JPH031908B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a switching regulator for voltage stabilization used in various electronic devices.

[Prior Art] Recently, switching regulators have been used as stabilized power sources used in various electronic devices.

As is well known, this switching regulator uses a switching pulse to drive a switching element provided on the primary side of a power transformer by controlling the pulse width of this switching pulse according to the output voltage. , which attempts to stabilize the output voltage.

Switching regulators have additional functions such as detecting overcurrent conditions on the primary side, providing safety measures for switching regulators.

A switching regulator with such an overcurrent protection function performs pulse control when an overcurrent is detected, or temporarily stops the supply of switching pulses to escape from an overcurrent state. A switching regulator is known that has a so-called overcurrent protection circuit that controls the pulse width again to obtain a predetermined stabilized output voltage when the voltage is exceeded.

FIG. 3 is a system diagram of the main parts of the switching regulator 1 having a control circuit 10 for carrying out such overcurrent protection.

In the figure, 7 is a bridge rectifier circuit into which a commercial AC voltage is input from a commercial AC source (not shown). This bridge rectifier circuit 7 is connected to one end of the primary coil 2a of the power transformer 2 via a smoothing circuit 8. The other end of the coil 2a is composed of a switching element (transistor, etc.).
(MOS type FET transistor) 21 is connected to the drain. The gate of the switching element 21 is connected to the integrating circuit 9 (in this figure, it consists of a resistor 23a and a capacitor 23b), and further,
It is connected to the pulse width discrimination circuit 11 in the control circuit 10. The control circuit 10 is usually integrated, and as a practical integrated circuit, commercially available products such as Mitsubishi M51977 and Matsushita AN8090 can be used.
The pulse width discrimination circuit 11 is connected in sequence to an AND circuit 12, a timer circuit 13, a power supply on/off control circuit 14, and the like, and then to an internal power supply circuit 15 of the IC. Further, the source of the switching element 21 is connected to a resistor 2 which functions as a current-voltage conversion means.
2, the source terminal is connected to the resistor 24
The connection point between a and the noise absorbing capacitor 24b is
It is connected to the overcurrent detection circuit 16 in the control circuit 10 and further connected to the AND circuit 12. Further, a coil 2b is provided on the secondary side of the power transformer 2. A diode rectifier circuit 3 and a capacitor smoothing circuit 4 are connected to the secondary coil 2b. A load 6 is connected to the rectifier circuit 3 with an output voltage detection circuit 5 interposed therebetween. The output voltage detection circuit 5 is connected to the pulse width control circuit 17 in the control circuit 10 after the primary side and the secondary side of the power transformer 2 are insulated and connected by an optical coupling circuit. A pulse oscillator 18 is connected to the pulse width control circuit 17,
A continuous pulse signal is supplied. The pulse oscillator 18 and overcurrent detection circuit 16 are connected to the internal power supply circuit 15 of the IC, from which a predetermined DC voltage Vcc is applied.
is being supplied with.

