JPH06113543A - Synchronous chopper circuit - Google Patents

Abstract

PURPOSE:To obtain a highly reliable power supply at low cost by decreasing the number of components. CONSTITUTION:When a triangular voltage, generated at a constant period from an inverter circuit 12, exceeds a predetermined level an inverter current into a secondary winding 14 to induce a rectangular pulse which is then rectified through a diode 40 and divided through a resistor to be applied on the gate of a thyristor 45 thus turning the thyristor 45 ON. Consequently, a pulse width control circuit 22 starts oscillation to increase the voltage at CT terminal 52 thereof thus increasing output from a control signal output terminal 50 gradually. When a predetermined level is exceeded, a switch element 21 is turned ON and drain current flows. In the pulse width control circuit 22, charging operation takes place upon increase of voltage at the CT terminal 52 and when the voltage reaches a predetermined level, a discharge circuit functions to turn the thyristor 45 OFF and to interrupt provision of output from the control signal output terminal 50 thus turning the switch element 21 OFF.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement of a chopper circuit for switching a fluctuating input voltage with a semiconductor switch to obtain a stabilized DC power supply.

[0002]

2. Description of the Related Art As shown in FIG. 8, a conventional step-down chopper circuit includes an inverter circuit 12 on the primary side and an inverter transformer 15 for transforming a high frequency pulse generated by the inverter circuit 12 by applying it to a primary winding 13. Then, the rectangular wave pulse of the secondary winding 14 is rectified by the rectifying diodes 16 and 17,
A rectifying / smoothing unit 20 for smoothing the choke coil 18 and the capacitor 19 to obtain an unstable DC voltage, and a MOS for stabilizing the unstable DC voltage to a predetermined voltage.
Turns on and off the switch element 21 such as a FET
After controlling by the signal of the pulse width control circuit 22 on the next side, the flywheel diode 23 commutates the current when the switch element 21 is off, and the choke coil 24 and the capacitor 25
And a step-down chopper portion 26 that smoothes and stabilizes again. 10, 11 are input terminals, 27,
28 is an output terminal.

The circuit shown in FIG. 9 uses the step-down chopper circuit as described above for a general multi-output power supply. In this circuit, a first chopper circuit 30a, a second chopper circuit 30b, ... Are respectively provided on the secondary side of the inverter transformer 15 via a first secondary winding 14a, a second secondary winding 14b ,. And the rectifying / smoothing circuit 31 and the output detecting section 34 are further connected via the secondary winding 14, and the error detecting section 35 is connected to the connection point of the resistors 32 and 33 of the output detecting section 34.
It is fed back to the inverter circuit 12 on the primary side via the insulating portion 36.

[0004]

As shown in FIG. 9, when the step-down chopper circuit is used for a general multi-output power source, each rectifier required for the input stage of each chopper circuit 30a, 30b ,. Since the diodes 16, 17, the choke coil 18, and the capacitor 19 are parts having a large shape, the area occupied on the printed circuit board and the ratio of the volume to the entire power source increase, and there is a problem that there is a limit to downsizing of the entire power source device. there were.

Also, for different switching frequencies,
Between the respective chopper circuits 30a, 30b, ..., The primary-side inverter circuit 12 and the respective chopper circuits 30a, 30b,
There is a problem that it tends to cause beat noise between the ... and abnormal oscillation, and reduces the reliability of the power supply device. The inverter circuit 12 may be, for example, a PWM IC.
60, a MOS FET 61, a capacitor 62, and a full-wave rectifier 63.

It is an object of the present invention to obtain a low cost and highly reliable power supply device while reducing the number of parts.

[0007]

According to the present invention, the output voltage of the secondary winding 14 of the inverter transformer 15 is set to the switching element 2.
1 is applied to the pulse width control circuit 22 to feed back the detection signal of the output detector 34 to the pulse width control circuit 22 to chopper the switch element 21 to stabilize the output voltage. And the switch element 21 are coupled only via the rectifying diode 16,
A synchronous chopper circuit, characterized in that the secondary winding 14 and the pulse width control circuit 22 are coupled via a diode 40 for supplying the secondary output voltage of the inverter transformer 15 as a synchronous signal. Is.

