the control transistor 5 becomes conductive, the current flow is instantaneously cut off, so that the voltage vR reaches its maximum value vR.
It suddenly drops from p to 0 and this is 1j4! return. When the current T is cut off, voltages of opposite polarity to the current voltage are generated in each coil 2a, 2b, 2c of the transformer 2. At this time, the voltage generated in the secondary coil 2a is absorbed by the snubber circuit 2o. In addition, the output coil 2c is the main transistor 10.
When conductive, the energy stored in the transformer 2 is released, rectified by the diode 17, charged to the capacitor 18, and supplied to the load 19. The voltage generated in the control coil 2b is rectified by the diode 14 and charged into the capacitor 13. Here, the voltage of the output coil 2C and the voltage of the control coil 2b are proportional to the turns ratio since the fills 2b and 2c are wound around the same core, and both capacitors 13 and 18 charged with these voltages are proportional to the turns ratio. The same applies to the voltage. In other words, the voltage V between the terminals of the capacitor 13. monitor,
This voltage V. If the output voltage is controlled to be constant, the output voltage can also be kept constant. So the voltage is V. If the voltage becomes high, the Zener diode 15 can absorb the base current of the main transistor 10 to reduce the current flow. If it becomes low, you can do the opposite. This 1 voltage VC is applied from the Zener voltage vz of the Zener diode 15 to the main transistor 10.
It is the value obtained by subtracting the maximum value VRp of the drop voltage vR of the current detection resistor 11 from the base-emitter cap layer voltage vB1o. By the way, the Zener voltage v2 is constant even with changes in the current, and the voltage ``BIO'' is also the characteristic value of the transistor and does not change, but the voltage vR of the resistor 11 increases linearly at first as already mentioned, and then suddenly increases. However, the maximum voltage VRp of this voltage vR is pulled from the Zener voltage. However, the maximum voltage vFL of this voltage vR varies depending on the magnitude of the power supply voltage and the magnitude of the load. Therefore, the voltage v0 has low stability, and the capacitor There is a drawback that the voltage across the terminal 18, that is, the stability of the output voltage is low, and it is not suitable as a stabilized power supply for electronic devices such as microcomputers that require high stability.

[Purpose of the invention]

SUMMARY OF THE INVENTION An object of the present invention is to provide a switching regulator that has less fluctuation in output voltage due to fluctuations in power supply voltage or load, without increasing the number of parts or cost.

[Key points of the invention]

The present invention provides a main current circuit including a single-layer coil of a transformer, a main transistor, and a current detection resistor connected in series, a control circuit, and a control circuit that is wound around the transformer to conduct the main transistor and connect the main current circuit through the control circuit. In the switching regulator, the switching regulator includes a control coil that controls a base current of a transistor, and a control transistor that suppresses the current of the current detection resistor when it exceeds a predetermined value, wherein the control coil is connected between the base and emitter of the main transistor. The control coil is connected between the base and emitter of the main transistor, and the current detection resistor is connected closer to the power supply than this control coil, so that the output voltage is not affected by the voltage drop of this current detection resistor. This is what I did. Note that if a shunt transistor controlled by a control circuit is connected in parallel with the control transistor, stability will be improved, and furthermore, changes in characteristics due to temperature changes of the main transistor can be compensated for.

[Embodiments of the invention]

Embodiments of the present invention will be described in detail with reference to FIGS. 1 and 2. Here, parts and circuits that have the same role as those in FIG. 3 are given the same reference numerals as in FIG. 3, and their explanations are omitted. In FIG. 1, the connections of the DC power supply 1, the transformer 2), the main current circuit 3, the control transistor 5, the output circuit 6, the snubber circuit 20, etc. are completely the same as those of the conventional one, so their explanation will be omitted. This circuit differs from conventional circuits in that it has a control coil 2b, and both ends of the control coil 2b are connected through a resistor 12 between the base and emitter of the main transistor 10. In this way, the current detection resistor 11 is connected so as not to affect the operation of the control circuit 4. Control circuit 4
In other words, a series circuit consisting of a capacitor 13 and a diode 14 connected to both ends of the control coil 2b.The operation of this repolulator is almost the same as that of a conventional one, but it must be constantly monitored and kept constant. The voltage V of the capacitor 13 is the voltage Vz of the Zener diode 15.
The voltage VB1o between the base and emitter of the main transistor 100 is subtracted from the voltage VB1o between the base and emitter of the main transistor 100.
FIIO is constant as already mentioned. Moreover, the voltage V
. If the voltage increases, the direct current of the Zener diode 15 increases, reducing the base current of the main transistor 10, reducing the current flow of the main current circuit 3, and lowering the voltage VC. Voltage V. When V decreases, the current 1 is increased by the reverse operation, and the voltage V is increased.

