JP6326947B2 - Isolated DC power supply - Google Patents

Description

  The present invention relates to an insulated DC power supply device, and more particularly to a technique effective when used in an insulated DC power supply device having an output voltage switching function.

The DC power supply device includes a rectification / smoothing circuit that rectifies and smoothes the AC power supply, and a DC-DC converter that steps down the DC voltage rectified and smoothed by the circuit and converts it to a DC voltage having a desired potential. There is an isolated AC-DC converter (AC adapter).
In recent years, with the diversification of microcomputer peripheral devices, etc., the AC-DC converter has a function that can be used by switching to any one of a plurality of output power DC voltages such as 20V / 5A and 5V / 2A. For example, it is required in the USB-PD specification.

  By the way, when a conventional isolated DC power supply device wants to output a large output power such as 20 V / 5 A and a small output power such as 5 V / 2 A, for example, the transformer turns ratio and current detection are performed to increase power efficiency. It was designed separately so that the circuit constants such as the resistance value were optimized. Specifically, when the output power is low, the current detection resistor is set to a large value, and when the output power is high, the current detection resistor is set to a small value. Therefore, when it is configured to switch to any one of a plurality of output powers with one DC power supply without taking any countermeasures, the power efficiency may be significantly reduced depending on the output power, or it may be wide from light loads to heavy loads. When the control is performed in the range, there is a possibility that the control becomes uneven.

For example, some switching control type power supply devices use a control IC (semiconductor integrated circuit) having an intermittent oscillation mode in which a switching element is operated intermittently at light loads. Such a control IC is used. When the power supply apparatus is configured to switch a plurality of output powers, the intermittent oscillation mode is controlled over the entire range from a light load to a heavy load during operation of low output power. As a result, there is a problem that the ripple of the output voltage becomes large.
Therefore, a switching resistor is provided in parallel with the current detection resistor connected in series with the switching element, and when switching the output power, the level of the current detection value fed back to the control IC is switched. An invention relating to a power supply device has been proposed (see, for example, Patent Document 1).

JP 2000-358375 A

  However, the power supply device disclosed in Patent Document 1 switches the connection state of the adjustment resistor provided in parallel with the current detection resistor by an external signal, and the output timing of the external signal, that is, the switching point is Although the setting is arbitrarily changed according to the weight of the load (circuit 1), Patent Document 1 does not describe that the switching signal is generated by determining the weight of the load. And the power supply device of patent document 1 is not an insulation type DC power supply device but a switching regulator, and the object of the invention is different from the present application.

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. In the power supply device, when one of a plurality of output voltages is selected and switched, the power efficiency differs significantly depending on whether the selected output voltage is large or small, or biased control is executed. It is an object of the present invention to provide a technique capable of preventing the above-described problem.
Another object of the present invention is to provide an insulated DC power supply device that can determine whether the output voltage is large or small by itself and switch the connection state of the adjustment resistor of the current detection resistor.

In order to achieve the above object, the present invention
Transformer for voltage conversion, switching element for flowing current to the primary winding of the transformer, current detection element for detecting current flowing to the primary winding of the transformer, and conversion by the current detection element And a primary side control circuit for generating and outputting a drive pulse for controlling on and off of the switching element by inputting a voltage and a feedback voltage from a secondary side of the transformer, and the primary side based on an output voltage A secondary side circuit including a feedback voltage generating means for generating a feedback voltage to be supplied to the control circuit;
The transformer includes an auxiliary winding that induces a voltage having the same polarity as the secondary winding,
On the primary side of the transformer,
A resistance element connected between a current detection terminal of the primary side control circuit to which a voltage converted by the current detection element is input, and a voltage extraction side terminal of the current detection element;
Switching means comprising one or more resistance adjusting elements connected in parallel with the current detection element via the resistance element;
The switching means is configured to change a voltage input to the primary side control circuit by switching a current path of the resistance adjusting element according to a voltage potential induced in the auxiliary winding.