[0008]

When the voltage of the triangular wave generated from the primary side inverter circuit 12 in a constant cycle exceeds a constant value at t2, the MO
The inverter current flows until t5 (t1) when the S-type FET 61 is turned on and falls. Along with this, the rectangular wave pulse generated in the secondary winding 14 of the inverter transformer 15 is rectified by the diode 40, divided by the resistor, and turned on in addition to the gate of the thyristor 45. Then, the secondary side pulse width control circuit 22 starts oscillating and the voltage at the CT terminal 52 rises. The output from the control signal output terminal 50 of the secondary side pulse width control circuit 22 gradually rises, and when it exceeds a predetermined value, the switch element 21 is turned on at t3 and a drain current flows. In addition, the pulse width control circuit 2 on the secondary side
In the inside of 2, the charging is started by the rise of the voltage of the CT terminal 52, and when the voltage reaches a specified value at t4, the discharging circuit operates to turn off the thyristor 45, and the output of the control signal output terminal 50 also. Then, the switch element 21 is turned off.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. First, the basic configuration and operation principle of the present invention will be described with reference to FIGS. 1 and 2, and the inverter circuit 12 on the primary side will be described.
Is connected to the primary winding 13 of the inverter transformer 15,
The drain of a switch element 21 such as a MOS FET is connected to the secondary winding 14 of the inverter transformer 15 via a rectifying diode 16, and the diode 40
The pulse width control circuit 22 on the secondary side is connected via. That is, only the rectifying diode 16 is interposed between the rectifying diode 16 and the switch element 21, and the conventional rectifying diode 17, the choke coil 18, and the capacitor 19 are directly connected without being interposed. The flywheel diode 2 is provided on the source side of the switch element 21 as in the conventional case.
3, the choke coil 24, and the capacitor 25 are connected, and the connection point between the resistors 32 and 33 of the output detector 34 is fed back to the pulse width control circuit 22.

In such a configuration, the output from the secondary winding 14 of the inverter transformer 15 is rectified into a rectangular wave pulse shown in FIG. Add. Similarly, the rectangular wave pulse rectified by the diode 40 is input to the secondary side pulse width control circuit 22 as a synchronization signal, and the switching frequency of the primary side inverter circuit 12 and the secondary side pulse width control circuit are input. The frequencies of 22 are the same. Then, in the rectangular wave pulse of FIG. 2A, the chopper operation is performed by the switch element 21 that is turned on and off as shown in FIG. 2B by the control signal of the pulse width control circuit 22 on the secondary side. In other words, only by rectifying with the rectifying diode 16, it is possible to directly perform the chopper operation in the unrectified rectangular wave pulse. In this way, by simply rectifying the voltage of the secondary winding 14 of the inverter transformer 15, a synchronous chopper circuit without the conventional rectifying diode 17, choke coil 18 and capacitor 19 can be obtained. Figure 2 (c)
Indicates the drain current of the switch element 21 such as a MOS FET.

Next, a specific embodiment of the present invention will be described with reference to FIG. Explaining the embodied portion in comparison with FIG. 1, a series circuit of a diode 40 and resistors 41 and 42 is connected between both ends of the secondary winding 14, and a connection point between the resistors 41 and 42 is a transistor. It is connected to the gate of a thyristor 45 composed of 43 and 44 and a capacitor 48. The other end of the capacitor 48 is connected to the timing capacitor 47 and the CT terminal 52 of the pulse width control circuit 22 on the secondary side.
The RT terminal 51 of the pulse width control circuit 22 on the secondary side is
The reference voltage output terminal 49 of the secondary side pulse width control circuit 22 is connected to the anode gate of the thyristor 45 via the timing resistor 46, and the reference voltage output terminal 49 of the secondary side pulse width control circuit 22 is connected to the anode of the thyristor 45. The control signal output terminal 50 is connected to the gate of the switch element 21 and
The feedback signal input terminal 53 of the pulse width control circuit 22 on the next side is connected to the connection point of the resistors 32 and 33. The timing resistor 46 and the timing capacitor 4
7 is inserted to determine the switching frequency of the pulse width control circuit 22 on the secondary side.

