JP3339543B2 - Switching power supply with remote sensing terminal - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an improvement of a switching power supply having a remote sensing terminal.

[0002]

2. Description of the Related Art Conventionally, in a switching power supply device, when a voltage drop of an external lead wire from an output terminal to an external load is large, a remote sensing terminal corresponding to each output terminal so that a stable power supply voltage can be supplied to the load. Is known. That is, as shown in FIG. 4, a predetermined frequency signal is oscillated by the switching transistor Q1 via the drive circuit 1 based on the power supply voltage applied to the input terminals P1, P2, and P3 from a DC power supply (not shown). Is added to the primary side t1 of the transformer T and the secondary side t
2, the output is rectified and smoothed by the rectifier diode D1 and the smoothing capacitor C1, and DC power is supplied from the output terminals P4 and P5 to the load 7 via the external leads 3 and 5.

Further, remote sensing terminals P6 and P7 corresponding to both output terminals P4 and P5 are provided, and a series circuit of resistors R1 and R2 is connected between the remote sensing terminals P6 and P7, so that the output terminal P4 and the remote sensing terminal are connected. A series circuit of a current limiting resistor R3, a photodiode D2 and a comparator IC1 is connected between P7 and resistors R1, R2
Is connected to the comparison terminal of the comparator IC1, and when the potential of the connection point S1 rises above a reference voltage built in the comparator IC1, the impedance of the comparator IC1 is reduced to reduce the impedance of the photodiode D2. On the other hand, when the light emission amount is increased, the impedance is increased when the potential of the connection point S1 falls below the reference voltage, and the light emission amount of the photodiode D2 is reduced.

Further, the light from the photodiode D2 is received by the phototransistor Q2, the control circuit 9 outputs a control signal corresponding to the magnitude of the received light signal to the drive circuit 1, and the drive circuit 1 switches the switching transistor. The duty ratio (ON period) of the oscillation signal of Q1 is variably controlled. Therefore, the power supply input terminal P
8, P9 and remote sensing terminals P10, P11
And the power input terminal P8 and the remote sensing terminal P10, and the power input terminal P9 and the remote sensing terminal P11 are short-circuited and connected to the remote sensing terminals P6 and P7 via the external leads 11 and 13, respectively. Initial stage, connection point S1 of resistors R1 and R2
Is lower than the reference voltage in the comparator IC1,
The light emission amount of the diode D2 is small, the duty ratio of the oscillation signal is large (the ON period is long), and the output voltage of the secondary side t2 of the transformer T increases.

When the potential of the connection point S1 of the resistors R1 and R2 rises and the light emission amount of the photodiode D2 increases, the increase in the duty ratio of the oscillation signal by the switching transistor Q1 is suppressed, and the resistance of the resistors R1 and R2 is reduced. When the potential of the connection point S1 exceeds the reference voltage in the comparator IC1, the duty ratio of the oscillation signal decreases, and the output voltage on the secondary side t2 of the transformer T decreases. Therefore, if the reference voltage in the comparator IC1 and the resistance values of the resistors R1 and R2 are appropriately selected, the photo diode D associated with the magnitude of the potential of the connection point S1 with respect to the reference voltage in the comparator IC1 will be described.
2, the secondary side t of the transformer T
2 can be stabilized at a desired level.

In addition, the external lead wires 3, 5, 11, 13
Becomes longer and the internal resistances r1 to r4 cannot be ignored, the potential of the connection point S1 of the resistances R1 and R2 becomes higher than that of the comparator IC.
1, the light emission amount of the photodiode D2 decreases, the induced voltage on the secondary side t2 of the transformer T increases, and the supply power supply voltage increases. As described above, in the conventional switching power supply with a remote sensing terminal, when the internal resistances r1 to r4 cannot be ignored due to the length of the external leads 3, 5, 11, and 13 being detected, the internal resistances r1 to r4 are detected. ~ R4 minutes can be corrected and stabilized without lowering the power supply voltage supplied to the load 7.