In other words, the output voltage is always kept constant. This circuit does not include the voltage drop V across the resistor 11, which tends to change due to fluctuations in the power supply voltage and load, as in conventional circuits. , so the output voltage is stabilized.

Next, FIG. 2 shows a different embodiment from FIG. 1, in which the main current circuit 3 and control transistor 5 are the same as those in FIG. 1, but a shunt transistor 21 is connected in parallel with the control transistor 5 and connected to the control coil 2b. capacitor 13 and diode 1
A resistor 22 and a Zener diode 15 are connected between the connection point of the series circuit of No. 4 and the base of the main transistor IO, and the point where the connection point of this resistor 22 and the Zener diode 15 is connected to the base of the shunt transistor 21. Different from Figure 1. The voltage v0 of the capacitor 13 of this control circuit 4 is obtained by subtracting the base-emitter enlayer voltage vB1o of the main transistor 100) from the Zener voltage v2, and
The value is the sum of the base-emitter cap layer voltage vB21 of 1. Although the main transistor 10 and the shunt transistor 21 have different types, they are both transistors, and the voltage vBIO and the M voltage vB21 are almost equal, so they cancel out the voltage V. is approximately equal to the always constant Zener voltage v2, and the fluctuation of the output voltage is further reduced. In this circuit, the main transistor 100 base current is absorbed by the shunt transistor 21, and the current in the main current circuit 3 is controlled.

In this embodiment, the cap layer voltage vB1o between the base and emitter of the main transistor 10 is affected by temperature. For example, when the temperature rises and the voltage "BIO" decreases, the cap layer voltage vB1o between the base and emitter of the shunt transistor 21 decreases accordingly.
i Voltage vB21 also becomes low. Moreover, the voltage VI31o? Since tFE and VB21 mutually cancel out tc with respect to voltage V0, they have the effect of compensating for the relatively large change in temperature characteristics of main transistor 1O(1).

Note that when the load is short-circuited, a large current flows through the main transistor and there is a risk that the main transistor will be destroyed, but in this case the control transistor suppresses the current in the main transistor to prevent this destruction.

The conventional device of FIG. 3 also serves to prevent saturation of the transformer.

〔Effect of the invention〕

As described above, according to the present invention, the control coil is connected between the base and emitter of the main transistor, so that the control circuit is not affected by the current detection resistor, so fluctuations in power supply voltage and load Even if the voltage drop across the current detection resistor fluctuates, a stable output voltage can be obtained, allowing it to be used in a wide range of applications as a stabilized power supply. In addition, if a shunt transistor is connected to the control circuit and controlled, this shunt transistor operates to obtain and compensate for higher output voltage stability, and the output voltage becomes more stable in response to temperature changes. big.

[Brief explanation of drawings]

Figures 1 and 2 are wiring diagrams showing different embodiments of switching regulators according to the present invention, Figure 3 is a wiring diagram showing an example of a conventional switching regulator, and Figure 4 is the switching regulator of Figure 3. FIG. 3 is a waveform diagram showing a voltage drop across a current detection resistor in FIG. l...DC power supply, 2...Transformer, 2a...-secondary coil, 2b...control coil, 3...main current circuit, 4
...Control circuit, 5...Main transistor, 11...
Current detection resistor, 21... shunt transistor. f'3 Mouth 4th ward

Claims (1)

[Scope of Claims] 1) A main current circuit in which a primary coil of a transformer, a main transistor, and a current detection resistor are connected in series, a control circuit, a main current circuit that is wound around the transformer, conducts the main transistor, and connects the control circuit. A switching regulator includes a control coil that controls the base current of the main transistor through a control transistor, and a control transistor that suppresses the current of the current detection resistor when it exceeds a predetermined value, the control coil connecting the base and emitter of the main transistor. A switching regulator characterized in that the switching regulator is connected between. 2) The switching regulator according to claim 1, wherein the control circuit controls the base current of the main transistor via a shunt transistor connected in parallel with the control transistor.