JPH0420206B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement of an error amplifier used in a positive/negative dual constant voltage power supply or the like.

Conventionally, in an error amplifier used in a positive/negative dual constant voltage power supply, when a reference voltage is provided from ground, the output voltage is divided between the ground and the ground.

When using the output controlled by the error amplifier as the power supply for one of the error amplifiers and the constant voltage diode When the power is turned on, the two inputs of the differential amplifier that constitute the error amplifier are generally at a constant voltage as a reference voltage source. Since diodes are used, both are at ground, and one power supply of the differential amplifier is also at ground, the output of the differential amplifier is no longer specified, and in some cases the output is fixed to ground and the normal voltage is There is a possibility that a situation may arise in which it is not possible to

In order to avoid such drawbacks, it is thought that measures have been taken to add a start circuit or the like, but this has resulted in drawbacks such as an increase in the number of components.

An object of the present invention is to provide an error amplifier that eliminates the above-mentioned drawbacks, is inexpensive, has good rise characteristics, and uses two types of positive and negative DC power supplies.

FIG. 1 shows an embodiment of a positive and negative dual constant voltage power supply using the error amplifier of the present invention as a positive polarity control circuit. In the figure, 1 is the input voltage terminal of the power supply, 2 is the positive output voltage terminal of the power supply, 3 is the negative output voltage terminal of the power supply, 4 is the positive polarity, and the control circuit for monitoring the output voltage (i.e., the error 12 is an input signal line of the amplifier); 5 is an output signal line of the control circuit 12 that controls the voltage conversion circuit 11; 10 is a positive power supply section that converts the voltage at terminal 1 and generates a stabilized positive output voltage; 20 is a negative power supply unit that converts the voltage at terminal 1 and generates a stabilized output voltage of negative polarity. The positive power supply section 10 is composed of a voltage conversion circuit 11 and a control circuit 12. In this way, the error amplifier of the present invention is used as a part of the control circuit of the positive power supply, and the power required for operation is supplied to the positive power supply section 10 on the one hand.
The other is supplied from the output of the negative power supply section 20.

The error amplifier of the present invention will be explained below with reference to FIG.

In Figure 2, a voltage dividing point a is obtained by dividing the voltage V ₁ of terminal 4 between the ground and the resistors 35 and 36.
and a voltage dividing point b obtained by dividing this voltage V ₁ and a DC power supply voltage V ₂ (voltage at terminal 7) of opposite polarity by elements 32 and 33 such as resistors, are connected by a diode 37,
It is constructed by connecting the voltage dividing point a to one input of a differential amplifier, and connecting the output c of a reference voltage source to the other input. 32 and 33 may be resistors, diodes, constant voltage diodes, or a combination thereof. In this figure, the connection direction of the diode 37 is when the voltage V ₁ is positive polarity, and when V ₁ is negative polarity, it is connected in the opposite direction.As a more specific circuit example,
FIG. 3 shows an example in which the element that divides the positive voltage V ₁ and the negative polarity DC power supply voltage V ₂ is composed of a constant voltage diode 42 and a resistor 43, and the reference voltage source 30 is composed of a constant voltage diode 52. show.

In FIG. 3, the forward voltage drop of the diode 37 is V _X1 , the Zener voltage of the constant voltage diode 52 is V _X2 , and the Zener voltage of the constant voltage diode 42 is
V _X3 , voltage at terminal 4 (output voltage of positive power supply section 11)
is V ₁ , the voltage at the voltage dividing point a is Va, the voltage at the connection point b between the constant voltage diode 42 and the resistor 43 is Vb, and the voltage at the connection point c between the constant voltage diode 52 and the resistor 51 is
Let it be Vc.

Here, if the voltage regulator diode ₄₂ is selected so that V _X1 < V _X3 < V ₁ −V _X2 + _V V _a becomes V _a =V _c =V _X2 .

Further, V _b is V _b =V ₁ −V _X3 .

At this time, the condition under which the diode 37 does not conduct is V _b >V _a −V _X1 .

Therefore, V ₁ −V _X3 ＞V _a −V _X1 ＝V _X2 −V _X1 V ₁ −V _X2 ＞V _X1 ＞ _V Voltage diode 42, diode 37 and resistor 43 are disconnected from the circuit, which is similar to a commonly used error amplifier.

Next, when the voltage _V1 is 0V, such as immediately after the power is turned on, Vb= _-VX3 . Also, the left side of the conditional expression in the third line above, V _X1 <
In the case of V _{X3 , the} diode 37 becomes conductive and Va=-V
When V ₁ is normal, the voltage V ₁ is reduced, and due to fluctuations in the load, input voltage (voltage at terminal 1), etc., the output 5 of the error amplifier controls the voltage conversion circuit 11 to increase the voltage V ₁ . It works to increase the voltage V ₁ and control it to the set value.

From the above, according to the present invention, it is possible to inexpensively and easily realize an error amplifier that can operate stably when the power is turned on.

[Brief explanation of drawings]

Figure 1 is a block diagram of a constant voltage power supply with two positive and negative outputs when the error amplifier of the present invention is used as a control circuit for a positive polarity power supply section, and Figure 2 is a general circuit configuration of the error amplifier of the present invention. As an example, FIG. 3 is a more specific circuit diagram example of FIG. 2. In the figure, 10 is a positive power supply section, 11 is a voltage conversion circuit, 12 is a control circuit, 20 is a negative power supply section, 1 is an input voltage terminal of the power supply, 2 and 6 are positive output voltage terminals of the power supply, and 3 is a power supply negative polarity output voltage terminal, 4
is the control circuit 1 for monitoring the positive output voltage.
2 is an input signal line, 5 is an output signal line of the control circuit 12 that controls the voltage conversion circuit 11, 30 is a reference voltage source, 31 is a differential amplifier, 32, 33 are elements such as resistors, 35, 36, 43, 51 is a resistor, 37 is a diode, and 42 and 43 are constant voltage diodes.

Claims (1)

[Claims] 1. An error amplifier using a first power source and a second power source with opposite polarities, including a differential amplifier having first and second input terminals and an output terminal, and an output connected to the first input terminal. a first voltage divider connected between the first power source and a certain potential and having a first voltage dividing point connected to the second input terminal; a second voltage divider connected between the second power source and having a second voltage division point; and a diode connected between the first and second voltage division points, When the output of the first power supply connected to the voltage divider does not appear when the first power supply is started, etc., the diode is made conductive, and when the output of the first power supply is a normal value, the diode is not made conductive. An error amplifier characterized in that the voltage division ratio of the second voltage divider and the direction of the diode are selected to be .