JP3132600B2 - Output voltage detection circuit of switching power supply - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a circuit for detecting the output voltage of a switching power supply with potential isolation using a photocoupler, and more particularly to an output voltage of a switching power supply having improved linearity between the output voltage and the detected voltage. It relates to a detection circuit.
In the drawings, the same reference numerals indicate the same or corresponding parts.

[0002]

2. Description of the Related Art FIG. 4 is a principle diagram of a general switching power supply (also simply called a switching power supply) for detecting an error between an output voltage detection value and a set value and performing feedback control by an insulation type output voltage detection circuit. It is. FIG. 1 includes a power supply unit 1, an output voltage detection unit 2, and an output voltage adjustment unit 3. The power supply unit 1 includes a switching transistor Tr
1, a choke coil L1 and a smoothing capacitor C1. Here, the switching transistor Tr1 repeatedly turns on the input voltage Vin to obtain a constant output voltage Vo,
Turning off, the choke coil L1 and the smoothing capacitor C1 smooth the intermittent voltage of the switching transistor Tr1.

The output voltage detector 2 includes resistors R4 to R4.
R6, Photocoupler PC1, Shunt regulator IC
Consists of one. Here, the shunt regulator IC1 is a semiconductor device that varies its inflow current IK so as to keep the input voltage Vr (referred to as a reference voltage, which is 2.5 V in this example) Vr to the reference terminal 5 equal to the internal reference voltage Vs. , The reference terminal voltage Vr is equal to the reference voltage Vs.
, The inflow current I
K increases and decreases rapidly, respectively.

In FIG. 4, the reference terminal voltage Vr is given by Vr = {R6 / (R5 + R6)} Vo with respect to the output voltage Vo by the voltage dividing resistors R5 and R6, so that the shunt regulator IC1 sets the output voltage Vo to a constant voltage. The current IK is varied so as to keep it.

The variable resistor R4 limits the current IK flowing through the photodiode of the photocoupler PC1, and the photocoupler PC1 responds to the current IK to provide the voltage adjustment unit 3 with the output voltage detection value V1 as the output of the phototransistor.
Is output and transmitted. Next, the output voltage adjusting unit 3 includes the resistors R1 to
R3, an error amplifier A1, and a PWM control circuit 4. Here, the resistors R1 and R2 apply a set voltage VS2 obtained by dividing the reference voltage VS1 to the positive input terminal of the error amplifier A1, and the error amplifier A1 outputs the set voltage VS2 and the output voltage applied to the negative input terminal. It compares the detected value V1 and outputs an error voltage between them.

The PWM control circuit 4 performs PWM control on the error output of the amplifier A1 so that the on-duty Don of the switching transistor Tr1 becomes zero so that the error voltage becomes zero.
Is determined. In this circuit, the output voltage Vo is Vo =
It is controlled by Don × Vin. Thus, in the circuit of FIG. 4, the input voltage Vin is controlled so that the output voltage Vo becomes constant.
, The on-duty Don is variably controlled.

[0007]

In the circuit shown in FIG. 4, when a resistor R4 for limiting the current IK of the photocoupler PC1 is used as a parameter, the output voltage Vo and the output of the photocoupler PC1 as a detection value of the output voltage Vo are used. The relationship with the voltage V1 is as shown in the characteristic diagram of FIG. That is, the circuit of FIG. 4 has the following problem.

The detected voltage V1 does not have a proportional characteristic with respect to a change in the output voltage Vo, the usable range is limited, and it is necessary to determine each constant of the circuit by experiments.
Gain of the detection circuit (△ V1 / △ V o) is, because determined by the shunt regulator IC1, the constant voltage control range is narrowed. The invention according to claim 1 solves this problem.
It is another object of the present invention to provide an output voltage detection circuit of a switching power supply capable of detecting voltage with higher accuracy .

[0009] In addition, this type of power supply, which requires high reliability, easily adjusts the output voltage to the upper or lower limit within an allowable range without any modification to the inside of the circuit after assembly and adjustment. It is desired to perform an operation test in such a manner as to stabilize the characteristics of circuit components and to eliminate an initial failure. Therefore, an object of the invention according to claim 2 is to provide an output voltage detection circuit of a switching power supply that can meet such a demand.

