JP2000078839A - Switching regulator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress a dynamic overvoltage state more quickly and, further, protect a load from the dynamic overvoltage state even if an output voltage tends to be put into the dynamic overvoltage state. SOLUTION: If it is detected by a Zener diode ZD that an output voltage VOUT is in an overvoltage state, a transistor Q which is provided so as to bypass an error amplifier Z during that time is forcibly transferred to an ON-state. As a result, the voltage drop of a light-emitting diode (in a photocoupler PC1) is larger, so that the diode is put into more intense light-emitting state. Therefore, the control response delay of a PWM control circuit IC is reduced and its dynamic covervoltage state can be quickly suppressed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention is directed to a state in which the output voltage is detected as being more emphasized even if the output voltage is going to be in a dynamic overvoltage state due to a sudden transition of the load to a light load state. In addition, by performing PWM control so as to suppress the dynamic overvoltage state more quickly, the switching circuit is configured to protect the load from the dynamic overvoltage.
It relates to a regulator.

[0002]

As shown in the Related Art For example FIG. 3, which in the up switching regulator, so the actual output voltage V _OUT is coincident at all times to the rated output voltage, the partial pressure output voltage V _OU T by resistance The state is compared with the reference voltage corresponding to the rated output voltage in the error amplifier Z as
The light emitting diode in the photocoupler PC1 is always in a light emitting state according to the comparison deviation.
Therefore, the impedance of the phototransistor in the photocoupler PC1 is also changed according to the comparison deviation. In a PWM control circuit IC, a switching element (in this example, a MOS-FET is used) in accordance with an impedance change in a phototransistor.
The on / off control signal for periodically putting the FET in the on / off state is generated as a variable pulse width. While the switching element FET is in the ON state, the DC voltage V _IN is applied to the primary winding of the power conversion transformer T via the switching element FET. This application induces a secondary voltage in the secondary winding of the power conversion transformer T. This secondary voltage is half-wave rectified by the diode D1 and smoothed by the capacitor C via the choke coil L. In addition, while the half-wave rectification is not performed by the diode D1, the electromagnetic energy that has been accumulated in the choke coil L is smoothed by the capacitor C via the commutation diode D2, so that the load is applied to the load LOAD. The output voltage V _OUT to be obtained is always obtained as a substantially rated output voltage.

As a technique relating to a switching regulator, for example, “Design Method of Forward Converter” (Practical Power Supply Circuit Design Handbook, CQ Publishing Co., Ltd., Oct. 10, 1988, pp. 148-151)
It has been known.

[0004]

The problem with the switching regulator is that, for example, when the load suddenly shifts to a light load state, the output voltage V _OUT falls within the allowable error range of the rated output voltage. Instead, it deviates greatly and rapidly from within the allowable error range, that is,
That is to say, a state of falling into a dynamic overvoltage state. As a method for coping with this dynamic overvoltage state, a series connection of a light emitting diode (in the photocoupler PC2), a current limiting resistor R and a zener diode ZD has been used as shown in FIG. It is considered that the output voltage V _OUT is applied to the power supply. If the Zener diode ZD responds to the dynamic overvoltage, the light emitting diode (in the photocoupler PC2)
Is in the light emitting state for the first time.
2 is notified to the PWM control circuit IC as an abrupt change in the impedance of the phototransistor in 2. In the PWM control circuit IC, when the impedance suddenly changes to a small value, an on / off control signal is generated so that the pulse width becomes smaller.

However, normally, no dynamic overvoltage is detected by the Zener diode ZD, and after the detection of the dynamic overvoltage, the PWM control circuit IC outputs the ON / OFF control signal for the first time so that the pulse width becomes smaller. The fact is that the dynamic overvoltage state cannot be suppressed more quickly because of the control response delay at that time.

Therefore, an object of the present invention is to suppress the dynamic overvoltage state more quickly even if the output voltage is going to be in a dynamic overvoltage state due to a sudden transition of the load to a light load state or the like. By performing PWM control as much as possible, a switching circuit that can protect the load from dynamic overvoltage is provided.
To provide a regulator.

