JPS62181670A - Switching power circuit - Google Patents

Abstract

PURPOSE:To shorten the time up to stationary operation from the start of the application of input DC voltage by starting a converter circuit after a capacitor is charged completely. CONSTITUTION:When a capacitor C1 is charged completely, only charging currents of a capacitor C2 are used approximately as input currents, and input DC voltage Vin reaches V0. The charging of the capacitor C2 is ended at a time t2 in the graph, and start is conducted when the voltage of the capacitor C2 reaches the breakdown voltage or more of a Zener diode ZD1. Consequently, output voltage Vout which has taken zero rises and reaches a specified value, and stationary input currents flow in response to the rise of the output voltage Vout and stationary operation is started. Accordingly, a converter circuit is started after the capacitor C1 is charged completely, thus shortening the time up to stationary operation from the start of the application of input DC voltage.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Field of Application of the Invention) The present invention relates to a switching power supply circuit, and particularly to a starting circuit thereof.

(Prior art and its problems) When power is supplied to an electronic circuit device using a DC power source with a voltage different from its operating DC voltage, a DC-DC converter with a constant voltage function having a basic circuit as shown in Figure 1 is used. Voltage conversion is performed using This circuit is called a linking choke converter, so-called RCCu circuit, and operates as follows. That is, when the DC input voltage Vin applied to the starting Zener diode ZDI via the starting resistor R1 rises above the breakdown voltage of the diode ZDI, a required base current flows through the main switching transistor Ql to turn it ON. and oscillation transformer T1
When a voltage is output to the winding NH, a collector current equal to or greater than the product (IIlxht,) of the base current Im determined by this output voltage and the base resistance R2 and the DC amplification factor hfa of the transistor Ql is caused to turn off the transistor Q1. As a result, the kick pulse sent out when the magnetic flux of the transformer T1 becomes zero turns the transistor Ql back to O.
Repeat this operation to generate oscillation. Then, the output voltage obtained by the winding NP by the winding NS is rectified and smoothed by the diode D3 and the capacitor C4 to obtain the DC output voltage Vout, thereby converting the voltage and supplying power to the load. It is.

Further, in this circuit, the voltage obtained at the winding NC of the transformer T1 is rectified and smoothed by the diode D2 and the capacitor C3, and a DC voltage proportional to the output voltage of the winding NS is detected.

This is then formed to be applied to Zener diode ZD2, and when the detected DC voltage exceeds the breakdown voltage of Zener diode ZD2, the detected DC voltage and the set voltage by Zener diode ZD2 are applied to the circuit of voltage dividing resistors R3 and R4. Transistor Q
By controlling the base current of the main switching transistor Q1, the base current of the main switching transistor Q1 is controlled so that the output DC voltage Vout does not rise above a predetermined value.

However, in order to stabilize the input DC voltage and prevent the oscillation operation from becoming unstable due to external noise, this circuit requires an input capacitor C1 with a relatively large capacity connected between the input DC voltage application terminals. . For this reason, when the human power DC voltage Vin is given by a power supply circuit (not shown) with constant current characteristics, for example, when the power supply current becomes 10 or more, the power supply circuit protects the circuit by limiting this to If such a converter circuit is used, the operation of the converter circuit is affected by the charging current of the input capacitor CI, and there is a drawback that good starting operation cannot be expected. That is, in this circuit, when the input DC voltage Vin, which increases with a time constant from the start of input voltage application, exceeds the breakdown voltage of the Zener diode ZDI, the main switching transistor Q1 is turned on to supply power to the load. At this time, a current equal to the sum of the load current Io and the charging current of the capacitor CI, which is about the same level or larger than the load current Io, flows through the power supply circuit. Therefore, the power supply circuit immediately lowers the power supply voltage using its constant current circuit to adjust the power supply current to the constant current setting value of 10.
However, this output voltage drop state is limited to capacitor C
This continues until the charging of I is completed and the supply current value decreases to IO. Therefore, during this time, the charging current of the capacitor CI decreases significantly, so a long time is required to complete charging, which lengthens the startup time from the start of application of the input DC voltage until the output voltage rises to the specified value. Furthermore, the output voltage of the secondary winding NS decreases due to the decrease in the supply voltage that continues during this period, and the decrease in the current flowing through the primary winding NP of the transformer T1 due to the decrease in the base current of the transistor Ql. Therefore, there is a problem that the output DC voltage Vout is lowered and the startup operation becomes unstable.

By the way, in order to eliminate the above-mentioned drawbacks, it is only necessary to start the converter after the input capacitor C1 is fully charged. For example, a voltage proportional to the change in current value between when the capacitor C1 is charged and when it is fully charged is used. A conceivable method is to detect the fully charged state by detecting this and operating a Zener diode, and then turning on the main switching transistor Q1 via this. However, Zener diodes are susceptible to changes in breakdown voltage due to changes in the temperature of the environment in which they are used, making it difficult to accurately detect full charge, resulting in high costs if improved accuracy is attempted.

The present invention makes it possible to eliminate the above-mentioned drawbacks by simply adding 4" L inexpensive elements to the conventional circuit, and will now be described in detail with reference to the drawings.