[0010]

According to a first aspect of the present invention, there is provided an output voltage detecting circuit for switching an input DC power supply (such as Vin) to a switching means (transistor Tr).
1) that repeatedly and intermittently obtain an output current voltage (such as Vo) at a predetermined level,
A photocoupler (such as PC1) that allows a current (such as IK) depending on the output DC voltage to flow through its own photodiode
Means for comparing the output voltage (such as V1) of the phototransistor of this photocoupler with a set voltage (such as VS2), and variably controlling the continuity ratio of the switching means (error amplifier A1, And a PWM control circuit 4).
Output voltage detecting means for making a current flowing through the photodiode proportional to a difference voltage between the output DC voltage and a predetermined reference voltage (such as Vo1) ;
1 (such as R4), the photodiode,
Regulator (IC1 etc.) to the polarity that can be operated sequentially
After connecting in series, the output
Current and apply the
A second and a third resistor in parallel with the series circuit of the regulator;
(R5, R6, etc.) in series, and the second resistor
The connection point between the resistor and the third resistor is connected to the shunt regulator.
Connected to the reference terminal of the second and third resistors.
The reference voltage must be generated at both ends of the resistor.
The first and second cores are connected in parallel to the second and third resistors, respectively.
Capacitor (C2, C3, etc.).

[0011]

Further, the output voltage detecting circuit according to claim 2 is
Item 1. The output voltage detection circuit according to Item 1,
4 (such as R5-1) and the second resistor
1st switch (SW1 etc.) for turning on in parallel
To the second resistor (connector CN1 etc.)
) In parallel and detachably provided in the same manner, and a fifth resistor (R
6-1), and the resistance is input in parallel with the third resistance.
Circuit with second switch (SW2 etc.)
In parallel with the third resistor (via the connector CN1 or the like).
To be detachably mounted on

[0013]

(1) Regarding the invention according to claim 1 , the current I flowing through the photodiode of the photocoupler PC1
K is set to be proportional to the difference voltage (Vo-Vo1) between the output voltage Vo and the constant voltage (output summer detection reference voltage) Vo1 generated by the shunt regulator IC1. That is, a current limiting resistor R4 that receives the difference voltage at both ends is provided, and a circuit is configured such that the current IK1 of the resistor R4 becomes equal to the photodiode current IK. As a result, the output voltage V
Good linearity can also be obtained between o and the output voltage (detected value of the output voltage Vo) V1 of the phototransistor of the photocoupler PC1.

(2) Regarding the invention according to claim 2 , the current limiting resistor R4, the photodiode, and the shunt regulator IC1 are sequentially connected in series, and an output voltage Vo is applied to both ends of the series circuit. A series circuit of resistors R5 and R6 is connected in parallel with the series circuit of the shunt regulator IC1, and by connecting the connection point of the resistors R5 and R6 to the reference terminal of the shunt regulator IC1, both ends of the series circuit of the resistors R5 and R6 are connected. , A reference voltage Vo1 is generated.

At the time of the power supply device test, a series circuit of a switch SW1 and a resistor R5-1 is detachably connected in parallel to the resistor R5, and a switch SW2 is detachably connected in parallel to the resistor R6.
And a series circuit of a resistor R6-1, and the output voltage Vo is biased to the upper and lower limit values by turning on the switch SW1 or SW2.

[0016]

EXAMPLES Hereinafter, based on FIGS. 1 to 3 will be described an embodiment of the invention according to claim 1. FIG. 1 is a circuit diagram showing a configuration as one embodiment of the present invention, and corresponds to FIG.
FIG. 1 includes a power supply unit 1, an output voltage detection unit 2A, and an output voltage adjustment unit 3. Here, the power supply unit 1, the output voltage adjustment unit 3
Is the same as that of FIG. 4 of the prior art, and the description is omitted. The new output voltage detector 2A is different from the detector 2 of FIG. 4 in that the upper end of the voltage dividing resistor R5 is basically connected to the lower end of the photocoupler current limiting resistor R4. In this circuit, the values of the voltage dividing resistors R5 and R6 are sufficiently larger than the internal impedances of the photocoupler PC1 and the shunt regulator IC1, and the current IK1 flowing through the current limiting resistor R4 is considered to be equal to the photodiode current IK of the photocoupler PC1. Good.

