JPS6253173A - Switching regulator - Google Patents

Abstract

PURPOSE:To stabilize operation by making output voltage to droop when the overcurrents of output currents from a switching regulator are detected. CONSTITUTION:When the closing of a power supply is instructed, a transistor 22 is held at OFF. Output voltage from a reference-voltage generating circuit 16 applied to an error amplifier 19 coincides with a reference voltage 13. The circuit 16 is operated so that the voltage of two input terminals for the error amplifier 19 is equalized approximately in this case, and output voltage from a switching regulator 25 is controlled stably at a fixed value. When output currents from the switching regulator 25 increase for some reason and the peak value of pulse voltage including a sawtooth waveform component as output voltage from a current detecting circuit 7 exceeds the voltage value of reference voltage 8, a comparator 9 starts switching operation in pulse width proportional to the increase of output currents. Accordingly, a transistor 11 is conducted, and the both end voltage of a capacitor 15 reduces, thus resulting in the drooping of output voltage from the switching regulator 25.

Description

[Detailed description of the invention] [Industrial application field] INDUSTRIAL APPLICATION This invention is used for a switching regulator.

[Conventional technology]

Conventional switching regulators are provided with an overcurrent protection circuit that cuts off the output voltage when the output current reaches a current value that should be protected.

[Problem that the invention seeks to solve]

In the conventional switching regulator described above, when the connected load is an intermittent load with inrush current, such as a relay circuit or a lamp circuit, or when electrostatic noise causes malfunction of the overcurrent protection circuit, the power supply is It had the disadvantage of frequent erroneous shutoffs.

Furthermore, even if the overcurrent protection circuit is activated due to a short-circuit accident on the load side, a short-circuit at the output terminal, etc., and the power is cut off, even if the cause is removed, the switching regulator will not function properly unless the reset operation is performed. There was a drawback that it did not return to normal operation.

Furthermore, in order to achieve the slow start function when starting the switching regulator, a complicated circuit was required.

The present invention eliminates the above-mentioned drawbacks, prevents multiple power supplies from being cut off due to malfunction, furthermore allows normal operation to be automatically restored after the power supply is interrupted and the cause of the failure is removed. , Equipped with a slow start function that has a slow start function when starting the power supply 1! An object of the present invention is to provide a switching regulator having a drooping type overcurrent protection circuit.

[Means for solving problems]

The switching regulator of the present invention includes: 1) C-L) C
a converter, a reference voltage generation circuit having a capacitor connected to a first reference voltage as a normal output voltage via a resistor, an output voltage detection circuit for detecting the output voltage of the DC-DC converter; The output of the output voltage detection circuit and the resistance division point of the first reference voltage are connected to one input terminal, and the output of the reference voltage generation circuit or the input terminal of another power source is connected to the main power of the DC-DC converter. an error amplifier for controlling a control element; a current detection circuit for detecting a pulse current flowing through the main power control element; and a current detection circuit for detecting a pulse current flowing through the main power control element; The reference voltage generation circuit includes overcurrent protection means for reducing the output voltage of the generation circuit, and voltage application means for reducing the output voltage of the reference voltage generation circuit when no power-on instruction is input.

〔Example·〕

Hereinafter, the unfired BA will be explained based on the drawings.

Is Figure 1 the first practical configuration of the present invention? FIG. 2 is a block diagram showing the configuration of a second embodiment M of the present invention.

First, the configuration of the first embodiment will be explained based on FIG. 1. Switching regulator 25L of this first embodiment
1 main power control element, a current transformer that detects the current flowing through this main power control element, a current transformer, a rectifying and smoothing circuit, main input terminals A and B, main output terminals C and D, and the above main power The input terminal E of the control on pulse that drives and controls the control element, and the output terminals F and G of the current transformer (when current flows through the main power control element,
A known single type DC-DC converter 2 including a polarity in which an output terminal F is positive with respect to an output terminal G is provided, and a DC power supply 1 and an output voltage detection circuit 3 are provided. Also, Sui.

The length regulator 25 is provided with a current detection circuit 7 that includes a diode 5 and a resistor 6 and extracts a voltage waveform similar to the pulse current flowing through the main power control element. Vessel 10.12, 17, 18,
21 and 23, transistors 11 and 22, and a first reference voltage 13° resistor 14. A reference voltage generation circuit 16 including a capacitor 15 is provided, and an error amplifier 19 and a pulse width control circuit 24 are further provided.

