JP2008054475A - Astable-insulating dc-dc converter and power supply unit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To surely protect converter and load such as synchronous rectification elements by detecting the state of protective operation against overcurrent or the like, as an astable-insulating DC-DC converter. <P>SOLUTION: The astable-insulating DC-DC converter comprises first and second power switches 3 and 4 on the primary side of a transformer 6. A control IC5 complementally turns on/off the first and second power switches 3 and 4 at on-duty ratio of about 50% in a normal condition. The control IC5 decreases the on-duty ratio of the power switches 3 and 4 when a dropping voltage of a current detection resistor 35 exceeds a threshold value. An integration circuit 37 drops its output voltage if the dropping of the on-duty ratio continues for specified hours to turn on transistors 22 and 23. If the state continues for specified hours, an FET28 is turned on by a charged voltage of a capacitor 26, and the control IC5 stop switching operation. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a non-stable insulated DC-DC converter, and more particularly to a non-stable insulated DC-DC converter with improved functions in protection operation against overcurrent and surge voltage, and a power supply device including the same.

  2. Description of the Related Art Conventionally, a DC-DC converter that converts a voltage of a DC (direct current) power supply is provided with a protection circuit that performs a protection operation against an overcurrent or a protection operation against an input surge voltage as disclosed in Patent Document 1, for example. ing.

  Here, the circuit of the DC-DC converter shown in Patent Document 1 is shown in FIG. The DC-DC converter includes a transformer 52, a latch stop unit 100, a PWM modulation unit 90, a power supply selection unit 91, a first rectification unit 93, a first smoothing unit 94, a second rectification unit 95, and a second The smoothing unit 96 is configured. The latch stop unit 100 includes a transistor 75, an FET 76, resistors 77, 78 and 79, and a capacitor 80.

  The power source selection unit 91 includes an FET 55, a Zener diode 58, and resistors 56 and 57.

The operation of the DC-DC converter shown in FIG. 1 is as follows.
First, at the time of start-up, the sub power supply voltage is not supplied from the second smoothing unit 96, and the gate potential of the FET 55 is fixed to a predetermined Zener voltage by the Zener diode 58. Therefore, the FET 55 is turned on and the resistor 56 is turned on. The power supply voltage of the DC power supply 51 is supplied to the power supply terminal VCC of the PWM control IC 54 through the power supply terminal VCC. The PWM control IC 54 outputs a PWM-controlled signal from the signal output terminal (OUT), and the main switch 53 that interrupts the current flowing through the primary winding 52a of the transformer 52 is interrupted by this signal.

  At this time, the transistor 75 is turned on via the resistor 79, and the collector current flows. However, the gate potential of the FET 76 does not rise until the FET 76 is turned on due to the time constant determined by the resistor 77 and the capacitor 80. , FET 80 maintains the off state.

  On the other hand, the electromotive voltage generated in the secondary winding 52 b by the current flowing through the primary winding 52 a is rectified by the first rectification unit 93, smoothed by the first smoothing unit 94, and supplied to the load 63.

  Further, the voltage induced in the tertiary winding 52c is rectified by the second rectification unit 95, smoothed by the second smoothing unit 96, supplied to the source of the FET 55 via the terminal Q, and the power source of the PWM control IC 54 Supplied as voltage.

  As a result, the gate potential with respect to the source of the FET 55 is lowered, the FET 55 is turned off, and the PWM control IC 54 is operated by the output voltage of the second smoothing unit 96.

  When the start-up is completed in this way and a steady state is reached, no current flows through the resistors 56 and 79, and the transistor 75 is turned off. Therefore, the FET 76 is also kept in the cutoff state.

