JPS6181171A - Switching regulator monitoring circuit - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a switching regulator monitoring circuit, and particularly to a duty cycle monitoring circuit suitable for a forward converter type switching regulator.

[Background of the invention]

As a method for preventing damage to the primary side main switching transistor, 1. For example, as shown in Japanese Patent Laid-Open No. 55-53183, overcurrent flowing through the transistor is detected, and when this value exceeds a specified value, immediate Methods of turning off transistors are known. This method constantly monitors the collector current of the transistor, so it can also detect instantaneous overcurrents, but since it only monitors only the collector current (large amplitude), the protection was not considered.

[Purpose of the invention]

An object of the present invention is to improve such conventional drawbacks, and to reliably detect when the collector current of the transistor exceeds the specified values of pulse amplitude and pulse width, and to switch the main switching transistor An object of the present invention is to provide a switching regulator monitoring circuit that can prevent damage to the switching regulator.

[Summary of the invention]

In order to achieve the above object, the switching regulator monitoring circuit of the present invention is a forward converter type switching regulator equipped with a circuit for identifying the pulse amplitude of the collector current of a switching transistor. An identification circuit for identifying the pulse width of the current, a setting circuit for setting the duty cycle of the pulse, and a determination circuit for determining the duty cycle are provided, and the output of the pulse width identification circuit and the output of the setting circuit are provided. A feature of the present invention is that the oscillation of the switching transistor is stopped when an abnormality is detected by comparison or when an abnormality is detected in the output of the pulse amplitude discrimination circuit.

[Embodiments of the invention] Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram of a switching regulator showing one embodiment of the present invention.

1.2 is a commercial AC input voltage receiving terminal, and the commercial AC input voltage is received here. 3 is a diode stack that rectifies the commercial AC input voltage and converts it into DC voltage. 4 is an aluminum electrolytic capacitor for removing the alternating current component contained in the direct current voltage. Reference numeral 5 denotes a current transformer, which detects the collector current of the primary side main switching transistor 6. 6 is 1
Next-side main switching power transistor (hereinafter referred to as

(simply referred to as a transistor), and is used to convert the DC voltage obtained by the diode stack 3 and capacitor 4 into a high-frequency AC voltage. The surge suppressor 6A consists of a capacitor 7, a diode 8, and a resistor 9.
By repeating oscillation, the transistor 6 absorbs the flyback voltage generated in the transformer 1o. 1
0 is a high frequency transformer, which serves to step down the high frequency AC voltage generated by the repeated oscillation of the transistor 6 and to insulate the primary circuit and the secondary circuit. IIA is a rectifying and smoothing circuit that converts high frequency AC voltage stepped down by a transformer 10 into DC voltage by a diode (center tap) 11, a choke coil 12, and an aluminum electrolytic capacitor 13. 14.15
is a DC supply terminal, from which DC output voltage is supplied. A diode 16 rectifies the output of the current transformer. 17 is a capacitor, 18 is a resistor, and a DC voltage proportional to the collector current is generated across the resistor 18. 19 is a Zener diode, 2
0, 21.23 are resistors, 22.24 are transistors, and these identify the primary side overcurrent detection circuit identification circuit 19.
It constitutes A.

25 is an auxiliary current transformer, and 26 is a diode stack that converts a commercial AC input voltage into a DC voltage.

27 is an aluminum electrolytic capacitor.

It has the role of reducing the alternating current component contained in the direct current voltage. 28 is a three-terminal regulator IC, which produces a specified DC output voltage. 34 is a control IC for a switching regulator, which houses a fixed frequency generator, a standard voltage generator, a pulse width control circuit, a duty cycle setting circuit, and the like. 30 is a resistor, which determines the oscillation frequency depending on the relationship with the capacitor 31. 32 and 33 are resistors, which determine the voltage to be compared with the DC output voltage between the DC output supply terminals 14 and 15. 35 and 36 are resistors, and 37 is a transistor, which constitute a shutdown circuit 35A. 38 and 39 are comparators. A reference voltage generator 40 generates a reference voltage inside the switching regulator control IC 34. 41
is a fixed frequency generator, and resistor 30. is a fixed frequency generator. capacitor 31
A fixed frequency is generated by Further, 42 is a flip-flop, and 43 is a NOR circuit.

44 is a transistor. 45, 46, 47 are resistors, and the duty cycle is set by inputting the voltage divided by the resistors 45, 46 to the comparator 39. 48 is an identification circuit that identifies the pulse width of the collector current of transistor 6; 49 is a duty cycle setting circuit; 50 is a duty cycle determination circuit;
A is a duty cycle monitoring circuit formed by 48°49.50.

The operation of these circuits will be explained below.

When a commercial AC input voltage is applied to the input voltage receiving terminals 1 and 2, this voltage is rectified in the diode stack 3, converted to a DC voltage, and applied to both ends of the aluminum electrolytic capacitor 4. This DC voltage is converted into a high-frequency AC voltage by the transistor 6 repeating oscillation 6. By repeating the oscillation of the transistor 6, a flyback voltage is generated in the transformer 10. The voltage is absorbed by a surge suppressor circuit 6A consisting of a capacitor 7, a diode 8° and a resistor 9. Further, when a commercial AC input voltage is applied to the terminal 1.2, the voltage is stepped down by the transformer 25, rectified by the diode stack 26, and a DC voltage is applied to both ends of the aluminum electrolytic capacitor 27. This DC voltage has poor voltage stabilization accuracy because it is an unstable DC voltage, and cannot drive logic elements. Therefore, the three-terminal regulator 28 converts the unstable DC voltage into a stabilized DC voltage, and supplies this stabilized DC voltage to the switching regulator control IC 34. When this voltage is supplied, a stabilized DC voltage is generated in the reference voltage generator 40, and this voltage is supplied to each main part inside the control IC. This generates a clock pulse and a sawtooth voltage in fixed frequency generator 41 determined by resistor 30 and capacitor 31 . Each of these outputs is sent to flip-flop 42 and comparator 39. Due to this.

