JP6409304B2 - Isolated DC power supply - Google Patents

Description

  The present invention relates to a DC power supply device, and more particularly to a technique effective for use in correcting an operating point of an overcurrent protection circuit in an insulated DC power supply device including a voltage conversion transformer.

  The DC power supply device includes an AC / DC converter composed of a diode bridge circuit that rectifies an AC power supply, and an isolated DC-DC converter that steps down the DC voltage rectified by the circuit and converts it into a DC voltage having a desired potential. -There is a DC converter. As such an AC-DC converter, for example, a switching element connected in series with a primary winding of a voltage conversion transformer is turned on / off by a PWM (pulse width modulation) control method, a PFM (pulse frequency modulation) control method, or the like. A switching power supply device is known in which the current flowing in the primary winding is controlled and the voltage induced in the secondary winding is controlled.

Incidentally, in an AC-DC converter, a rated load current (or maximum load current) is defined, and the power supply apparatus is damaged when an overcurrent state occurs in which the current flowing on the secondary side increases more than the rated load current. In some cases, the primary side control circuit is often provided with an overcurrent detection function and an overcurrent protection function for stopping the control operation when an overcurrent is detected.
As a method of detecting the overcurrent of the secondary side output in the switching control type AC-DC converter, a current detection resistor is provided in series with the primary side switching element, and a voltage (current-voltage converted by the resistor ( A method of monitoring a triangular waveform or a trapezoidal wave voltage peak value) is generally used (see Patent Document 1).

  By the way, the AC-DC converter of the world wide input specification needs to be configured so that the input AC voltage can be operated with respect to a relatively wide range of voltage such as 85V to 276V. However, in the system in which the overcurrent protection function is activated by monitoring the current-voltage converted voltage, the primary-side peak current Ip changes as shown in FIG. 3 depending on the magnitude of the AC input voltage VAC. Therefore, if no countermeasure is taken, there is a problem that the overcurrent protection operating point (the load current value Idet when the overcurrent protection is activated) is shifted.

FIG. 9 shows the change in the operating point of the overcurrent protection circuit with respect to the magnitude of the AC input voltage VAC. When no countermeasure is taken, the overcurrent protection circuit is shown in FIG. The operating point Idet changes, and appropriate overcurrent protection cannot be performed. The ideal characteristic is that the VAC-Idet characteristic becomes flat.
As a countermeasure against the AC input voltage dependency of the overcurrent protection operating point as described above, in the AC-DC converter as shown in FIG. 1, the node N1 to which the pulsating voltage rectified by the diode bridge 12 is applied, and the current A method of connecting a correction resistor Rb between the detection resistor Rs and the node N2 between the current detection terminal CS of the control IC as shown by a broken line is conceivable.

JP 2005-341730 A JP 2012-235561 A

  However, in the countermeasure for connecting the correction resistor Rb as described above, as shown by the broken line B in FIG. 9, although the change in the overcurrent protection operating point Idet is smaller than that without the resistor, The flatness of the VAC-Idet characteristic is poor, and the change of the overcurrent protection operating point in the range of 100 to 200 V is not sufficiently reduced. Moreover, since a useless current flows by providing the correction resistor Rb, there is a problem that power loss increases.

Therefore, the present inventors detect the duty of a control signal (pulse) that turns on and off a switching element that supplies current to the primary winding in an AC-DC converter of a switching control system, and according to the detected duty An invention for reducing the AC input voltage dependency of the overcurrent protection operating point by correcting the threshold voltage Vth of the comparator for overcurrent protection was filed earlier (see Patent Document 2).
However, the invention disclosed in Patent Document 2 has a problem that the duty detection circuit is complicated, and when the primary side power supply control circuit is formed as a semiconductor integrated circuit, the chip size increases and the cost increases. is there.

  The present invention has been made in the background as described above, and its object is to provide an insulation type direct current circuit that includes a voltage conversion transformer and controls the output by turning on and off the current flowing through the primary winding. To provide a technique capable of correcting an overcurrent protection operation point and performing appropriate overcurrent protection for a wide range of input voltages without causing an increase in power loss or an increase in circuit scale in a power supply device. is there.