Here, “switching the current path” includes preventing current from flowing through the resistance adjustment element.
According to the insulation type DC power supply device having the above configuration, when selecting and switching one of a plurality of output voltages, a result equivalent to the optimization of the current detection resistor can be obtained. It is possible to prevent the power efficiency from being remarkably different depending on whether the selected output voltage is large or small, or uneven control to be executed.

  Also, a resistance element (input resistance element) connected between the current detection terminal of the primary side control circuit and the voltage extraction side terminal of the current detection element is provided, and in parallel with the current detection element via the resistance element Since the switching means including one or two or more resistance adjustment elements connected is provided, switching noise can be reduced by preventing a large current from flowing through the resistance adjustment element. At the same time, since the voltage input to the current detection terminal is determined by the resistance ratio of the two series resistors, the resistance ratio becomes a predetermined value even if the resistance values of the resistance elements used vary. By setting in this way, it is possible to increase the accuracy of the voltage input to the current detection terminal without using an expensive element with high resistance value accuracy as the resistance adjustment element.

Here, preferably, the switching means includes:
A voltage dividing circuit connected between the output terminal of the rectifying / smoothing circuit connected to one terminal of the auxiliary winding and a ground point;
Switch means connected in series with the resistance adjusting element and turned on or off by a voltage divided by the voltage dividing circuit,
Depending on the voltage value to be output from the secondary side of the transformer,
The switch means is turned on when the voltage to be output from the secondary side is the first value, and the switch means is turned off when the voltage to be output from the secondary side is the second value. As described above, the voltage dividing ratio of the voltage dividing circuit is set.
According to such a configuration, the switching means can be realized by a relatively simple circuit, and an increase in the number of elements can be suppressed and a circuit having a desired function can be easily designed.

Preferably, the feedback voltage generation means includes
A voltage dividing resistor element in series for dividing the voltage on the secondary side of the transformer;
One or two or more resistance adjusting elements connected in parallel with any one of the voltage dividing resistance elements, and secondary-side switching means connected to the resistance adjusting elements, and the voltage dividing resistance elements Generating a feedback voltage to be supplied to the primary side control circuit based on the compressed voltage;
The secondary side switching means switches the current path of the resistance adjusting element based on an external signal, and changes the feedback voltage supplied to the primary side control circuit.

  According to such a configuration, the primary-side control circuit can recognize that the output voltage has been switched based on the change in the feedback voltage without receiving the output voltage switching signal, and the output after switching. Control according to the voltage can be automatically performed, and there is no need to provide a transmission means such as a photocoupler for supplying an output voltage switching signal from the secondary side to the primary side control circuit.

Desirably, two or more resistance adjusting elements are provided,
The secondary side switching unit is configured to select and output any one of a plurality of voltages by switching current paths of the two or more resistance adjusting elements based on an external signal.
According to such a configuration, the output voltage can be switched to any one of three or more voltage values for output.

Preferably, the secondary side circuit is connected between a communication means for transmitting / receiving a signal to / from an external device and a terminal for outputting a DC voltage generated by the secondary side circuit. A capacitive element, and
The communication means is configured to be able to communicate with an external device using an AC signal via the capacitive element.
According to such a configuration, it is possible to communicate with an external device without providing a communication terminal separately from a terminal for outputting a DC voltage, and output from the secondary circuit from the outside using the communication function. Information on the power value can be acquired.

  According to the present invention, an insulation type DC power supply device that includes a voltage conversion transformer and controls the output by turning on and off the current flowing in the primary winding is configured to switch to one of a plurality of output voltages. In this case, it is possible to prevent power efficiency from being remarkably different depending on whether the selected output voltage is large or small, or uneven control to be performed. In addition, there is an effect that it is possible to realize an isolated DC power supply device that can determine whether the output voltage is large or small and switch the connection state of the adjustment resistor of the current detection resistor.