The shunt regulator IC shown in FIG.
1 is a current I so that the voltage (reference voltage) Vr of the reference terminal 5 is kept equal to the internal reference voltage Vs.
Since K is variable, the voltage across the voltage dividing resistors R5 and R6 (referred to as an output voltage detection reference voltage) Vo1 is kept constant.
On the other hand, this current IK is given by the following equation.

IK = (Vo-Vo1) / R4 As a result, a photodiode current IK proportional to the change in the output voltage Vo is obtained. The photocoupler PC1 outputs an output voltage detection value V1 corresponding to the photodiode current IK while insulating the output voltage detection unit 2A and the output voltage adjustment unit 3 from each other. FIG. 2 is a characteristic diagram showing the relationship between the output voltage Vo when the resistance R4 in FIG. 1 is used as a parameter and the detected voltage V1, and corresponds to FIG.

In the circuit of FIG. 1, as shown in FIG.
The output voltage detection value V1 can be made proportional to the change in the output voltage Vo, and the gain (△ V1 / △ Vo)
Can be adjusted by the resistor R4. FIG. 3 shows an embodiment of the output voltage detector 2A. By connecting capacitors C2 and C3 having appropriate values to both ends of the voltage dividing resistors R5 and R6 as shown in FIG. 3, the response of Vo1 to a change in the output voltage Vo can be delayed. As a result, Vo1 is stabilized against an instantaneous change of Vo.
Further, highly accurate voltage detection becomes possible.

The circuit system of the present invention can be applied not only to the chopper system described in the above embodiment, but also to any switching power supply including a converter system using a transformer system. Next, referring to FIG. 6 and FIG.
An embodiment of the invention relating to No. 2 will be described. FIG. 6 shows a modified embodiment of the output voltage detector 2A of FIG. In FIG. 6, switches SW1, S are connected to the circuit of FIG.
The output voltage compulsory bias circuit 11 composed of W2 and resistors R5-1 and R6-1 is added. Here, the switches SW1 and SW2 may be switches provided on the front surface of the apparatus or operation switches provided at a remote place outside. FIG. 7 is a characteristic diagram of the output voltage Vo for explaining the operation of the bias circuit 11 versus the output voltage detection value V1.

The purpose of using the bias circuit 11 is as follows. The output voltage detector 2A of the power supply device is assembled once using resistors R4 and R5 having predetermined values and a variable resistor R6. The output voltage Vo is adjusted to VSET in FIG. 7 by absorbing the variation of the reference voltage Vr of the shunt regulator IC1 by variable.

However, in order to ship this power supply as a highly reliable finished product, a high-temperature operation test (burn-in) for the purpose of stabilizing the characteristics of the electronic circuit parts and eliminating the initial failure must be performed in advance. It is desirable to do this without altering the inside of the regulated circuit of this power supply.
It is necessary to increase or decrease the output voltage Vo within an allowable range while operating the power supply device under test in a high temperature state. The bias circuit 11 outputs the output voltage V
In order to forcibly set the bias o, it is detachably added to the output voltage detection unit 2A via the connector CN1 only during this test, and the switch SW1 of the bias circuit 11 is turned on to turn on the resistor R5-1. Is connected in parallel to the resistor R5, the output voltage Vo can be forcibly set to the VOL (allowable lower limit value) in FIG. 7, and the switch SW2 of the bias circuit 11 is similarly turned on to turn on the resistor R6-.
1 in parallel with the resistor R6, the output voltage V
o can be forcibly set to the VOU (allowable upper limit) in FIG.

After the high-temperature operation test, the output voltage forced bias circuit 11 is removed at the connector CN1, and the power supply returns to the circuit configuration before the test and is shipped as a finished product.