In order to achieve the above object, the present invention
A transformer for voltage conversion, a switching element for intermittently passing a current through the primary winding of the transformer, a voltage proportional to the current flowing through the primary winding of the transformer, and a secondary side of the transformer When an output voltage detection signal is input, a drive pulse for controlling on / off of the switching element is generated, and when the load is heavy , the frequency of the drive pulse is constant and output, and according to the output voltage detection signal at a light load In an isolated DC power supply device having a power supply control circuit that varies and outputs the frequency of the drive pulse,
The power supply control circuit
An overcurrent detection circuit for comparing a voltage proportional to the current flowing through the primary winding and a comparison voltage to detect an overcurrent state on the secondary side of the transformer;
An overcurrent protection circuit that turns off the switching element in response to the overcurrent detection circuit detecting an overcurrent state;
The comparison voltage is corrected according to the ON time of the drive pulse of the switching element.

  According to the above configuration, since the overcurrent protection operating point hardly changes even when the AC input voltage is different, the AC input voltage-overcurrent protection operating point characteristics are almost flat, and the AC input voltage can be applied to a wide range of AC input voltages. Overcurrent protection can be performed at an appropriate point.

Here, preferably, the overcurrent protection circuit includes:
A reference voltage source for generating a comparison reference voltage Vth which is a reference for the comparison voltage Vthc ;
A constant current source, a switch element, and a capacitor connected in series between a power supply voltage terminal and a ground point, and by turning on and off the switch element based on an on / off signal of the switching element, the switch element and the capacitor and on-time detection circuit from the connection terminal for outputting a voltage Vton corresponding to on-time of the switching element,
On the basis of the ON time detecting circuit wherein from Ru output voltage Vton, the comparison voltage Vthc is, a correction circuit for correcting such changed according Vthc = Vth + Vton × k (constant) becomes equation,
It comprises so that it may be provided.
Thereby, overcurrent protection can be performed at an appropriate point with respect to a wide range of AC input voltages, and an overcurrent protection circuit can be easily designed.

Preferably, the voltage proportional to the current flowing through the primary side winding is a voltage that is current-voltage converted by a current detection resistor connected in series with the switching element.
Thereby, the voltage monitored for overcurrent protection can be obtained easily.

Preferably, the power supply control circuit is formed as a semiconductor integrated circuit on one semiconductor chip, and has a first terminal to which a voltage converted from current to voltage by the resistance for current detection is input, and the transformer And a second terminal to which an output voltage detection signal from the secondary side is input.
Thereby, while reducing the number of parts which comprise an insulation type DC power supply device, size reduction of a power supply device can be achieved.

  According to the present invention, in an isolated DC power supply device that includes a voltage conversion transformer and controls the output voltage by turning on and off the current flowing through the primary winding, the power loss increases and the circuit scale increases. In addition, there is an effect that the correction characteristic of the overcurrent protection operating point can be made substantially flat and appropriate overcurrent protection can be performed for a wide range of input voltages.

It is a circuit block diagram which shows one Embodiment of the AC-DC converter as an insulation type DC power supply device which concerns on this invention. FIG. 2 is a circuit configuration diagram illustrating a configuration example of a primary side control circuit (power control IC) of the transformer in the AC-DC converter of FIG. 1. It is a graph which shows the relationship between AC input voltage VAC and the peak current of the primary side under the load constant conditions in an AC-DC converter. It is a graph which shows the relationship between AC input voltage VAC and the voltage of a current detection terminal on load constant conditions in an AC-DC converter. It is a graph which shows the relationship between AC input voltage VAC in an AC-DC converter, and primary side ON time. It is a circuit block diagram which shows the specific example of the ON time detection circuit and voltage correction circuit in the AC-DC converter of embodiment. It is a graph which shows the load current-input voltage characteristic before correction | amendment of the overcurrent protection operating point in an AC-DC converter, and after correction | amendment. It is a graph which shows the load current-output voltage characteristic before correction | amendment of the overcurrent protection operation point in an AC-DC converter, and after correction | amendment. It is a graph which shows the input voltage characteristic of the overcurrent protection operation point in the AC-DC converter which does not correct | amend an overcurrent protection operating point, and the AC-DC converter which corrected the operating point by resistance.

DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, preferred embodiments of the invention will be described with reference to the drawings.
FIG. 1 is a circuit configuration diagram showing an embodiment of an AC-DC converter as an insulated DC power supply device to which the present invention is applied.