[Structure of the Invention] (Means for Solving the Problems) FIG. 2 is a circuit diagram of an embodiment of the present invention (the same reference numerals as in FIG. 1 indicate equivalent parts), which shows the features of the present invention. The point to be made is as follows. That is, in the present invention, the starting resistor R1 and the starting Zener diode ZDI shown in FIG.
A time constant capacitor C2 whose charging time constant is determined by the resistor R1 is connected between the connection point of the input DC voltage Vin and the negative polarity application terminal 0 of the input DC voltage Vin, and the operation of the converter circuit is controlled in parallel with the resistor R1. Capacitor C when stopped
A diode DI is connected to discharge the charge of 2.

Therefore, the time τ2 from the start of charging of capacitor C2 to the end of charging due to the application of human DC voltage is equal to the time τ1 until the end of charging of capacitor CI, which starts charging at the same time as capacitor C2 (τ1 = τ2), or the circuit Taking into account variations in the characteristics of component parts such as starting Zener diode ZD1, main switching transistor Ql, starting resistor R1, and capacitors C1 and C2, the time required to complete charging of capacitor CI is determined from the time τ1 required to complete charging of capacitor CI. Set the time constant of the charging circuit for capacitor C2 so that τ2 is long, that is, (τ1<τ2),
This embodiment is characterized in that the converter circuit is activated by the Zener diode ZDI after the capacitor C1 is fully charged.

Next, the operation of this circuit will be explained with reference to the waveform diagram for explaining the operation of 01 shown in FIG. 3 when the time required to complete charging of capacitors C2 and C1 is τ1<τ2.

(Function and Effect) When input DC voltage is applied at time t0 in FIG. 3, capacitor C1 is charged and capacitor C2 is charged via resistor R1, but the sum of these currents is as described above. Since the current exceeds Io, which is the constant current setting value of the power supply circuit having a constant current characteristic, the power supply current and therefore the input current of the circuit become constant at 10 as shown in FIG. 3(b). Therefore, it becomes a constant current charging state, and the input DC voltage Vin increases as shown in Fig. 3 (al.
It rises linearly as shown in . And time L in Figure 3
1, when charging of capacitor C1 is completed, the input current becomes almost only charging current Ic2 of capacitor C2,
The input DC voltage Vin becomes vo. And Figure 3(a)
At time t2, when charging of the capacitor C2 is completed and its voltage becomes equal to or higher than the breakdown voltage of the Zener diode ZDI, startup is performed. Therefore, as shown in Figure 3 (C), the output DC voltage VouL, which had been zero, rises and becomes constant at the specified value Vcc, and in response, the steady input current I, as shown in Figure 3 (bl), increases. flows and enters steady operating state.

That is, in the present invention, since the converter circuit is started after the capacitor C1 is fully charged,
This is to ensure that the time from the start of input DC voltage application to steady operation becomes longer than in the conventional circuit described above, the startup becomes impossible, or even the load operation becomes unstable due to a drop in the output voltage. can be prevented. In addition, according to the present invention, a small capacitance time constant capacitor C2 is added to the conventional circuit.
Since the purpose can be achieved by simply adding a discharge diode DI and a discharge diode DI, the cost is not increased unlike the above-mentioned means of detecting full charge of the capacitor CI using a constant voltage element with good temperature stability.

Although the present invention has been described above using one embodiment, the present invention operates in the same way even when applied to a circuit that does not have a constant voltage circuit such as a Zener diode ZD2. Further, although the above description has been made regarding a DC-DC converter, the present invention can be similarly applied to this type of switching power supply circuit such as an RCC inverter circuit that obtains an arbitrary AC output voltage from a DC power supply and supplies current to a load. You can explore the effects on startup.

[Brief explanation of drawings]

FIG. 1 is a conventional circuit diagram, FIG. 2 is a circuit diagram of an embodiment of the present invention, and FIG. 3 is a waveform diagram for explaining its operation. TI...transformer, NP, NS, NB, NC...transformer winding, Ql...main switching transistor,
C2...control transistor, R1...starting resistor, R2...base resistor, R3#4...voltage dividing resistor,
Dl...discharge diode, D2. D3... Rectifier diode, ZDI... Zener diode for starting, Z1]2... Zener diode for constant voltage detection. Patent applicant: 1 person other than Shindengen Kogyo Co., Ltd.

Claims (1)

[Claims] The input DC voltage is applied through the starting resistor, and the starting Zener diode causes base current to flow through the main switching transistor connected in series with the primary winding of the transformer to start the transformer, and also to control the output voltage of the feedback winding and the kick at the time of transformer reset. In a switching power supply circuit equipped with an input capacitor between application terminals of input DC voltage, the main switching transistor is turned ON and OFF by pulses to obtain an output voltage on the secondary winding side of the transformer. Connect a time constant capacitor through a discharge diode between the positive and negative application terminals, and connect the series connection point of this discharge diode and time constant capacitor to the series connection point of the starting resistor and starting Zener diode. , the time constant capacitor is configured to be charged through the starting resistor, and the time from the start of input DC voltage application to the end of charging of the time constant capacitor is equal to or longer than the time until the end of charging of the input capacitor. A switching power supply circuit characterized in that a charging time constant of a time constant capacitor is selected in accordance with the present invention.