JP3242471B2 - Switching regulator - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a switching regulator for controlling an output voltage to be constant, and more particularly to a dummy load circuit connected to an output side thereof.

[0002]

2. Description of the Related Art FIG. 3 is a circuit diagram of a conventional switching regulator. In FIG. 3, the switching regulator transformer 1 has a switching transistor 1c connected in series to its primary winding 1a, and when a pulse voltage is applied to the primary winding 1a, an exciting current intermittently flows through the primary winding 1a. Thus, a secondary voltage is generated at both ends of the secondary winding 1b and the auxiliary winding 1f. Further, an auxiliary winding side diode 1d and an auxiliary winding side capacitor 1e are connected to the auxiliary winding 1f to form a half-wave rectifier circuit. The auxiliary voltage is obtained from both ends of the capacitor 1e and is used as a power supply for the pulse width control circuit 5 and the like. As this auxiliary voltage, a voltage of about 12 V to 15 V is always required.

The rectifying / smoothing circuit 2 includes a rectifying diode 2
a, a smoothing choke 2b, a smoothing capacitor 2c, and a flywheel diode 2d. The hot side of the secondary winding 1b of the switching regulator transformer 1 is connected to the anode of the rectifier diode 2a, and the cold side is connected to the ground. Rectifier diode 2a
Is connected to a flywheel diode 2d. The anode of the flywheel diode 2d is connected to the ground. One end of a smoothing choke 2b is connected to the cathode of the flywheel diode 2d, and the other end of the smoothing choke 2b is connected to one end of a smoothing capacitor 2c. This smoothing capacitor 2c
Is connected to the ground. This rectifier / smoothing circuit is the secondary winding 1 of the switching regulator transformer.
The voltage b is rectified and smoothed, and an output voltage is applied to the load 4.

A dummy load resistor 3b is connected in parallel to the rectifying / smoothing circuit 2. If the output voltage is constant, the dummy load current flowing through it is also unchanged. Load 4 is rectified
The output voltage of the rectification / smoothing circuit 2 is applied in parallel with the smoothing circuit 2.

[0005] The pulse width control circuit 5 detects an output voltage from both ends of the rectified and smoothed output and compares it with a preset reference voltage. The output voltage is controlled to be constant by adjusting the drive time (duty ratio) of the switching transistor 1c of the switching regulator transformer 1 according to the fluctuation of the output voltage.

Next, the operation will be described. The conventional switching regulator is configured as described above. When the operation of the switching regulator starts, the load voltage starts to rise, and the output voltage reaches a constant value when the output voltage reaches a constant value by the above-described operation of the pulse width control circuit 5. Since the auxiliary voltage is obtained from the capacitor 1e of the half-wave rectifier circuit based on the capacitor input method, the ratio of the period during which the diode 2a is on to one cycle of the switching of the transistor 1c is obtained from the auxiliary winding 1f. Since the duty ratio is proportional to the auxiliary voltage, an almost constant auxiliary voltage can be obtained if it is several percent or more.

By the way, when the load impedance increases and the load current decreases, the duty ratio of the voltage waveform generated in the auxiliary winding 1f also changes in proportion to the load current and decreases. When reduced to zero ", de
The duty ratio becomes extremely small. In such a state, the auxiliary voltage also decreases, and the pulse width control circuit 5 of the switching regulator cannot operate normally. In order to prevent such an adverse effect, as shown in FIG.
b is connected in parallel with the load circuit 4 and a certain amount of current flows through it.

[0008]

However, the output voltage is controlled to be constant, and a constant current flows through the dummy load resistor 3b irrespective of the magnitude of the load current. Therefore, even if it becomes unnecessary to supply a current to the dummy load resistor 3, the dummy load current flows, and there is a problem that the efficiency of the switching regulator is reduced.

SUMMARY OF THE INVENTION The present invention has been made to solve such a problem, and a switching device having an improved efficiency by connecting a dummy load only at no load and light load and cutting off the load at other times.・ To provide a regulator.

[0010]

A switching regulator according to the present invention comprises a dummy load circuit in which a dummy resistor and a switching element are connected in series, and this series circuit is connected in parallel to a rectifying / smoothing circuit; A bias circuit that supplies a bias voltage for driving the element and constantly drives the switching element, and is connected to the positive output side.
Voltage of the energy stored in the choke coil
Rectified and smoothed, and the smoothed voltage exceeds a predetermined value
And a bias voltage adjusting circuit that adjusts a bias voltage of the bias circuit to make the switching element non-drive state.

[0011]

According to the present invention, when the load current is small, the switching element is driven by the bias circuit and a dummy current flows through the dummy load resistor. As a result, an appropriate output voltage is applied to the auxiliary winding of the switching regulator. can get. If the load current is large ,
The discharge voltage of the stored energy is rectified and smoothed, the bias voltage of the switching element is reduced, the switching element is in a non-driving state, and the dummy current does not flow through the dummy load resistor. Since the dummy load current is cut off in a region where it is not necessary to flow, the efficiency of the switching regulator can be improved.

[0012]

FIG. 1 is a circuit diagram of a switching regulator according to an embodiment of the present invention. "1", "2", "
Those indicated by 4 "and 5" are the same as those shown in Fig. 3. Numeral 3 denotes a dummy current control circuit, which includes a dummy load circuit 31, a bias circuit 32 and a bias voltage adjustment circuit 33. It is configured.