  The AC-DC converter according to this embodiment includes a noise blocking filter 11 including a common mode coil, a diode bridge circuit 12 that rectifies an AC voltage (AC) and converts it into a DC voltage, and smoothes the rectified voltage. A voltage converting transformer T1 having a smoothing capacitor C1, a primary winding Np, a secondary winding Ns and an auxiliary winding Nb, and a primary winding Np of the transformer T1 connected in series. It has a switching transistor SW composed of an N-channel MOSFET, and a power supply control circuit 13 that drives the switching transistor SW. In this embodiment, the power supply control circuit 13 is formed as a semiconductor integrated circuit (hereinafter referred to as a power supply control IC) on a single semiconductor chip such as single crystal silicon.

  The secondary side of the transformer T1 is connected between the rectifying diode D2 connected in series with the secondary side winding Ns and between the cathode terminal of the diode D2 and the other terminal of the secondary side winding Ns. Smoothing capacitor C2 is provided, and the primary side winding Np is rectified and smoothed by rectifying and smoothing the AC voltage induced in the secondary side winding Ns by passing a current intermittently through the primary side winding Np. And a DC voltage Vout corresponding to the winding ratio of the secondary winding Ns.

  Further, the secondary side of the transformer T1 is provided with a coil L3 and a capacitor C3 that constitute a filter for reducing switching ripple, noise, etc. generated by the switching operation on the primary side, and detects the output voltage Vout. And a photodiode 15a as a light-emitting side element of a photocoupler that is connected to the detection circuit 14 and transmits a signal corresponding to the detection voltage to the primary power supply control circuit 13 is provided. On the primary side, a phototransistor 15b is provided as a light receiving side element that is connected between the feedback terminal FB of the power control IC 13 and a ground point and receives a signal from the detection circuit 14.

  The primary side of the AC-DC converter of this embodiment is connected between the rectifying diode D0 connected in series with the auxiliary winding Nb and between the cathode terminal of the diode D0 and the ground point GND. A rectifying / smoothing circuit including a smoothing capacitor C0 is provided, and a voltage rectified and smoothed by the rectifying / smoothing circuit is applied to the power supply voltage terminal VDD of the power supply control IC 13. At the same time, the voltage before being rectified by the diode bridge circuit 12 or the DC voltage after being rectified is applied to the high-voltage start terminal HV of the power supply control IC 13 via the diode D1 and the resistor R1, thereby The power supply control IC 13 can be operated before a voltage is induced in the auxiliary winding Nb.

  Further, in the present embodiment, a current detection resistor Rs is connected between the source terminal of the switching transistor SW and the ground point GND, and the node N3 between the switching transistor SW and the current detection resistor Rs and the power source A resistor R2 is connected between the current detection terminal CS of the control IC 13. Further, a capacitor C4 is connected between the current detection terminal CS of the power supply control IC 13 and the ground point, and a low-pass filter is configured by the resistor R2 and the capacitor C4. Note that the resistor Rb between the nodes N1 and N2 is an element that is not connected in the present embodiment.

Next, a specific configuration example of the power control IC 13 will be described.
In the power supply control IC 13 of this embodiment, an input terminal is connected to a terminal CS to which a voltage to be monitored, which is current-voltage converted by a current detection resistor Rs, is applied, and a voltage Vcs input to the terminal CS and a predetermined voltage Control circuit (comparator) for detecting an overcurrent state by comparing with a comparison voltage (threshold voltage), and for controlling the switching transistor SW to be turned on or off with a comparison voltage supplied to the monitoring circuit (comparator) The correction is made in accordance with the ON period (pulse width) of the signal (pulse). In the AC-DC converter according to the present embodiment, the ON / OFF control cycle (= oscillation frequency of the oscillator) of the switching transistor SW is constant.

  By the way, the conventional monitoring circuit for overcurrent protection is capable of determining by comparing the constant comparison voltage with the voltage converted by the resistor Rs regardless of the magnitude of the AC input voltage. This is the reason why the input voltage characteristic (VAC-Idet characteristic) at the operating point of the protection circuit is not flat. The inventor corrects the input voltage characteristics of the operating point of the overcurrent protection circuit by changing the comparison voltage (threshold voltage) of the monitoring circuit (comparator) according to the magnitude of the AC input voltage VAC. I thought it was possible.