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. It is a circuit diagram which shows the specific example of the switching circuit in the AC-DC converter of embodiment shown in FIG. It is a circuit block diagram which shows the specific example of the secondary side control circuit in the AC-DC converter of embodiment. It is a circuit block diagram which shows the 1st modification of the AC-DC converter of embodiment. It is a circuit block diagram which shows the 2nd modification of the AC-DC converter of embodiment. It is a circuit block diagram which shows 2nd Embodiment of the AC-DC converter to which this invention is applied.

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 alternating voltage (AC), and a smoothing capacitor C1 that smoothes the rectified voltage. And a voltage converting transformer T1 having a primary winding Np, a secondary winding Ns and an auxiliary winding Nb, and an N-channel MOSFET connected in series with the primary winding Np of the transformer T1. A switching transistor SW1 and a primary side control circuit 13 for driving the switching transistor SW1 are included. In this embodiment, the primary side control circuit 13 is formed as a semiconductor integrated circuit (control IC) on one semiconductor chip such as single crystal silicon.

The auxiliary winding Nb is a coil wound in a direction having the same polarity as the secondary winding Ns, and induces an AC voltage in phase with the AC voltage induced in the secondary winding Ns and proportional to the turn ratio. It is configured to be.
The secondary side of the transformer T1 is connected between the rectifying diode D2 connected in series with the secondary winding Ns, and the cathode terminal of the diode D2 and the other terminal of the secondary winding Ns. Smoothing capacitor C2 is provided, and by rectifying and smoothing the AC voltage induced in the secondary winding Ns by passing a current intermittently through the primary winding Np, the primary winding Np A DC voltage corresponding to the turn ratio with the secondary winding Ns is output. The secondary side is provided with a coil L3 and a capacitor C3 that constitute a filter for cutting off switching ripple, noise, and the like generated by the switching operation on the primary side. The filter coil L3 and the output terminal OUT1 The output cutoff MOS transistor Q2 and the isolation coil L4 are connected in series, and the DC voltage Vout is output from the output terminal OUT1 through these elements.

Further, on the secondary side of the transformer T1, a photodiode 15a as a light-emitting side element of a photocoupler that transmits a feedback voltage proportional to the output voltage Vout to the primary-side control IC 13, and the photodiode according to the output voltage Vout A secondary side control circuit 20 for driving 15a is provided.
The primary side of the transformer T1 is provided with a phototransistor 15b as a light receiving side element that is connected between the feedback terminal FB of the primary side control IC 13 and a ground point and receives a signal from the photodiode 15a. Yes. The primary side control IC 13 controls the ON time of the switching element SW1 according to the feedback voltage VFB to the feedback terminal FB.

  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 16 including a smoothing capacitor C0 is provided, and a voltage rectified and smoothed by the rectifying / smoothing circuit 16 is applied to the power supply voltage terminal VCC1 of the primary side 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 starting terminal VCC0 of the primary side control IC 13 via the diode D1 and the resistor R1. The primary side 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 Rsns is connected between the source terminal of the switching transistor SW1 and the ground point GND, and a connection node N1 between the switching transistor SW1 and the current detection resistor Rsns The resistor R2 is connected to the current detection terminal CS of the primary side control IC 13, and the voltage generated at the current detection resistor Rsns is applied to the current detection terminal CS of the primary side control IC 13 via the resistor R2. Yes. The primary-side control IC 13 controls the off timing of the switching element SW1 according to the voltage of the current detection terminal CS, that is, the change in the current flowing through the current detection resistor Rsns. Further, a capacitor C4 is connected between the current detection terminal CS and the ground point, and the input resistor R2 and the capacitor C4 constitute a low-pass filter that removes or reduces high-frequency components.

