JPH04248317A - Dc power supply - Google Patents

Abstract

PURPOSE:To prevent breakdown of component or burning of pattern by detecting abnormal output of one secondary winding other than that being monitored thereby interrupting output from each secondary winding quickly. CONSTITUTION:An output monitoring coil 15 is inserted into the line of the secondary winding 3b of a transformer and an output prohibiting signal is generated and applied on a PWM control circuit 11. An abnormality detecting circuit 30 is connected through a load C with DC output for the secondary winding 3d. A voltage to be applied on the load C is divided by resistors 31, 32 to produce a detection voltage which is then compared through a comparator 35 with a reference voltage, i.e., a voltage divided by resistors 33, 34. When an abnormality occurs under a state where protection is not taken through the output monitoring coil 15 and the output voltage from the secondary winding 3d exceeds a prescribed level, the divided voltage increases to produce an output prohibition signal from the comparator 35 and the output prohibition signal is applied onto the PWM control circuit 11 thus turning a transistor 4 OFF. Consequently, a switching regulator 1 is disabled resulting in prevention of breakdown of component or burning of pattern.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a DC power supply device that detects abnormal operation of the power supply and turns off the power supply.

0002

2. Description of the Related Art For example, a copying machine requires a plurality of DC outputs with different voltage values. For this purpose, a switching regulator type power supply device having a plurality of output systems is used, and its switching operation is performed using a PWM (pulse width modulation) signal. Generally, a DC power supply device includes a protection circuit that detects an overcurrent and turns off the power output, and a protection circuit that turns off the power if a predetermined operation is not completed within a specified time. Also, in order to stabilize the output voltage, one of the output lines (for example, 5
The output current (V output) is monitored, the detected value is fed back to the PWM control circuit, and control is performed to stop the output when it is determined that an overcurrent has occurred.

0003

However, in the above-mentioned prior art, if a short circuit occurs in the output line when the output monitoring coil that monitors the output current is in an open state,
Since PWM control is performed to raise the line to the target voltage, there is a problem in that the output voltage of the unmonitored system increases. At this time, the current abnormality is detected by a heat-sensitive element that detects the ambient temperature, and the power transistor etc. generate heat due to the excessive current, detecting the rise in ambient temperature and shorting the primary winding of the output transformer. This prevents output voltage from occurring on the secondary side. Alternatively, a primary current detection coil detects an overcurrent of the current flowing through the primary circuit, and the circuit operation is stopped. However, in both cases, it takes a considerable amount of time for the detection to reach a steady state, and it takes several minutes for the protective operation to start, so parts such as smoothing capacitors may be destroyed due to the voltage increase during these few minutes. , or the pattern may be burned out. SUMMARY OF THE INVENTION An object of the present invention is to provide a DC power supply device in which a protective operation can be performed quickly and damage to parts and pattern burnout can be prevented.

0004

[Means for Solving the Problems] In order to achieve the above object, the present invention controls current flow to a primary winding of a transformer having a plurality of secondary windings by a switching element to control the energization of the plurality of secondary windings. While generating AC voltage in each,
A DC power supply device that monitors the output of one of the plurality of secondary windings and performs stabilization based on the monitoring result,
Voltage monitoring means for monitoring the output of one secondary winding other than the monitored secondary winding, and control for stopping each output of the plurality of secondary windings based on abnormality detection by the means. The means are provided.

[0005]

[Operation] According to the above-mentioned means, even if the conventionally provided voltage monitoring means for the main output does not function or the temperature abnormality detection means is inactive, the voltage monitoring provided in other output systems Since the means monitor the voltage in parallel, abnormalities can be detected immediately, and countermeasures such as stopping the output can be quickly taken. Therefore, component destruction and pattern burnout can be prevented.

[0006]

Embodiments Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a circuit diagram showing an embodiment of a DC power supply device according to the present invention. The DC power supply shown here is mainly composed of a switching regulator 1 and an abnormality detection circuit 30 according to the present invention, and the switching regulator 1 has three independent outputs (+5V, a first +24V, and a second output). +24V). A bridge diode 2 is connected to a commercial power source (AC 100V), and a primary winding 3a of a transformer 3 and a PNP type transistor 4 are connected in series between the outputs of the bridge diode 2. Transistors 5 and 6 connected in series are used to bypass the current flowing through the primary winding 3a of the transformer 3 based on the detected temperature value.
(Both are NPN type) connected in parallel to the primary winding 3a. A heat sensitive element 7 and a Zener diode 8 are inserted in series between the base of the transistor 5 and the negative line. A primary current detection coil 9 is provided on the negative line, and a comparator 10 is provided to compare the detected value with a set value. The comparator 10 is provided with a PWM control circuit 11 for applying a PWM signal to the base of the transistor 4, and this circuit includes an error amplifier 11a and a PWM comparator 11b.

