JPH01315260A - Switching regulator power source circuit - Google Patents

Abstract

PURPOSE:To prevent a switching element from damaging by forming a correcting current proportional to an input voltage, detecting both the correcting current and the current of the element, and so controlling ON, OFF that they do not become predetermined value or more. CONSTITUTION:A separately-excited switching regulator voltage circuit is composed of bridge rectifying diodes 8-11, a capacitor 12, an oscillation controller 16, a driving circuit 16, an output transistor(Tr) 14, a switching transformer 13, rectifying diode 19 and smoothing capacitor 20 of the secondary side of the transformer to supply power to a load 21. A detector 18, an overcurrent control circuit 17, and a detecting resistor 5 are provided as a feedback loop. In this case, an auxiliary winding (a) is provided in the transformer 13, its one end is connected to a series circuit of a resistor 3 and a Zener diode 4, the other end is connected to the input terminal of the control circuit 17, and the other end of the winding (a) is connected to the source of the Tr 14. Thus, an overcurrent controlling operation can be effectively conducted.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a switching regulator power supply circuit that generates a direct current voltage from a commercial power source.

2. Description of the Related Art In recent years, switching regulator power supply circuits have been widely used as power supplies for various devices. Many power supply circuits equipped with various protection circuits, such as overcurrent protection circuits or overvoltage protection circuits, are also in use.

An example of a conventional power supply circuit will be described below with reference to the drawings.

FIG. 7 is a circuit diagram of an example of a separately excited switching regulator power supply circuit equipped with an overcurrent control circuit. In other words, in Figure 7 ((a) and (b) are commercial power input terminals,
A sinusoidal AC voltage is applied, this AC voltage is rectified by bridge rectifier diodes 8, 9, 10.11, and further smoothed by a capacitor 12 to form a DC voltage. On the other hand, a switching signal is propagated from the oscillation control circuit 16 to the drive circuit 16 and further to the output transistor 14, and energy is supplied to the secondary side of the transformer via the switching transformer 13 during the ON period of the transistor 140. . In addition, 19 is a rectifier diode of the output of the secondary side of the transformer, 2o is a smoothing capacitor, and 21 is a load.

As a feedback loop for controlling the secondary side output voltage level to a constant level, a detection circuit 18 detects the transformer secondary side output voltage, and an oscillation control circuit 16 controls the on-duty ratio while keeping the oscillation period constant.

Reference numeral 6 denotes an overcurrent detection resistor, and the magnitude of the source current flowing through this resistor 6 is detected by the overcurrent control circuit 1 to control the oscillation of the oscillation control circuit 16. In addition, it is a leader resistance that divides the voltage drop of the overcurrent detection voltage 6 into resistors 1 and 2,
6 is a noise removal capacitor.

The operation of the switching regulator power supply circuit configured as described above will be described below.

First, an excessive current flows through the output transistor 14 during a transient period when the power supply circuit starts operating, or during an abnormal state. This current causes a voltage drop across resistor 6. When the reference potential of the circuit is set to the source potential of the output transistor 14,
A negative voltage is generated across the resistor 6. The voltage waveform is as shown in FIG. The voltage generated across resistor 6 is divided by resistors 1 and 2, and the voltage across resistor 10 is applied to overcurrent control circuit 17. When the voltage across the resistor 1 exceeds the threshold voltage vth of the overcurrent control circuit 1, the oscillation control circuit 16 is controlled to perform a so-called intermittent oscillation operation to temporarily stop oscillation. As a result, output transistor 1
It becomes possible to protect the element from accidents such as destruction without overdriving the element.

Problem to be Solved by the Invention The waveform of the drain current flowing through the output transistor in a switching regulator power supply circuit with a constant oscillation period is
The peak current value changes depending on the AC input voltage level.

In particular, when handling a wide range of input voltages (for example, 80V to 270V), the peak current value of the drain current changes nearly three times between the minimum and maximum values of the input voltage. Since the load is constant as a power supply circuit, as the input voltage increases, the current in the circuit decreases.

