JP3523091B2 - Switching power supply - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a current mode control type switching power supply device having a constant current feedback loop.

[0002]

2. Description of the Related Art Conventionally, a power MOS-FET has been used as a main switching element of a large capacity DC-DC converter.
(Metal oxide semiconductor semiconductor field effect transistor) is used.

FIG. 11 shows an example of a switching power supply device using a power MOS-FET as a main switching element, where T is a transformer having a primary winding and a secondary winding,
Q10 is a MOS-FET, OP1 and OP2 are operational amplifiers, R
11 is a current detection resistor. Primary winding of transformer T, MO
The DC power supply voltage from the DC power supply E is applied to the series circuit of the S-FET Q10 and the current detection resistor R11. C
Reference numeral 1 is a capacitor on the input side, which is connected in parallel to the DC power source E. The secondary winding of the transformer T is connected with a diode D2 and a capacitor C3 which form a rectifying and smoothing circuit,
The load LD is connected to the secondary winding via this. The operational amplifier OP1 compares the voltage across the load, that is, the output voltage, with the reference voltage Vref. When the output voltage is reduced under heavy load, a high comparison output voltage is applied to the operational amplifier OP2, and the output voltage is reduced under light load. Is rising, a low comparison output voltage is applied to one end of the operational amplifier OP2. Therefore, in the case of heavy load, since the comparison output voltage at one end of the operational amplifier OP2 is high, the on-state of the MOS-FET Q10 is continued until the detection value of the current detection resistor R11 applied to the other end becomes large (turn-off timing). Will be delayed).
On the contrary, when the load is light, the comparison output voltage at one end of the operational amplifier OP2 is low, so that the MOS-FET Q10 is turned off (the turn-off timing is advanced) with a small detection value of the current detection resistor R11 applied to the other end.

As described above, the circuit of FIG. 11 constitutes a current mode control type switching power supply device having a constant current feedback loop to stabilize the output voltage on the secondary side of the transformer.

[0005]

By the way, as shown in FIG. 11, when the current detecting resistor R11 is inserted between the source of the MOS-FET Q10 and the ground, the circuit configuration becomes simple, but is shown by the dotted line in the figure. The detection voltage of the current detection resistor R11 is influenced by the gate capacitance (Ciss: total FET capacitance seen from the gate), the gate-drain capacitance, and the gate-source capacitance of the MOS-FET Q10. That is, MO
When the S-FET Q10 is turned on, as shown in FIG. 12A, a spike-shaped current resulting from the charge current of the gate capacitance (Ciss) and the discharge current of the gate-drain capacitance and the gate-source capacitance. Is superimposed on the transformer primary current.
Therefore, under heavy load or full load, MOS-FET Q1
There is no problem because the detection level of the transformer primary current that turns off 0 is higher than the peak of the spike-shaped current, but no load or light load is applied to the MOS-FET Q10.
In some cases, the detection level of the primary current of the transformer that turns off is lower than the peak of the spike-like current, which causes the output voltage stabilizing operation to become unstable. That is, if the transformer primary current is equal to or lower than the peak of the spike-shaped current, there is a risk that the spike-shaped current is erroneously recognized as the transformer primary current and controlled.

Incidentally, as a known technique, Japanese Patent Laid-Open No. 4-2178.
No. 59, a current detecting means is inserted between the source and the ground of the MOS-FET, and the spike-like current is removed by the filter function of the resistance and capacitor of the peak detecting circuit. However, since the MOS-FET is for high power and the peak of the spike-like current is high, and the removal of the spike-like current by the filter action is incomplete, the operation becomes unstable and the switching frequency is increased. In that case, it becomes difficult to select the constants of the resistors and capacitors.

Another conventional technique avoids the above problem by disconnecting the current detection circuit only during a period (several nsec to several hundreds nsec) in which the main switching element is turned on to generate a spike-shaped current. However, since the minimum ON period is determined by this dead time, it is difficult to increase the frequency and the operation near a no load may become unstable.

In view of the above points, the present invention eliminates the instability of the output stabilization control caused by the charging / discharging current of the electrostatic capacity of the main switching element, and provides stable output from no load to full load. An object is to provide a controllable switching power supply device.

Other objects and novel features of the present invention will be clarified in the embodiments described later.

