JPH0370470A - Power source device - Google Patents

Abstract

PURPOSE:To secure output voltage accuracy enough at a low cost by deciding the voltage across a capacitor by the terminal voltage of the constant voltage element of a first circuit and the resistance ratio of a second circuit. CONSTITUTION:The cathode potential of a Zener diode ZD3 becomes the noninversion input terminal potential of an operation amplifier A1, and when the operation amplifier A1 is operating in a linear region, from the relation of imaginary short circuit, the potential at point B becomes the potential almost the same as that at point A. Moreover, when power source input voltage changes, or output load current changes, the potential of the output terminal C of an integration circuit 3 changes. Hereby, the base current of a transistor Tr2 is controlled. Moreover, in the case that the output load current changes, as the switching-on time needs to be controlled, the base currents are changed.

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Field of Industrial Application This invention relates to an RCC power supply device, and particularly to a power supply device that provides stable output characteristics.

(B) Prior Art Conventionally, there is a basic circuit of a well-known RCC type power supply device as shown in FIG. This power supply has
When the input terminal ■ is applied, the switching transistor Tr is applied through the resistor RG.

A base current flows through the transistor Tr+, the transistor Tr+ is turned on, a current flows through the primary winding wANp, a voltage is induced in the control winding, the transistor Tr+ continues to be turned on, and a constant current flows through the base.

However, the collector current of the transistor Tr increases linearly, and when it becomes unable to continue in the on state, it rapidly decreases, the base current also decreases, and the transistor Tr rapidly turns off. When the transistor Tr is turned off, a back electromotive force is generated in each winding of the transformer, and a diode D is also generated in the secondary winding N.

A load current flows through it and an output is derived. This load current becomes O for a certain period of time, the transistor Try is turned on again as described above, and the switching operation is repeated. In addition, in this power supply device, the Zener diode Z
D, is used to perform constant voltage operation.

This basic power supply, when increasing the output power,
A large drive current must flow, and the current branched to the Zener diode ZD increases accordingly, which causes the Zener potential of the Zener diode ZD to fluctuate, making it difficult to obtain a stable output voltage as the output current increases. Therefore, in practice, the power supply device shown in FIG. 3 was used. This power supply device additionally includes a transistor Tr.
.

Zener diode ZD between the base and the 5th vine.

Most of the increase in drive current due to the increase in output power is connected to the collector current of transistor Tr.

It was designed to flow as follows. This power supply has
Assuming that the current flowing through the Zener diode ZD is 12,
I'z = I c / h FE, and the current ■2 is the collector current ■. The output current-voltage characteristics are those shown in FIGS. 5(A) and 5(B), which are improved compared to the basic circuit.

(c) Problems to be Solved by the Invention The power supply device shown in FIG. 3 described above is practical as a power supply device for simple electronic equipment used in Japan. However, even with this power supply device, when the output power changes greatly, the Zener voltage of the Zener diode ZD and the transistor Tr
, the base-emitter voltage of the transistor Tr, and the voltage across the resistor R2 change,
There was a problem in that the voltage of the capacitor C2 fluctuated, making it impossible to obtain a highly accurate output voltage.

Therefore, in order to improve the output voltage accuracy, there is a method that uses a photocoupler and a shunt regulator to feed back the secondary side output to the primary side, but this technology has the problem of high cost because it uses a photocoupler. there were.

This invention was made in view of the above-mentioned problems, and aims to provide a power supply device that does not require as much cost as when using a photocoupler, and yet can ensure sufficient output voltage accuracy. There is.

(d) Means and operation for solving the problem The power supply device of the present invention switches a DC voltage (V) with a switching transistor (Try), and a power transformer (T).
The primary winding (NP), control winding (N, ) and secondary winding (N
), the rectifier circuit (D!, Cs) rectifies the voltage to derive the output voltage, and the primary winding (NP
) is fed back to the switching transistor ('r r l) via the control winding (N, ) to perform self-excitation, and the control winding of the power transformer (T) (Nll), a rectifier circuit consisting of a diode (D,) and a capacitor (C2) connected in parallel to the capacitor (C2), and a first circuit (1 ), a second circuit (2) connected in parallel to both ends of the capacitor (C2), and in which first and second resistors (R, , Re) are connected in series, and an operational amplifier (A1), This operational amplifier (A,)
The constant voltage element (
ZD3) includes an integrating circuit (3) whose other input terminal is connected to the connection point of the resistor of the second circuit (2), and responds to the output of this integrating circuit (3) and connects the switching transistor ( Try) Base control circuit that controls the base current (
4).