When the output voltage of the secondary circuit falls below a predetermined voltage, such as when the load 63 is short-circuited during such a steady state, the output voltage of the second smoothing unit 96 is lowered in proportion thereto. As a result, when the potential difference between the source and gate of the FET 55 increases, the FET 55 is turned on, and a current flows through the resistors 56 and 79. As a result, the transistor 75 is turned on, and when the output voltage drop state continues beyond the time constant determined by the resistor 77 and the capacitor 80, the FET 76 is turned on, and the operation control input terminal ( OFF) becomes almost the ground potential, the PWM control IC 54 stops its operation, and the main switch 53 is kept off. As a result, the power supply to the load 63 is also cut off, and the output voltage of the second smoothing unit 96 remains lowered, so that the on state of the transistor 75 is maintained and the circuit stops latching.
Japanese Patent No. 3397189

  By the way, in a non-stable insulated DC-DC converter, when driving a synchronous rectifier element with a voltage generated in a coil of a transformer, primary power switches are complementarily turned on and off at an on-duty ratio of approximately 50%. In steady operation, the synchronous rectification element is turned on almost throughout the rectification period. However, when the on-duty ratio is reduced due to overcurrent protection, input surge voltage protection, or overheat protection, it is turned on only in one part of the rectification period, and in other parts, the parasitic diode of the synchronous rectifier element is energized. In such an operation mode, since the conduction loss of the synchronous rectifier element is large, there is a possibility that the synchronous rectifier element will be overheated and destroyed when energized continuously. In the case of on-duty ratio reduction due to overcurrent, continuation of the overcurrent state is a heavy burden on other converter components and loads, so if the on-duty ratio reduction state by overcurrent protection continues for a certain period or longer, switching There is a need to protect the converter components such as the synchronous rectifier element and the load by latching the operation or shifting to a hiccup mode (operation mode in which the operation is temporarily stopped and restarted after a predetermined time).

  However, in the non-stable insulated DC-DC converter, the operation of detecting a drop in the output voltage during the overcurrent protection operation and stopping the latch as disclosed in Patent Document 1 is impossible. That is, in the non-stable insulation type DC-DC converter, the output voltage changes according to the change of the input voltage, so the rectified smoothing voltage of the transformer coil also changes according to the change of the input voltage. Therefore, even if the rectified and smoothed voltage of the transformer coil is compared with the reference voltage, the reduced state of the on-duty ratio cannot be detected.

  Accordingly, an object of the present invention is to provide a stable operation that detects a protective operation state against an overcurrent or the like and reliably protects a converter component such as a synchronous rectifier and a load while being an unstable stable DC-DC converter. An object of the present invention is to provide an insulated DC-DC converter and a power supply device including the same.

The non-stable insulated DC-DC converter of the present invention comprises at least two first and second power switches on the primary side of the transformer, and the first and second input voltages and output currents are within a steady range. The on-duty ratio of each of the power switches is complementarily turned on and off at approximately 50%, and a voltage substantially proportional to the input voltage is output.
A protection circuit for detecting an abnormal increase in conversion power or an abnormal operation of the circuit to reduce the on-duty ratio of the first and second power switches;
An integrating circuit for integrating the drive signal of the first or second power switch;
A continuous stop circuit that continuously stops (latches stop) the switching operation of the first and second power switches when the output voltage of the integrating circuit falls below a predetermined threshold;
It is characterized by having.

  Moreover, it replaces with the said continuous stop circuit, and the temporary stop circuit which makes the mode (hiccup mode) after which switching operation | movement of the said 1st, 2nd power switch stops temporarily is provided.

  In addition, the non-stable insulated DC-DC converter of the present invention includes a synchronous rectifier circuit including a synchronous rectifier element driven by a voltage generated in the coil of the transformer on the secondary side of the transformer.

  The power supply apparatus according to the present invention receives the output voltage by feedback control for detecting the output voltage by inputting the non-stable isolated DC-DC converter and an intermediate bus voltage that is an output voltage of the non-stable isolated DC-DC converter. And a stable non-insulated DC-DC converter that is stabilized.

  The power supply device of the present invention includes a stable non-insulated DC-DC converter that stabilizes an output voltage by feedback control that detects the output voltage, and an intermediate bus voltage that is an output voltage of the stable non-insulated DC-DC converter. And the above-described unstable insulation type DC-DC converter.