In FIG. 4, reference numeral C2 denotes an input capacitance on the load 7 side, and reference numerals t3 and t4 denote other secondary sides of the transformer T. Reference numerals D3, D4, C3, C4 and 15,
Reference numeral 17 denotes a rectifier diode, a smoothing capacitor, and a load connected to the secondary side t3 and t4 of the transformer T.

[0008]

However, in the conventional switching power supply with a remote sensing terminal, the external leads 3 and 11 are disconnected or disconnected from the output terminal P4 and the remote sensing terminal P6. , 11 are fixed to the output terminal P4 or the remote sensing terminal P6 by loosening or coming off, and the potential of the connection point S1 of the resistors R1 and R2 is kept low. Supply voltage continues to rise, resulting in an overvoltage, which is not preferable.

However, as shown in FIG. 5, a series circuit of a zener diode D5, a current limiting resistor R4 and a photo diode D6 is formed at both ends of the smoothing capacitor C1. Zener voltage of D5 and photodiode D6
When the overvoltage is exceeded by exceeding the drop voltage, the zener diode D5 is turned on and the photodiode D5 is turned on.
6 is operated to emit light, the photodiode D7 receives the light, and based on the received light signal, an overvoltage protection circuit is formed so that the driving circuit 1 stops the oscillation operation of the switching transistor Q1, and the power supply to the load 7 is cut off. There is also proposed a configuration for performing the above.

However, in the configuration in which the overvoltage protection circuit is provided as shown in FIG. 5, when there is a load circuit (not shown) to which the power is supplied from the secondary side t2, the power supply to the load circuit is stopped. As shown in FIG.
In the case of 2 to t4, since the driving circuit 1 and the switching circuit including the switching transistor Q1 are common, there is a disadvantage that the outputs from the secondary sides t3 and t4 are also stopped. Further, even when the external lead wire 13 comes off the remote sensing terminal P7, the potential of the connection point S1 of the resistors R1 and R2 viewed from the point of the remote sensing terminal P7 remains low, and the supply to the load 7 is continued. Voltage rises,
When the overvoltage protection circuit of FIG. 5 operates, the power supply is stopped, and there is a disadvantage that the outputs from all the secondary sides t2 to t4 decrease.

For this reason, in a device equipped with an alarm circuit or the like, for example, in which it is not necessary to shut off the power supply, there is a disadvantage that the function of the device does not operate and the use of the entire device is restricted. The present invention has been made under such a circumstance. Even when an output terminal or a remote sensing terminal is opened, an overvoltage is suppressed, and a switching power supply with a remote sensing terminal capable of securing a necessary power supply is provided. For the purpose of providing.

[0012]

According to the present invention, as shown in a schematic block diagram of FIG. 1, a switching section 19 for oscillating a predetermined signal and an oscillation of the switching section 19 are provided. A transformer T whose output is connected to a primary side t1, and a pair of output terminals P4 and P5 connected to a secondary side t2 of the transformer T via a rectifying and smoothing unit 21
And a pair of remote sensing terminals P6 and P7, which are respectively connected to these two output terminals P4 and P5 by short-circuiting them, and both remote sensing terminals are inserted between the two output terminals P4 and P5 and are connected to different voltage dividing points on the way. Sensing terminal P6,
The potential at the voltage dividing section 23 to which P7 is connected, and the potential at the comparative voltage dividing point different from the voltage dividing point to which the remote sensing terminals P6 and P7 are connected are compared with the reference voltage in this voltage dividing section 23 to determine the magnitude of the potential. A detecting unit 25 for detecting, and the detecting unit 25
A control unit 27 the potential of the comparison voltage dividing point based on the output variably controls the oscillation operation of the switching unit 19 to approach the reference voltage, the remote corresponding to the output terminal of the hand
The potential of the voltage dividing point connected to the sensing terminal is
Lowers the oscillation output when increased by current
And an on-control section for controlling the above-mentioned control section .

Further, in the present invention, a switch section for intermittently supplying power from the rectifying / smoothing circuit to an output terminal thereof, and a potential at a voltage dividing point to which a remote sensing terminal corresponding to one of the output terminals is connected to a load. It is preferable to provide a switch control unit for shutting off the switch unit when the load is increased by the load current.

