JPS6227624B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a switching control pulse generation circuit for use in a current feedback transistor DC stabilized power supply device or the like.

In FIG. 1, which shows a conventional single-stone current feedback transistor DC stabilized power supply device, a DC power supply 1 includes a primary winding 3 of an output transformer 2, a current feedback transformer 4, a feedback winding 5 of a CT, and a DC power supply 1. The switching transistor 6 is connected through the output transformer 2.
A load 9 is connected to the secondary winding 7 of the feedback transformer 4 via a rectifier circuit 8, a base drive winding 10 of the feedback transformer 4 is connected between the base and emitter of the transistor 6, and an on/off control winding 11 of the feedback transformer 4 is connected to the base drive winding 10 of the feedback transformer 4. A capacitor 12 is connected in series with the winding 11 and the capacitor 12, and a power supply line (+
A transistor 13 is connected to selectively apply a voltage of V), and a transistor 14 is connected in parallel to the winding 11 and the capacitor 12 to selectively form a discharge circuit for the capacitor 12. Reference numeral 15 denotes a control pulse generation circuit, which provides an on-drive pulse to the transistor 13 and an off-drive pulse to the transistor 14 in response to detection of the DC output voltage. 16 is a reset circuit for the transformer 2.

In the power supply circuit configured in this way, when the transistor 13 is turned on, a current flows through the winding 11 to charge the capacitor 12, and the voltage induced in the base drive winding 10 causes the switching transistor 6 to Turns on. When the switching transistor 6 is turned on, a collector current flows, which is fed back to the base by the transformer 4, thereby maintaining the conduction of the transistor 6. When turning off the transistor 6, one transistor 13 is kept off while the other transistor 14 is turned on to form a discharge circuit for the capacitor 12, thereby causing a current in the opposite direction. flows, generating a voltage in the opposite direction in the base drive winding 10, turning off the transistor 6.

By the way, when controlling the switching transistor 6, it is conceivable to adopt a method of keeping the frequency, that is, the on/off period constant, and controlling the on period. However, if the on-period of the transistor 6 is shortened during a light load or droop-type overcurrent protection operation, on-pulses and off-pulses overlap, causing problems such as saturation of the feedback transformer 4 and generation of abnormal signals. For this reason, a frequency control method is generally adopted in which the on-period is kept constant and the off-period is varied. However, when a frequency control method is adopted, the operating frequency changes in response to voltage fluctuations, which increases the possibility that electronic equipment such as computers that use this DC power supply will malfunction due to noise that is an integral multiple of the operating frequency.

Although the current feedback type transistor DC stabilized power supply device has been described above, similar problems exist in other frequency control type pulse width control systems.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a switching control pulse generation circuit that can reduce frequency fluctuations and reduce malfunctions.

In order to achieve the above object, the present invention provides a triangular wave generating circuit formed so that the period changes in response to a voltage change of a first control signal corresponding to the output voltage of a switching circuit, and a triangular wave generating circuit formed from the triangular wave generating circuit. The obtained triangular wave is compared with a second control signal corresponding to the input voltage of the switching circuit, and the voltage of the triangular wave is set to the first level (for example, low level) during a period when the voltage of the triangular wave is higher than the voltage of the second control signal. and a voltage comparator that generates an output of a second level (for example, a high level) during a period in which the voltage of the triangular wave is lower than the voltage of the second control signal. The present invention relates to a switching control pulse generation circuit that generates control pulses for switching control from a switching control pulse.

According to the present invention, in addition to frequency control based on the output voltage, a comparator is provided to compare the frequency-controlled triangular wave and the input voltage, and pulse width control is also performed. If only the input voltage changes, it is possible to change only the pulse width without changing the frequency. Therefore, frequency fluctuations are reduced, and the possibility that electronic equipment malfunctions due to noise due to integral multiples of frequencies is reduced.

Embodiments of the present invention will be described below with reference to FIGS. 2 to 4. However, in Figure 2, the symbol 1
10 and 16 are substantially the same as those indicated by the same reference numerals in FIG. 1, and therefore their explanations will be omitted.

In Figure 2, the error amplifier 1 for voltage detection
A voltage detection line 18 is coupled to one input terminal of 7, and a reference voltage source 19 is connected to the other input terminal. Therefore, a voltage corresponding to the difference between the output voltage and the reference voltage is obtained as a first control signal on the line 20 connected to the output terminal. In addition to the first control signal input from line 20 to the control pulse generation circuit 21 shown surrounded by a dotted line, a second control signal corresponding to the input voltage is input from the output line 23 of the input voltage detection circuit 22.

