JPH04365109A - Error amplifying circuit - Google Patents

Abstract

PURPOSE:To satisfactorily use the dynamic range of a DAC and to protect a load circuit just after application of an input supply voltage by providing a voltage controlled current source to digitally control the output voltage of a DC-DC converter. CONSTITUTION:A voltage controlled current source 17 is connected to the intersection between output voltage setting resistances 6 and 7 of a DC-DC converter 5, and the voltage output of the DAC is connected to the control voltage input of the voltage controlled current source 17, thereby digitally controlling the DC-DC converter output voltage. As the result, the control input and the output have linear relations, and further, destruction of the load of a constant voltage generating circuit is prevented because the constant voltage generating circuit generates a minimum voltage in the control voltage range as the output voltage at the time of application of the input voltage. Further, an error amplifying circuit consisting of a smaller number of parts is obtained.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention relates to a constant voltage generation circuit (DC-
This invention relates to an error amplification circuit of a constant voltage generation circuit for digitally controlling voltage in a DC converter.

0002

[Prior Art] In recent years, attempts have been made to introduce DC-DC converters with low power loss as a technology for controlling DC voltage, and volume has been used to set the voltage, but recently, in order to automate factory adjustments, Digital control methods have been introduced in

[0003] Control of a conventional constant voltage generating circuit will be explained below. FIG. 2 shows a block diagram of a conventional constant voltage generation circuit. In FIG. 2, 1 is a current source (or resistor), 2 is a reference voltage, 3 is an operational amplifier, 4 is an output circuit, and 5 is a DC-DC circuit consisting of 1, 2, 3, and 4.
Converter, 6, 7, 8, 10, 12, are resistors, 9, 1
0 is a transistor, 13 is a volume, and 14 is a DC power generator. First, when a DC voltage is not applied to the base of the transistor 11 by the volume 13, the transistor 11 does not operate, so the collector current of the transistor 1 does not flow. Therefore, resistance 1
Since no voltage is generated across the resistor 9, the resistor 9 does not operate (cutoff state), which is equivalent to a state in which the resistor 6, the resistor 8, and the resistor 9 are not connected in parallel. Here, the output voltage of the output terminal 16 of the DC-DC converter 5 is determined by the ratio of the resistance values of the resistors 6 and 7.
Next, when a voltage is applied to the base of the transistor 11 from the volume 13, the transistor 11 starts operating, a collector current starts flowing, and a voltage is generated across the resistor 10.

Therefore, in order for the transistor 9 to start operating, it becomes equivalent to connecting the resistor 8 and the resistor 9 in parallel with the resistor 6, and the resistance ratio of the resistors 6 and 7 decreases, and the output voltage at the output terminal 16 decreases. . Here again,
When the base voltage of the transistor 11 is increased, the collector current of the transistor 11 increases, the voltage across the resistor 10 increases, the resistance value between the emitter and the collector of the transistor 9 decreases, and the output voltage at the output terminal 16 decreases. As described above, voltage control of the DC-DC converter is performed.

[0005]

[Problems to be Solved by the Invention] However, in the conventional configuration described above, since the Vbe-Ic characteristic is used when the transistor 11 starts operating, the relationship between the control input voltage and the output voltage is not linear. When the input voltage is applied, the transistor 11 starts operating in an off state, so that the output voltage of the constant voltage generating circuit generates the highest voltage in the control voltage range, which causes the problem of destroying the load of the constant voltage generating circuit.

The present invention solves the above conventional problems by making the relationship between the control input voltage and the output voltage linear,
Furthermore, when an input voltage is applied, the output voltage of the constant voltage generation circuit generates the lowest voltage in the control voltage range, and the purpose is to provide an error amplification circuit that does not destroy the load of the constant voltage generation circuit and has a small number of components. do.

[0007]

[Means for Solving the Problems] In order to achieve this object, the error amplification circuit of the present invention has a power supply voltage connected to one of the first current sources, and the other of the first current sources is a reference voltage generation source. The other end of the reference voltage generator is connected to ground. The reference voltage output of the reference voltage source is connected to the normal terminal of the operational amplifier (when the power supply voltage is positive), and the output of the operational amplifier is connected to the output circuit, and the output of the output circuit is connected to the operational amplifier through the first resistor. A second resistor is connected between the inverting terminal of the operational amplifier and ground, and a voltage-controlled current source is connected between the inverting terminal of the operational amplifier and ground. It has a configuration in which a DAC (digital to analog converter) is connected to the voltage input.

