JPH0217860A - Switching power supply device - Google Patents

Abstract

PURPOSE:To reduce a board in size and a cost by forming a load short-circuit detection protective circuit of a plurality of current detection resistors on the output side of a power source and switching means through diodes. CONSTITUTION:A switching power supply device rectifies and smoothes an AC output from a commercial AC power source by a full-wave rectifier 2 and a smoothing capacitor 3, and supplies it to an oscillation driving circuit 4. The DC input power of the circuit 4 is supplied to a series resonance circuit formed of the primary winding NR of a power insulation transformer 8 and a capacitor 9 through the primary winding Na of a power regulation transformer 7. Rectifying and smoothing circuits 10-12 are respectively connected to the secondary windings N2-N4 of the transformer 8, and their outputs are supplied to a control circuit 13, etc. Further, the outputs of abnormal current detecting resistors R1-R3 at the time of short-circuit of a load are to a load short-circuit detecting protective circuit 14, and supplied as the collector output of its transistor QF to the control winding Nc of the transformer 7 through a control circuit 13.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a switching power supply device used for example in a television receiver, etc., and in particular to detecting and protecting a short circuit in a load provided in a DC power output line. The present invention relates to a switching power supply device having a load short-circuit detection protection circuit for operation.

[Summary of the invention]

In a switching power supply device that rectifies and smoothes a commercial AC input power supply and switches the rectified and smoothed DC power supply to obtain a plurality of stabilized DC power outputs, an abnormal current detection resistor is provided on each of the plurality of power supply output sides, Connect one end of a diode to each of these abnormal current detection resistors,
By connecting the other ends of these diodes in common and providing a load short-circuit detection protection circuit that discriminates the output level from this common connection terminal, the number of circuit components and board area can be reduced and the accompanying Cost reductions are achieved, and the abnormal current detection level, which varies due to changes in ambient temperature, can be stabilized.

(Prior art) A conventional switching power supply device is disclosed in, for example, Japanese Patent Application Laid-Open No. 62-6
A switching power supply device as disclosed in Japanese Patent No. 4171 is widely known, and FIG. 5 shows a switching power supply device in which a load short-circuit protection circuit is provided in this switching power supply device.

In FIG. 5, the switching power supply device has, for example, a commercial AC input fil! By rectifying and smoothing X51 with a diode bridge type full-wave rectifier 52 and a smoothing capacitor 53, it is converted to a DC power source and supplied to the DC input section of the oscillation drive circuit 54.

A power switch 55 and a resistor 56 for limiting inrush current (inrush ring 2it) are connected in series between the AC input type a51 and the full-wave rectifier 52, respectively.

The above DC input power supply is powered by a power regulation transformer (
The power is supplied to the primary winding N5 of the power isolation transformer (PIT) 5B and the series resonant capacitor C2 via the primary winding N of the power isolation transformer (PIT) 57.

The IT source regulation transformer 57 has a primary winding N8, two secondary windings N0 and Nl+2, and a control winding Nc.
have. In conjunction with the power regulation transformer 57, the oscillation drive circuit 54 controls on/off switching of the current of the DC input Ti source.

This oscillation drive circuit 54 includes a switching transistor Q
11 and a diode DS1 connected between the emitter and base of this switching transistor Q1, and -
A pair of transistor Q2 and diode D! The transistor Q1 is inserted and connected between the DC input power source and the primary winding N of the power regulation transformer 57, and the transistor Q is connected to N3 of the power regulation transformer 57 and ground. Inserted and connected between. Between the emitter and base of the transistor Q1, a secondary winding N11. and resistor R3I and capacitor C3
A series resonant circuit is connected between the emitter and base of the transistor Q2, and the secondary winding N8□ of the power regulation transformer 57 and the resistor R1 are connected in parallel with the diode DSZ.
A series resonant circuit consisting of the capacitor C2 and the capacitor C2 is connected.

Further, starting resistors R33 and R54 are inserted and connected between the DC input power source and the bases of the switching transistors Q1 and Q2, respectively.

Next, the secondary windings N8, Nx, N of the power isolation transformer 58
Rectifying and smoothing circuits 59, 60, and 61 are respectively provided in a, and each constant voltage direct current is supplied from the output line.