[0007] The transformer 3 has secondary windings 3b, 3c, 3d.
, each corresponding to a 5V and two 24V outputs. A rectifying diode 12 is installed in the secondary winding 3b.
A smoothing inductor 13 is connected to this output, and a capacitor 14 and a load A are connected between the outputs of this smoothing inductor 13. Furthermore, the secondary winding 3
An output monitoring coil 15 is inserted into the line b, and its output is applied to a comparator 16 that generates an output prohibition signal and transfers it to the PWM control circuit 11. A rectifying diode 17 is connected to the secondary winding 3c, a smoothing inductor 18 is connected to this output, and a Zener diode 19 is connected between the outputs to stabilize the output voltage. . Further, a smoothing capacitor 20 is connected in parallel with the Zener diode 19. Furthermore, a rectifying diode 21 is connected to the secondary winding 3d, a smoothing inductor 22 is connected to this output, and a Zener diode 23 is connected between the outputs to stabilize the output voltage. A smoothing capacitor 24 is connected in parallel with this Zener diode 23.

A load C is applied to the DC output to the secondary winding 3d.
is connected to the load C, and a detection input section of the abnormality detection circuit 30 is connected to the load C. That is, the voltage applied to the load C is detected by the resistors 31 and 32, and the output voltage at the resistance voltage division point becomes the detected voltage (monitoring voltage). This detected voltage is compared by a comparator 35 using the output voltage at the resistance voltage dividing point of the resistors 33 and 34 connected to the stabilized power source as a reference voltage. A control unit 40 of the copying machine is connected to the comparator 35 . The control unit 40 is
Input port 4 that accepts signals from comparator 35
1. C that processes the signal taken in by this input port 41
PU (central processing unit) 42 and operation panel (not shown)
It is configured to include an output port 43 for transferring display information to a display control section (not shown) for driving a display provided in the display.

In the above configuration, the 100V AC power supply is double-wave rectified by the bridge diode 2, and its DC output is transmitted to the transistor 5 and the primary winding 3a of the transformer 3.
is supplied to. On the other hand, the PWM control circuit 11
The PWM output signal shown in FIG. 2 is applied to the base of transistor 4 from
is turned on, and a current flows through the path of + output of bridge diode 2 → primary winding 3 a → emitter of transistor 4 → collector of transistor 4 → - output of bridge diode 2. Then, when the PWM output signal changes to the "H" level, the transistor 4 is turned off and no current flows through the primary winding 3a. By repeating this operation at regular intervals, an alternating current voltage is generated in each of the secondary windings 3b, 3c, and 3d of the transformer 3 according to the winding ratio. The output of the secondary winding is half-wave rectified by each of rectifying diodes 12, 17, and 21, and this is smoothed by inductors 13, 18, and 22 and capacitors 14, 20, and 24, respectively, and the resulting DC output is distributed to each load. is supplied to.

[0010] Here, the output voltage of the secondary winding 3b (+5V
) is applied to the error amplifier 11a of the PWM control circuit 11 as an error input, and the reference voltage VREF
Error amplification is performed using the other input voltage as the other input voltage. This amplified output is compared with a triangular wave signal by the PWM comparator 11b, and by controlling the pulse width according to the comparison result, the output voltage of 5V is controlled to always be a constant voltage, that is, stabilized. It will be done. Note that the output voltage of the DC output of the secondary winding 3c and the secondary winding 3d is stabilized by the Zener diode 19 and the Zener diode 23, and the abnormality detection circuit 3 described later
This prevents abnormal voltage from occurring even if 0 becomes inactive. Note that if a voltage exceeding the standard value of the Zener diode 19 and capacitor 20 is applied to each, these diodes will be destroyed. Then, the current detection value of the primary current detection coil 9 increases, and the state becomes [Ref1 (=allowable value 1)>detection value], and the switching regulator 10 generates an output prohibition signal. The PWM control circuit 11 that received this signal outputs the PWM output signal as “
H" level, turns off the transistor 4, stops the operation of the switching regulator 1, and prevents output voltage from being generated in each secondary winding. At this point, the protection means by the output monitoring coil 15 functions normally. When you are doing
If a short circuit occurs between the load A or the output lines of the secondary winding, the load current change is detected by the output monitoring coil 15, and the comparator 16 determines whether or not it exceeds the allowable value Ref2. The judgment result is
If detected value > tolerance value], PWM control circuit 1
Outputs an output prohibition signal to 1. The PWM control circuit 11 sets the PWM output signal to "H" level, turns off the transistor 4, stops the operation of the switching regulator 1, and prevents output voltage from being generated in each secondary winding. Furthermore, when the load current increases due to a short circuit in the output line, etc., the transistor 4 performing a switching operation also generates more heat, raising the ambient temperature thereof. This temperature change is detected by the heat sensitive element 7 and its internal resistance decreases. Then, the additional voltage applied to the Zener diode 8 becomes smaller, and the voltage applied to the transistor 5 becomes smaller.
A base voltage, which had not occurred before, is generated and transistor 5 is turned on. As a result, the current flowing through the primary winding 3a is significantly reduced, and the voltage generated in the secondary winding is kept significantly below the specified value.

