JPH08103075A - Semiconductor integrated circuit device for insulated switching power supply - Google Patents

Abstract

PURPOSE: To prevent a break of parts such as a rectifier diode due to short circuit of a secondary wiring of a transformer or short circuit of an auxiliary winding. CONSTITUTION: A switching element 1 at the primary side of a transformer 30 is controlled by a PWM control circuit 12 or the like. For feeding to the PWM control circuit 12 or the like, a power supply input terminal 2A, to which a voltage of an AC power supply 3 is applied after rectifying and smoothing, and a power supply input terminal 2B, to which a voltage of an auxiliary winding 5 of a transformer 30 is applied, are respectively provided. And, at the time of starting, a drive current is supplied from a power supply input terminal 2A to PWM control circuit 12 and the like and, when the voltage of the auxiliary winding 5 exceeds a predetermined voltage, the supply of a drive current from the first power supply input terminal 2A is stopped, and a drive current is supplied from a power supply input terminal 2B to the PWM control circuit 12 and the like. Also, if the voltage of the auxiliary winding 5 drops below the predetermined voltage value, then the switching element 1 performs a intermittent operation.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor integrated circuit device for an insulation type switching power supply device.

[0002]

2. Description of the Related Art In recent years, electronic devices having a rechargeable power source have been widely used, and most of the power sources used as chargers carry out constant current charging. An insulated switching power supply device is shown in FIG. 4 as an example of the constant current charging circuit. As shown in FIG. 4, this insulation type switching power supply device rectifies and smoothes the AC voltage of the AC power supply 3b by the rectification bridge 25b and the smoothing capacitor 26b, and the obtained DC voltage is supplied from the MOSFET to the primary winding of the transformer 30b. It is adapted to be applied intermittently via the switching element 1b. Then, the induced voltage in the secondary winding of the transformer 30b is applied to the diode 22b and the smoothing capacitor 28b.
The DC voltage is supplied to the load after being rectified and smoothed by.

At this time, the switching element 1b is controlled by the control circuit 2b, and its operating power is supplied from the rectifying bridge 25b at the time of starting, but the transformer 30b.
When the induced voltage of the auxiliary winding 5b exceeds a certain value, the induced voltage of the auxiliary winding 5b is supplied from the auxiliary winding rectifying / smoothing circuit 33b including a diode and a smoothing capacitor.

Further, in order to make the current supplied to the load a constant current, a secondary side current detecting resistor 39 is inserted in the power feeding path from the secondary winding of the transformer 30b to the load, and the secondary side current is detected. The voltage drop of the detection resistor 39 is compared with the reference voltage 41 output from the reference voltage generation circuit 40 including a Zener diode and a resistor with the operational amplifier 27b, and the difference signal between the two voltages is fed back to the control circuit 2b via the photocoupler 9b. are doing.

Here, the feedback operation will be described in detail. The secondary side current of the transformer 30b is detected as a voltage by the secondary side current detection resistor 39, this voltage is compared with the reference voltage 41 created by the reference voltage creating circuit 40, and control is performed so that both are equal. Is going. That is, when the voltage of the secondary-side current detection resistor 39 becomes higher than the reference voltage 41, the function of reducing the on-duty of the switching element 1b works, thereby reducing the secondary-side current and applying negative feedback. Has become.

In order to apply this negative feedback, it is necessary to transmit the feedback signal on the secondary side to the primary side. At that time, in order to electrically insulate the primary side and the secondary side, as described above. The photo coupler 9b is used. Also, in order to detect the current on the secondary side and convert this into a photocoupler signal,
The operational amplifier 27b is used. This operational amplifier 27
As the operation of b, when the output current increases, the operational amplifier 2
When the negative input voltage of 7b rises and becomes higher than the positive input voltage, the output of the operational amplifier 27b falls, a current flows through the photodiode 9b, and a current signal is transmitted to the primary side. As the photocoupler current increases, the control circuit 2b on the primary side
In the above, the operation of reducing the on-duty of the switching element 1b works to reduce the secondary side output current.