In this power supply device, the voltage across the capacitor is determined by the terminal voltage of the constant voltage element of the first circuit and the resistance ratio of the second circuit, and the voltage across the capacitor is determined by the switching transistor and the base current of this switching transistor. It has nothing to do with fluctuations in the voltage between the control base and the capacitor, and even if the voltage between the base and the capacitor of these transistors fluctuates due to fluctuations in input voltage or output current, the voltage across the capacitor will not change. has no effect, and a constant output voltage is always derived on the output side of the secondary winding.

(E) Examples The present invention will be explained in more detail with reference to Examples below.

FIG. 1 is a circuit diagram of a power supply device employing an RCC method showing an embodiment of the present invention. In the same figure, one end of the primary winding NF of the transformer T is connected to the switching transistor Tr.
, and the other end is connected to the collector of the transistor Tr through the resistor R.

connected to the base of. At both ends of the control winding N,
A rectifier circuit consisting of a diode D and a capacitor C2 is connected in parallel, and one end of the control winding N3 is connected to a resistor R1.
connected to the base of the transistor Tr via the capacitor C2, and the emitter of the transistor Tr;
It is connected to the collector of the transistor Tr3, and further connected to the base of the transistor Tr via the resistor R1. Further, a rectifier circuit consisting of a diode D and a capacitor C3 is connected to the secondary winding N, and an output voltage vo is output from the rectifier circuit. Note that the circuit consisting of the transistor Tr 3 , the resistor R2, the resistor R3, and the diode D4 is a rush current protection circuit for the transistor Tr. The circuits and connections described above are not particularly different from the conventional circuit shown in FIG.

This embodiment of the power supply device differs from the one in FIG. 3 in that a series circuit t' (first circuit) consisting of a resistor R5 and a Zener diode ZD is connected in parallel to the capacitor C2, and furthermore, across the capacitor C2, Series circuit 2 of resistors R7 and R6 (
second circuit) is connected. A connection point A between the resistor R4 and the Zener diode ZD3 is connected to the non-inverting input terminal of the operational amplifier A1, and a connection point B between the resistors R7 and R8 is connected to the inverting input terminal of the operational amplifier A1. Operational amplifier A
, constitutes an integrating circuit 3 with a capacitor C5.

Furthermore, a Zener diode ZDa is connected between the output terminal C of the integrating circuit 3 and the base of the transistor Trz. Further, a capacitor C4 is connected between the collector and base of the transistor Tr.

The transistor T r z , the resistor R11, the Zener diode ZD, and the capacitor C4
A base current control circuit 4 is configured to control the base current of .

Next, the reason why the output voltage accuracy is improved in the example circuit configured as described above and the operation thereof will be explained.

In the example circuit, the control winding N on the primary side of the transformer T
! The number of turns of + is na, the number of turns of secondary winding N is n, the voltage drop of diode DI is ■□, the voltage drop of diode D3 connected to secondary winding N3 is VF3, capacitor C
If the voltage across 2 is vc, the output voltage vo can be expressed as 8. According to this formula, if the voltage VC is kept constant, the output voltage Vo can be kept constant.

In the embodiment device, the setting of the voltage V is determined by the integrating circuit 3 comprising an operational amplifier A1 with the cathode of the Zener diode ZD as a reference potential. In other words, the cathode potential of the Zener diode ZD becomes the non-inverting input terminal potential of the operational amplifier A, and when the operational amplifier A1 is operating in the linear region, that is, the output of the operational amplifier A1 is operating without saturation, the imaginary Due to the short-circuit relationship, the potential at point B is approximately the same as the potential at point A. Therefore it becomes. As is clear from this equation, the voltage VC is determined only by the voltage drop Vll of the Zener diode ZD and the resistance ratio, so it is not affected by changes in the power input terminal or output load current. The voltage is maintained at a constant level without any interference, and highly accurate output can be obtained. Also, the voltage vc
Since is constant, the current flowing through the Zener diode ZD becomes constant, and the voltage VO2 is also stabilized.