However, the above-mentioned protection means requires time until the protection function of the heat-sensitive element 7 and transistor 5 starts operating if the protection means of the output monitoring coil 15 does not operate as described above. There is a risk of component destruction or pattern burnout. Therefore, in the present invention, the output voltage of the secondary winding 3d is constantly monitored by the comparator 35, so that even if the protection means by the output monitoring coil 15 does not operate, protection measures can be taken. That is, the comparator 35 compares the divided voltage VA across the resistors 31 and 32, which changes in accordance with the output voltage value of the secondary winding 3d, with the reference voltage VB across the resistors 33 and 34, and normally VB > VA. is in a state of now,
If an abnormality occurs in a state where the protection measures by the output monitoring coil 15 are not performed and the output voltage (load applied voltage) of the secondary winding 3d exceeds [24V + specified value], then Accordingly, the divided voltage VA increases and VA
>VB, and the comparator 35 generates an output prohibition signal. This output prohibition signal is applied to the PWM control circuit 11, and upon receiving it, the PWM control circuit 11 sets the PWM output signal to "H" level and turns off the transistor 4. As a result, the switching regulator 1 stops operating, and no output voltage is generated in each secondary winding. At the same time, the control unit 40 that receives the output prohibition signal from the comparator 35 drives a display provided on the operation panel to display "DC power supply abnormality" to warn the user of the occurrence of the abnormality. As mentioned above, even if the protection function by the output monitoring coil 15 is not activated,
It becomes possible to deal with power supply abnormalities.

0012

As is clear from the above, according to the present invention, the switching element controls the energization to the primary winding of a transformer having a plurality of secondary windings, and the alternating current is applied to each of the plurality of secondary windings. In a DC power supply device that generates a voltage, monitors the output of one of the plurality of secondary windings, and performs stabilization based on the monitoring result, one of the secondary windings other than the secondary winding being monitored Since voltage monitoring means for monitoring the outputs of the two secondary windings and control means for stopping each output of the plurality of secondary windings based on abnormality detection by the means are provided, parts breakage and pattern burnout are prevented. can be prevented from occurring.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing an embodiment of a DC power supply device according to the present invention.

[Figure 2] PWM output from the PWM control circuit
FIG. 3 is a waveform diagram showing an output signal waveform.

[Explanation of symbols]

1 Switching regulator 3 Transformer 3a Primary winding 3b Secondary winding 3c Secondary winding 3d Secondary winding 4 Transistor 5 Transistor 6 Transistor 7 Heat sensitive element 8 Zener diode 9 Primary current detection coil 10 Comparator 11 PWM control circuit 12 Diode 14 Capacitor 15 Output monitoring coil 16 Comparator 17 Diode 19 Zener diode 20 Capacitor 21 Diode 23 Zener diode 24 Capacitor 30 Abnormality detection circuit 31 Resistance 32 Resistance 33 Resistance 34 Resistance 35 Comparator 40 Control unit

Claims (1)

[Claims] 1. Current supply to a primary winding of a transformer having a plurality of secondary windings is controlled by a switching element to generate an alternating current voltage in each of the plurality of secondary windings; In a DC power supply device that monitors the output of one of the wires and stabilizes it based on the monitoring result, voltage monitoring means monitors the output of one secondary winding other than the monitored secondary winding. and a control means for stopping each output of the plurality of secondary windings based on abnormality detection by the means.