Comparator 39 connects the output signal of error amplifier 38 and resistor 4
Comparing this sawtooth voltage with the voltage level determined by 5.46 will produce a pulse width modulated output. This pulse width modulation output is output from the NOR circuit 43.
is time-divided by each output of the flip-flop in 2
divided into two pulses. In this way, NOR
The pulse width modulated outputs of the comparator 39 appear alternately at the output of the circuit 43 once every two periods of the clock, but the widths of these pulses are narrowed by a predetermined pulse width depending on the values of the resistors 45 and 46. In other words.

The maximum pulse width is determined by the values of resistors 45 and 46.

The output of this NOR circuit 43 is transmitted to the transistor 44, and since the transistor 44 repeats oscillation, the transistor 6 also repeats oscillation, and the aluminum electrolytic capacitor 4
The DC voltage across the is converted to a high frequency AC voltage. This high-frequency AC voltage is stepped down by the transformer 10 and converted to a DC voltage in the rectifying and smoothing circuit 11A consisting of the diode 11, choke coil 12, and aluminum electrolytic capacitor 13, so that a DC output voltage is generated at the terminal 14.15. . This DC voltage becomes the input of the error amplifier 38, so that a constant DC output voltage is always obtained at 14°15 compared to the reference voltage. When the transistor 37 constituting the shutdown circuit 35A is turned on, the input of the comparator 39 decreases and the oscillation of the transistor 44 stops, so the oscillation of the transistor 6 also stops, and the DC output voltage of the terminal 14.15 drops. do.

When the terminals 14 and 15 are shorted, the collector current of the transistor 6 increases, and the current flowing through the current transformer 5 also increases, so that the voltage generated across the resistor 18 also increases.

When that voltage reaches or exceeds the Zener voltage of Zener diode 19, transistor 22 turns on. When transistor 22 is turned on, transistor 24 is also turned on,
The signal is input to the shutdown circuit 35A of the switching regulator control C34, and the transistor 37 can be turned on. Therefore, as described above, the input of the comparator 39 decreases, and the oscillation of the transistor 44 is stopped, so that the input of the transistor 6
oscillation is stopped, and as a result, the DC output voltage at terminals 14 and 15 drops.

Note that the maximum value of the on/off duty of the transistor 44 is determined by the voltage division ratio of the resistor 45.46. Ideally, transistor 44 and transistor 6 should be turned on/off.
Although the duty should be the same, it differs depending on the switching time of the transistor 6 and the like.

Normally, the on/off duty of transistor 6
Because there is a phenomenon that affects the on/off duty of the transistor 44, it is not enough to simply determine the on/off duty of the transistor 44.

In the event of an abnormality such as a load short circuit, the transistor 6 can be turned on/off.
The duty may exceed a specified value and the transistor 6 may be damaged. Therefore, in this embodiment, the pulse width is measured by the identification circuit 848 provided in parallel with the identification circuit A, and compared with the pulse width set in advance in the duty cycle setting circuit 49, the measured pulse width is determined to be the duty cycle. - If the pulse width is larger than the pulse width set in the cycle setting circuit, the duty cycle determination circuit 50 determines that the duty cycle is abnormal. Then, by transmitting a signal to the identification circuit (A) 19A of the primary side overcurrent detection circuit, the transistor 24 is turned on. Since the subsequent operations are the same as described above, the explanation will be omitted.

Note that various well-known timer circuits and the like can be used as the identification circuit (B) 48 and the duty cycle setting circuit 49. Further, the present invention is not limited to the embodiment shown in FIG. 1, but is of course applicable to all duty cycle monitoring circuits of forward converter type switching regulators.

〔Effect of the invention〕

As explained above, according to the present invention, in parallel with the identification circuit that identifies the magnitude (pulse amplitude) of the output of the rectifier circuit,
An identification circuit that identifies the output size and pulse width of the rectifier circuit and a Vyoty cycle monitoring circuit are installed.
The collector current of the switching transistor is the specified value (
(pulse amplitude, pulse width), this can be reliably detected and has the effect of preventing damage to the transistor.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a switching regulator monitoring circuit showing one embodiment of the present invention. 1.2: Commercial AC input voltage receiving terminal, 14.15: DC output supply terminal, 19: Zener diode, 19A: Identification circuit A, 25: Low frequency transformer, 26: Diode
Stack, 28:3 terminal regulator IC134 control IC135A for switching regulator:
Shutdown circuit, 38, 39: Comparator, 4o
: Reference voltage generator, 41: Fixed frequency generator, 42: Flip flop, 43: NOR circuit, 48: Identification circuit B
, 49: Duty cycle setting circuit, 50: Duty cycle determination circuit, 50: Duty cycle monitoring circuit.

Claims (1)

[Claims] A forward converter type switching regulator including a circuit for identifying a pulse amplitude of a collector current of a switching transistor, further comprising: an identification circuit for identifying a pulse width of the collector current in parallel with the identification circuit; A setting circuit for setting the duty cycle and a judgment circuit for judging the duty cycle are provided, and the output of the pulse width identification circuit and the output of the setting circuit are compared to detect an abnormality, or the output of the pulse amplitude identification circuit is A switching transistor characterized by stopping the oscillation of the switching transistor when an abnormality is detected.
Regulator monitoring circuit.