  According to the present invention, although it is a non-stable insulated DC-DC converter, a protection operation state against an overcurrent or the like can be detected, and at the time of the protection operation, a so-called latch stop mode or a hiccup mode is entered. Thus, it is possible to reliably protect the converter parts and the load.

  Further, by forming a power supply device by cascading the unstable stable DC-DC converter and the stable unstable DC-DC converter according to the present invention, the unstable stable DC-DC converter and the stable unstable insulation type are configured. Utilizing the features of each DC-DC converter, the overall efficiency can be improved. For example, a power supply device that drives a plurality of loads by outputting an intermediate bus voltage from a first-stage DC-DC converter and operating a plurality of second-stage DC-DC converters by inputting the intermediate bus voltage. Can improve the reliability.

<< First Embodiment >>
A non-stable insulated DC-DC converter and a power supply device including the same according to a first embodiment of the present invention will be described with reference to FIGS.

  FIG. 2 is a diagram showing the configuration of two types of power supply devices according to the present invention. In the example of FIG. 2A, the first-stage non-stable insulated DC-DC converter 202 receives the DC input power supply 201 and outputs a voltage transformed at a predetermined transformation ratio as the voltage of the intermediate bus 205. The second-stage stable non-insulated DC-DC converter 203 receives the intermediate bus voltage and supplies a stable DC power supply voltage to the load device 204.

  In the example of FIG. 2B, the first-stage stable non-insulated DC-DC converter 203 receives the DC input power supply 201 and outputs a predetermined stabilized DC voltage to the intermediate bus 205. The second stage non-stable insulated DC-DC converter 202 transforms the voltage of the intermediate bus at a predetermined transformation ratio and supplies it to the load device 204.

  In particular, in the type shown in FIG. 2A, the first-stage non-stable insulation type DC-DC converter 202 is a power supply circuit for communication equipment mounted on a utility pole, for example. Since the intermediate bus between the DC converter 202 and the second-stage stable non-insulated DC-DC converter 203 is relatively long and there is a voltage drop in the line, the non-stable isolated DC-DC converter 202 is simply Used as a converter for voltage conversion (voltage drop). The stable non-insulated DC-DC converter 203 is provided in the load device 204 or on the side close to the load device, and supplies a stable power supply voltage to the load device.

  FIG. 3 is a circuit diagram showing a specific configuration of the non-stable insulated DC-DC converter 202 shown in FIG. The non-stable insulated DC-DC converter 202 includes a transformer 6, first and second power switches 3 and 4, a control IC, an integration circuit 37, a latch stop circuit 38, an auxiliary rectification smoothing circuit 39, and a synchronous rectification circuit 40. , And an output filter 41. In the configuration shown in FIG. 2A, the load 13 in FIG. 3 corresponds to the stable non-insulated DC-DC converter 203 and the load device 204.

  At both ends of the DC input power supply 1 (between the + terminal and the − terminal), first and second power switches 3 and 4 (hereinafter, the power switch 3 is a “high side switch” and the power switch 4 is a “low side switch”). And a series circuit of resistors 35 for current detection. Similarly, capacitors 7 and 8 are connected to both ends of the DC input power source 1. One end of the primary coil 6-1 of the transformer 6 is connected to the connection point between the high side socks 3 and the low side switch 4, and the other end is connected to the connection point between the capacitors 7 and 8. Thus, a half bridge circuit is configured. The control IC 5 turns on and off the high-side switch 3 and the low-side switch 4 in a complementary manner with approximately 50% duty in accordance with output signals from the high-side switch drive terminal 5-4 and the low-side switch drive terminal 5-5.

  The auxiliary rectifying / smoothing circuit 39 is composed of a diode 16 and a capacitor 15 connected to the quaternary coil 6-4 of the transformer 6. The series regulator 14 stabilizes the output voltage of the auxiliary rectifying / smoothing circuit 39 and supplies power to the control IC 5. A control voltage is supplied to the terminal 5-1.

