JPH0545117Y2 - - Google Patents

Description

[Detailed description of the invention] This invention turns DC current on and off using a transistor, causes the current to flow intermittently through the input winding of a conversion transformer, rectifies and smoothes the AC output generated in the output winding, and generates DC power. This invention relates to a protection circuit for a so-called switching power supply device that supplies a load.

The following description will be given with reference to the drawings.

Figure 1 is a circuit diagram of a conventional power supply device, Figure 2 is an explanatory diagram of its operation, and Figure 3 is a diagram of a power supply device according to the present invention.
This is an example. In the figures, the same symbols represent equivalent parts.

A conventional device for obtaining a plurality of DC outputs having different output voltages will be explained with reference to FIG.

Q ₁ is the main switching transistor, E ₁ is the power supply,
T ₁ is a conversion transformer, n ₂₁ , n ₂₂ are output windings, D ₁ ,
D ₂ is a diode, L ₁ is a smoothing inductor, C ₂ is a smoothing capacitor, and L ₀₁ and L ₀₂ are loads.

This device is roughly divided into two DC outputs, an A circuit, a B circuit, and a primary side control circuit.

The A circuit rectifies and smoothes the output of the output winding 21 and supplies it to the load _L01.The A circuit applies the detected value of the output voltage to the pulse width control circuit PWM, and outputs the output voltage from the main transistor _Q1.
The output voltage V _{01 is stabilized by controlling the on-width of the voltage V 01} .

The B circuit consists of rectifier diodes D ₃ and D ₄ connected to the output of output winding n ₂₂ , smoothing inductor L ₂ , capacitor C ₃ , saturable inductor L ₃ , error amplifier M ₁ , and transistor Q ₂ control circuit G ₂ ;
A current limiting circuit consisting of a current transformer CT ₂ , a diode D ₈ , a resistor R ₁₂ , a capacitor C ₁₂ , and an error amplifier M ₃ .

Consists of CL ₂ . In addition, the current limit detection circuit CL ₁ on the primary side includes a current transformer CT ₁ , a diode D ₇ , and a resistor.
It consists of R ₁₁ , capacitor C ₁₁ , error amplifier M ₂ , and power supply EL. Note that PWM is the control circuit for the main switching transistor, and ER is the power supply.
In this circuit operation, first, the load currents of loads LO ₁ and LO ₂ are detected by current transformers CT ₁ and CT ₂ , respectively, and
A voltage is generated across the resistor R ₁₁ , the capacitor C ₁₁ or the resistor R ₁₂ , and the capacitor C ₁₂ through the diode D ₇ or D ₈ and is amplified by the error amplifier M ₂ or M ₃ ,
It is input to the control circuit PWM, which controls the on-width of the main switching transistor _Q1 and causes the voltage of each output circuit to drop. In such a conventional circuit, the output circuit B detects the current with the current transformer _CT2 , amplifies it with the error amplifier _M3 , and limits the ON width of the switching transistor _Q1 , as shown in Fig. 2a.
The ON width of the main switching transistor _Q1 is as follows: _t1
As shown in Figure 2b, the time difference _t3 between the conduction angle _t2 of the saturable inductor _L3 is such that the output of the output circuit B cannot be reduced unless the ON width _t1 of the main switching transistor _{Q1 is} reduced. . In other words, load changes due to load fluctuations, etc.
If overcurrent flows to LO ₂ , there is a time of t ₃ , so
Since there is a period when the output voltage cannot be controlled, the main switching transistor _Q1 is often damaged. At the same time, the main switching transistor
_A signal loop (CT _{1 −D 7} −M _{2 −PWM−}
Q ₁ −CT ₁ ) and detected by current transformer 2, the control circuit
The signal loop (CT ₂ −D ₈ −M ₃ −PWM− _{Q 1}
-T ₁ -CT ₂ ), there is a gain difference, so there is a drawback that disturbances are likely to occur at the switching point of drooping operation due to overcurrent.

The present invention was developed in view of these points, and the third
One example is shown in the figure. The present invention includes a magnetic amplifier controlled output circuit B including an output winding n ₂₂ , a saturable inductor L ₃ , diodes D ₃ , D ₄ , D ₅ , D ₉ , an error amplifier M ₁ , and a smoothing inductor L ₂ , a smoothing capacitor C ₃ , a shunt resistor R ₁₃ for limiting current detection, and transistors Q ₂ and Q ₆ .

Next, we will discuss its operation. Now, if the current in the load LO ₂ increases, the voltage across the shunt resistor R ₁₃ increases, the transistor Q ₆ becomes conductive, the collector current is applied to the saturable inductor L ₃ through the diode D ₉ , and the transistor Q The induced energy of the smoothing inductor _L2 during the off period of ₁ is expressed as the reset current of the saturable inductor _L3 as _L2 −
The current is controlled by flowing through the path Q ₂ −L ₃ −n ₂₂ −D ₄ −L ₂ .

As described above, by using the circuit according to the present invention, the overcurrent of the load can be reliably controlled, the operation is stable, the conversion efficiency is good, the circuit is simple, the number of parts is small, and the multi-winding output type switching power supply Its practicality and effectiveness as a protection circuit for devices is great.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram of a conventional power supply device, FIG. 2 is an operation explanatory diagram, and FIG. 3 is an embodiment of the power supply device according to the present invention. Q ₁ ... Main switching transistor, Q ₂ , Q ₃
...transistor, E ₁ ... power supply, T ₁ ... converter,
n ₂₁ , n ₂₂ ... Output winding, CT ₁ , CT ₂ ... Current transformer,
D ₁ , D ₂ , D ₃ , D ₄ , D ₅ , D ₆ , D ₇ , D ₈ ... Rectifying diode, L ₁ , L ₂ ... Smoothing inductor, L ₃
...Saturable inductor, C ₁ , C ₂ , C ₃ , C ₄ ,
C ₁₁ , C ₁₂ ... Smoothing capacitor, L ₀₁ , L ₀₂ ... Load, M ₁ , M ₂ , M ₃ ... Error amplifier, PWM ... Control circuit, R ₁₁ , R ₁₂ , R ₁₃ ... Resistance, EL, ER...
power supply.

Claims (1)

[Scope of utility model registration request] In a multi-winding output switching power supply device having a direct output circuit and a magnetic amplifier-controlled output circuit on the secondary side, the magnetic amplifier-controlled output circuit has a shunt between the inductor and the capacitor of the smoothing circuit. 1. A multi-winding output type switching power supply device comprising a resistor and a transistor driven by a detection signal of a current flowing through the shunt resistor to reset a magnetic amplifier circuit and droop the output.