The rectifying and smoothing circuits 59, 60, and 61 are each provided with abnormal current detection resistors R+, Rz, and Rz, and the detection outputs from the resistors R, , R, and R are used to detect the respective load short circuits. Sent to detection protection circuits 62, 63, 64.

For example, the load short circuit detection protection circuit 62 includes a transistor QLl, a pace emitter voltage (Vat) reverse protection diode D connected between the pace emitter of the transistor QLl, and the transistor QL+.
A resistor R1 is installed between the base and the installation to limit the base current.
and a large-capacity smoothing electrolytic capacitor C for preventing malfunction, which is installed between the anode of the diode DL+ and the installation.
It is composed of LI.

Note that the other load short circuit protection circuits 63 and 64 have the same configuration as the load short circuit protection circuit 62 described above.

The collectors of the transistors Q L l, Q t t, and Qt of the load short-circuit protection circuit 62.63.64 are commonly connected, and this detection protection circuit 62.63.6
The detection output from 4 is sent to control circuit 65.

This control circuit 65 controls the switching operation and stabilizes the output voltage by controlling the power supply to the control winding N according to at least one output of the plurality of DC power supply outputs. Furthermore, the control current is supplied to the power regulation transformer 57 according to the detection output.
control winding N.

The switching power supply device is protected by limiting the current supplied to the primary winding N of the power isolation transformer 58.

In addition, the low voltage transformer 66, which is supplied with AC power from the commercial AC power source, supplies a current that has been rectified and smoothed to a constant voltage by a rectification and smoothing circuit 67 and a Zener diode 68 to a switch drive circuit 69. . In this switch drive circuit, a relay 71 is actuated by a signal inputted from an input terminal 70, and the switch 55 is controlled to be turned on or off.

Therefore, malfunctions occurred despite the provision of smoothing electric field capacitors to prevent malfunctions.

The present invention has been made in view of these circumstances,
Since it can be configured with a small number of components, the installation board area can be reduced and costs can be reduced.Also, in terms of functionality, we provide a switching power supply that is equipped with a load short circuit detection protection circuit that is not affected by ambient temperature changes. purpose.

[Problem to be solved by the invention]

However, conventional switching power supplies are equipped with a load short circuit detection protection circuit for each DC constant voltage output line to detect abnormal current in the event of a load short circuit. 100
A large capacitance of 0μ/6.3V was required. Further, the load short circuit detection and protection circuit has a large number of components, and the board area on which these components are installed is large, resulting in high cost.

Furthermore, as the ambient temperature rises, the pace-emitter voltage (V□) of the transistor decreases. In a switching power supply device that rectifies and smoothes a commercial AC input power supply and performs switching control on the rectified and smoothed DC power supply to obtain a plurality of stabilized DC power outputs, a current is provided at each of the plurality of power supply output sides. Load short circuit detection consisting of a detection resistor, diodes whose one end is connected to each of these current detection resistors and whose other ends are commonly connected, and a switching means that discriminates the output level from the common connection terminal of these diodes. The above-mentioned problem is solved by using a switching power supply device having a protection circuit.

[For production]

In the switching power supply device according to the present invention, the load short-circuit detection protection circuit can be configured with a small number of components, so it is possible to reduce the size of the installed board and reduce costs.

Furthermore, since the load short circuit detection and protection circuit operates without being affected by changes in ambient temperature, the switching power supply device can be reliably protected.

〔Example〕

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of a switching source device according to the present invention will be described with reference to the drawings.

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

In the switching power supply device of FIG. 1, for example,
By rectifying and smoothing the AC output from the 100cm commercial power current R1 using a diode bridge type full-wave rectifier 2 and a smoothing capacitor 3, the AC power is converted to DC power, and the oscillation drive circuit 4 It is supplied to the DC input section of the

A power switch 5 and a resistor 6 for limiting inrush current are connected in series between the commercial current R1 and the gold wave rectifier 2, respectively.

The DC input power supplied to the DC input section of the oscillation drive circuit 4 is connected to one of the power regulation transformers (PRTs) 7.
1 of the power isolation transformer (PIT) 8 through the next winding N,
It is supplied to a series resonant circuit formed by the next winding Nll and the series resonant capacitor 9 of the power isolation transformer 8.