An input resistor 24 for determining the charging time constant is connected in series to the line 20 into which the second control signal proportional to the output voltage is input, and a triangular wave generating capacitor is connected between the output end of this resistor 24 and the ground line. 25 are connected. Further, the upper end of the capacitor 25 is connected to both the input line and the output line of a voltage comparator 26 having hysteresis, which is shown surrounded by a dotted line. Comparator 26 is comprised of an operational amplifier 27 and resistors 28, 29, 30, 31, and 32. The output terminal of the input resistor 24, that is, the upper end of the capacitor 25 is connected to the inverting input terminal of the operational amplifier 27, and the output terminal of the operational amplifier 27 is connected to the upper end of the capacitor 25 via the resistor 31. Therefore, an astable multivibrator is formed by the capacitor 25 and the comparator 26, and a triangular wave as illustrated in FIGS. 3A and 4A is generated on the triangular wave output line 33 connected to the upper end of the capacitor 25. can get.

34 is an on-drive voltage comparator composed of an operational amplifier, and its non-inverting input terminal is connected to a voltage dividing point formed by a resistor 35 and a resistor 36, and is also connected to the input voltage detection circuit 22 via a resistor 37. It is connected. Further, the inverting input terminal of the comparator 34 is coupled to the triangular wave output line 33. 38
is an off-drive voltage comparator composed of an operational amplifier, whose non-inverting input terminal is coupled to the triangular wave output line 33, and whose inverting input terminal is connected to the voltage dividing point between the resistors 35 and 36. , are connected to the input voltage detection circuit 22 via a resistor 37.

39 is an on-pulse width setting circuit, which includes a capacitor 41 connected in series to the output line 40 of the comparator 34 in the previous stage, and the output line 40 and the power supply line +
It consists of discharge resistors 42 and 43 connected between V and V. Note that the output terminal of the capacitor 41 is coupled to the base of the on-drive transistor 13. 4
4 is an off-pulse width setting circuit, which consists of a capacitor 46 connected in series to the output line 45 of the comparator 38 in the previous stage, and discharge resistors 47 and 48 connected between the output line 45 and the power supply line +V. Become. Note that the output terminal of the capacitor 46 is coupled to the base of the transistor 49. Further, the transistor 49 is Darlington connected to the second driving transistor 14 at the next stage. That is, its emitter is coupled to the base of the next stage transistor 14, and its collector is commonly connected to the next stage's collector. Also, its emitter and power line +V
A resistor 50 is connected between them.

The on/off control winding 11 is configured in a center tap type, with the lower half used as the on drive winding 11a and the upper half used as the off drive winding 11b, the center tap of which is grounded. The on-drive transistor 13 is connected between one end of the on-drive winding 11a and the positive power supply line (+V), and the off-drive winding 1
An off-drive transistor 14 is connected between one end of 1b and a positive power supply line (+V).

Next, the operation of the circuit shown in FIG. 2 will be explained with reference to the waveforms shown in FIGS. 3 and 4.

Now, in the circuit of Fig. 2, the output voltage, that is, the first
Assuming that the control signal of is kept constant,
A triangular wave A having a constant period or frequency is obtained on the triangular wave output line 33 as shown in FIG. 3A, and this becomes one input of the comparators 34 and 38. Comparator 3
4 and 38, a second control signal proportional to the input voltage obtained by combining the voltage applied from the input voltage detection circuit 22 and the voltage obtained by dividing the power supply voltage +V by the resistor 35 and the resistor 36. enters. If the voltage level of this second control signal, which is proportional to the input voltage, is the solid line 23a in FIG.
The first comparator 34 compares the triangular wave A and the second control signal voltage, and the first comparator 34 provides low-level pulse width control having the pulse width of the on time T _ON shown in FIG. 3B. I get a signal. Also, from the second comparator 38, the output of the first comparator 34 and 180
A low level signal having a pulse width of off time T _OFF with a degree phase difference is obtained as shown in FIG. 3C.

On the other hand, if the input voltage changes as shown by the dotted line 23b in FIG. 3A, the outputs of the comparators 34 and 38 also change as shown by the dotted lines in FIGS. 3B and 3C. If the switching circuit is not of the current feedback type, the low level pulse width control signal shown in FIG. 3B may be used, for example, as the base signal of the switching transistor. However, since the switching circuit of this embodiment is configured as a current feedback type, the on-pulse width setting circuit 39 and the drive transistor 13
Accordingly, the on-pulse shown in FIG. 3D is generated at the rising edge of the pulse shown in FIG. 3B, while the off-pulse setting circuit 39 and the transistor 14
The off-pulse shown in FIG. 3E is generated at the rising edge of the pulse shown in FIG. 3C.