Note that the method of generating the control signal of the switching element SW1 based on the voltage of the current detection terminal CS and the voltage of the feedback terminal FB in the primary side control IC 13 of this embodiment is the same as that of a conventional general primary side control IC. Therefore, the illustration and description of the specific configuration of the internal circuit of the primary side control IC 13 are omitted.
In the AC-DC converter of the present embodiment, the resistance value of the current detection resistor Rsns is set to be optimal when the output voltage Vout on the secondary side is as small as 5V. A switching circuit 14 for switching the apparent resistance value of the current detection resistor Rsns is provided between the connection node N2 between the current detection terminal CS and the resistor R2 and the ground point.

FIG. 2 shows a specific circuit example of the switching circuit 14.
As shown in FIG. 2, in the switching circuit 14, a resistor R3 and a MOS transistor Q1 functioning as a switch are connected in series between a current detection terminal CS and a ground point. Further, in parallel with the smoothing capacitor C0 for smoothing the voltage induced in the auxiliary winding Nb and generating the operating voltage of the primary side control IC 13, between the cathode terminal of the rectifying diode D0 and the ground point GND. Connected voltage dividing resistors R4 and R5 are provided, and the potential of the connection node N3 of the resistors R4 and R5 is applied to the gate terminal of the switch MOS transistor Q1.
Note that the resistance ratio between the resistors R4 and R5 is set to such a value that the switch MOS transistor Q1 is not turned on by the potential of the node N3 when the output voltage Vout on the secondary side is small. Therefore, when the output voltage Vout is small, no current flows through the resistor R3, and the voltage generated at the current detection resistor Rsns is applied to the current detection terminal CS of the primary side control IC 13 as it is.

Next, the operation of the switch MOS transistor Q1 in the switching circuit 14 will be described.
As described above, an AC voltage having a magnitude proportional to the AC voltage induced in the secondary winding Ns is induced in the auxiliary winding Nb. Therefore, when the output level on the secondary side is switched and the output voltage Vout changes, the voltage induced in the auxiliary winding Nb also changes in proportion to this. The resistance ratio between the resistors R4 and R5 is set to such a value that the switch MOS transistor Q1 is not turned on by the potential of the node N3 when the output voltage Vout on the secondary side is small, so that the output voltage Vout is small. In some cases, Q1 is off. In this state, when the output level on the secondary side is switched to a higher level and the output voltage Vout increases, the voltage induced in the auxiliary winding Nb also increases.

  In this embodiment, the resistance ratio of the resistors R4 and R5 is set so that the switch MOS transistor Q1 is turned on by the potential of the node N3 when the output voltage Vout is changed to 12V. Therefore, a current flows through the resistor R3, and a voltage obtained by dividing the voltage of the current detection resistor Rsns by the resistance ratio of the resistors R2 and R3 is applied to the current detection terminal CS of the primary side control IC 13 to detect the current. The voltage (the voltage at the current detection terminal CS) becomes low. Therefore, by appropriately setting the resistance ratio of the resistors R2 and R3, the voltage of the current detection resistor Rsns applied to the current detection terminal CS can be adjusted, and the current detection resistor Rsns is indirectly optimized. A result equivalent to is obtained.

  In the present embodiment, the switching resistor 14 is provided by providing the input resistor R2 between the node N1 and the current detection terminal CS to which the voltage detected by the current detection resistor Rsns is input. It is possible to reduce the current flowing through the constituting resistor R3. That is, since the resistance value of the current detection resistor Rsns is set to be small in order to suppress power loss, the transistor R1 is turned on without providing the resistor R2, and the resistor R3 provided in parallel with the current detection resistor Rsns. When a voltage of a desired level is input to the current detection terminal CS by passing a current, the resistance value of the resistor R3 must be reduced, thereby generating a large switching noise when the Q1 is turned on / off. Resulting in. On the other hand, according to the configuration of the embodiment in which the resistor R2 is provided, the voltage input to the current detection terminal CS is determined by the resistance ratio of the two series resistors R2 and R3. By increasing the value, switching noise can be reduced by preventing a large current from flowing through the resistor R3, and the voltage input to the current detection terminal is determined by the resistance ratio of the two series resistors. Therefore, even if the resistance values of the resistance elements to be used vary, by setting the resistance ratio to be a predetermined value, the resistance adjustment elements (R2, R3) are expensive with high accuracy of the resistance value. The accuracy of the voltage input to the current detection terminal can be increased without using the.