[0008]

[Operation] With this configuration, when the voltage-controlled current source is not operating, the output of the output circuit is determined by the first resistor and the second resistor, and is the lowest voltage value in the control range. Here, if a voltage-controlled current source with a linear relationship between the control input voltage and output current is used, the current flowing into the voltage-controlled current source is a part of the current flowing through the first resistor, so the output of the output circuit Starting from the lowest voltage value in the control range, the voltage can be varied according to the product of (current flowing into the voltage-controlled current source) and (first resistance value).

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. In Figure 1, 1 is a current source (or resistor), 2 is a reference voltage source, 3 is an operational amplifier,
4 is an output circuit 5 is a DC composed of 1, 2, 3, and 4
-DC converter, 6 and 7 are resistors, 17 is a voltage controlled current source, and 18 is a DAC.

The operation of the error amplifier configured as described above will be explained with reference to FIG. First, DAC1
8 and the voltage-controlled current source 17 are not operating (immediately after the input power supply voltage is applied, the DAC 18 is normally in the reset state, so the voltage is zero, and the voltage-controlled current source 17 also does not output current. (not pulled), the voltage of the output circuit 4 is determined by the resistors 6 and 7. At this time, the voltage of the output circuit 4 is the voltage generated in the resistor 6 when the current flows through the resistor 6 due to (reference voltage of the reference voltage source 2)/(resistance value of the resistor 7), and the reference voltage of the reference voltage source 2. It becomes the added voltage of .

Here, when data is given to the DAC 18 to generate a voltage, the voltage controlled current source 17
begins to draw current. This voltage controlled current source 1
Since the current drawn by 7 is supplied through resistor 6, the voltage developed across resistor 6 increases. Therefore, the voltage of the output circuit 4 increases because it is given by the addition of the voltage generated across the resistor 6 and the reference voltage of the reference voltage generation source 2.

Next, the voltage-controlled current source 17 will be explained using FIG. 3. In FIG. 3, 19 is a transistor, 20 is a resistor, and 21 is an operational amplifier, and the voltage value applied to the non-inverting input terminal of the operational amplifier 21 and the voltage value applied to the inverting input terminal of the operational amplifier 21 are equal. Since the operational amplifier 21 operates in this manner, the emitter voltage of the transistor 19 becomes equal to the voltage value applied to the non-inverting input terminal of the operational amplifier 21. Therefore, the emitter current of the transistor 19 is (voltage value applied to the non-inverting input terminal of the operational amplifier 21)/(resistance value of the resistor 20). If the forward current amplification degree of the transistor 19 is assumed to be infinite, the emitter current and the collector current of the transistor 19 will be equal. Therefore, the voltage value applied to the normal input terminal of the operational amplifier 21 and the collector current of the transistor 19 have a linear relationship.

As described above, since the voltage generated across the resistor 6 has a linear relationship with the output voltage of the DAC 18, the output voltage of the output circuit 4 has a linear relationship with the output voltage of the DAC 18.

[0014]

As described above, the present invention makes it possible to control the output voltage of a DC-DC converter by digital control by providing a voltage-controlled current source and a DAC, and the dynamic range of the DAC can be fully extended. Furthermore, in order to start from the minimum voltage in the control voltage range of the DC-DC converter immediately after applying the input power supply voltage, D
It can also have a protection function for the load circuit connected to the output of the C-DC converter, and furthermore, since the number of parts is small, it is possible to realize an excellent error amplification circuit that can reduce costs.

[Brief explanation of drawings]

FIG. 1 is a configuration diagram of an error amplification circuit in an embodiment of the present invention.

[Figure 2] Configuration diagram of a conventional error amplification circuit

FIG. 3 is a configuration diagram of a voltage-controlled current source in an embodiment of the present invention.

[Explanation of symbols]

1 Current source 2 Reference voltage source 3 Operational amplifier 4 Output circuit 5 DC-DC converter 6 Resistance 7 Resistance 15 Input power supply voltage 16 Output voltage 17 Voltage controlled current source 18 DAC 19 Transistor 20 Resistance 21 Operational amplifier

Claims (1)

[Claims] Claim: 1. A power supply voltage is connected to one of a first current source or a first resistor, the other of the first current source or the first resistor is connected to a reference voltage generation source, and the first current source or the first resistance is connected to a reference voltage generation source. The other end is grounded, the reference voltage output terminal from which the reference voltage has been generated is connected to the normal rotation terminal of the operational amplifier, the output terminal of the operational amplifier is connected to the output circuit, and the output of the output circuit is passed through the second resistor to the operational amplifier. A third resistor is connected between the inverting terminal of the operational amplifier and ground, and a voltage-controlled current source is connected between the inverting terminal of the operational amplifier and ground. The error amplifier circuit has a digital-to-analog converter connected to its voltage input.