The on-pulse width setting circuit 39 consists of a capacitor 41 for determining the pulse and resistors 42 and 43 forming a discharge circuit for the capacitor 41. By adjusting the capacitance of the capacitor 41, the on-pulse width setting circuit 39 is set to be longer than the rise time t _r of the switching transistor 6. On-pulse width ( _t1 to _t2 )
is set to obtain an on-pulse. On the other hand, the off-pulse width setting circuit 44 consists of a capacitor 46 that determines the pulse width and resistors 47 and 48 that form this discharge circuit, and by adjusting the capacitance of the capacitor 46, the storage time (t _stg ) of the switching transistor 6 can be adjusted. It is set to obtain an off-pulse with an off-pulse width ( _t5 to _t6 ) that is slightly longer than the sum of the fall time ( _tf ).

When the output of the comparator 34 becomes low level as shown in the period t ₁ to _{t 5} in FIG. 3B, since the comparator 34 is configured as a constant current drawing type,
Then, the charging current of the capacitor 41 flows through the emitter base of the transistor 13 and the capacitor 41, the transistor 13 is turned on, and the on-pulse determined by the capacitance _C1 of the capacitor 41 is applied to the on-drive winding of the transformer 4. 11a, and the switching transistor 6 is turned on. On the other hand, in the period _t5 to _t7 in FIG. 3, when the output of the second comparator 38 becomes low level and conversely, the output of the first comparator 34 becomes high level, The charge in the capacitor 41 of the on-pulse width setting circuit 39 is discharged by a circuit including resistors 42 and 43. In addition, in response to the low level output of the second comparator 38, a circuit including the power supply line +V, the emitter-base of the transistor 14, the emitter-base of the transistor 49, the capacitor 46, and the comparator 38 The capacitor 46 is charged. At this time, since the comparator 38 is configured as a constant current drawing type, the capacitor 46 is charged with a constant current, and the width of the on-pulse is determined by the capacitance C ₂ of the capacitor 46.
determined by. In addition, two transistors 1
4 and 49 are connected in a Darlington manner to increase the current amplification factor, it is possible to obtain a sufficient off-pulse in response to the charging waveform of the capacitor 46. The off pulse is the off drive winding 11 of the transformer 4.
When applied to b, transistor 6 is reverse biased and turned off.

Next, when the input voltage is constant and only the output voltage changes, as shown in FIG. 4A, the voltage level of the second control signal is kept constant as shown by the solid line 23a, and the output voltage Only the triangular wave A changes in response to the corresponding first control signal. That is, the period of the triangular wave of the astable multivibrator composed of the capacitor 25 and the comparator 26 changes as shown by the dotted line in FIG. To explain this in more detail, as the first control signal voltage on line 20 increases in response to an increase in output voltage, capacitor 2
5, the charging voltage rises faster. When this voltage becomes higher than the reference voltage of the operational amplifier 27, the output of the operational amplifier 27 is inverted to a low level.
A discharge circuit for the capacitor 25 is formed by a circuit including the capacitor 25, a resistor 31, and an operational amplifier 27. By the way, since the operational amplifier 27 is configured as a constant current attraction type, it only allows a constant current to flow in when the output is reversed to a low level. During the discharge period of the capacitor 25, the capacitor 25
If only the operational amplifier 27 is connected, the capacitor 25 will always be discharged with a constant current.
A first control signal line 20 is connected to the output terminal of the operational amplifier, and the voltage of this line 20 changes according to the output voltage, so that the combined current of the first control signal and the charging voltage of the capacitor 25 flows through the operational amplifier. If the first control signal, that is, the output voltage is high, the current component based on this will inevitably increase, and conversely, the discharge current of the capacitor 25 will decrease, and the comparator 26 will flow into the output terminal of the comparator 26. It takes longer to reach the low level trigger point of hysteresis. Therefore, the generation cycle of the triangular wave A becomes longer, and the on/off cycle of the switching transistor 6 also changes from _T1 to _T2 . Incidentally, since the intersection point between the triangular wave A and the second control signal shown by the solid line 23a is set relatively above the triangular wave A, the triangular wave A
Even if the cycle of T changes in response to the output voltage, the on time T _ON hardly changes, and the off time T _OFF changes mainly. As is clear from the above, when the output voltage changes, the switching frequency of the switching transistor 6 changes based on the change in the off time T _OFF , resulting in control that keeps the output voltage constant.