Therefore, as shown in FIG. 9, the overcurrent detection voltage EPo with respect to the input voltage decreases with a constant slope as the input voltage increases.

On the other hand, since the operation start voltage (threshold voltage ■th) of the overcurrent control circuit is constant, the higher the AC input voltage is, the lower the overcurrent detection voltage is with respect to the operation start voltage. For this reason, during the power-on rush, the overcurrent control circuit works well at low input voltages and there is no problem, but at high input voltages, the overcurrent control circuit does not work and the safe operating area of the output transistor is exceeded, resulting in the output There was a problem that the transistor was destroyed.

SUMMARY OF THE INVENTION In view of the above problems, the present invention provides a switching regulator power supply circuit that has a simple circuit configuration and is equipped with a circuit that guarantees sufficient overcurrent control operation over a wide range of AC input voltages.

Means for Solving the Problem In order to achieve the above object, the switching regulator power supply circuit of the present invention creates a correction current proportional to the input voltage applied to the switching transformer, and connects this correction current to the switching element in the on state. Both of the flowing currents are detected and the on/off period of the switching element is controlled so that the sum of these two currents does not exceed a predetermined value.

Operation With the above configuration, a correction current proportional to the input voltage to the switching transformer is created, and this correction current and the current flowing through the switching element are superimposed and detected, and the switching voltage decreases as the input voltage increases. By compensating for and detecting the decrease in the current flowing through the elements, it is possible to reliably detect overcurrents that flow in excess of the ratings of the circuit elements, such as when the power is turned on (inrush), even at high input voltages. Accurate circuit protection against current can be achieved.

Embodiment Hereinafter, a Swissinda regulator power supply circuit according to an embodiment of the present invention will be described with reference to the drawings. FIG. 1 shows the configuration of a switching regulator power supply circuit in a first embodiment of the present invention. Components similar to those shown in FIG. 9 are designated by the same reference numerals, and detailed description thereof will be omitted.

In this embodiment, in addition to the configuration shown in FIG. 9, the switching transformer 13 is provided with an auxiliary winding a, one end of the switching transformer auxiliary winding l is connected to a series circuit of a resistor 3 and a Zener diode 4, The other end of this series circuit is connected to the input end of the overcurrent control circuit, and the other end of the auxiliary winding g is connected to the source of the transistor 14.

The operation of the switching regulator power supply circuit configured as described above will be explained below with reference to FIGS. 1 to 4.

Figure 2 shows the main voltage waveforms of this example, and ('b)
shows the waveform at point 0)) in FIG. The overcurrent control circuit 17 transmits the overcurrent control correction current obtained through the auxiliary winding e.
Since the current is fed back to the switching transformer auxiliary winding l even during the OFF period of the output run sister 4, a voltage of 7E is generated on the positive side as well. Since the correction current is flowing at the negative peak, the voltage -EP is higher than that shown in FIG. 8. Same figure (
a) is the auxiliary winding output voltage waveform, the ON period of the output transistor is heavy pressure -El, and the FF period is R2.

FIG. 3 is a graph showing the dependence of the auxiliary winding output voltage -El on the AC input voltage, and its absolute value increases as the AC input voltage increases.

Under the above circumstances, the correction current i for overcurrent control. Analyze.

(1) Output transistor ON period However, E...Auxiliary winding output voltage, vZ...
... Zener voltage, VC ... Overcurrent control circuit input voltage, R3 ... Correction circuit resistance ((2)
Output transistor OFF period However, R2...
...Auxiliary winding output voltage vF...Zener diode forward drop voltage In order to appropriately correct for a wide range of input voltages, in equation (1), when AC input voltage soV,
Correction current, VZ=E1 (80V)
-VC? ! : fx D, Zener voltage can be set. Therefore, by selecting El (80V)=vZ+vc, the correction current when the AC input voltage SOV can be set to zero using the Zener diode. Then, for an AC input voltage of 2 oV from soV, the corrected resistance value R is calculated according to equation (1).
3 as appropriate and superimposing the correction current on the leader resistor 1, it is possible to maintain a constant overcurrent control input voltage with respect to the AC input voltage, as shown in FIG.