Next, the secondary side control circuit 20 of the AC-DC converter of this embodiment will be described.
The AC-DC converter according to the present embodiment is an AC-DC converter compatible with the USB-PD specification of the USB standard, and is provided between the secondary-side filter coil L3 and the output terminal OUT1. A MOS transistor Q2 and an isolation coil L4 that function as a switch for cutting off or permitting the output of the electric power induced by the signal, and a communication chip 31 provided in the USB device 30 connected to the output terminal OUT1. A communication & control circuit 21 having a communication function for communication and a function for on / off control of the MOS transistor Q2 is provided.

  The communication & control circuit 21 may be composed of two or more ICs such as a communication chip, a decoder, and a CPU (microprocessor). By providing the isolation coil L4, as will be described later, when the communication is performed via the output terminal OUT1 via the USB-PD standard Vbus, the feedback voltage VFB by the communication signal (digital signal) is provided. The influence on can be reduced. Note that when the control signal is directly input to the communication & control circuit 21, the isolation coil L4 can be omitted.

Further, the secondary side control circuit 20 divides the output voltage Vout and divides the voltage by the series resistors R11 and R12 for generating the feedback voltage VFB supplied to the primary side control IC 13 and the resistors R11 and R12. An error amplifier 22a for current extraction that drives the photodiode 15a in response to the applied voltage and a diode D21 for preventing backflow are provided.
Of the voltage dividing resistors R11 and R12 for generating the feedback voltage VFB, adjusting resistors R13 and R14 are provided in parallel with the resistor R12. The adjusting resistors R13 and R14 are switches made of MOS transistors or the like. S13 and S14 are connected, and the switches S13 and S14 are configured to be controlled to be turned on or off by the communication & control circuit 21.

  Further, a second current extracting error amplifier 22b for driving the photodiode 15a, a backflow preventing diode D22, and a sense resistor Rsns2 for detecting an output current connected between the output terminal OUT2 and the ground point, The voltage converted by the sense resistor Rsns2 is input to the inverting input terminal of the error amplifier 22b via the resistor R10, and the reference voltage Vref is applied to the resistors R20 and R21 at the non-inverting input terminal of the error amplifier 22b. The voltage divided by is input. Further, adjustment resistors R23 and R24 are provided in parallel with the resistor R21, and switches S23 and S24 are connected to the adjustment resistors R23 and R24, and S23 and S24 are controlled to be turned on or off by the communication & control circuit 21. It is configured to be.

  Of the adjusting resistors, R13 and R14 are for adjusting output voltage, and R23 and R24 are for adjusting output current. Depending on the value of output voltage and output current required from the device receiving power supply, the switches The on / off states of S13, S14 and S23, S24 are determined. When one of S13 and S14 is turned on, the potential at the connection node of the voltage dividing resistors R11 and R12 decreases, and the potential of the feedback voltage VFB supplied to the primary side control IC 13 decreases, whereby the primary side control IC13. Can recognize that the required voltage has been switched, and drives the switching element SW1 to output the required voltage. In the primary circuit, the voltage induced in the auxiliary winding Nb changes as described above in response to the change in the potential of the feedback voltage, and the switch MOS transistor Q1 ( The apparent resistance value of the current detection resistor (Rsns) is switched by switching between the on and on states in FIG.