[0010]

In order to achieve the above object, the invention of claim 1 of the present application is a transformer, a switching element for connecting and disconnecting a current of a primary winding of the transformer, and a secondary winding of the transformer. In a current mode control type switching power supply device comprising a rectifying / smoothing circuit for rectifying and smoothing the induced voltage of the rectifying smoothing circuit, and a stabilizing control circuit for controlling an output voltage of the rectifying / smoothing circuit and a current flowing through the switching element Current detecting means for detecting a current flowing through the primary winding is inserted between the side of the switching element not connected to the switching element and the DC power supply, or between the primary winding and the switching element , the current detecting means is the primary Winding
DC power supply and the side of the switching element not connected
Or between the primary winding and the switching element
Insert a resistor to connect the bases of the first and second transistors
The second transistor of the current mirror circuit connected in common
Connect the emitter of the resistor to one end of the sensing resistor and
The first transformer is connected to a constant current source or a resistor.
The emitter of the transistor is connected to the other of the detection resistor through a series resistor.
The current to be detected flowing through the detection resistor is connected to the first end.
The feature is that detection is performed on the collector side of the first transistor .

[0011]

[0012]

[0013]

According to a second aspect of the present invention, a choke coil and a switching element for connecting and disconnecting the current of the choke coil are provided.
A current mode control type switching power supply including a rectifying and smoothing circuit that rectifies and smoothes an induced voltage on the output side of the choke coil, and a stabilization control circuit that controls an output voltage of the rectifying and smoothing circuit and a current flowing through the switching element. In the device, a current detecting means for detecting a current flowing through the switching element is inserted between the input side of the choke coil and a DC power source, or between the choke coil output side and the switching element, and the current detecting means is A detection resistor is inserted between the input side of the choke coil and the DC power source, or between the output side of the choke coil and the switching element, and the bases of the first and second transistors are connected in common to the second mirror of the current mirror circuit. Connect the emitter of the transistor to one end of the sensing resistor and connect the collector to a constant current source or resistor. The emitter of the first transistor is connected to the other end of the detection resistor via a series resistor, and the detected current flowing through the detection resistor is characterized by detecting at a collector side of the first transistor.

[0015]

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT An embodiment of a switching power supply device according to the present invention will be described below with reference to the drawings.

FIG. 1 shows a first embodiment of the present invention. In a current mode control type switching power supply device (DC-DC converter) having a constant current feedback loop, the current detection means DT is replaced by a transformer T. It is inserted between the side of the primary winding where the switching element is not connected and the DC power source E. The source of the MOS-FET Q10 as a switching element is directly connected to the ground.

Since the current detecting means DT is inserted on the positive side of the DC power source E, it is necessary to devise a method for obtaining a current detected value with the ground level as a reference. FIG. 2 shows a first specific example of the current detecting means DT in consideration of this point. The current detecting means DT is a current detecting circuit using a current mirror circuit, and the emitter of the second transistor Q2 of the current mirror circuit in which the bases of the first and second PNP transistors Q1 and Q2 are connected in common is used. Detection resistor R1
Of the first transistor Q1 to the other end (current inflow end) a of the detection resistor R1 via the series resistor R2. The detection resistor R1 is connected in series with the current detection line. The detected current Iin flowing through the detection resistor R1 is detected from the detection signal current Iout on the collector side of the first transistor Q1.

It is desirable to use a pair of monolithic transistors for Q1 and Q2. Further, it is premised that the current detection line has a high potential with respect to the ground line, and a protection resistor R31 of the transistor Q1 and an output detection resistor R32 are connected between the collector of the transistor Q1 and the ground, A detection signal voltage (current detection value) proportional to the detection signal current Iout is taken out from the output terminal c.

In the case of the circuit of FIG. 2 in which the emitter of the first transistor Q1 is connected to the detection resistor R1 via the series resistor R2, the detection signal current Iout changes almost linearly with respect to the current Iin to be detected. The primary current of the transformer T (current of MOS-FET Q10) can be detected from the detection signal voltage across R32 to stabilize the output voltage of the switching power supply device. The rest of the configuration is similar to that of FIG. 11 described above.

FIG. 12B is an example of the detected current Iin flowing through the detection resistor R1 under full load and light load, and shows the gate capacitance (Ciss), the gate-drain capacitance, and the gate of the MOS-FET Q10. -It can be seen that it is not affected by the capacitance between sources.

According to the first embodiment, the following effects can be obtained.

(1) Since the current detecting means DT is inserted between the DC power source E and the side of the primary winding of the transformer T to which the switching element is not connected, the detected current Iin flowing through the detecting resistor R1 in the current detecting means DT. Is not affected by the gate capacitance (Ciss), the gate-drain capacitance, and the gate-source capacitance of the MOS-FET Q10. Therefore, stable output stabilization control is possible from no load to full load.