  The AC-DC converter of this embodiment performs output voltage control by detecting the peak value of the voltage (triangular wave or trapezoidal wave) at the current detection terminal CS during normal operation. The overcurrent protection is performed by limiting the peak value of the voltage Vcs at the current detection terminal CS to a certain value or less. However, since the peak value of the voltage Vcs at the current detection terminal CS changes depending on the level of the AC input voltage, the operating point for output overcurrent protection also varies. Note that the voltage Vcs of the current detection terminal CS is proportional to the primary side current.

Therefore, the present inventor examined the characteristics of the AC input voltage versus the primary peak current, and as a result, had the right-down concave shape as shown in FIG.
As a result of investigating whether or not the power supply device has characteristics close to the characteristic curve shown in FIG. It has been found that the ON time (Ton) of the drive pulse ON / OFF of the transistor SW has a similar curve with respect to the AC input voltage as shown in FIG.

The present invention has been made on the basis of the above knowledge, and an on-time detection circuit for detecting an on-time (Ton) of a drive pulse ON / OFF of the switching transistor SW in the power supply control IC 13 and the detection circuit A correction circuit is provided for correcting the comparison voltage (threshold voltage) of the overcurrent protection comparator according to the on-time detected by.
Specifically, as shown in FIG. 2, the power supply control IC 13 of this embodiment includes an oscillator 31 that oscillates at a predetermined frequency, and a primary-side switching transistor SW based on an oscillation signal generated by the oscillator 31. Depending on the output of the clock generation circuit 32 formed of a circuit such as a one-shot pulse generation circuit for generating the clock signal CK that gives the timing to turn on, the RS flip-flop 33 set by the clock signal CK, and the output of the flip-flop 33 And a driver (drive circuit) 34 for generating a drive pulse ON / OFF of the switching transistor SW.

  The power supply control IC 13 also includes a level shift circuit 35 that shifts the voltage Vcs input to the current detection terminal CS to a potential suitable for the internal circuit, and the potential Vcs ′ shifted by the level shift circuit 35 and the overcurrent state. Comparator 36a as a voltage comparison circuit that compares a comparison voltage (threshold voltage) Vthc for monitoring the signal, and a comparator that compares the potential Vcs' shifted by the level shift circuit 35 and the voltage VFB of the feedback terminal FB 36b and an OR gate 37 that takes the logical sum of the outputs of the comparators 36a and 36b, and the output of the OR gate 37 is input to the reset terminal of the flip-flop 33 so that the switching transistor SW is turned off. It is configured. Note that a pull-up resistor is provided between the external terminal FB and the internal power supply voltage terminal, and a current flowing through the phototransistor 15b is converted into a voltage by the resistor.

Further, the power supply control IC 13 of the present embodiment monitors the output of the flip-flop 33 to detect the ON time (Ton) of the drive pulse ON / OFF, and the ON time detection circuit 38. And a voltage correction circuit 39 that corrects the comparison reference voltage Vth based on the on-time detected by (1) and supplies it to the comparator 36a as the comparison voltage Vthc.
The voltage correction circuit 39 performs correction as expressed by Vthc = Vth + Vton × k. Here, Vton is a voltage proportional to the ON time (Ton) of the drive pulse ON / OFF, and k is a constant. In this embodiment, the on-time detection circuit 38 is configured to output a voltage represented by Vton or (Vton × k).

For example, as shown in FIG. 6, the on-time detection circuit 38 connects a constant current source CC, a switch SW1, and a capacitor C5 in series between the internal power supply voltage terminal Vcc and the ground point, and connects the switch SW1 to the flip-flop 33. This is realized by a circuit that is turned on and off by the output Q of the circuit and that takes out the output from the connection node between the switch SW1 and the capacitor C5.
When the on-time detection circuit 38 is a circuit as shown in FIG. 6, the voltage correction circuit 39 may be configured by an addition circuit ADD that adds the comparison reference voltage Vth to the output voltage Vton of the on-time detection circuit 38. it can. The comparison reference voltage Vth can be generated by a known reference voltage circuit.

In this embodiment, the on-time detection circuit 38, the correction circuit 39, and the comparator 36a constitute an overcurrent protection circuit. The reference voltage circuit for generating the comparison reference voltage Vth is configured by a variable voltage source, and the variable voltage source is configured so that the correction circuit 39 generates the comparison reference voltage Vth corresponding to the voltage from the on-time detection circuit 38. It may be configured to control and change the comparison voltage along a desired characteristic curve. As described above, the correction circuit that generates the voltage for controlling the variable voltage source according to the detected ON time can be realized by an operational amplifier circuit or the like.
Further, the on-time detection circuit 38 may be configured by an integration circuit using an operational amplifier. In that case, the voltage correction circuit 39 can be realized by providing a multiplication circuit for increasing the output voltage by k times and an addition circuit for adding Vth at the subsequent stage of the integration circuit.