On the other hand, when one of the switches S23 and S24 is turned on, the potential of the connection node of the voltage dividing resistors R20 and R21, that is, the voltage of the non-inverting input terminal of the error amplifier 22b is lowered, and the feedback supplied to the primary side control IC 13 As the voltage VFB decreases, the primary side control IC 13 can recognize that the required current has been switched, and drives the switching element SW1 so that the required current is output.
In this embodiment, the primary circuit is a switch in the switching circuit 14 even when the current path of the output current adjusting resistors R23 and R24 is switched in the secondary control circuit 20 and the potential of the feedback voltage VFB changes. The constants of each circuit and element are set so that the MOS transistor Q1 (FIG. 2) is not switched on and off, that is, the apparent resistance value of the current detection resistor (Rsns) is not switched. Yes. The increase / decrease in the output current is because, unlike the increase / decrease in the output voltage, it is possible to design circuit constants such that the power efficiency does not change greatly even if switching without changing the resistance value of the current detection resistor (Rsns). is there.

Next, specific functions and operations of the communication & control circuit 21 will be described.
The secondary output terminal OUT1 of the AC-DC converter of this embodiment is connected to a V bus (VBUS) defined by the USB standard. Therefore, the communication & control circuit 21 is connected to the output terminal OUT1 via the coupling capacitor C11, and the communication chip 31 on the USB device side is also connected to the V bus terminal VBus via the coupling capacitor C12. It is configured to perform serial communication using signals.

When the communication & control circuit 21 detects that the USB device is connected to the output terminal OUT1, the communication & control circuit 21 communicates with the communication chip 31 using the communication function and acquires the voltage / current required by the USB device 30. To do. Based on the acquired value, the on / off states of the switches S13 and S14 are determined, and a signal for control is output. When the output voltage Vout reaches the required voltage, the MOS transistor Q2 is controlled to be turned on, and power is supplied to the USB device connected to the output terminal OUT1.
In the AC-DC converter of the present embodiment, by adopting the above-described configuration, for example, 5V / 2A (10W), 12V / 3A (36W), 12V / 5A (60W), 20V / 3A (60W) , 20V / 5A (100W) such as a plurality of output voltages / output currents can be selected and output.

Next, a modification of the AC-DC converter of the above embodiment will be described.
As shown in FIG. 4, the first modification is obtained by replacing the voltage dividing resistor R4 shown in FIG. 2 with a Zener diode D4. The rest of the configuration is the same as that of the AC-DC converter shown in FIG. 1, and the operation is almost the same as that of the AC-DC converter shown in FIG.

As shown in FIG. 5, the second modification is provided with two sets of switching circuits including voltage dividing resistors R4 and R5 and a switch MOS transistor Q2 shown in FIG. Note that the resistance ratio of the voltage dividing resistors R4 and R5 and the resistance ratio of the resistors R4 ′ and R5 ′ in the switching circuit 14 of FIG. 5 are set to different values. Further, the resistance values of the resistors R3 and R3 ′ are also set to different values.
As in this modification, by providing two sets of switching resistors for switching the adjustment resistor and the current path of the resistor, for example, when the output voltage level has three stages such as 5V, 12V, and 20V, The current detection voltage applied to the current detection terminal CS can be adjusted according to each output level, and there is an advantage that the same result as that obtained by optimizing the current detection resistor Rsns can be obtained.

Next, a second embodiment of the AC-DC converter according to the present invention will be described.
In the second embodiment, as shown in FIG. 6, between the diode bridge circuit 12 and the transformer T1, a power factor improving IC 41 and a switching element SW2 that is on / off controlled by the power factor improving IC 41. And a power factor correction circuit 40 including a current detection resistor Rs connected in series with the switching element SW2.
By providing the power factor correction circuit as in the present embodiment, for example, without switching the transformer according to the level of the output voltage, the power efficiency close to the AC-DC converter in which the transformer constant is optimally set. There is an advantage that can be obtained.

  The power factor improving circuit 40 operates the power factor improving circuit when the output power is low when the turn ratio of the transformer is designed so that the efficiency is high when the output power is large. When the transformer turns ratio is designed so that the efficiency is high when the output power is small, the power factor correction circuit may be operated when the output power is large. Thereby, the power efficiency of the converter can be increased while suppressing an increase in power consumption accompanying the provision of the power factor correction circuit.