Next, the operation will be explained. A commercial AC voltage input from a commercial AC power supply (not shown) is passed through a bridge rectifier circuit 7 and a smoothing circuit 8 to a power transformer 2.
DC voltage is supplied to the switching element 21 via the primary side coil 2a. A continuous pulse signal (hereinafter referred to as a switching pulse) is supplied to the switching element 21 from the control circuit Vout terminal as shown in FIG. 4A, and intermittent (switching) control is performed. As a result, a pulse voltage corresponding to the above-mentioned intermittent control is generated in the coil 2b on the secondary side of the power transformer. This pulse voltage is supplied to a rectifier circuit 3 and a smoothing circuit 4, regenerated into a DC voltage, and supplied to an output voltage detection circuit 5 and a load 6. The output voltage detection circuit 5 supplies an output indicating fluctuations in the output voltage supplied to the load 6 to a pulse width control circuit 17 in a control circuit 10 provided on the primary side of the power transformer 2 through an optical coupling circuit. Further, the pulse width control circuit 17 is supplied with a continuous pulse signal from the pulse oscillator 18, and the pulse width of this pulse signal is controlled according to fluctuations in the output voltage. The switching pulse whose pulse width is controlled in this way is outputted from Vout of the control circuit 10.
The signal is output from the terminal and supplied to the switching element 21. The above is the operation of a general switching regulator, but in this control circuit, a heavy load condition due to a short circuit of the load while supplying a stabilized voltage to the load, or an overload condition close to that, is detected. A timer-type protection circuit described below is provided for the purpose of protecting the switching regulator device by stopping power supply to the load when it is in a loaded state. That is, between the source and ground of the switching element 21, there is a resistor 22 that functions as current-voltage conversion means.
is connected to the source terminal (connection point a), and the state of the current flowing through the coil 2a based on the current i flowing through the resistor 22 appears as a voltage fluctuation. This source voltage is then applied to the control circuit 10 through a resistor 24a and a noise absorbing capacitor 24b.
The current is supplied to the overcurrent detection circuit 16, where it is detected whether or not there is an overcurrent state. By the way, to explain when an overcurrent condition is detected,
For example, in the case of a capacitive load, an overcurrent condition occurs when the power is turned on. Furthermore, a load such as a motor may repeatedly enter an instantaneous overcurrent state during normal operation. Further, an integrating circuit 9 consisting of a resistor 23a and a capacitor 23b is connected to the gate of the switching element 21, and integrates the switching pulse supplied to the gate, and calculates the DC level according to the pulse width of the switching pulse. The integrated output is supplied to the pulse width discrimination circuit 11. Figure 4B is
The switching pulse shown in FIG.
The integrated outputs obtained by integrating at are shown in the positive load state (indicated by the broken line) and in the overload state (indicated by the solid line). Now, the pulse width determination circuit 11 determines from the DC level of the integral output whether the conduction period of the switching element 21 during intermittent control is below a permissible range. However, depending on the type of load, the load may temporarily become light during normal operation.
In this case, since the pulse width of the switching pulse becomes narrow, the DC level of the integral output may fall below the allowable range. Similarly, when the power is turned on without connecting a load (no load), the DC level of the integral output falls below the allowable range. Therefore, this control circuit 1
0, both the detection output from the overcurrent detection circuit 16 indicating that there is an overcurrent state and the discrimination output from the pulse width discrimination circuit 11 indicating that the conduction period of the switching element 21 during intermittent control is below the allowable range. The timer circuit 13 is driven only when the signal is supplied to the AND circuit 12. The driven timer circuit 13 supplies the timer control output to the power supply on/off control circuit 14 for a certain period of time, and the internal power supply circuit 1
5 is stopped for a certain period of time. As a result, power supply from the internal power supply circuit 15 to the pulse oscillator 18 is stopped for a certain period of time, and oscillation is stopped. Therefore, in the above-mentioned heavy load state (or an overload state close to it), power supply to the load is instantaneously stopped for a limited period of time. Thereafter, the same operation is repeated. Therefore, when a heavy load condition continues due to a load short circuit, etc., the power supply to the load remains stopped, and if the overload condition is temporary, the power supply to the load is resumed once the overload condition is resolved. Power is supplied.

[Problems to be solved by the invention] By the way, in this type of switching regulator, depending on the type of load, even if the load temporarily becomes slightly excessive during normal operation, the load can be lightened immediately. If this happens, you may want to lower the sensitivity of the timer protection circuit so that it does not operate each time. However, in this switching regulator, the resistor and capacitor constitute an integrating circuit as described above, so the charging path shares the discharging path, and the DC level of the integral output is lower than the switching level during normal operation. Limited by the pulse width of the pulse. As a result, the DC level of the integral output, which is the standard for determining whether it is a positive load state or an overload state, is within an extremely limited range, so the DC level of the integral output in a positive load state cannot be set to a large value.
There was a problem in that the sensitivity of the timer type protection circuit could not be lowered freely.

[Means for Solving the Problems] Therefore, in the present invention, in the switching regulator having the above-mentioned timer type protection circuit,
The present invention is characterized in that the charging path and the discharging path of the integrating circuit that integrates the switching pulse are configured to be different.

[Function] Since the charging path and the discharging path of the integrating circuit are made different, the DC level of the integral output in a positive load state can be freely set without being limited by the pulse width of the switching pulse during normal operation.