FIG. 5 shows a specific example of the control circuit 2b.
An example of a circuit in which the on-duty of the switching element 1b is controlled by changing the photocoupler current has been shown. A reference voltage of 1.25 V is applied to the positive input of the error amplifier 48. Therefore, the negative input terminal 42 of the error amplifier 48 is controlled to be 1.25V. That is, since the negative input terminal of the error amplifier 48 is constant at 1.25V, if the current of the photocoupler 9b increases,
The output voltage 46 of the error amplifier 48 must be low. The output voltage 46 of this error amplifier 48 is input to the negative input of the comparator 44, and the positive input terminal 45
A triangular wave 45 that rises and falls between 1.25 V and 2.3 V is input to the.

Here, the comparator 44 compares the output of the error amplifier 48 with the triangular wave 45 and transmits the information signal thereof to the logic circuit 49. The switching element 1b has the upward slope of the triangular wave 45 and the comparator. When the output of 44 is "0", it is turned on. Therefore, when the photocoupler current increases and the output voltage 46 of the error amplifier 48 decreases as shown in FIG. 6A, the voltage of the triangular wave 45 is lower than the output voltage 46 of the error amplifier 48 in the upward slope of the triangular wave 45. The period is shortened, the ON period of the switching element 1b, that is, the ON duty is reduced, and the waveform 47 of FIG. 6B is obtained.

[0009]

In the conventional circuit shown in the preceding paragraph, when the secondary side constant current control is performed and the secondary side load is in an overload state or a load short circuit occurs, If the output current on the secondary side always keeps the maximum value or if the output voltage on the secondary side drops too much, the operational amplifier 27b detects the secondary side current and supplies a photodiode current.
Is stopped, and on-duty control of the switching element 1b is no longer effective.

This imposes a burden on the secondary side rectifying diode 22b and the like, and if the burden is too large, it causes damage. In addition, when a short-circuit state occurs between the auxiliary winding 5b of the transformer 30b and the ground line, a large current also flows in this line, and a rectifying diode (in the auxiliary winding rectifying / smoothing circuit 33b) of the auxiliary winding line flows. Also becomes a burden, and in this case too large a burden leads to destruction.

Therefore, it is an object of the present invention to prevent destruction of parts such as a rectifying diode due to a short circuit of a secondary winding of a transformer or a short circuit of an auxiliary winding, and enhance the safety of an insulated switching power supply device. An object is to provide a semiconductor integrated circuit device for an insulation type switching power supply device.

[0012]

A semiconductor integrated circuit device for an insulation type switching power supply device of the present invention comprises a control circuit for controlling a switching element connected to a primary winding of a transformer of the insulation type switching power supply device, and an alternating current It has a first power supply input terminal to which a voltage obtained by rectifying and smoothing the AC voltage of the power supply is applied, and a second power supply input terminal to which the voltage of the auxiliary winding of the transformer is applied. When the drive current is supplied from the terminal to the control circuit and the voltage of the auxiliary winding becomes equal to or higher than the predetermined first voltage, the supply of the drive current from the first power supply input terminal is stopped and the drive current is supplied from the second power supply input terminal to the control circuit. And has a second function of intermittently switching the switching element when the voltage of the auxiliary winding falls below the second voltage equal to or higher than the first voltage.

That is, according to the present invention, in the insulated switching power supply device, the auxiliary winding voltage of the transformer is detected, and when the voltage becomes equal to or lower than the specified value, that is, equal to or lower than the second voltage, the switching element is intermittently operated. Switch operation. The auxiliary winding voltage is proportional to the secondary output voltage, so if the secondary load is short-circuited and the secondary voltage drops, the auxiliary winding voltage drops. The switching operation is performed. When the auxiliary winding is short-circuited with the ground line, the auxiliary winding voltage drops, and the switching element also operates intermittently. The intermittent operation is an operation in which a period in which a switching element performs a switching operation at a normal switching frequency and a period in which the switching element is completely stopped are alternately repeated at a constant cycle.