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 diode rectification type circuit is illustrated as the secondary side rectification circuit of the transformer, but a synchronous rectification type circuit may be used as the secondary side rectification circuit.
In the above embodiment, the secondary control circuit has been described to acquire the value of the voltage to be output in communication with an external device using an AC signal via a coupling capacitor. Alternatively, a voltage value to be output by wireless communication may be acquired.

  Furthermore, the present invention is not limited to an AC-DC converter that switches and outputs a plurality of output voltages such as 5V, 12V, and 20V defined in the USB-PD specification as described above, and a multi-output AC-DC. It can be widely applied to DC converters in general.

12 Diode bridge circuit (rectifier circuit)
13 Primary side control circuit (Primary side control IC)
DESCRIPTION OF SYMBOLS 14 Switching circuit 15a Light emitting side diode of photocoupler 15b Light receiving side transistor of photocoupler 20 Secondary side control circuit 21 Communication & control circuit 30 USB device 31 Communication chip

Claims (5)

Transformer for voltage conversion, switching element for flowing current to the primary winding of the transformer, current detection element for detecting current flowing to the primary winding of the transformer, and conversion by the current detection element And a primary side control circuit for generating and outputting a drive pulse for controlling on and off of the switching element by inputting a voltage and a feedback voltage from a secondary side of the transformer, and the primary side based on an output voltage A secondary side circuit including a feedback voltage generating means for generating a feedback voltage to be supplied to the control circuit;
The transformer includes an auxiliary winding that induces a voltage having the same polarity as the secondary winding,
On the primary side of the transformer,
A resistance element connected between a current detection terminal of the primary side control circuit to which a voltage converted by the current detection element is input, and a voltage extraction side terminal of the current detection element;
Switching means comprising one or more resistance adjusting elements connected in parallel with the current detection element via the resistance element;
The switching means switches the current path of the resistance adjusting element according to the potential of the voltage induced in the auxiliary winding, and changes the voltage input to the primary side control circuit. Type DC power supply. The switching means is
A voltage dividing circuit connected between the output terminal of the rectifying / smoothing circuit connected to one terminal of the auxiliary winding and a ground point;
Switch means connected in series with the resistance adjusting element and turned on or off by a voltage divided by the voltage dividing circuit,
Depending on the voltage value to be output from the secondary side of the transformer,
The switch means is turned on when the voltage to be output from the secondary side is the first value, and the switch means is turned off when the voltage to be output from the secondary side is the second value. The insulated DC power supply device according to claim 1, wherein a voltage dividing ratio of the voltage dividing circuit is set. The feedback voltage generating means includes
A voltage dividing resistor element in series for dividing the voltage on the secondary side of the transformer;
One or two or more resistance adjusting elements connected in parallel with any one of the voltage dividing resistance elements, and secondary-side switching means connected to the resistance adjusting elements, and the voltage dividing resistance elements Generating a feedback voltage to be supplied to the primary side control circuit based on the compressed voltage;
2. The secondary side switching unit switches the current path of the resistance adjusting element based on an external signal, and changes the feedback voltage supplied to the primary side control circuit. 2. The insulated DC power supply device according to 2. Comprising two or more resistance adjusting elements,
The secondary side switching means is configured to be able to select and output any one of a plurality of voltages by switching current paths of the two or more resistance adjusting elements based on an external signal. The insulated direct-current power supply device according to claim 3. In the secondary side circuit, a capacitive element connected between a communication means for transmitting / receiving a signal to / from an external device and a terminal for outputting a DC voltage generated in the secondary side circuit, Is provided,
The insulated DC power supply device according to claim 4, wherein the communication unit is configured to be able to communicate with an external device through an AC signal through the capacitive element.

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