The operation of the half bridge circuit and the synchronous rectifier circuit 40 is as follows.
When the high side switch 3 is turned on, a current flows through a path of the positive terminal of the DC input power source 1 → the high side switch 3 → the transformer primary coil 6-1 → the capacitor 8 → the negative terminal of the DC input power source 1. As a result, an induced voltage is generated in the transformer tertiary coil 6-3, and a current flows through a path of -output of the converter → synchronous rectifier 9 → transformer tertiary coil 6-3 → choke coil 11 → plus output of the converter.

  When the low-side switch 4 is turned on, a current flows through a path of the positive terminal of the DC input power source 1 → the capacitor 7 → the transformer primary coil 6-1 → the low-side switch 4 → the negative terminal of the DC input power source. As a result, an induced voltage is generated in the transformer secondary coil 6-2, and the converter -output → synchronous rectification element (commutation element) 10 → transformer secondary coil 6-2 → choke coil 11 → converter + output terminal path Current flows.

  The synchronous rectifying elements 9 and 10 are driven by the induced voltage of the transformer quinary coil 6-5. The resistors 33 and 34 adjust the DC voltage, and the diodes 29, 30, 31 and 32 distribute the induced voltage of the transformer quaternary coil 6-5 to the gates of the synchronous rectifier elements 9 and 10 with AC0V as a boundary. Works. The output filter 41 composed of the choke coil 11 and the capacitor 12 acts so as to suppress a drop in the output voltage during a period in which both the high side switch 3 and the low side switch 4 are turned off. Since the sum of the on-duty ratios of the high side switch 3 and the low side switch 4 is close to 100%, the inductance of the choke coil 11 can be set small.

Next, operations of the integration circuit 37 and the latch stop circuit 38 will be described.
For example, when an overcurrent flows through the converter due to a short circuit of the load 13 or the like, the drop voltage of the current detection resistor 35 increases, and when the voltage exceeds a predetermined threshold, the control IC 5 causes the high side switch 3 and the low side switch to The on-duty ratio of the switch 4 is reduced. That is, it becomes an overcurrent protection state.

  4A is a waveform diagram of each part of the circuit in a steady state where the high-side switch 3 and the low-side switch 4 operate at an on-duty ratio of approximately 50%, and FIG. 4B is a waveform diagram in the overcurrent protection state. is there. In the steady state, as shown in (a), the gate voltages of the low-side switch 4 and the high-side switch 3 sandwich a predetermined dead time (a period for preventing the high-side switch 3 and the low-side switch 4 from being simultaneously turned on). The high-level switch 3 and the low-side switch 4 are turned on and off complementarily at an on-duty ratio of approximately 50%. As described above, since the synchronous rectifier elements 9 and 10 are driven by the induced voltage of the transformer quinary coil 6-5, the synchronous rectifier elements 9 and 10 are turned on and off in synchronization with the on and off of the high side switch 3 and the low side switch 4.

  When the overcurrent protection is activated, both the on-duty ratios of the high-side switch 3 and the low-side switch 4 are reduced. Only during the ON period, the gate drive signal is supplied. Therefore, in other periods, the choke coil 11 is turned off and the current of the choke coil 11 flows via the parasitic diodes of the synchronous rectifier elements 9 and 10. A large conduction loss occurs due to the forward voltage drop of the parasitic diode.

  The integrating circuit 37 shown in FIG. 3 includes a resistor 17 and a capacitor 18, and integrates the gate voltage (drive signal) of the low-side switch 4. The peak value of the low-side switch drive signal is substantially equal to the operating voltage VCC of the control IC 5, and the integrated voltage Vint is proportional to VCC and the on-duty ratio D of the low-side switch drive signal. That is, the following equation is established.