Next, the operation of the power supply control IC 13 of this embodiment will be described.
In the power supply control IC 13 of the present embodiment, in the normal state where the secondary current is equal to or lower than the rated load current or the maximum load current, the potential Vcs ′ obtained by level shifting the voltage Vcs of the current detection terminal CS is greater than the comparison voltage Vthc. The output of the comparator 36a is at a low level (the overcurrent protection function does not work). When the potential Vcs ′ obtained by level shifting the voltage Vcs of the current detection terminal CS becomes lower than the input voltage VFB of the terminal FB, the output of the comparator 36b changes to the high level and the flip-flop 33 is reset via the OR gate 37. As a result, the switching transistor SW is turned off.

  Further, as the output voltage Vout is lower, the forward current of the photodiode 15a as the light emitting side element of the photocoupler of FIG. 1 decreases, and therefore the collector current of the phototransistor 15b as the light receiving side element also decreases. As a result, since the voltage VFB of the feedback terminal FB increases, the determination of the comparator 36b that gives the SW off timing by comparing the voltage VFB with the potential Vcs ′ (triangular wave) obtained by level shifting the voltage Vcs of the current detection terminal CS. The level will also rise. As a result, the timing for resetting the flip-flop 33 is delayed, the pulse width of the drive pulse is increased, the primary peak current and the average current are increased, and the output voltage Vout is increased. In this way, feedback control (PWM control) is performed in which Vout is kept constant.

On the other hand, when the secondary current is in an overcurrent state exceeding the rated load current, the potential Vcs ′ obtained by level shifting the voltage Vcs of the current detection terminal CS becomes higher than the comparison voltage (threshold voltage) Vthc, and the comparator The output of 36a changes to a high level and the flip-flop 33 is reset via the OR gate 37, thereby turning off the switching transistor SW. As a result, the primary side current is limited, and the output voltage Vout decreases.
In the power supply control IC 13 of the above embodiment, the output of the comparator 36a is supplied to the reset terminal of the flip-flop 33 via the OR gate 37, but the output of the comparator 36a is directly supplied to the driver (drive circuit) 34. The switching transistor SW may be configured to be turned off when an overcurrent state is detected.

FIG. 7 shows an excessive voltage with respect to the input voltage VAC in the power supply control IC 13 in which the correction circuit 39 gives the comparison voltage (threshold voltage) Vth a curve corresponding to the characteristic curve shown in FIG. The characteristics of the current protection operating point (load current value Idet when overcurrent protection is activated) are shown.
In FIG. 7, the solid line B corrects the VAC-Idet characteristic of the overcurrent protection operating point in the power supply control IC 13 of the above embodiment having the correction circuit 39 for the comparison reference voltage Vth, and the solid line A corrects the comparison reference voltage Vth. The VAC-Idet characteristic in a power supply control IC not provided with the correction circuit 39 is shown.
7 that the flatness of the VAC-Idet characteristic can be greatly improved by providing the correction circuit 39 as compared with the case where the correction circuit 39 is not provided. Also, it can be seen that the flatness is improved compared to the broken line B in FIG. 9 showing the VAC-Idet characteristic when the correction resistor Rb as shown by the broken line in FIG. 1 is connected.

  FIG. 8 shows the load current-output voltage characteristics. In FIG. 8, a solid line A is a characteristic when an overcurrent state is caused at 100 VAC in the AC-DC converter using the power supply control IC 13 of the above embodiment, and a broken line B is a characteristic when an overcurrent state is caused at 230 VAC. It is. In FIG. 8, the alternate long and short dash line C is a characteristic when an overcurrent state is caused at 100 V AC in an AC-DC converter using a power supply control IC without a correction circuit, and the dotted line D is at 230 V AC without a correction circuit. This is a characteristic when an overcurrent state occurs.

  As shown in FIG. 8, when the correction circuit is not provided, the overcurrent protection operating point Idet, that is, the current value at which the output voltage starts to decrease is shifted by the AC input voltage as in C and D, whereas the correction circuit 39 In the AC-DC converter using the power supply control IC 13 of the above embodiment having the above, even if the AC input voltage changes as in A and B, the output voltage decreases from the almost same overcurrent protection operating point Idet. I can see that it starts.