[0014]

Embodiments of the present invention will be described below with reference to the drawings. Note that the same reference numerals are given to portions common to the conventional example. FIG. 2 is a circuit diagram showing a specific embodiment of the switching power supply device with a remote sensing terminal according to the present invention shown in FIG. In FIG.
Input terminals P1, P2 connected to a DC power supply (not shown)
Of P3, the input terminal P1 is connected to one end of the primary side t1 of the transformer T, the input terminal P2 is connected to the drive circuit 1 and the control circuit 9, and the input terminal P3 is a common terminal thereof.

The driving circuit 1 has a collector connected to the other end of the primary side t1 of the transformer T and an emitter connected to the base of a switching transistor Q1 connected to the input terminal P3, and drives the switching transistor Q1 to perform variable oscillation driving. It is. For example, when a control signal from the control circuit 9 described later is not input, the switching transistor Q1 is driven to perform variable oscillation so that the duty ratio of the oscillation signal is sequentially increased, and the variable oscillation control of the switching transistor Q1 is performed as described later. Things. Details will be described later. The drive unit 1 and the switching transistor Q1 form the switching unit 19 in FIG.

The transformer T has a conventionally known configuration, and includes a primary side (winding) and, for example, a plurality of secondary sides (windings) t2 and t2.
The anode of the rectifier diode D1 is connected to one end of the secondary side t2, and a smoothing capacitor C is connected between the cathode side of the rectifier diode D1 and the other end of the secondary side t2.
1 are formed to form the rectifying / smoothing section 21 of FIG.
Output terminal P4 and low potential side (cold side) output terminal P
5 is connected. Rectifier diodes D3 and D4 as rectifying and smoothing units and smoothing capacitors C3 and C4 are also connected to the secondary sides t3 and t4 of the transformer T, and power is directly supplied to the loads 15 and 17 without passing through external leads. ing.

The resistors R5, R6, R7, R8, R are connected between the output terminals P4 and P5, that is, both ends of the smoothing capacitor C1.
Nine series circuits are connected and function as the voltage dividing unit 23 in FIG. The connection point between the resistors R5 and R6 is connected to the diode D from the remote sensing terminal P6 corresponding to the output terminal P4.
8 is connected in the forward direction, a connection point between the resistors R7 and R8 is connected to a remote sensing terminal P7 corresponding to the output terminal P5, and a connection point between the resistors R8 and R9 is used as an ON control unit, which will be described later. The base of the transistor Q3 is connected.

The series circuit of the resistors R5 to R7 includes a resistor R
3. A series circuit of a comparator IC1 comprising a photodiode D2 and a shunt regulator is connected to
The collector of the transistor Q3 is connected to the connection point between the photodiode D2 and the comparator IC1, and the emitter is connected to the output terminal P5. The comparator IC1 incorporates a predetermined reference voltage and has a comparison terminal. The impedance of the comparator IC1 changes according to the magnitude of the potential applied to the comparison terminal.
2 changes the amount of light emission.

That is, the comparison terminal of the comparator IC1 is connected to the connection point S2 of the resistors R6 and R7, and the voltage between both ends of the resistor R7 is compared with the reference voltage in the comparator IC1. When the voltage becomes higher than the reference voltage, the impedance decreases and the light emission amount of the photodiode D2 increases. When the voltage across the resistor R7 becomes lower than the reference voltage, the impedance increases and the photodiode D2 increases.
And the duty ratio is changed according to the magnitude of the control signal. The phototransistor Q2, which receives light from the photo diode D2, converts the amount of received light into an electric signal corresponding to the intensity and outputs the electric signal to the control circuit 9.
Together with this, a photocoupler is formed to insulate the primary and secondary sides of the transformer T.