[0014]

According to the structure of the present invention, when the secondary load of the transformer is short-circuited, the switching element intermittently performs the switching operation, so that the power supply to the secondary side of the transformer is reduced during the intermittent switching operation. Will be done. This also reduces the power loss in the rectifier diode on the secondary side of the transformer. By reducing the power loss,
Heat generation in the rectifier diode on the secondary side is reduced, and damage to the rectifier diode can be avoided. When the auxiliary winding and the ground line are short-circuited, a short-circuit current flows in the rectifier diode of the auxiliary winding.At this time as well, the switching element performs intermittent switching operation, so during the intermittent switching operation, The power loss in the rectifying diode of the auxiliary winding is reduced, and heat generation is suppressed. That is, by taking the means of the present invention, it is possible to avoid the risk of ignition from the components when a failure occurs in the insulated switching power supply device,
The safety of the power supply can be increased.

[0015]

FIG. 1 is a block diagram of a semiconductor integrated circuit device for an insulating type switching power supply device for controlling the primary side of an insulating type switching power supply device used as a constant current charging type power supply device as an example of the embodiment of the present invention. 2 shows an example of a circuit in the semiconductor integrated circuit device for an insulation type switching power supply device embodying the present invention. In this section,
The embodiment will be described with reference to these drawings.

In the embodiment shown in FIG. 1, a switching element 1 composed of a MOSFET and a BiC as a control circuit thereof are provided.
In the semiconductor integrated circuit device 2 for an insulating type switching power supply device in which a MOS circuit is mounted in the same chip, the AC voltage of the AC power supply 3 on the primary side of the insulating type switching power supply is rectified and smoothed by the rectifying bridge 25 and the smoothing capacitor 26. Part 4
And a voltage obtained by rectifying / smoothing the voltage of the auxiliary winding 5 by the auxiliary winding rectifying / smoothing circuit 33 are applied to the first and second power supply input terminals 2A and 2B, respectively. 25 and smoothing capacitor 26 for rectification
A control circuit, for example, a PWM, is applied to the semiconductor integrated circuit device 2 for the isolated switching power supply device by the voltage of the smoothed portion 4.
After supplying the drive current for driving the control circuit 12 and the like, after starting,
That is, when the auxiliary winding voltage becomes higher than a predetermined voltage, the rectifying bridge 25 and the smoothing capacitor 26 rectify /
The voltage application from the smoothed portion 4 is stopped, and the control circuit is driven in the semiconductor integrated circuit device 2 for the isolated switching power supply device by the voltage obtained by rectifying and smoothing the voltage of the auxiliary winding 5 by the auxiliary winding rectifying / smoothing circuit 33. Drive current is supplied. Switching the power supply path in this manner is based on the function of the pre-regulator circuit described below.

A pre-regulator circuit (corresponding to the first function in the claims) for producing a stabilized voltage 6 for the power supply of an internal circuit is provided in the semiconductor integrated circuit device 2 for an insulating type switching power supply device. 7, a bandgap circuit that creates an internal reference voltage, an oscillator 8 that creates the oscillation frequency (rectangular wave, clock pulse, sawtooth wave) of the switching element 1, and error amplifiers 10A and 10B that perform PWM control with the current of the photocoupler 9, Comparator 1
1 and the like, a PWM control circuit 12, a timer circuit 13 for intermittently performing a switching operation of the switching element 1 when the current of the photocoupler 9 is exhausted, a switching element 1
Overcurrent protection circuit 14, secondary side overvoltage protection circuit 1
5, a stabilized power supply voltage drop detection circuit 17 for stopping the switching element 1 by detecting that the stabilization voltage 6 inside the semiconductor integrated circuit device 2 for the insulating type switching power supply device 2 has dropped, and a logic for controlling the switching element 1. The circuit 18, the overheat protection circuit 19 and the like are incorporated.