. The main input terminals C and B of the DC-DC converter 2 are connected to the positive and negative terminals of the DC power supply l, respectively, and the main output terminal C
and D are connected to load 4. Output terminal F is connected to the anode of diode 5, the cathode of diode 5 is connected to the other end of resistor 6 whose one end is connected to ground potential, and output terminal G is connected to ground potential. The connection point between the diode 5 and the resistor 6 is connected to the non-inverting input terminal of the comparator 9 as the output of the current detection circuit 7. The inverting input terminal of the comparator 9 is connected to the second reference voltage, and the output of the comparator 9 has one end connected to the power supply VccK and the other end of the resistor lO, the emitter of which is connected to the ground potential, and the collector of which is connected to the resistor lO. Vessel 1
The transistor 110 connected to one end of the transistor 2 is connected to the connection point with the pace. The other end of the resistor 12 is connected to the other end of a resistor 14, one end of which is connected to the first reference voltage 13, a capacitor 15 and an error amplifier 19, one end of which is connected to ground potential.
A resistor 21 is connected to a connection point with one input terminal of the resistor 21, whose emitter is connected to ground potential at one end, and whose pace is connected to a power supply Vcc at one end, and a power-on signal. Transistor 2 connected to the connection point of 20
The resistor 23 is connected to the other end of the resistor 23, which is connected to the collector of the resistor 23. The other input terminal of the error amplifier 19 has one end connected to the first reference voltage 13 and the other end of the resistor 17 and an output voltage connected to the main output terminals C and D of the single type DC-DC converter 2. It is connected to a connection point with the other end of a resistor 18 whose one end is connected to the output of the detection circuit 3 . The output of the error amplifier 19 is connected to the input of a pulse width control circuit 24, and the output of the pulse width control circuit 24 is connected to the input terminal EK of the single type DC-DC converter 2.

Next, the operation of this first embodiment will be explained based on FIG. If there is a power-on instruction, the power-on signal 20
is "0" and transistor 22 is held off. Therefore, the output voltage of the reference voltage generation circuit 16 applied to the error amplifier 19 is equal to the voltage value of the first reference voltage 13. During this period, the voltages at the two input terminals of the error amplifier 19 are approximately equal. The output voltage of the switching regulator 25 is V. is stably controlled to a constant value.

On the other hand, if there is no power-on instruction, the power-on signal 20
is "1" and the C transistor 22 is kept on.

Therefore, the output voltage of the reference voltage generation circuit 16 applied to the error amplifier 19 is the voltage value of the first reference voltage 13, the collector saturation voltage of the transistor 22, and the resistor 14.23.
Determined by

Therefore, by appropriately selecting the values of resistors 14.17 and 18.23, the output voltage of reference voltage generation circuit 16 can be lower than the divided voltage of resistor 17.18. is not output.

Next, when a power-on instruction is input, when the power-on signal 20 changes from rlJ to "0", the output voltage of the reference voltage generation circuit 16 is
gradually increases to the voltage value of the first reference voltage 13 with a time constant,
Sui, output voltage of Ching Regulator 25■. 1 gradually increases accordingly, and after a certain period of time, is stably controlled to a constant value.

Next, when there is a power-on instruction and the power-on signal is "0" and the output current I0 of the switching regulator 25 is within the rated value range of the switching regulator 25, the comparator 9 The output is "0" and the transistor 11 is kept off.

Therefore, the reference voltage given to the error amplifier 19 is
This corresponds to the voltage value of the first reference voltage 13.

During this period, the error amplifier 19 operates so that the voltages at the two input terminals are approximately equal, and the output voltage Void of the switching regulator 25 is stably controlled to a constant value.

Here, since the pulse current flowing through the main power control element is mainly the excitation current of the choke coil that constitutes the smoothing circuit in the single type DC-DC converter 2, the pulse current that flows through the main power control element is a sawtooth-shaped current that increases over time Contains wave-forming components,
The output voltage of the current detection circuit 7, which is similar to this pulse current waveform, also has a similar pulse waveform.