Vint = D · VCC
Since the VCC is stabilized by the series regulator 14, the on-duty ratio D can be detected from Vint after all.

  A reference voltage obtained by dividing VCC by resistors 19 and 20 is applied to the base of the transistor 22, and Vint is input to its emitter. When the emitter potential Vint of the transistor 22 becomes lower than the base-emitter saturation voltage compared to the base potential, the transistor 22 is turned on. That is, the transistor 22 and the resistors 19 and 20 constitute a comparison circuit.

  When the on-duty ratio D decreases and Vint decreases due to an overcurrent protection operation or the like, and the base-emitter voltage of the transistor 22 reaches the on-voltage, the transistor 22 is turned on and a current flows through the resistor 21. . As a result, the transistor 23 is also turned on. When the transistor 23 is turned on, the capacitor 26 is charged according to the time constant of the resistor 24 and the capacitor 26. When the charging voltage of the capacitor 26 (gate voltage of the FET 28) reaches the threshold voltage, the FET 28 is turned on. When the FET 28 is turned on, the voltage at the on / off control terminal 5-2 of the control IC 5 decreases, and the control IC 5 stops the switching operation.

  Since the N-channel MOSFET 28 and the PNP transistor 23 constitute a thyristor, the stop state is latched. To release this latch stop state, both ends of the capacitor 26 may be short-circuited to discharge the accumulated charge.

  At the time of starting the converter, for the soft start operation by the control IC, the on-duty ratio of the high-side switch 3 and the low-side switch 4 is gradually increased to increase the on-duty ratio to almost 50%. However, if the time constants of the resistor 24 and the capacitor 26 are set sufficiently longer than the soft start period, the problem that the FET 28 is turned on and the latch is stopped at the soft start time does not occur.

  As described above, it is possible to detect a protection operation state in which the on-duty ratio of the power switch on the primary side of the transformer is reduced in spite of being unstable and prevent the reduced state of the on-duty ratio from continuing for a certain period of time. . This reliably prevents overheating and destruction of the converter components and load.

<< Second Embodiment >>
FIG. 5 is a circuit diagram showing a configuration of an unstable stable DC-DC converter according to the second embodiment. In the first embodiment, the control IC 5 is configured to stop latching when detecting a continuous decrease in the on-duty ratio of the power switch on the primary side of the transformer for a certain period of time. However, in the second embodiment, It is configured to operate in a so-called hiccup mode in which it is temporarily stopped and then restarted. 5 is different from the circuit shown in FIG. 3 in that a temporary stop circuit 43 is provided in place of the latch stop circuit 38. The temporary stop circuit 43 includes resistors 19, 20, 21, a transistor 22, and a monostable multivibrator 42. The operation of the temporary stop circuit 43 is as follows.

  When the on-duty ratio of the high-side switch 3 and the low-side switch 4 is reduced by the protection operation of the control IC 5, the charging voltage of the capacitor 18 of the integrating circuit 37 is lowered and the transistor 22 is turned on. When the transistor 22 is turned on, the control terminal voltage of the monostable multivibrator 42 becomes low level, and the output voltage is made low level for a certain time. The control IC 5 stops the switching operation while the voltage of the on / off control terminal 5-2 is at the low level. Since this switching operation is paused for a period during which the monostable multivibrator 42 is operated and then returned, a hiccup mode protection operation can be realized as a result.

  In both the first and second embodiments, the half-bridge circuit is configured as the power conversion circuit. However, the present invention is not limited to this and is applicable to other topologies such as push-pull, full-bridge, and two-stone forward circuits. Is possible.

  In addition, the on-duty ratio is reduced not only during overcurrent protection as a protective operation, but also when, for example, a transient surge voltage is applied to the input of the unstable stable DC-DC converter, or when the unstable stable DC-DC A circuit configuration that reduces the on-duty ratio when the temperature of a specific part of the DC converter exceeds a reference value may be employed. For this purpose, a circuit for detecting the application of a surge voltage or a circuit for detecting an overheated state of a specific part of the unstable-stable DC-DC converter is provided, and the voltage switch of the voltage switch is received in response to a detection signal from these circuits. A function for reducing the on-duty ratio may be provided in the control IC.