The control circuit 9 outputs a control signal for varying the duty ratio of the oscillation signal oscillated by the switching transistor Q1 to the drive circuit 1 based on the strength of the converted signal to control the drive signal. The control unit 27 shown in FIG. 1 is formed by the transistor Q2 and the control circuit 9. The load 7 to which power is supplied by the switching power supply device with the remote sensing terminal is a conventionally known load, and is connected to the output terminal P4 via the external lead wire 3.
, A power input terminal P9 connected to the output terminal P5 via the external lead wire 5, and a remote sensing terminal P10 connected to the remote sensing terminal P6 via the external lead wire 11. And a remote sensing terminal P11 connected to the remote sensing terminal P7 via the external lead wire 13. The power input terminal P8 and the remote sensing terminal P10 and the power input terminal P9 and the remote sensing terminal P11 are short-circuited. . Symbol C2 is an input capacity.

The resistance value of the resistor R5 is set sufficiently larger than the internal resistances r1 and r3 of the external lead wires 3 and 11, and the resistance values of the resistors R8 and R9 are set sufficiently larger than the internal resistances r2 and r4 of the external lead wires 5 and 13. Have been. Therefore, the output terminal P4 and the remote sensing terminal P6 are short-circuited by the external lead wires 3 and 11, and the internal resistances r1 and
In a state where r3 is negligible, the potential at the connection point of the resistors R5 and R6 is almost equal to the potential of the output terminal P4, the output terminal P5 and the remote sensing terminal P7 are short-circuited by the external lead wires 5 and 13, and the internal resistance r2 , R4 can be neglected, the potential at the connection point of the resistors R7 and R8 is almost the potential of the output terminal P5.

Next, the operation of the switching power supply with a remote sensing terminal shown in FIG. 2 will be described. Drive circuit 1 based on the DC voltage applied to input terminals P1 to P3
Drives the switching transistor Q1 to perform switching driving, a predetermined oscillation signal is applied to the primary side t1 of the transformer T, the induced output of the secondary side t2 is rectified and smoothed by the rectifier diode D1 and the smoothing capacitor C1, and the output terminals P4, P5 The supply of power to the load 7 via the external leads 3 and 5 is the same as in the conventional example.

Here, the external lead wires 3, 5, 11, 13
Is short and the internal resistances r1 to r4 can be ignored, and the potential of the connection point (voltage division point) S2 of the resistances R6 and R7 is
The resistances R5 to R9 are set to be substantially equal to the reference voltage within 1.
If at least the resistors R5 to R7 are selected, when the internal resistances r1 to r4 of the external lead wires 3, 5, 11, and 13 become so large that they cannot be ignored, the potential at the connection point (voltage division point) of the resistors R5 and R6 will Decreases, the potential of the connection point S2 also decreases, and becomes lower than the reference voltage of the comparator IC1.
The light emission amount of the photodiode D2 decreases. In this state, since the resistors R8 and R9 are short-circuited by the external lead wires 5 and 13 having a smaller resistance value, no bias is applied to the transistor Q3 and the transistor Q3 does not turn on.

Therefore, based on the control signal from the control circuit 9, the drive circuit 1 drives the switching transistor Q1 so as to increase the duty ratio of the oscillation signal, so that the output of the secondary side t2 of the transformer T rises. Connection point S
The potential of 2 also increases. The potential of the connection point S2 is equal to the comparator IC1.
, The amount of light emitted from the photodiode D2 settles to a predetermined amount, and the output of the secondary side t2 of the transformer T settles slightly higher. Therefore, the external leads 3, 5, 1
The voltage drop caused by the internal resistances r1 to r4 of the power supply circuits 1 and 13 can be corrected, and a stable power supply voltage can be supplied to the load 7.

When the output terminal P4 and / or the remote sensing terminal P6 is opened due to disconnection of the external lead wires 3 and 11, the voltage between the output terminal P4 and the remote sensing terminal P7 is divided by the resistors R5 to R7. And the potential of the connection point S2 decreases, and the comparator IC
Thus, the light emission amount of the photodiode D2 decreases slightly below the reference voltage of unity. Therefore, the switching transistor Q1 is driven to increase the duty ratio of the oscillation signal, and the output of the secondary side t2 of the transformer T slightly increases. However, when the potential of the connection point S2 reaches the reference voltage of the comparator IC1, The light emission amount of the photodiode D2 is settled to a predetermined amount, and the output of the secondary side t2 of the transformer T is settled slightly higher.