The auxiliary winding voltage drop is detected by the comparator 20A that the auxiliary winding voltage is lower than the specified voltage value (corresponding to the second voltage in the claims) according to the present invention. A detection circuit (corresponding to the second function in the claims) 20 is built-in, and when the auxiliary winding voltage drop detection circuit 20 detects the voltage drop of the auxiliary winding 5, the auxiliary winding voltage drop detection circuit The output of 20 is transmitted to the logic circuit (corresponding to the second function in the claims) 18 and the timer circuit (corresponding to the second function in the claims) 13 is operated to operate the switching element 1 Is switched intermittently. The auxiliary winding voltage drop detection circuit 20 compares the voltage of the auxiliary winding 5 or the voltage obtained by resistance-dividing the voltage of the auxiliary winding 5 with a reference voltage to reduce the voltage of the auxiliary winding 5. It is configured to detect. The specified voltage value is set to the voltage of the auxiliary winding 5 when the voltage application from the portion 4 rectified and smoothed by the rectifying bridge 25 and the smoothing capacitor 26 is stopped, or a predetermined voltage higher than that. To be done.

In the intermittent operation, constant-current charging / discharging (here, the charging current is 10 μA and the discharging current is 2.5 μA) is repeated in the external capacitor 21 to generate a triangular waveform, and its upslope is generated. At times, the switching element 1 performs a normal switching operation, and stops the switching operation at a downward slope. Since the time of the upslope is 1/4 of the time of the downslope, the power loss in the rectifier diode 22 on the secondary side, the inside of the semiconductor integrated circuit device 2 for the isolated switching power supply device, etc. during the intermittent switching operation is , About 1/5 before entering. These operations are performed by detecting the voltage of the capacitor 21 by the comparators 23 and 24.

The secondary side output of the transformer 30 is rectified and smoothed by the secondary side rectifying diode 22 and the smoothing capacitor 28. The secondary current is detected as a voltage by the resistor 29, and the operational amplifier 27 and the photo coupler 9 are used to detect the secondary current.
0 is transmitted to the primary side as a feedback signal. When the output current on the secondary side increases, the output of the operational amplifier 27 increases, the current of the photodiode 9 increases, and the on-duty of the switching element 1 is narrowed down.

FIG. 2 shows another example of a circuit for detecting when the voltage of the auxiliary winding 5 drops below a certain voltage. Here, when the voltage on the cathode side 34 of the equivalent diode 37 becomes lower than the stabilization voltage 6 (5.8 V) inside the semiconductor integrated circuit device 2 for the isolated switching power supply device, the mirror circuit 38 outputs the output of the mirror circuit 38. The voltage of the portion 35 becomes high, and the detection signal of the auxiliary winding voltage drop is transmitted to the logic circuit 18 (see FIG. 1). That is,
The voltage of the auxiliary winding 5 is higher than the internal stabilizing voltage 6 of the semiconductor integrated circuit device 2 for the isolated switching power supply device by one equivalent diode 37, that is, a voltage (specified voltage value) higher by about 0.6V. When also decreases, the intermittent switching operation of the switching element 1 starts. 36 is a constant current source.

Also, in the case of a short circuit between the auxiliary winding 5 and the ground line, the auxiliary winding voltage drops and the same function works. By the way, in the insulating type switching power supply device which is performing the constant current output control, the case where the switching element 1 has the function of performing the intermittent switching operation by detecting the auxiliary winding voltage (solid line) and the case where it does not have the function (broken line) The output voltage-current characteristics are shown in FIG. Without this intermittent switching function, if the output voltage drops, the operation of the operational amplifier 27 on the secondary side of FIG. 1 stops, and feedback from the secondary side becomes impossible, so the current value increases.
If there is this intermittent switching function, the intermittent operation starts from the constant current region, so the output characteristic becomes a so-called fold-back characteristic, and the load on the rectifying diode 22, the rectifying diode of the auxiliary winding rectifying / smoothing circuit 33, and the like. Is reduced.