(2) By using the current detection circuit utilizing the current mirror circuit of FIG. 2 as the current detection means DT, the current detection value based on the ground level can be easily obtained, and the detected current Iin A current detection value that is directly proportional to is obtained, and highly accurate control is possible.

FIG. 3 shows a second embodiment of the present invention.
In this case, the current detecting means DT is inserted between the primary winding of the transformer T and the switching element. The source of the MOS-FET Q10 as a switching element is directly connected to the ground. Other configurations and operational effects are similar to those of the first embodiment described above.

FIG. 4 shows a third embodiment of the present invention, which is an example of a chopper type switching power supply device (DC-DC converter) using a choke coil CH instead of a transformer. In this case, the current detecting means DT is inserted between the input side of the choke coil CH (the side to which the switching element is not connected) and the DC power source E. The source of the MOS-FET Q10 as a switching element is directly connected to the ground. The other configurations are the same as those of the first
The same reference numerals are given to the same or corresponding parts.

In the case of the third embodiment, the configuration for stabilizing the output is the same as that of the above-described first embodiment, except for the operating principle of the chopper system, and the same operational effect. Can be obtained.

FIG. 5 shows a fourth embodiment of the present invention, which is an example of a chopper type switching power supply device (DC-DC converter) using a choke coil CH instead of a transformer. In this case, the current detecting means DT is inserted between the output side of the choke coil CH and the MOS-FET Q10 as a switching element. However, the diode D2 of the rectifying / smoothing circuit is connected to the drain of the MOS-FET Q10. The source of the MOS-FET Q10 is directly connected to the ground. The other configurations and effects are the same as those of the third embodiment described above, and the same or corresponding parts are designated by the same reference numerals.

FIG. 6 shows a fifth embodiment of the present invention, which is an example of a chopper type switching power supply device (DC-DC converter) using a choke coil CH instead of a transformer. In this case, the current detecting means DT is inserted between the MOS-FET Q10 and the connection point between the output side of the choke coil CH and the diode D2 of the rectifying and smoothing circuit. The source of the MOS-FET Q10 is directly connected to the ground. Note that the other configurations and effects are the same as those of the above-described fourth embodiment, and the same or corresponding parts are designated by the same reference numerals.

In the current detecting means DT of FIG. 2, a phenomenon called the Early effect occurs in which the detection signal voltage (current detection value) changes as the voltage between the current inflow end a of the detection resistor R1 and the ground changes. However, the second specific example of the current detecting means DT of FIG. 7 shows a circuit configuration in which a Wilson current mirror circuit (Wilson mirror circuit) is applied in order to eliminate the Early effect. In this figure, a third transistor Q3 having the same polarity as the first transistor Q1 is inserted in series on the collector side of the first transistor Q1, and the bases of the transistors Q1 and Q2 are connected to the emitter of the third transistor Q3. , The third transistor Q3
Is connected to the collector of the second transistor Q2, and the collector of Q3 is connected to the output terminal c. The rest of the configuration is the same as that of the first specific example of the current detecting means DT of FIG. 2 described above.

In the second specific example of FIG. 7, the Early effect is eliminated, and the detection signal voltage (current detection value) accompanying a change in the voltage between the current inflow end a of the detection resistor R1 and the ground.
Can be eliminated, the current detection accuracy can be further improved, and it can be applied to each of the above-described embodiments.

FIG. 8 shows a third concrete example of the current detecting means DT which can be used in each of the embodiments. The constant current source on the collector side of the second transistor Q2 in the first concrete example of FIG. It is realized by R5 and constant voltage diode ZD.
Further, a series circuit of resistors R31 and R32 for flowing the detection signal current Iout is connected between the collector of the first transistor Q1 and the ground, and the connection point of the resistors R31 and R32 is the output terminal c. Other configurations are similar to those of the above-described first specific example.

FIG. 9 shows a fourth concrete example of the current detecting means DT which can be used in each of the embodiments. A constant current source on the collector side of the second transistor Q2 in the second concrete example of FIG. It is realized by R5 and constant voltage diode ZD.
Further, a series circuit of resistors R31 and R32 for flowing the detection signal current Iout is connected between the collector of the third transistor Q3 and the ground, and the connection point of the resistors R31 and R32 is the output terminal c. Other configurations are similar to those of the second specific example described above.

FIG. 10 shows a fifth specific example of the current detecting means DT which can be used in each of the embodiments. The current transformer (current transformer) CT and the current-voltage converter for converting the detected current value by the current transformer into a voltage. It is composed of A1. The voltage output value of the current-voltage converter A1 may be added to the operational amplifier OP2 shown in FIG.