The power regulation transformer 7 has a primary winding N1
．． It has two secondary windings N0, No and a control winding N. In association with the power supply regulation transformer 7, an oscillation drive circuit 4 is provided for controlling on/off switching of the current of the DC input power supply. This oscillation drive circuit 4 includes a switching transistor Q
1 and a pair of diodes [ls+ and - connected between the emitter and base of this switching transistor Q1.
A set of transistors Qt and a set of diodes OSZ are connected in series, the transistor Q1 is inserted and connected between the DC input power supply and the primary winding N of the power regulation transformer 7, and the transistor Q is connected to the power regulation transformer 7. It is inserted and connected between the primary winding N of No. 7 and ground. Between the emitter and base of transistor Q1,
Diode D! A series resonant circuit consisting of a secondary winding Nml of the power regulation transformer 7, a resistor R3+, and a capacitor C3 is connected in parallel with the secondary winding Nml of the power regulation transformer 7, and a secondary winding of the power regulation transformer 7 is connected between the emitter base of the transistor Q2 in parallel with Winding N0 and resistance 1'? sz
A series resonant circuit consisting of the capacitor C2 and the capacitor C2 is connected.

Furthermore, starting resistors R1 and R34 are inserted and connected between the DC input power source and the bases of the switching transistors Q, Q, Q, respectively.

A rectifying and smoothing circuit 10 consisting of rectifying diodes D, D, and a smoothing capacitor C3 is connected to the secondary winding N2 of the power insulating transformer 8.
3 has diodes D, , D4 and smoothing capacitor C4
A rectifying and smoothing circuit 11 consisting of
Rectifier and smoothing circuits 10 to 12 each consisting of diodes DS and DA and a smoothing capacitor C2 are connected to the next winding N4, and for example, the DC output power (for example, 15V output voltage) from this rectifier and smoothing circuit 11 is controlled. The current is converted into a control current by the circuit 13 and sent to the control winding Nc of the power regulation transformer 7.

The secondary windings Nt, N3, and N4 of the power isolation transformer 8 are provided with abnormal current detection resistors R+, Rt, and Ri, respectively, which detect abnormal current when the load is short-circuited. The detection outputs detected by Rz and R3 are sent to the load short circuit detection protection circuit 14.

The load short circuit detection protection circuit 14 includes a detection diode D+
, Dz, Dx, a transistor QF, a diode D for reverse protection of the base-emitter voltage of the transistor QF, a resistor RF for limiting the base current of the transistor Qr, and a small capacitance (for example, about 10 μF). It consists of a smoothing electrolytic capacitor CF to prevent malfunction.

The anodes of the detection diodes D+, Dt, and Dz are commonly connected, and the transistors Q,
is connected to the emitter of The diode DF is inserted and connected between the emitter and base of this transistor QF, and a resistor R1 is provided between the base and ground.

The smoothing electrolytic capacitor CF is connected in parallel with the series circuit of the diode D and the resistor R4. The detection output is sent to the control n circuit 13 as the collector output of the transistor Q of the load short circuit detection protection circuit 14.

This control circuit 13 includes a transistor Q1 whose base is connected to voltage dividing resistors RKI and RK2 for dividing and detecting a constant voltage DC output, a resistor R1 connected to the emitter of this transistor Qx+, and a reference voltage. A transistor Q whose base is connected to the Zener diode D and the collector of this transistor Q++ through a resistor R. and a resistor RKS connected between the collector of the transistor Q, 11 and the emitter of the transistor Qxz.
The collector output of the transistor Q0 is connected to the control winding N of the power regulation signaling transformer 7.

is being supplied to.

The AC power from the commercial AC power supply 1 is also supplied to a low voltage transformer 15 for supplying circuit power, and the low voltage AC power is supplied to the rectifier and smoothing circuit 1 via this low voltage transformer 15.
6 is converted into a DC power supply, and the voltage is regulated by a Zener diode 18 via a resistor 17 for inrush current limitation, and then the switch drive circuit! 9 is supplied.

In the switch drive circuit 19, the transistor Qs is driven to switch by a control signal input to an input terminal 20, and the switch 5 is controlled to be turned on or off by a relay 21.