[0023]

According to the semiconductor integrated circuit device for an insulating type switching power supply device of the present invention, a function of detecting a drop in the voltage of the auxiliary winding of the transformer and intermittently switching the switching element is provided. When the secondary side load is short-circuited, the burden on the secondary side or auxiliary winding side parts such as the rectifying diode can be reduced, and an insulated switching power supply device excellent in safety can be realized.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing a configuration of an insulating switching power supply device having a semiconductor integrated circuit device for an insulating switching power supply device according to an embodiment of the present invention.

FIG. 2 is a circuit diagram showing a part of the internal circuit of the semiconductor integrated circuit device for the insulating type switching power supply device.

FIG. 3 is an output voltage-output current characteristic diagram of the insulation type switching power supply device.

FIG. 4 is a circuit diagram of an example of a conventional insulated switching power supply device that performs constant current charging.

5 is a specific circuit diagram of the control circuit of FIG.

6 is a time chart showing the relationship between photocoupler current and on-duty in the circuit of FIG.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 switching element 2 semiconductor integrated circuit device for insulation type switching power supply device 2A power supply input terminal 2B power supply input terminal 3 AC power supply 5 auxiliary winding 7 pre-regulator circuit 8 oscillator 9 photocoupler 10 error amplifier 11 comparator 12 PWM control circuit 13 timer circuit 14 Overcurrent protection circuit 15 Overvoltage protection circuit 17 Stabilized power supply voltage drop detection circuit 18 Logic circuit 19 Overheat protection circuit 20 Auxiliary winding voltage drop detection circuit 38 Mirror circuit 21 External capacitor 22 Rectifier diode 23, 24 Comparator 25 Rectifier bridge 26 smoothing capacitor 27 operational amplifier 28 smoothing capacitor 29, 39 resistor 30 transformer 31 capacitor 32 capacitor 33 auxiliary winding rectification / smoothing circuit 36 constant current source 37 equivalent diode

Claims (4)

[Claims] 1. A first power supply input, comprising a control circuit for controlling a switching element connected to a primary winding of a transformer of an insulated switching power supply device, to which a voltage obtained by rectifying and smoothing an AC voltage of an AC power supply is applied. A terminal and a second power supply input terminal to which the voltage of the auxiliary winding of the transformer is applied, and at the time of start-up, a drive current is supplied from the first power supply input terminal to the control circuit to generate a voltage of the auxiliary winding. Has a first function of stopping the drive current supply from the first power supply input terminal and supplying a drive current from the second power supply input terminal to the control circuit when An insulated switching power supply device having a second function of intermittently switching the switching element when the voltage of the auxiliary winding falls below a second voltage equal to or higher than the first voltage. Semiconductor integrated circuit device. 2. The second function is to compare the voltage of the auxiliary winding or the voltage generated by resistance-dividing the voltage of the auxiliary winding with a reference voltage inside the control circuit, and the reference voltage is higher. The semiconductor integrated circuit device for an insulated switching power supply device according to claim 1, which has a function of intermittently performing a switching operation of the switching element when the voltage is high. 3. A semiconductor integrated circuit for an isolated switching power supply device according to claim 2, wherein the circuit for comparing the voltage of the auxiliary winding or the voltage generated by dividing the voltage of the auxiliary winding with the reference voltage is a comparator. apparatus. 4. A semiconductor integrated circuit for an isolated switching power supply device according to claim 2, wherein the voltage of the auxiliary winding or the circuit for comparing the voltage generated by dividing the voltage of the auxiliary winding with the reference voltage is a mirror circuit. Circuit device.