Therefore, when the output terminal P4 and / or the remote sensing terminal P6 are opened, the voltage across the smoothing capacitor C1 slightly increases, but the operation of the switching unit 19 is secured, and the load 7 and the load (not shown) Power can be supplied to the circuit, and the occurrence of overvoltage can be suppressed. Of course, the secondary side t of the transformer T
Similarly, power can be supplied to 3 and t4. When the output terminal P4 is opened, the power supply to the load 7 is stopped. When the remote sensing terminal P6 is opened, the power supply is not stopped. The voltage drop due to r1 cannot be corrected.

When the remote sensing terminal P7 is opened, the voltage between the output terminals P4 and P5 is reduced by the resistors R5 to R5.
9, the potential at the connection point S2 drops slightly below the reference voltage of the comparator IC1, the light emission amount of the photodiode D2 decreases, and the output of the secondary side t2 of the transformer T slightly increases. However, immediately, the potential of the connection point S2 is
When the reference voltage of C1 is reached, the output of the secondary side t2 of the transformer T is settled slightly higher. Also in this case, since the divided potential of the resistors R8 and R9 is small, the transistor Q3 does not turn on.

Therefore, even if the remote sensing terminal P7 is opened, although the voltage between both ends of the smoothing capacitors C1, C3 and C4 slightly increases, the secondary side t2 to t2 of the transformer T
Power can be supplied from t4, overvoltage can be suppressed, and the internal resistances r1,
r3 can be corrected. However, the voltage drop due to the internal resistance r2 of the external lead wire 5 cannot be corrected. further,
When the output terminal P5 is opened, the load current flowing from the output terminal P4 to the load 7 flows through the external lead wire 13, the remote sensing terminal P7, and the resistors R8 and R9 . Potential is negative
As the load increases, the voltage drop due to the resistors R8 and R9 increases, the potential at the connection point (voltage division point) between the resistors R8 and R9 increases, and the transistor Q3 turns on.

Therefore, regardless of the potential level at the connection point S2 between the resistors R6 and R7, the amount of light emitted from the photodiode D2 increases and the output of the secondary side t2 of the transformer T sequentially decreases, and finally the smoothing capacitor The voltage across C1 decreases. The secondary sides t3 and t4 of the transformer T also decrease.
That is, oscillation is caused by the ON operation of the transistor Q3.
The control unit 9 is turned on so as to reduce the output.

Next, another embodiment of the switching power supply device with a remote sensing terminal according to the present invention will be described.
FIG. 3 is a main part circuit for explaining another embodiment of the switching power supply device with a remote sensing terminal according to the present invention. The description of the parts common to the embodiment of FIG. 2 is omitted. In FIG. 3, the cathode of the rectifier diode D1 is connected to the emitter of a transistor Q4 as a switch, and the collector of the transistor Q4 is connected to an output terminal P4.
And the transistor Q4 is turned on / off.
The operation connects / disconnects the supply of power to the output terminal P4.

The connection point between the resistors R8 and R9 and the output terminal P5
A time constant circuit including a capacitor C5 and a resistor R10 is connected in parallel between the resistors, that is, both ends of the resistor R9, and a gate of the thyristor Th is also connected to a connection point between the resistors R8 and R9. The anode of the thyristor Th is connected to the cathode side of the rectifier diode D1 via the current limiting resistor R11, is connected to the base of the transistor Q5, is further connected to the reset terminal P12, and is connected to the output terminal of the thyristor Th. Connected to P5.

The transistor Q5 has a collector connected to the base of the transistor Q4, and an emitter connected to the output terminal P5.
The transistor Q4 is intermittently operated by this on / off operation. Note that reference numerals R12 and R13 in FIG. 3 denote bias resistors of the transistors Q5 and Q4, and other configurations in FIG. 3 are almost the same as those in FIG. 2, but the photodiode D2 is shown near the resistor R3.