In the above structure, the triangular wave voltage as shown in FIG. 4A is generated at a constant cycle from the PWM IC 60 of the primary side inverter circuit 12. When the voltage of this triangular wave exceeds a certain value at t2, the MOS type FET 61
Is turned on and the inverter current as shown in FIG. 4B flows until time t5 (t1) when the voltage of the triangular wave falls. Along with this, a voltage as shown in FIG. 4C is generated in the secondary winding 14 of the inverter transformer 15. Secondary winding 14
The rectangular wave pulse of is rectified by the diode 40, the resistor 41,
The voltage is divided by 42, and the obtained voltage is applied to the gate of the thyristor 45 and turned on. Then, the secondary side pulse width control circuit 22 starts oscillating and the voltage at the CT terminal 52 rises. The output from the control signal output terminal 50 of the secondary side pulse width control circuit 22 gradually rises as shown in FIG. 4 (d), and when it exceeds a predetermined value, the switch element 21 turns on at t3, and FIG. 4 (e). A drain current like this flows.

Further, inside the secondary side pulse width control circuit 22, charging is started by the rise of the voltage of the CT terminal 52, and when the voltage reaches a specified value at t4, the discharge circuit operates to operate the thyristor. 45 is turned off, the output of the control signal output terminal 50 is also cut off, and the switch element 21 is turned off.

The operation at this time will be described in more detail.
Since the CT terminal 52 side of the capacitor 48 before the start of discharge is at a high potential inside the secondary side pulse width control circuit 22, the timing capacitor 47 is changed by the discharging circuit of the secondary side pulse width control circuit 22. By being discharged, the thyristor 45 including the transistors 43 and 44 is turned off, and the oscillation operation of the pulse width control circuit 22 on the secondary side is stopped.

A thyristor 45 is composed of the transistors 43 and 44, and the reference voltage of the reference voltage output terminal 49 is supplied to the timing capacitor 4 by the timing resistor 46.
Since the charging current for charging 7 is less than the holding current of the thyristor 45, it turns off when the gate (base) signal disappears. Further, the maximum on-duty of the secondary side pulse width control circuit 22 needs to be equal to or less than the on-duty of the primary side inverter circuit 12 in order to control the pulse width in the rectangular wave pulse. Is 1
The switching frequency of the inverter circuit 12 on the next side is set as follows. The signal timing at this time is as shown in FIG. Switching frequency of pulse width control circuit 22 ≧ switching frequency of inverter circuit 12 PWM IC 60 used in the synchronous chopper circuit of the present invention
Is not a specific one, but can be applied to a general-purpose PWM IC by devising a synchronization signal and adding it to the CT terminal 52.

In the above-mentioned embodiment, the rectifying diode 16 has two diodes.
Although it is connected to one end of the secondary winding 14, as shown in FIG. 5, if this rectifying diode 16 is connected to multiple ends of the secondary winding 14 and is connected to the flywheel diode 23 of the step-down chopper part as a common anode. Inexpensive devices in one package can be used.

In the above embodiment, the switch element 21 is inserted in series between the secondary winding 14 and the DC output terminal 27,
Although the case of the step-down type in which the output voltage is stepped down with respect to the input voltage has been described, as shown in FIG. 6, the switch element 21 is inserted in parallel between the secondary winding 14 and the DC output terminal 27,
It is also possible to use a synchronous chopper circuit in which the output voltage is boosted with respect to the input voltage.