Next, the general operation of the switching power supply device having the above configuration will be explained.

First, when the power switch 5 is turned on to turn on the AC power, it is converted to DC input power by the full-wave rectifier and smoothing capacitor 3 via the inrush current limiting resistor 6, and the starting resistor R53, Rsa of the oscillation drive circuit 4 is turned on. A starting current flows through the bases of the switching transistors Q1 to Qz, kicking these transistors Q, , Q, and starting a switching operation. During steady state, the switching transistor Q1 is driven by the sinusoidal alternating current flowing through the secondary winding N□ due to the series resonant circuit of the inductance of the secondary winding N□ of the power regulation transformer 7, the resistor R□, and the capacitor CI. When the current reaches O, the switching transistor Q2 is driven to the ON state by the inductance of the secondary winding N of the power regulation transformer 7, the resistor R52, and the capacitor C2 in a series resonant circuit, and this is repeated to perform the switching operation. continue.

A control current from a control circuit 13 is supplied to the control winding Nc of the power regulation transformer 7. This control current is obtained by detecting the DC output voltage of the power isolation transformer 8.

That is, the control circuit 13 controls the control current flowing through the control winding N of the power regulation transformer 7 so that the DC output voltage from the power isolation transformer 8 is always constant despite fluctuations in the DC output voltage. Volume 2! I
A N a +, the inductance of Na2 is controlled,
The oscillation frequency of the oscillation drive circuit 4 is controlled.

Next, a case where a load short circuit occurs, that is, a case where the amount of current in the DC power output line becomes excessive will be explained in more detail.

First, FIG. 2 shows a switching power supply device according to the present invention.
A waveform diagram of the collector current 1cI of the switching transistor Q, the collector current 1cI of the switching transistor Q2, and the detection current ID of the load short-circuit detection resistor (for example, R,) during normal operation is shown.

In this FIG. 2, the collector current 1cI of the switching transistor Q, and the switching transistor Q
The collector current +cz of No. 2 is 4AP-P, and the detection current ■ of the load short circuit detection detection resistor R1 is 1.5A.
It is P-F.

On the other hand, FIG. 3 shows the collector current rc+ of the switching transistor Q when the load is short-circuited, and the switching transistor Q! A waveform diagram of the collector current m1c2 and the detection current (2) of the load short-circuit detection detection resistor (for example, R,) is shown.

In this FIG. 3, the switching transistor Q,
, Q, the collector current 1 c +, rct is, for example, 5AP-P, which is the detection current of the load short circuit detection resistor R3. becomes 2AP-P, and it can be seen that an excessive amount of current (abnormal current) flows when a load short circuit occurs compared to normal times.

When this abnormal current flows through the load short circuit detection resistor R3 of the line where the load short circuit has occurred, the terminal voltage of this load short circuit detection resistor R1 decreases compared to the normal state, and the detection diode D becomes conductive. The detection output from this diode is the transistor Q
When this emitter voltage exceeds a predetermined value, transistor Q becomes conductive. When this transistor QF becomes conductive, the base voltage of the transistor Ql+2 of the control circuit 13 decreases, and by forcibly controlling this transistor Q11 to be conductive, the current supplied from the low voltage transformer 15 is transferred to the backup diode D, The power is supplied to the control winding Nc of the power regulation transformer 7 via.

Then, a control current flows to limit the collector currents of the switching transistors Q1 and Qz to a constant value, and by ultimately suppressing the DC output power supply, the components of the switching power supply are protected. ing.

By the way, the operating condition of the transistor Q is when at least one of the detection diodes D1 to D3 is conductive, and even when a load short circuit occurs in another DC power supply line, the diode D1 or D! Transistor Q becomes conductive.

conducts, so the same protection operation as described above is performed.

FIG. 4 shows a temperature characteristic graph of this load short circuit detection protection circuit 14. The solid line is a load short circuit detection protection circuit according to an embodiment of the present invention, and the dotted line is a conventional load short circuit detection protection circuit.