Furthermore, when the power supply input voltage changes or the output load current changes, the potential at the output terminal C of the integrating circuit 3 changes.

This changes the collector current of the transistor Tr, and controls the base current of the transistor Tr. To give a concrete example, when each circuit constant has a certain value, for example, when the power supply input terminal is 85V, the potential of the output terminal C of the integrating circuit 3 is -2,4
If the power supply input voltage becomes as large as 264V, the potential of the output terminal C of the integrating circuit 3 will be -3V, for example.
, 6V. This is because as the input voltage rises, the voltage of the control winding N3 rises, and the current that can flow through the base of the transistor Tr increases, so the transistor Tr keeps the base current constant, allowing more current to escape. , the potential of the output terminal C decreases, and as a result, the transistor Tr,
A large current flows through the base ti of the transistor Tr.
This is because it is controlled to be constant.

Furthermore, when the output load current changes, it is necessary to control the switching-on time, so it is necessary to change the base current. For example, if each circuit constant has a certain value, the load power is 1.8 W, and the power input terminal is 100V, the potential of the output terminal C is -2.5V, then the load power has decreased to 0.2W. In this case, the voltage of the control winding N becomes large, and the potential of the output terminal C of the integrating circuit 3 becomes -2.8■, causing more current to flow through the transistor Trz. As a result, the base current of the transistor Tr becomes This means that it has decreased.

In this example circuit, if we take the power supply input terminal as a parameter and take the output current-output voltage characteristics, we get the characteristics shown in Figures 4 (A) and 4 (B), and the output voltage is stable up to a large output current. can be obtained.

(F) Effects of the Invention According to this invention, a first circuit including a constant voltage element and a second circuit including a first and second resistor are connected in parallel to a capacitor connected to a control winding. , each connection point of the first and second circuits is connected to the inverting input terminal and the non-inverting input terminal of the operational amplifier constituting the integrating circuit, respectively, and the voltage across the capacitor is equal to the terminal voltage of the first constant voltage element. Since it is determined by the resistance ratio of the second circuit, it is not affected by changes in the power supply input voltage or output load current, and therefore a highly accurate output voltage can be obtained.

Furthermore, since only an integrating circuit, a resistor, and a Zener diode are added, the structure is simple and inexpensive, and stability comparable to that obtained when using a photocoupler or shunt regulator can be obtained.

[Brief explanation of drawings]

FIG. 1 is a circuit connection diagram of a power supply device showing an embodiment of the present invention, FIG. 2 is a circuit connection diagram showing the basic circuit of a conventional power supply device, and FIG. 3 is a circuit diagram showing a conventional power supply device. Connection diagram,
FIG. 4(A) is a diagram showing the output current-output voltage characteristics of the power supply device according to the above embodiment, FIG. ) is a diagram showing the output current-output voltage characteristics of the power supply device shown in FIG.
FIG. 5(B) is an enlarged diagram of the same characteristic diagram for an output current of 0 to 150 mA. Tr, switching transistor, Trz: base current control transistor, N,: primary winding, N,:
Secondary winding, N: Control winding, D, -D3: Diode, ZD,
・ZD: Zener diode, Al: operational amplifier, 1: first circuit, 2: second circuit, 3: integrating circuit, 4: base current control circuit.

Claims (1)

[Claims] (1) Switch the DC voltage with a switching transistor, convert the voltage with the primary winding, control winding and secondary winding of the power transformer, rectify it with the rectifier circuit to derive the output voltage, and In a self-excited switching power supply device that performs self-excitation by feeding back the voltage of a winding to the switching transistor via a control winding, a rectifier consisting of a diode and a capacitor connected in parallel to the control winding of the power transformer. a first circuit connected in parallel to both ends of the capacitor and including a constant voltage element;
a second circuit connected in parallel to both ends of the capacitor and having first and second resistors connected in series; and an operational amplifier;
The constant voltage element of the first circuit is connected to one input terminal of the operational amplifier, and an integrating circuit is connected to the other input terminal of the operational amplifier to which the connection point of the resistor of the second circuit is connected, and the operational amplifier responds to the output of the integrating circuit. A power supply device comprising: a base control circuit for controlling a base current of the switching transistor.