The dummy load circuit 31 is formed by connecting a dummy resistor 3b and a transistor 3e in series and connecting them in parallel to the rectifying / smoothing circuit 2.

In the bias circuit 32, a resistor 3a and a resistor 3g are connected in series, this is connected in parallel to the rectifier / smoothing circuit 2, and a connection point of the resistor 3a and the resistor 3g is connected in series to the base of the transistor 3e. It is formed by being done. The bias circuit 32 supplies a bias voltage for driving the transistor 3e, and constantly drives the transistor 3e.

The bias voltage adjusting circuit 33 includes a capacitor 3f connected between the base of the transistor 3e and the ground.
And a resistor 3d having one end connected to the base of the transistor 3e, a diode 3c having an anode connected to the other end of the resistor 3d, and a cathode connected to the cathode of the rye diode 2d. The bias voltage adjusting circuit 33 rectifies and smoothes the voltage between both ends of the flywheel diode 2d, and when the voltage between both ends exceeds a predetermined value, adjusts the bias voltage of the bias circuit 32 to put the transistor 3e into a non-driving state.

FIG. 2 is a timing chart of the operation of the embodiment of FIG. When the load current is small as shown in the area A in FIG. 2, the forward voltage of the flywheel diode 2d decreases with the decrease in the flywheel current due to the output characteristics of the diode 2d (d in FIG. 2). This means that the voltage between the connection point of the diodes 2a, 2d, and 3c and the ground is reduced. Therefore, diode 3
Since the forward voltage applied to c is small, the current does not flow in the forward direction (f in FIG. 2), and the bias voltage by the bias circuit 32 is applied to the base of the transistor 3e to drive the transistor 3e. (G in FIG. 2). As a result, a dummy current flows through the dummy load resistor 3b.
A necessary auxiliary voltage can be obtained on the output side of the auxiliary winding 1f as before. The operation of the switching regulator can be performed normally.

When the load current is large as shown in the area B in FIG. 2, the forward voltage of the flywheel diode 2d becomes large (FIG. 2e). Accordingly, the forward voltage applied to the diode 3c of the bias voltage adjusting circuit 33 increases, and a forward current flows. As a result, the current intermittently flows from the capacitor 3f toward the diode 3c. , The bias voltage becomes lower than the bias voltage determined by the voltage division ratio of 3g, the base voltage of the transistor 3e decreases (g in FIG. 2), and the transistor 3e enters a non-driving state. Therefore, the collector current of the transistor 3e, that is, the dummy current becomes zero (FIG. 2).
H), since unnecessary dummy current does not need to flow,
This will increase the efficiency of the switching regulator.

[0018]

As described above, according to the present invention, at the time of no load and at the time of light load, a dummy current is caused to flow so that the output voltage of the auxiliary winding becomes appropriate, and unnecessary dummy current is generated.
Since the dummy current is cut off when the load is large, the effect of improving the efficiency of the switching regulator can be obtained.

[Brief description of the drawings]

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

FIG. 2 is a timing chart showing the operation of the embodiment in FIG.

FIG. 3 is a circuit diagram of a conventional switching regulator.

[Explanation of symbols]

 Reference Signs List 1 switching regulator transformer 1a primary winding 1b secondary winding 1c switching transistor 1d auxiliary winding side rectifier diode 1e auxiliary winding side capacitor 1f auxiliary winding 2 rectifying / smoothing circuit 2a diode 2b smoothing choke 2c capacitor 2d flywheel Diode 3 Dummy current control circuit 31 Bias circuit 32 Dummy load circuit 33 Bias voltage adjustment circuit 3a Divider resistor 3b Dummy load resistor 3c Diode 3d resistor 3e Transistor 3f Capacitor 3g Divider resistor 4 Load 5 Pulse width control circuit

Claims (1)

(57) [Claims] 1. A switching regulator having a primary winding, a secondary winding, and an auxiliary winding, wherein a pulse voltage is applied to the primary winding, and an output of the auxiliary winding is a switching regulator used as an auxiliary power supply. A rectifier element, a choke coil connected to the rectifier element, a smoothing capacitor connected to an output side of the choke coil, and a flywheel diode connected to a connection point between the rectifier element and the choke coil. A rectifying / smoothing circuit that rectifies and smoothes the output voltage of the secondary winding and outputs the rectified / smoothing circuit, and adjusts a pulse width of a pulse voltage applied to the primary winding to keep the output voltage of the rectifying / smoothing circuit constant A switching regulator having a dummy resistor and a transistor having a collector connected in series and an emitter grounded in series with the dummy resistor; A path comprising a dummy load circuit connected in parallel to the rectifying / smoothing circuit, a first resistor and a second resistor connected in series, and a connection point between the first resistor and the second resistor; A bias circuit that supplies a bias voltage for driving the transistor to the base of the transistor, and constantly drives the transistor; and a bias circuit connected between the base of the transistor and ground. , A third resistor having one end connected to the base of the transistor, and a diode having an anode connected to the other end of the third resistor and a cathode connected to the cathode of the flywheel diode. Rectifying and smoothing the voltage across the flywheel diode, and when the voltage across the flywheel diode exceeds a predetermined value, the bias circuit Switching regulator and having a bias voltage adjustment circuit adjusts the bias voltage to the transistor in a non-driven state.