In addition, when there is no need to increase the accuracy that much, the input voltage is 8.
The correction current does not necessarily have to be set to zero at 0V.

As described above, according to this embodiment, by flowing the correction current to the overcurrent control circuit 17 through the switching transformer auxiliary winding 4, the resistor 3, and the Zener diode 4, it can be applied even to a wide range of AC input voltages. The overcurrent control input voltage can be maintained at a constant level, and the overcurrent control operation can be ensured.

In the embodiment shown in FIG. 1, a diode 22 may be added to the correction circuit 7 in the direction in which the Zener current flows as shown in FIG. At this time, IC (
OFF) current becomes zero, and the overcurrent control input voltage waveform also becomes as shown in FIG.

In the embodiment shown in FIG. 1, the overcurrent control input voltage is treated as a negative voltage, but the circuit may be configured as a positive voltage as shown in FIG. In FIG. 6, an overcurrent detection resistor 5 is inserted into the source circuit, and its voltage drop is divided between leader resistors 1 and 2. Therefore, the polarity of the switching transformer auxiliary winding and the polarity of the Zener diode 4 are reversed.

Also, the switching transformer auxiliary winding is not a dedicated winding, but
It can also be used in conjunction with other windings if the polarities match.

Furthermore, even without the Zener diode 4, by superimposing the correction current obtained from the auxiliary winding on the detection output of the overcurrent detection resistor 5, the decrease in the detection current of the resistor 6 at the time of high input voltage can be compensated for. Although the accuracy is lower than that using a Zener diode, its characteristics can be corrected.

Effects of the Invention As described above, the present invention creates a correction current proportional to the input voltage for a wide range of AC input voltage to the switching transformer, and detects this correction current and the current flowing through the switching element together. By controlling the switching elements to turn on and off so that the sum of the double currents does not exceed a predetermined value, stable overcurrent control is performed to prevent current from exceeding the rated value flowing through the switching elements even when the input voltage is high. This makes it possible to protect the device from accidents such as destruction without overdriving the output transistor in response to transient conditions.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram of a switching regulator power supply circuit in an embodiment of the present invention, Fig. 2 is a voltage waveform diagram of the main part of Fig. 1, and Figs. 3 and 4 are voltage waveform diagrams of the main part of Fig. 1. FIG. 6 is a circuit diagram of a main part of another embodiment of the present invention, FIG. 6 is a circuit diagram of another embodiment of the present invention, and FIG. 7 is a conventional switching The circuit diagrams of the regulator power supply circuit, FIGS. 8 and 9, are waveform diagrams and characteristic diagrams illustrating the operation of the conventional example. 8.9,10,11.19.22...Diode, 4...Zener diode, 6,12.2
0... Capacitor, 1.2, 3.5...
・Resistance, 13...Switching transformer, 14
...Output field effect transistor, 16...
...Drive circuit, 16...Oscillation control circuit, 1
7...Overcurrent control circuit, 18...Secondary output voltage detection circuit, 21...Secondary circuit load. Name of agent: Patent attorney Toshio Nakao and one other IA
Figure I Figure 2 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9 Length Cutting voltage

Claims (1)

[Claims] a DC power supply circuit, a switching transformer having one end of a primary winding coupled to the output of the DC power supply circuit and a secondary winding coupled to a load; and a switching transformer having an output side coupled to the other end of the primary winding of the switching transformer. , a switching element that is periodically controlled on and off by a control signal input to a control terminal, and a correction current generating means that generates a correction current proportional to the DC power supply circuit output from the output of the switching transformer; a control means that detects the current flowing through the switching element in the on state and the correction current, and supplies the control signal to the switching element to control on/off so that the sum of these two currents does not exceed a predetermined value; A switching regulator power supply circuit comprising: