JPH0683574B2 - Switching Regulator - Google Patents

Description

TECHNICAL FIELD The present invention relates to a switching regulator, and more particularly to a multi-output switching regulator that outputs a plurality of stabilized DC voltages.

2. Description of the Related Art Conventionally, this type of circuit has the same pulse as that appearing in the main output secondary winding from a second secondary winding different from the main output first secondary winding provided in the transformer. Take a pulse of width,
There is a method of rectifying and smoothing this to obtain an unstable direct current, and then switching and rectifying and smoothing this by a so-called series switching method to stabilize it. Yet another method is to compare the main output already created on the circuit with a sawtooth or triangular wave used to control the output by error amplifying the second output voltage. There is also one that stabilizes the second DC output by controlling the conduction angle of the pulse appearing in the second secondary winding of the.

However, in the former case, two smoothing circuits are required to form the series switching regulator, and a circuit such as an oscillator is also required, which not only complicates the circuit but also has a drawback that the power conversion efficiency is poor. In the latter case, the control pulse that is obtained by comparing the above-mentioned sawtooth wave or triangular wave with the output obtained by error-amplifying the main output voltage is generally divided, and then only one is switched. Since it is used for controlling the transistor, the control pulse for controlling the switching of the second output also needs to be frequency-divided, so that a frequency-dividing circuit is further required and the circuit becomes complicated. Further, this method cannot be adopted when the main output control circuit is an integrated circuit and the sawtooth wave or the triangular wave cannot be taken out to the outside.

OBJECT OF THE INVENTION The object of the present invention is to eliminate the above-mentioned drawbacks. The object of the present invention is to switch the second output with a simple circuit and even if a part of the main control circuit is integrated. It is an object of the present invention to provide a multi-output switching regulator that can easily generate a control pulse for controlling and can obtain a second output with high power conversion efficiency.

According to the present invention, a transformer having a primary winding and first and second secondary windings, a main DC voltage obtained from the first secondary winding of the transformer, and a predetermined reference voltage are provided. Means for generating an error voltage according to the difference between the error voltage and the ramp voltage, and a pulse obtained by this comparison for the conduction of the switching element provided on the primary winding side of the transformer. A switching regulator including means for controlling an angle, the time constant circuit being charge / discharge controlled by using the pulse obtained by the comparing means, and the sub DC voltage obtained from the second secondary winding of the transformer. And an output voltage of the time constant circuit, and a means for generating an error voltage according to the difference between the reference voltage and the predetermined reference voltage. Departure A multi-output switching regulator guide is obtained which controls the conduction angle of a switching circuit provided on the side of the second secondary winding for the purpose of liveness.

EXAMPLES Next, the present invention will be described with reference to the drawings. FIG. 1 is a circuit block diagram showing an embodiment of the present invention, in which a transformer 4, a switching transistor 1 and diodes 3 and 20 are provided.
And the smoothing circuit 5 is the main circuit portion of the switching regulator, and a first DC output (main output) V01 is obtained. Reference numeral 2 is a drive circuit for driving the switching transistor 1. The control circuit 19 is a circuit for controlling the voltage V01 of the main output to be constant, and is composed of a sawtooth wave or triangular wave generation circuit 12, an error amplifier 13, a comparator 11, a flip-flop 10, and two input canand circuits 8 and 9. There is.

The switching circuit 6, the smoothing circuit 7, and the diode 21 are for further switching the pulse appearing in the secondary winding N4 of the transformer 4 to obtain a stabilized second DC output (sub output) V02. Further, the portion composed of the resistor 15 and the capacitor 16 is a time constant circuit for generating the second sawtooth wave, and the diode 14 is for preventing backflow. The second error amplifier 18 outputs the second DC output V02 to the reference voltage Vref2.
The second comparator 17 compares the output of the error amplifier 18 with the sawtooth wave appearing in the capacitor 16 to generate a control pulse that determines the conduction angle of the switching circuit 6. belongs to.

Next, the operation of FIG. 1 will be described with reference to FIG.
Now, the DC output voltage V01 and the reference voltage Vref1
By comparing the voltage obtained by comparison and amplification at 13 with the waveform from the sawtooth wave or triangular wave generating circuit 12, a control pulse for determining the conduction angle of the switching transistor 1 is obtained at the output of the comparator 11. This control pulse is a flip-flop
10 and NAND circuits 8 and 9 divide the frequency into two, of which the pulse output Va is applied to the base of the switching transistor 1 through the drive circuit 2 and the first DC output V01 is stabilized.

Therefore, the other pulse output Vb divided in two is represented by the waveform in FIG. Since this output is connected to the time constant circuit of the resistor 15 and the capacitor 16 via the diode 14, the voltage Vc of the capacitor 16 becomes a sawtooth wave as shown in FIG. On the other hand, when the voltage of the DC output 2 is lower than the reference voltage Vref2 due to the action of the amplifier 18, the voltage V of the one input terminal of the comparator 17 is
d decreases, and conversely increases as it works. Therefore, the output pulse Ve of the comparator 17 spreads when the voltage of the DC output 2 decreases, and vice versa when it rises.

In this way, the control pulse Ve corresponding to the DC output voltage V02 is sent to the switching circuit 6, the conduction angle of the power pulse Vf appearing in the winding N4 of the transformer 4 is controlled, and the controlled power pulse Vg is sent to the smoothing circuit 7. Therefore, the second DC output V02 is kept constant.

The diode 14 is for preventing backflow, and may be omitted when the output of the NAND circuit 9 is an open collector, or a resistor having a small value may be provided between the output of the NAND circuit 9 and the capacitor 16 for protection. Further, the connecting positions of the rectifying diodes 20 and 21 do not necessarily have to be the positions shown in FIG. In FIG. 1, the control circuit 19 is generally integrated and is a so-called
It has become common to use ICs. Furthermore, as a remark about FIG. 1, rectifying and smoothing is performed only once from the winding N4 to the output, and therefore, it is of course expected that sufficiently good power conversion efficiency is expected.

EFFECTS OF THE INVENTION As described above, according to the present invention, a new main output control pulse output obtained by frequency division is taken out and connected to a time constant circuit so that a new cycle is generated at the switching frequency of the main circuit. By creating a sawtooth wave and using it to control the switching circuit to obtain the second DC output, a switching regulator with a simple circuit and good power conversion efficiency is also realized for the second DC output. The effect is that you can do it. Further, since the remaining pulse Vb of the pair of pulses obtained by the flip-flop 10 and the NAND circuits 8 and 9 is used as a control pulse for stabilizing the sub DC output, it is used in the main control circuit. Even when the sawtooth wave or the triangular wave that is generated cannot be taken out to the outside on the circuit, there is an effect that it is not bound at all.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a circuit diagram of an embodiment of the present invention, and FIG. 2 is a voltage waveform diagram of respective parts showing the operation of the circuit of FIG. Explanation of symbols of main parts 1 …… Switching transistor 4 …… Transformer 5,7 …… Smoothing circuit 6 …… Switching circuit 11,17 …… Comparison circuit 12 …… Slope signal generating circuit 13,18 …… Error amplifier 15 , 16 …… Time constant circuit component 19 …… Control circuit

Claims (1)

[Claims] 1. A transformer having a primary winding and first and second secondary windings, and a transformer according to a difference between a main DC voltage obtained from the first secondary winding of the transformer and a predetermined reference voltage. Means for generating an error voltage, a comparing means for comparing the error voltage with the ramp voltage, and a pulse obtained by this comparison to control the conduction angle of the switching element provided on the primary winding side of the transformer. A time constant circuit that is charge / discharge controlled using the pulse obtained by the comparison means, a sub-DC voltage obtained from the second secondary winding of the transformer, and a predetermined reference voltage. A means for generating an error voltage corresponding to the difference between the error voltage and the output voltage of the time constant circuit, and a comparator means for comparing the error voltage with the output voltage of the time constant circuit. The above Multiple-output switching regulator and controlling the conduction angle of the switching circuit provided in the secondary winding side.