The present invention is a current mode control type switching power supply device having a constant current feedback loop.
Obviously, it can be applied to various circuit configurations.

Further, in the first to fourth specific examples of the current detecting means DT, a low pass filter may be further added to the output terminal c side.

Although the embodiment of the present invention has been described above, it is obvious to those skilled in the art that the present invention is not limited to this and various modifications and changes can be made within the scope of the claims. Ah

[0038]

As described above, according to the switching power supply device of the present invention, it is stable from no load to full load without being affected by the charge / discharge current of the electrostatic capacity of the main switching element. Such control is possible, and in particular, there is an advantage that it is possible to cope with an increase in output power and an increase in switching frequency.

[Brief description of drawings]

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

FIG. 2 is a circuit diagram of a first specific example of current detection means DT usable in each embodiment.

FIG. 3 is a circuit diagram showing a second embodiment of the present invention.

FIG. 4 is a circuit diagram showing a third embodiment of the present invention.

FIG. 5 is a circuit diagram showing a fourth embodiment of the present invention.

FIG. 6 is a circuit diagram showing a fifth embodiment of the present invention.

FIG. 7 is a circuit diagram of a second specific example of current detection means DT usable in each embodiment.

FIG. 8 is a circuit diagram of a third specific example of current detection means DT usable in each embodiment.

FIG. 9 is a circuit diagram of a fourth specific example of the current detection means DT usable in each of the embodiments.

FIG. 10 is a current detection means DT usable in each of the embodiments.
It is a circuit diagram of the 5th specific example of.

FIG. 11 is a circuit diagram of a conventional switching power supply device.

FIG. 12 is a waveform diagram showing the current detection waveforms of the related art and each embodiment of the present invention in comparison.

[Explanation of symbols]

A1 current-voltage converter C1 and C3 capacitors CH choke coil D2 diode E DC power supply LD load Q1, Q2, Q3 transistors Q10 MOS-FET OP1, OP2 operational amplifier R1, R2, R4, R5, R11, R31, R32 resistance T transformer ZD constant voltage diode

─────────────────────────────────────────────────── --- Continuation of the front page (56) References JP-A-4-21362 (JP, A) JP-A-4-87558 (JP, A) JP-A-9-140129 (JP, A) JP-A-10- 127049 (JP, A) JP 10-174428 (JP, A) JP 1-67613 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) H02M 3/28 H02M 3 / 335

Claims (2)

(57) [Claims] 1. A transformer, a switching element for connecting and disconnecting a current in a primary winding of the transformer, a rectifying / smoothing circuit for rectifying and smoothing an induced voltage in a secondary winding of the transformer, and an output voltage of the rectifying / smoothing circuit. In a current mode control type switching power supply device including a stabilization control circuit that controls a current flowing through the switching element, a current detection unit that detects a current flowing through the switching element, the switching element of the switching element of the primary winding. Inserted between the unconnected side and the DC power supply, or between the primary winding and the switching element , the current detection means is the switching of the primary winding.
Between the unconnected side of the element and the DC power supply, or the primary winding
A detection resistor is inserted between the switching element and
And a curren in which the bases of the second transistor are commonly connected
In front of the emitter of the second transistor of the mirror circuit
Connect to one end of the detection resistor and connect the collector to a constant current source or
Connected to a resistor and the emitter of the first transistor is a direct
Connect to the other end of the detection resistor via a column resistor to detect the
The detected current flowing through the resistor is
A switching power supply device characterized by detection on the side of the reflector . 2. A choke coil, a switching element for connecting and disconnecting the current of the choke coil, and a rectifying / smoothing circuit for rectifying and smoothing an induced voltage on the output side of the choke coil.
In a current mode control type switching power supply device including a stabilization control circuit that controls an output voltage of the rectifying and smoothing circuit and a current that flows in the switching element, current detection means that detects a current flowing in the switching element, Inserted between the input side of the choke coil and the DC power supply, or between the choke coil output side and the switching element, the current detection means, between the input side of the choke coil and the DC power supply, or the choke coil output side and the A detection resistor is inserted between the switching elements, the emitter of the second transistor of the current mirror circuit in which the bases of the first and second transistors are commonly connected is connected to one end of the detection resistor, and the collector is a constant current source. Alternatively, the emitter of the first transistor is connected to a resistor, and the emitter of the first transistor is connected to the detection resistor Connected to the other end, a switching power supply apparatus characterized by detecting at a collector side of the current to be detected flowing through the detection resistor said first transistor.