[Embodiment] FIGS. 1 and 2 are circuit diagrams showing preferred embodiments of the present invention. Each figure has substantially the same configuration as FIG. Since the only difference is the circuit configuration, the description of what was explained in FIG. 3 will be omitted here. Note that the symbols attached to each figure indicate the same thing.

In the integrating circuit 30 in FIG. 1, a resistor 31 and a resistor 33 are connected to the gate of the switching element 21.
is connected, and the resistor 31 is further connected to the diode 32
connected to the anode of the And diode 3
The cathode of No. 2 is connected to a resistor 33, and the connection point thereof is connected to a capacitor 34 and also to the pulse width discrimination circuit 11.

Next, the operation of the integrating circuit 30 will be explained. The capacitor 34 is charged by the current flowing through the resistor 33 and the current flowing through the resistor 31 and the diode 32, and is then discharged via the resistor 33. In this integrating circuit 30, since the charging path and the discharging path of the capacitor 34 are different, the resistor 33 and the resistor 31
Also, the charging time constant set by the diode 32 can be freely set regardless of the discharging time constant set by the resistor 33. Therefore, when integrating the switching pulse supplied from the gate of the switching element 21, the DC level of the integrated output in a positive load state can be set fairly freely.

Furthermore, in the integrating circuit 40 in FIG. 2, a resistor 41 and a resistor 43 are connected to the gate of the switching element 21, and the resistor 41 is further connected to the anode of a diode 42. Also, resistor 4
3 is further connected to the cathode of a diode 44. The cathode of the diode 42 is connected to the anode of the diode 44, and the connection point thereof is connected to the capacitor 45 and also to the pulse width discrimination circuit 11.

Next, the operation of the integrating circuit 40 will be explained. The capacitor 45 includes a resistor 41 and a diode 42.
It is charged only by the current flowing through the diode 44 and discharged only through the diode 44 and the resistor 43. In this integrating circuit 40 as well, since the charging path and the discharging path of the capacitor 45 are different, the charging time constant set by the resistor 41 and the diode 42 and the discharging time constant set by the resistor 43 and the diode 44 can be freely set separately. can. In this case as well, when integrating the switching pulse supplied from the gate of the switching element 21, the DC level of the integrated output in the positive load state can be set fairly freely.

[Effects of the Invention] As explained above, according to the present invention, in a switching regulator having a timer type protection circuit, the charging path and the discharging path of the integrating circuit are made different, so that the integral output in the load state is The DC level can be freely set to a large value without being limited by the pulse width of the switching pulse during normal operation, and the sensitivity of the timer type protection circuit can be freely lowered.
Therefore, depending on the type of load, even if the load temporarily becomes slightly excessive during normal operation, if the load immediately drops, it is possible to prevent the timer-type protection circuit from operating each time. It has excellent effects such as:

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram of a first preferred embodiment of the present invention;
FIG. 2 is a circuit diagram of a second preferred embodiment of the present invention, FIG. 3 is a circuit diagram of a conventional example, and FIG. 4 is a waveform diagram explaining the operation of FIG. 3. 2...Power transformer, 2a...Primary side coil, 6...Load, 11...Pulse width determination means, 1
2, 13, 14... protection circuit, 16, 22... overcurrent detection means, 21... switching element, 3
0,40... Integral circuit.

Claims (1)

[Claims] 1. By applying a DC voltage to the primary coil of the power transformer and controlling the switching element connected to the primary coil intermittently using switching pulses, Overcurrent detection means is provided, which is configured to obtain a DC voltage supplied to the load from the secondary side, converts the current flowing through the switching element into voltage, and detects overcurrent on the primary side based on this voltage. With,
Pulse width determining means is provided for determining whether the conduction period of the first switching element during intermittent control is below a permissible range based on the DC level obtained by integrating the first switching pulse, and the overcurrent detecting means The switch has a protection circuit that stops intermittent control of the first switching element for a certain period of time when the first half pulse width determining means determines that the conduction period of the first half switching element during intermittent control is below the allowable range when an overcurrent on the next side is detected. 1. A switching regulator characterized in that the charging path and the discharging path of an integrating circuit that integrates an early switching pulse are made different.