In such a switching power supply with a remote sensing terminal, when the circuit is operating normally, it operates in the same manner as the normal operation of FIG.
Since the potential at the connection point of R9 is low, the gate voltage of the thyristor Th is low and this does not turn on. Therefore, the base of the transistor Q5 is biased, the transistor Q5 is turned on, and the transistor Q4 is also turned on. In this state, power is supplied from the output terminals P4 and P5 to the load 7 side. When the output terminal P4 and the remote sensing terminals P6 and P7 are opened, the operation is performed in the same manner as the operation in FIG. 2, but the potential at the connection point between the resistors R8 and R9 is similarly low, so that the thyristor Th is turned on. Instead, a DC power supply voltage is generated at both ends of the smoothing capacitor C1. If the external leads 3 and 5 are connected to the output terminals P4 and P5, power is supplied to the load 7 side.

Although the voltage drop due to the internal resistance r1 of the external lead wire 3 connected to the output terminal P4 cannot be corrected, the internal resistance of the external lead wires 5 and 13 connected to the output terminal P5 and the remote sensing terminal P7 cannot be corrected. r2, r4
Is possible to correct the voltage drop. On the other hand, the output terminal P
When the transistor 5 is opened, the potential at the connection point of the resistors R8 and R9 increases, so that the gate voltage of the thyristor Th rises and this turns on, the base of the transistor Q5 becomes a low potential and turns off, and the transistor Q5 turns off. Since the transistor Q4 is also turned off, the power supply to the load 7 is cut off, the load current stops flowing through the resistors R8 and R9, and the resistors R8 and R9 are turned off.
Can be avoided.

That is, the capacitor C5 and the resistor R10
R13, thyristor Th, transistors Q4, Q5
This is a protection circuit when the output terminal P5 is opened, and is a connection point between the resistors 7 and R8, that is, a remote sensing terminal P7.
When the potential of the connection point with the switch rises due to the load current, the switch detects the rise and functions as a switch control unit that controls the switching off of the transistor Q4. The time constant circuit of the capacitor C5 and the resistor R10 in FIG. 3 prevents a malfunction of the thyristor Th when a pulse signal is mixed into the gate circuit of the thyristor Th for some reason.

In the embodiment shown in FIG. 3, the reset terminal P
If the thyristor Th is reset by, for example, setting the H level to 12, the transistors Q5 and Q4 are turned on, and the power supply to the load 7 is restored. by the way,
In each of the embodiments described above, an example has been described in which the switching transistor Q1 is driven such that the duty ratio of the oscillation signal is sequentially changed by the control signal from the control circuit 9, but the present invention is not limited to this.

For example, the drive circuit 1 is formed so that the oscillation frequency is increased when the potential of the voltage dividing point S2 is lower than the reference voltage, and the oscillation frequency is reduced when the potential is higher than the reference voltage. The object of the present invention can be achieved by variably controlling the oscillation operation of the switching unit 19 so that the potential of the voltage dividing point S2 approaches the reference voltage by the control signal. Further, in the above-described embodiment, it is needless to say that the configuration in which the external lead wires 3, 5, 11, and 13 are not used can be similarly applied when the power supply lead wire to the load is long inside the device.

[0038]

As described above, according to the present invention, a predetermined signal is oscillated in the switching section and induced from the primary side of the transformer to the secondary side, and this is rectified and smoothed by the rectifying and smoothing circuit to form a pair of output terminals. Output to the load side, and insert a voltage divider connected with remote sensing terminals to different voltage divider points in the middle between the two output terminals. In this voltage divider, the voltage divider connected to these remote sensing terminals is connected The detection section compares and detects the potential of the comparison voltage dividing point and the magnitude of the reference voltage,
Based on the output of the detection unit, the control unit variably controls the oscillation operation of the switching unit so that the potential of the comparison voltage dividing point approaches the reference voltage, and the remote sensor corresponding to one output terminal
The potential of the voltage dividing point connected to the
When the oscillation output rises, the oscillation output is
Because the above control unit is configured to be turned on so that
Even if the output terminal or the remote sensing terminal is in an open state, a necessary power supply can be secured and generation of an overvoltage can be suppressed. In addition, a switch section for intermittently supplying power to the output terminals from the rectifying and smoothing circuit, and a potential of a voltage dividing point connected to a remote sensing terminal corresponding to one of the output terminals has been increased by a load current to the load. In a configuration in which a switch control unit that controls the switch unit to shut off is provided , even if one of the output terminals is opened, supply of power to the load side can be cut off to prevent circuit damage.