  Although the invention made by the present inventor has been specifically described based on the embodiment, the present invention is not limited to the embodiment. For example, in the above-described embodiment, the switching transistor SW that allows current to flow intermittently through the primary winding of the transformer is a separate element from the power supply control IC 13. However, the switching transistor SW is incorporated into the power supply control IC 13. You may comprise as one semiconductor integrated circuit.

In the power supply control IC 13 of the above embodiment, the comparator 36b is configured to compare the voltage VFB of the feedback terminal FB and the voltage Vcs ′ obtained by level shifting the voltage Vcs of the current detection terminal CS. And a predetermined reference voltage may be compared, or a potential obtained by level shifting the voltage VFB of the terminal FB and a voltage Vcs ′ obtained by level shifting the voltage Vcs of the terminal CS may be compared. Also good.
Also, in order to prevent the overcurrent protection circuit from accidentally working at the time of system startup, for example, when the duty (ON time) of the drive pulse is within a predetermined range or after a predetermined time has elapsed since the power supply startup, The correction circuit 39 that corrects the reference voltage Vth may be configured to operate.

  Furthermore, the present invention is not limited to the power supply control IC of the type in which the frequency of the oscillator is fixed and the switching element is driven by the PWM pulse as described above. Normally, in power supply control ICs with this kind of light load frequency reduction function, the maximum frequency (rated frequency) is reached at the load current where overcurrent protection works, so the oscillator frequency is changed according to the feedback voltage. The present invention can also be applied to a power supply control IC of a system. In the above embodiment, the case where the present invention is applied to the primary side power supply control IC constituting the flyback type AC-DC converter has been described. However, the present invention is not limited to the forward type or pseudo-resonant type AC-DC. The present invention can also be applied to a power supply control IC constituting a converter, and further to a non-insulated power supply control IC.

12 Diode bridge circuit (rectifier circuit)
13 Power control circuit (Power control IC)
14 Secondary side detection circuit (IC for detection)
15a Photocoupler light emitting diode 15b Photocoupler light receiving transistor 31 Oscillator circuit 32 Clock generator circuit 34 Driver (drive circuit)
36a Comparator (overcurrent detection circuit)
38 On-time detection circuit 39 Correction circuit

Claims (3)

A transformer for voltage conversion, a switching element for intermittently passing a current through the primary winding of the transformer, a voltage proportional to the current flowing through the primary winding of the transformer, and a secondary side of the transformer When an output voltage detection signal is input, a drive pulse for controlling on / off of the switching element is generated, and when the load is heavy , the frequency of the drive pulse is constant and output, and according to the output voltage detection signal at a light load And an isolated DC power supply device having a power supply control circuit for varying the frequency of the drive pulse and outputting it,
The power supply control circuit
An overcurrent detection circuit for comparing a voltage proportional to the current flowing through the primary winding and a comparison voltage to detect an overcurrent state on the secondary side of the transformer;
An overcurrent protection circuit that turns off the switching element in response to the overcurrent detection circuit detecting an overcurrent state;
With
The overcurrent protection circuit is
A reference voltage source for generating a comparison reference voltage Vth which is a reference for the comparison voltage Vthc;
A constant current source, a switch element, and a capacitor connected in series between a power supply voltage terminal and a ground point, and by turning on and off the switch element based on an on / off signal of the switching element, the switch element and the capacitor An on-time detection circuit that outputs a voltage Vton corresponding to the on-time of the switching element from the connection terminal;
A correction circuit that corrects the comparison voltage Vthc so as to change according to an expression of Vthc = Vth + Vton × k (constant) based on the voltage Vton output from the on-time detection circuit;
An insulated DC power supply device comprising:   2. The insulation according to claim 1, wherein the voltage proportional to the current flowing through the primary winding is a voltage that is current-voltage converted by a current detection resistor connected in series with the switching element. Type DC power supply.   The power supply control circuit is formed as a semiconductor integrated circuit on one semiconductor chip, and has a first terminal to which a voltage converted from current to voltage by the current detection resistor is input, and a secondary side of the transformer. The insulated DC power supply device according to claim 2, further comprising a second terminal to which the output voltage detection signal is input.

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