When both the input voltage and the output voltage change simultaneously, the control is a combination of those shown in FIGS. 3 and 4.

As is clear from the above, the device of this embodiment has the following advantages.

(a) When the input voltage changes, the on-time T _ON
Since the voltage is adjusted by changes in , the switching frequency does not change. Therefore, frequency changes are reduced, and the possibility of electronic equipment malfunctioning due to noise that is an integral multiple of the operating frequency is reduced. still,
The output voltage fluctuates due to fluctuations in the load 9, and the switching frequency changes, but if the switching frequency changes due to a light load, the current in the main circuit of the power supply is small, so The noise level is low and the possibility of malfunction is low. Furthermore, since it is an abnormal situation when the drooping overcurrent protection is activated, there is little possibility that it will cause a noise disturbance.

(b) Since an on-pulse width setting circuit 39 and an off-pulse width setting circuit 40 are provided, and the off-pulse width is set larger than the on-pulse width, it is possible to limit the drive current from continuing to flow more than necessary when turning on the switching transistor 6. This makes it possible to reduce drive power loss.

(c) Capacitors 41, 46 and windings 11a, 11b
Transistors 13 and 14 are interposed between the
Further, since a margin is provided for the current increase rate of the transistors 13 and 14, it is possible to obtain a steep waveform that allows the charging waveform of the capacitor to be ignored, and it is possible to increase the switching speed.

(d) Since the variable frequency oscillator is constituted by the astable multivibrator consisting of the capacitor 25 and the comparator 26, the frequency of the triangular wave can be relatively easily changed in accordance with the output voltage.

Although the embodiments have been described above, the present invention is not limited thereto and can be further modified. For example, the present invention is not limited to a single transistor type DC power supply, but can also be applied to a parallel inverter type circuit in which switching transistors are connected to both ends of a transformer having a center tap, or a bridge inverter circuit. It is also applicable to the case where the signal shown in FIG. 3B is directly used as a driving signal for a switching transistor without using a current feedback type. Furthermore, instead of providing the pair of comparators 34 and 38, for example, an inverted signal from one of the comparators 34 may be formed, thereby creating an off pulse. Alternatively, an off pulse may be generated in response to the high level period of one of the comparators 34.
Further, the low level outputs of the comparators 34 and 38 are used as pulse width control signals, but the transistors 13 and 14 are configured to respond to high level base signals to generate high level outputs from the comparators 34 and 38. You can do it like this. Further, the first and second control signals may be any signals as long as they are equal to or proportional to the output voltage and the input voltage. It is also applicable to circuits that use thyristors and the like as switching elements other than transistors.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram of a conventional current feedback transistor DC stabilized power supply device, Fig. 2 is a circuit diagram of a power supply device according to an embodiment of the present invention, and Figs. 3 and 4 are A to A in Fig. 2. FIG. 3 is a waveform diagram showing the state of point F. FIG. In the symbols used in the drawings, 4 is a current feedback transformer, 5 is a current feedback winding, 6 is a switching transistor, 10 is a base drive winding, and 1 is a current feedback transformer.
1 is an on-off control winding, 11a is an on-drive winding,
11b is an off-drive winding, 13 and 14 are transistors, 21 is a control pulse generation circuit, 34 is a voltage comparator, 38 is a voltage comparator, 39 is an on-pulse width setting circuit, 41 is a capacitor, 44 is an off-pulse width setting circuit, 46 is a capacitor.

Claims (1)

[Claims] 1. A first circuit corresponding to the output voltage of the switching circuit.
a triangular wave generation circuit formed so that the period changes in response to a voltage change of a control signal; and a comparison between the triangular wave obtained from the triangular wave generation circuit and a second control signal corresponding to the input voltage of the switching circuit. and the voltage of the triangular wave is
a voltage comparator that generates a first level output during a period when the voltage of the triangular wave is higher than the voltage of the control signal, and generates a second level output during a period when the voltage of the triangular wave is lower than the voltage of the second control signal; A switching control pulse generation circuit for generating a control pulse for switching control from the voltage comparator. 2. The switching control pulse generation circuit according to claim 1, wherein the triangular wave generation circuit is an astable multivibrator that generates a triangular wave in response to the first control signal.