In this FIG. 4, transistors Q L l, Q of the load short-circuit detection protection circuit 62, 63, 64 of the conventional configuration provided in the conventional switching power supply shown in FIG.
L! , QL3, as each base-emitter voltage Vat decreases as the ambient temperature rises, for example, when the ambient temperature is 25°C, the detected current of the abnormal current detection resistors R1 to R1 is 1.5 A, causing a load short circuit. Detection protection circuit 62.63.64
Even if the CLI is set to operate, if the ambient temperature reaches 40°C, the large-capacity electrolytic capacitor CLI to prevent malfunction will be removed.
, CtZ, and C10, the load short circuit detection protection circuits 62, 63, and 64 were activated when the detected current of the abnormal current detection resistors R and -Rj was 1.3 A.

However, by adopting a configuration similar to the load short circuit detection protection circuit 14 of the switching power supply according to the present invention, the smoothing electrolytic capacitor C1 for preventing malfunction does not malfunction due to the small capacity of 101IF, and at the same time, the smoothing electrolytic capacitor C1 for preventing malfunction can be prevented from malfunctioning due to the small capacitance of 101IF. Voltage ■.

The decrease in the forward voltage drop (2) of the detection diodes D+, Dz, and Ds increases and cancels each other out, so that it remains constant even if the abnormal current detection level changes from 110°C to 60°C. Furthermore, negative charges are always stored in the conventional large-capacity electrolytic capacitors Ct+, CtZ, and C10 for preventing malfunction shown in FIG. 5, but the small-capacity electrolytic capacitor C for preventing malfunction of this embodiment .

The load short-circuit current is detected, and after the load short-circuit detection diodes D, D, , 03 are turned on, a negative charge is charged, thereby improving the long-term reliability of the capacitor.

In addition, the smoothing electrolytic capacitors CLI and CL for preventing malfunction mentioned above
t, C10, and C1 are provided to prevent the transistor Q from malfunctioning when the load current increases instantaneously when switching channels or turning on the power.

As is clear from the above description, in the switching power supply device according to the present invention, by providing the load short circuit detection protection circuit with the above-described configuration, the load short circuit detection protection circuit operates without being affected by the ambient temperature. , the protection of the switching power supply becomes more reliable. In addition, the smoothing electrolytic capacitor for malfunction prevention can be of small capacity, and the number of components of the load short-circuit detection protection circuit can be significantly reduced, which reduces the board area for installing the components and reduces costs accordingly. is achieved.

〔Effect of the invention〕

In the switching power supply device according to the present invention, by providing the load short circuit detection protection circuit with the above-described configuration, the load short circuit detection protection circuit operates without being affected by the ambient temperature, so that the switching power supply device can be more reliably protected. become. In addition, the smoothing electrolytic capacitor for preventing malfunction can be of small capacity, and since the capacitor is charged only when the load is short-circuited, the long-term reliability of the capacitor is improved.

Furthermore, since the number of components of the load short-circuit detection and protection circuit can be significantly reduced, the area of the board for installing the components can be reduced, and the costs associated therewith can be reduced.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing a switching power supply as an embodiment of the present invention, FIG. 2 is a current waveform diagram of each part during normal operation, and FIG. 3 is a current waveform diagram of various parts when a load is short-circuited. FIG. 4 is a temperature characteristic diagram of the embodiment of the present invention and a conventional load short-circuit detection protection circuit, and FIG. 5 is a circuit diagram showing a conventional switching power supply device. 2.52・ 4.54・ 7.57・・Full wave rectifier・・Oscillation drive circuit・・Power regulation transformer (PRT) 8.58・・Power isolation transformer (PIT) 59–61
．． 10~12... Rectifier smoothing circuit 14.62~64...
・Load short circuit detection protection circuit 13.65... Control circuit 19.69... Switch drive circuit 16.67... Rectification smoothing circuit 15.66... Low voltage transformer (PT) Figure 2 Figure 3 6゜55 degrees ("C) - Figure 4

Claims (1)

[Scope of Claims] A switching power supply device that rectifies and smoothes a commercial AC input power supply, and performs switching control on the rectified and smoothed DC power supply to obtain a plurality of stabilized DC power outputs, wherein each of the plurality of power supply output sides A current detection resistor provided, a diode whose one end is connected to each of these current detection resistors, and whose other ends are commonly connected, and a switching means that discriminates the output level from the common connection terminal of these diodes. A switching power supply device comprising a load short circuit detection protection circuit.