[0007]

SUMMARY OF THE INVENTION The object of the present invention is basically to provide a light emitting diode connected in series to an error amplifier while an actual output voltage is detected by a Zener diode as being in an overvoltage state. This is achieved by configuring the voltage drop to be greater. More specifically, the transistor provided to bypass the error amplifier is forcibly turned on while the zener diode detects that the actual output voltage is in an overvoltage state. Alternatively, a zener diode for detecting that the actual output voltage is in an overvoltage state may be configured in a state of being connected in parallel to the error amplifier.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described with reference to FIGS. FIG. 1 shows an example of the configuration of the switching regulator according to the present invention. As will be understood from this, a substantial difference from that shown in FIG. The photocoupler PC2 for detecting the dynamic overvoltage is unnecessary. As shown, Zener diode Z
An output voltage V _OUT is applied to a series connection body composed of D and current limiting / voltage dividing resistors R1 and R2.
Has been applied to the base of the transistor Q which is provided so as to bypass the, if it is detected that the output voltage VO _UT is in an overvoltage condition at the Zener diode ZD, while provided in order to bypass the error amplifier Z The transistor Q is forcibly turned on. Thereby, the light emitting diode (in the photocoupler PC1) connected in series to the error amplifier Z
Is higher, and thus the light emitting diode is in a stronger light emitting state, so that the PW
In the M control circuit IC, the dynamic overvoltage state can be suppressed more quickly by reducing the control response delay.
The load LOAD can be protected from dynamic overvoltage. Incidentally, in this example, the transistor Q is provided to bypass the error amplifier Z via the resistor R3, but in some cases, the resistor R3 is unnecessary.

FIG. 2 also shows a main configuration of another example of the switching regulator according to the present invention. In this case, the transistor Q is not required, and the output voltage V _OUT becomes overvoltage. The Zener diode ZD for detecting the state is in a state of being connected in parallel to the error amplifier Z.
If the Zener diode ZD detects that the output voltage V _OUT is in an overvoltage state, the light emitting diode (photocoupler PC1) connected in series to the error amplifier Z during that time.
Voltage drop in the
Since the light emitting diode is in a stronger light emitting state, the same effect can be obtained by simplifying the configuration.

[0010]

As described above, according to the first to third aspects, even if the output voltage is put into a dynamic overvoltage state due to a sudden transition of the load to a light load state, etc. By performing PWM control to suppress the dynamic overvoltage state more quickly, a switching regulator capable of protecting the load from the dynamic overvoltage is obtained.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of an example of a switching regulator according to the present invention;

FIG. 2 is a diagram showing a configuration of a main part in another example.

FIG. 3 is a diagram illustrating a configuration of an example of a switching regulator according to the related art;

[Explanation of symbols]

IC: PWM control circuit, FET: Switching element, T
... power conversion transformer, D1, D2 ... diode, C ... capacitor, L ... choke coil, PC1 ... photocoupler, Z ... error amplifier, ZD ... Zener diode, Q ...
Transistor

Claims (3)

[Claims] An error amplifier detects a deviation between the output voltage and a rated output voltage using an actual output voltage as an operation power supply, and a light emitting diode connected in series to the error amplifier responds to the deviation. In the light emitting state, the PWM voltage is controlled by the PWM control IC with the pulse width of the switching element varied periodically according to the impedance state of the phototransistor paired with the light emitting diode. While applied to the primary winding of the power conversion transformer via the element, the secondary voltage induced in the secondary winding of the power conversion transformer is rectified by a diode and smoothed by a capacitor via a choke coil. Switching regulator, and that the actual output voltage is in an overvoltage condition A switching regulator which is emphasized so that a voltage drop in a light emitting diode connected in series to the error amplifier is detected while detecting the voltage. 2. An error amplifier detects a deviation between the output voltage and a rated output voltage using an actual output voltage as an operation power supply, and a light emitting diode connected in series to the error amplifier responds to the deviation. In the light emitting state, the PWM voltage is controlled by the PWM control IC with the pulse width of the switching element varied periodically according to the impedance state of the phototransistor paired with the light emitting diode. While applied to the primary winding of the power conversion transformer via the element, the secondary voltage induced in the secondary winding of the power conversion transformer is rectified by a diode and smoothed by a capacitor via a choke coil. Switching regulator, and that the actual output voltage is in an overvoltage condition During the detection, the transistor provided to bypass the error amplifier is forcibly turned on.
regulator. 3. An error amplifier detects a deviation between the output voltage and a rated output voltage using an actual output voltage as an operation power supply, and a light emitting diode connected in series to the error amplifier responds to the deviation. In the light emitting state, the PWM voltage is controlled by the PWM control IC with the pulse width of the switching element varied periodically according to the impedance state of the phototransistor paired with the light emitting diode. While applied to the primary winding of the power conversion transformer via the element, the secondary voltage induced in the secondary winding of the power conversion transformer is rectified by a diode and smoothed by a capacitor via a choke coil. A switching regulator for detecting that an actual output voltage is in an overvoltage state. A switching regulator with a configuration in which a shunt diode is connected in parallel to an error amplifier.