[Brief description of the drawings]

FIG. 1 is a schematic block diagram schematically showing a switching power supply device with a remote sensing terminal according to the present invention.

FIG. 2 is a circuit diagram showing a specific embodiment of the switching power supply device with a remote sensing terminal of FIG. 1;

FIG. 3 is a circuit diagram showing another embodiment of the switching power supply device with a remote sensing terminal of the present invention.

FIG. 4 is a circuit diagram showing a conventional switching power supply device with a remote sensing terminal.

FIG. 5 is a schematic circuit diagram showing a main part of a conventional switching power supply device with a remote sensing terminal.

[Explanation of symbols]

REFERENCE SIGNS LIST 1 drive circuit 3, 5, 11, 13 external lead wire 7, 15, 17 load 9 control circuit 19 switching unit 21 rectifying / smoothing unit 23 voltage dividing unit 25 detection unit 27 control unit C1, C2, C3, C4, C5 capacitor D1 , D3, D4 Diode D5 Zener diode D2, D6 Photodiode IC1 Comparator P1, P2, P3 Input terminal P4, P5 Output terminal P6, P7, P10, P11 Remote sensing terminal P8, P9 Power input terminal P12 Reset terminal Q1 , Q4, Q5 Transistor Q2 Phototransistor Q3 Transistor (ON control unit) R1, R2, R3, R4, R5, R6, R7, R8, R
9, R10, R11, R12, R13 Resistance r1 to r4 Internal resistance Th Thyristor T Transformer t1 Primary side t2, t3, t4 Secondary side

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-1-303055 (JP, A) JP-A-8-44438 (JP, A) JP-A-7-241074 (JP, A) 36616 (JP, U) Japanese Utility Model Showa 57-5725 (JP, U) (58) Fields investigated (Int. Cl. ⁷ , DB name) H02M 3/28 G05F 1/10 G05F 1/56

Claims (2)

(57) [Claims] A switching unit for oscillating a predetermined signal; a transformer having an oscillation output from the switching unit connected to a primary side; and a pair of outputs connected to a secondary side of the transformer via a rectifying and smoothing circuit. A pair of remote sensing terminals respectively connected to the two output terminals in a short-circuited manner; and a voltage divider inserted between the two output terminals and having the remote sensing terminals connected to different voltage dividing points on the way. And a detection unit that compares the potential of the comparison voltage dividing point different from the voltage dividing point connected to the two remote sensing terminals with the reference voltage in the voltage dividing unit and detects the magnitude of the reference voltage. A control unit that variably controls the oscillation operation of the switching unit so that the potential of the comparison voltage dividing point approaches the reference voltage, and the remote unit corresponding to one of the output terminals Sensing
The potential of the voltage dividing point connected to the terminal is
Therefore, when the oscillation output rises,
A switching power supply with a remote sensing terminal, comprising: an on-control unit for controlling the control unit . 2. A switching section for oscillating a predetermined signal.
And the oscillation output of this switching section is connected to the primary side.
Lance, is connected via a rectifier smoothing circuit on the secondary side of the transformer
A pair of output terminals and a pair of
The remote sensing terminal is inserted between the two output terminals,
Each of the remote sensing terminals is connected to a pressure point.
Pressure section, and the connection between the two remote sensing terminals in the voltage division section.
The potential and reference voltage of the comparison voltage division point different from the
A detecting unit for comparing and detecting the magnitude thereof, and based on an output of the detecting unit, the potential of the comparative voltage dividing point is set to the
Oscillation operation of the switching unit so as to approach the reference voltage
A control unit that variably controls the power supply, a switch unit that interrupts power supply from the rectifying and smoothing circuit to the output terminal, and a potential at a voltage dividing point connected to the remote sensing terminal corresponding to one of the output terminals. when raised by the load current of the load, remote sensing terminal with a switching power supply apparatus characterized by comprising a switch control unit for cutting off controlling the switch unit.