[0024]

According to the first aspect of the present invention, there is provided a switching power supply device for obtaining an output DC voltage Vo of a predetermined level by repeatedly turning on and off an input DC power supply Vin via a transistor Tr1 as a switching means. A photocoupler PC1 for supplying a current IK dependent on the DC voltage Vo to its own photodiode;
The output voltage V1 of the first phototransistor is set to the set voltage VS
2, a switching power supply circuit including an error amplifier A1, a PWM control circuit 4 and the like as means for variably controlling the continuity ratio of the switching means so that the two voltages coincide with each other. A resistor R as output voltage detecting means for making IK proportional to a difference voltage between the output DC voltage Vo and a predetermined reference voltage Vo1.
4-R6, shunt regulator IC1 , capacitor C
2, C3, etc., it is possible to efficiently design and adjust a high-precision constant voltage control circuit of the switching power supply device, thereby improving the reliability and economy of the switching power supply.

According to the second aspect of the present invention, a series circuit of the switching SW1 and the resistor R5-1 is detachably connected in parallel to the resistor R5 constituting the output voltage detecting section 2A, and the detecting section 2A is similarly constituted. Since a series circuit of a switch SW2 and a resistor R6-1 is detachably provided in parallel with the resistor 6, and the switch SW1 or SW2 is turned on, the output voltage Vo can be set to the allowable upper and lower limit values. By operating the switches SW1 and SW2 on the front of the power supply or at a remote location, it is possible to easily and automatically perform a high-temperature operation test or the like before shipping the power supply without modifying the inside of the circuit when the power supply is assembled. This can be performed as much as possible, and the efficiency of the device test can be increased.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing a configuration as one embodiment of the present invention.

FIG. 2 is a characteristic diagram showing a relationship between an output voltage and an output voltage detection voltage of the circuit of FIG. 1;

FIG. 3 is a circuit diagram showing an embodiment of an output voltage detector of FIG. 1;

FIG. 4 is a conventional circuit diagram corresponding to FIG.

FIG. 5 is a conventional characteristic diagram corresponding to FIG.

FIG. 6 is a circuit diagram showing a modified example of the output voltage detector of FIG. 1;

FIG. 7 is a characteristic diagram for explaining the operation of FIG. 6 ;

──────────────────────────────────────────────────続 き Continuation of the front page (56) References Japanese Utility Model Sho 64-47587 (JP, U) (58) Fields investigated (Int. Cl. ⁷ , DB name) H02M 3/155 G05F 1/10 301 G01R 19 / 165

Claims (2)

(57) [Claims] 1. A switching power supply apparatus for obtaining an output current voltage of a predetermined level by repeatedly intermittently inputting and outputting an input DC power supply via switching means, comprising: a photocoupler for flowing a current dependent on the output DC voltage to a photodiode of the switching power supply; And a means for comparing the output voltage of the phototransistor of the photocoupler with a set voltage and variably controlling the continuity ratio of the switching means so that the two voltages coincide. Output voltage detecting means for making a current proportional to a difference voltage between the output DC voltage and a predetermined reference voltage, wherein the output voltage detecting means comprises a first resistor, the photodiode, and a shunt regulator.
Connected in series to polarities that can be operated sequentially.
The output DC voltage is applied to both ends of the series circuit, and the output of the photodiode and the shunt regulator are directly connected.
A series circuit of second and third resistors is connected in parallel with the column circuit
And, said shunting the connection point between the second resistor and the third resistor
Connect the second terminal to the reference terminal of the regulator.
And generating the reference voltage across both ends of a third resistor.
Be configured to, the second, first, second capacitor in parallel respectively to a third resistor
Switching power supply device
Output voltage detection circuit. 2. The output voltage detection circuit according to claim 1,
And at least a fourth resistor and the resistor are arranged in parallel with the second resistor.
A series circuit with a first switch for closing the column.
Detachably attached in parallel to the second resistor, as well as the resistance of the fifth, in parallel the resistor to the third resistor
A series circuit with a second switch to be turned on is connected to the third circuit.
Characterized in that it is detachably provided in parallel with a resistor of
Output voltage detection circuit of the switching power supply.