In the above embodiment, the rectifying diode 16, the choke coil 24, and the flywheel diode 23 are inserted in series between the secondary winding 14 and the DC output terminal 27, and one end side of the secondary winding 14 is inserted. However, as shown in FIG. 7, the flywheel diode 23 is inserted in series between the secondary winding 14 and the DC output terminal 27, and the choke coil 24 is inserted in parallel. Then 2
A so-called inverting type synchronous chopper circuit in which one end side of the secondary winding 14 is negative can be used.

[0019]

(1) When the synchronous chopper circuit of the present invention is used for a multi-output power supply, each chopper circuit 30a, 30
Since the rectifying diode 17, the choke coil 18, and the capacitor 19, which are large-sized components in the input stages b, ...

(2) Since the switching frequencies are synchronized, the primary-side inverter circuit 12 and the chopper circuits 30a, 30a are provided between the chopper circuits 30a, 30b ,.
The beat sound and abnormal oscillation between b, ... Are eliminated, and the reliability of the power supply device can be improved.

[Brief description of drawings]

FIG. 1 is a principle electric circuit diagram showing an embodiment of a synchronous chopper circuit according to the present invention.

FIG. 2 is a waveform diagram of each part of FIG.

FIG. 3 is a specific electric circuit diagram of FIG.

FIG. 4 is a waveform diagram of each part of FIG.

FIG. 5 is an electric circuit diagram showing a second embodiment of the present invention.

FIG. 6 is an electric circuit diagram showing a third embodiment of the present invention.

FIG. 7 is an electric circuit diagram showing a fourth embodiment of the present invention.

FIG. 8 is an electric circuit diagram of a conventional chopper circuit.

FIG. 9 is an electric circuit diagram in which a conventional chopper circuit is used for a multi-output power supply.

[Explanation of symbols]

10 ... Input terminal, 11 ... Input terminal, 12 ... Primary side inverter circuit, 13 ... Primary winding, 14 ... Secondary winding, 15 ...
Inverter transformer, 16 ... Rectifying diode, 17 ... Rectifying diode, 18 ... Choke coil, 19 ... Capacitor, 20 ... Rectifying / smoothing section, 21 ... Switch element such as MOSFET, 22 ... Secondary side pulse width control circuit, 23 ... Fly Wheel diode, 24 ... Choke coil, 25
... Capacitor, 26 ... Step-down type chopper section, 27 ... Output terminal, 28 ... Output terminal, 30 ... Chopper circuit, 31 ... Rectifying / smoothing circuit, 32 ... Resistor, 33 ... Resistor, 34 ... Output detecting section, 35 ... Error detecting section , 36 ... Insulating part, 40 ... Diode, 41 ... Resistor, 42 ... Resistor, 43 ... Transistor, 4
4 ... Transistor, 45 ... Thyristor, 46 ... Timing resistor, 47 ... Timing capacitor, 48 ... Capacitor, 49 ... Reference voltage output terminal, 50 ... Control signal output terminal, 51 ... RT terminal, 52 ... CT terminal, 53 ... Feedback signal Input terminal, 60 ... PWM IC, 61 ... MO
S-type FET, 62 ... Capacitor, 63 ... Full-wave rectifier.

Claims (4)

[Claims] 1. A secondary winding 14 of an inverter transformer 15.
Of the output voltage of the output detector 3
In the chopper circuit in which the detection signal of No. 4 is fed back to the pulse width control circuit 22 and the switch element 21 is chopper operated to stabilize the output voltage, between the secondary winding 14 and the switch element 21, The inverter transformer 15 is coupled between the secondary winding 14 and the pulse width control circuit 22 by coupling only through the rectifying diode 16.
A synchronous chopper circuit characterized by being coupled via a diode 40 for supplying the secondary output voltage of 1) as a synchronizing signal. 2. The synchronous chopper circuit according to claim 1, wherein the output voltage is a step-down type with respect to the input voltage. 3. The synchronous chopper circuit according to claim 1, wherein the output voltage is a boost type with respect to the input voltage. 4. The synchronous chopper circuit according to claim 1, wherein the output voltage is an inverting type with respect to the input voltage.