Next is the output current of the switching regulator 25. increases for some reason, and as a result, the peak value of the pulse voltage including the sawtooth waveform component determined by the output voltage of the current detection circuit 7 becomes a value sufficient to exceed the voltage value of the second reference voltage 8. Then, the switching operation starts with a pulse width proportional to the increase in the output current I0 of the comparator 9Vi. During the period when the output of the comparator 9 is "1", the transistor 11 is biased through the resistor 10 and becomes conductive. transistor 11
becomes conductive, the charge on capacitor 15 is transferred to resistor 1
2 is released. Further, during the period when the output of the comparator 9 is "0", the charge of the capacitor 15 is equal to the first reference voltage 1.
3 through the resistor 14. capacitor 15
．． By appropriately choosing the values of resistors 12 and 14,
The voltage across the capacitor 15 is sufficiently smoothed, and
Appropriate response speed and output current. decreases with .

As a result, the output voltage v0 of the switching regulator 25 drops.

When the cause of the increase in the output current I0 is removed, the output of the comparator 9 becomes "0", the transistor 11 becomes constantly non-conducting, and therefore the reference voltage applied to the error amplifier 19 becomes the first one. Upon reaching the voltage value of the reference voltage 13, the switching regulator 25 returns to normal operation, and the output voltage v0 is stably controlled to a constant value.

Next, a second embodiment will be described based on FIG. 2. This second embodiment uses a bush-pull type DC-DC converter 2 instead of the DC-DC converter section 2 shown in FIG.
' is provided. In this figure, the numbers 1,3~6.8~
24 and A to G correspond to the same reference numerals shown in FIG. The difference between Fig. 2 and Fig. 1 is that the bush-pull type DC-DC converter 2' has at least two main power control elements, each of which is divided into two phases and performs switching operation. , the output of the current transformer for detecting the current flowing through the main power control element has a center tap and is connected to the output terminal H. Furthermore, outputs F and q are connected to the anodes of diodes 5 and 5', respectively'c (7L).

The cathodes of diodes 5 and 5' are connected, and the connection point is a resistor 6 whose one end is connected to ground potential.
A current detection circuit 7' is formed by the output terminal Hμ connected to the other end, the diodes 5 and 5', and the resistor 6 connected to the ground potential. With this configuration, the current flowing through each main power control element is divided into two phases and detected at the same time, and other operations are the same as in the first embodiment.

〔Effect of the invention〕

As described above, the present invention has the advantage that the slow start function when starting up the switching regulator can be achieved with a simple circuit.

In addition, when an overcurrent condition is detected in the output current of the regulator, the output voltage of this regulator is lowered, so it does not respond to causes of malfunction due to static electricity noise, etc. Switching regulators can be used to stabilize the effect.

Furthermore, once the cause of the overcurrent condition is removed, normal operation is restored without manual reset, which simplifies driving operations.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing the configuration of a first embodiment of the present invention, and FIG. 2 is a schematic diagram showing the configuration of a second embodiment of the present invention. 1...DC power supply, 2-...Single type DC-DC converter, 2'...Push pull type DC-DC converter, 3...Output voltage detection circuit, 4...Load, 5,5'...-
Diode, 6,10°12.14,17,18,21
．． 23...Resistor, 7.7'...Current detection circuit, 8...Second reference voltage, 9...
...Comparator, 11.22...Transistor, 1
3...First reference voltage, 15...Capacitor, 16...Reference voltage generation circuit, 19...
...Error amplifier, 20...Power-on signal,
24... Pulse width control circuit, 25, 26...
...Switching regulator. Agent: Susumu Uchihara, patent attorney 82nd year of employment, 5th year of employment E q
:Hishizuku revision 1i13: Prison voltage tb, Kitan dynamic perseverance 19: Kaizasho rumor school 20: Arrival at the port 2
5: Spanke Shijire Akira LL-Yu 24; no de I
Part 1 of Hiding My Voice @

Claims (1)

[Claims] a DC-DC converter, a reference voltage generation circuit having a capacitor connected via a resistor to a first reference voltage that is a normal output voltage, and an output voltage detection circuit that detects the output voltage of the DC-DC converter. The output of the output voltage detection circuit and the resistance dividing point of the first reference voltage are connected to one input terminal, and the output of the reference voltage generation circuit is connected to the other input terminal of the DC-DC converter. an error amplifier for controlling a main power control element; a current detection circuit for detecting a pulse current flowing through the main power control element; A switching regulator comprising: overcurrent protection means for reducing the output voltage of the voltage generation circuit; and power supply means for reducing the output voltage of the reference voltage generation circuit when no power supply instruction is input.