1 is a circuit diagram of a DC-DC converter disclosed in Patent Document 1. FIG. It is a block diagram which shows the structure of the power supply device which concerns on 1st Embodiment. 1 is a circuit diagram of a non-stable insulated DC-DC converter according to a first embodiment. It is a wave form diagram of each part of the converter. It is a circuit diagram of the unstable stable type DC-DC converter which concerns on 2nd Embodiment.

Explanation of symbols

1 ... DC input power supply 3 ... Primary side power switch (high side switch)
4 ... Primary side power switch (low side switch)
5 ... Control IC
5-1 ... Power supply terminal 5-2 ... On / off control terminal 5-3 ... Ground terminal 5-4 ... High side switch drive terminal 5-5 ... Low side switch drive terminal 5-6 ... Overcurrent protection terminal 6 ... Transformer 6 -1 ... primary coil 6-2 ... secondary coil 6-3 ... tertiary coil 6-4 ... quaternary coil 6-5 ... quintic coil 9, 10 ... synchronous rectifier 11 ... choke coil 13 ... load 14 ... Series regulator 37 ... Integral circuit 38 ... Latch stop circuit 39 ... Auxiliary rectifying / smoothing circuit 40 ... Synchronous rectifier circuit 41 ... Output filter 42 ... Monostable multivibrator 43 ... Temporary stop circuit 201 ... DC input power source 202, 212 ... Unstable insulation type DC-DC converter 203 ... Stable non-insulated DC-DC converter 204 ... Load device 205 ... Intermediate bus

Claims (5)

At least two first and second power switches are provided on the primary side of the transformer, and the on-duty ratio of the first and second power switches is approximately 50% under a steady range of input voltage and output current. In a non-stable isolated DC-DC converter that is complementarily turned on / off and outputs a voltage approximately proportional to the input voltage,
A protection circuit for detecting an abnormal increase in conversion power or an abnormal operation of the circuit to reduce the on-duty ratio of the first and second power switches;
An integrating circuit for integrating the drive signal of the first or second power switch;
A continuous stop circuit for continuously stopping the switching operation of the first and second power switches when the output voltage of the integrating circuit is below a predetermined threshold for a certain period of time;
A non-stable insulated DC-DC converter. At least two first and second power switches are provided on the primary side of the transformer, and the on-duty ratio of the first and second power switches is approximately 50% under a steady range of input voltage and output current. In a non-stable isolated DC-DC converter that is complementarily turned on / off and outputs a voltage approximately proportional to the input voltage,
A protection circuit for detecting an abnormal increase in conversion power or an abnormal operation of the circuit to reduce the on-duty ratio of the first and second power switches;
An integrating circuit for integrating the drive signal of the first or second power switch;
A temporary stop circuit for temporarily stopping the switching operation of the first and second power switches when the state in which the output voltage of the integrating circuit is below a predetermined threshold value continues for a certain period of time;
A non-stable insulated DC-DC converter.   3. The non-stable insulated DC-DC converter according to claim 1, further comprising a synchronous rectification circuit including a synchronous rectification element driven by a voltage generated in a coil of the transformer on a secondary side of the transformer. The non-stable insulated DC-DC converter according to claim 1, 2, or 3,
A stable non-insulated DC-DC converter that receives an intermediate bus voltage that is an output voltage of the non-stable insulated DC-DC converter and stabilizes the output voltage by feedback control that detects the output voltage;
A power supply device comprising: A stable non-insulated DC-DC converter that stabilizes the output voltage by feedback control that detects the output voltage;
The non-stable insulated DC-DC converter according to claim 1, 2 or 3, wherein an intermediate bus voltage that is an output voltage of the non-insulated DC-DC converter is used as an input power source.
A power supply device comprising:

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