JPH069587Y2 - Switching Regulator - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial application] The present invention relates to a switching regulator.

[Summary of the Invention] A shunt regulator is added to the secondary circuit of the switching regulator, and this shunt regulator is controlled by the AC error component of the secondary rectified output to reduce AC fluctuations. It is a switching regulator in which the output voltage is fed back from the secondary circuit to the primary circuit and stabilized.

[Conventional technology]

In general, a switching regulator has a low DC impedance but a high AC impedance, and therefore has a poor transient response characteristic and a low ripple compression ratio, which often causes a problem in an analog circuit or a digital circuit of a load.

Therefore, a shunt regulator has been added to the switching regulator to reduce the output impedance and a switching regulator that has a low ripple output has been proposed.

[Problems to be solved by the invention]

Since the shunt regulator sends a current for stabilization to a shunt circuit in parallel with a load, it has a large power loss, a large amount of heat generation in the shunt circuit, and a large space loss for heat dissipation.

In view of this problem, the present invention aims to reduce the AC output impedance of a switching regulator with low power loss.

[Means for solving problems]

As shown in FIG. 1, the switching regulator of the present invention has a switching circuit (switching transistor 4) and its control circuit (pulse width modulation oscillator 5) on the primary side of a transformer 3, and a rectifier on the secondary side of the transformer. A high-pass filter including a switching regulator circuit in which the output is fed back to the control circuit 5 to stabilize the output, and a high-pass filter including a capacitor C4 for extracting the AC component of the rectified output voltage on the secondary side of the transformer 3, A shunt regulator circuit 11 having a current control element (transistor 15) for flowing a current for reducing the AC component in parallel with the load current from the rectification output point on the transformer secondary side based on an error voltage corresponding to the AC component is provided. ing.

[Action]

For the AC error of the switching regulator output,
A shunt regulator that responds only to the AC component stabilizes. The steady DC component of the shunt current may be a small current value commensurate with the maximum AC amplitude. Therefore, current loss and heat generation in the shunt regulator are significantly reduced. On the other hand, DC
The error is stabilized by the error feedback from the secondary of the switching regulator to the primary.

〔Example〕

FIG. 1 is a circuit diagram of a switching regulator to which the present invention is applied.

Commercial AC power is supplied to the rectifier 1, and the rectified output is smoothed by the capacitor C1 and supplied to the primary coil 3a of the transformer 3. A switching transistor 4 driven by a pulse width modulation oscillator 5 is connected to the primary coil 3a, and a voltage due to a switching pulse of its output is induced in a secondary coil 3b of the transformer 3. The secondary output voltage of the regulator is fed back to the oscillator 5, and the reference voltage source 6
The pulse width modulation is performed by the comparison with the voltage E of 1 to stabilize the secondary output voltage.

The output of the secondary coil 3b of the transformer 3 is the diode 7a,
Both waves are rectified by 7b and supplied to the load 10 ( _RL ) through a ripple filter including choke coils 8 and 9 and capacitors C2 and C3. The terminal voltage of the load 10 is fed back to the oscillator 5 on the primary side.

The terminal voltage of the load 10, that is, the regulator output is also supplied to the shunt regulator circuit 11. The shunt regulator circuit 11 is added to lower the AC output impedance of the switching regulator and increase the ripple compression rate.

The output voltage of the switching regulator is given to one end of a capacitor C4 that constitutes a high-pass filter, and the AC component is extracted by a detection amplifier including resistors R1, R2, R3 and an operational amplifier 12. This detection amplifier is about 1/10
, And the gain can be adjusted by the variable resistor R2. The resistor R4 is for DC bias, and the capacitor C5 is provided for low pass for reducing the high frequency gain. This detection amplifier detects an increase / decrease in the ripple voltage of the regulator output with reference to the ground potential.

The output of the detection amplifier is the resistors R5 and R6 and the operational amplifier 13.
Is supplied to the current drive circuit composed of the operational amplifier 14. The capacitor C6 of the operational amplifier 13 is for low pass. The operational amplifier 14 drives the base of this transistor so that its input voltage becomes equal to the emitter voltage of the transistor 15, and the input voltage is about 0.5V.
A shunt current of about 500 mA corresponding to the input voltage of is applied through the transistor 15. The emitter side resistor R8 of the transistor 15 is for current driving, and the collector side resistor R7 is for current limiting. The shunt current of the transistor 15 flows from the output end of the choke coil 8, which is the output point of the switching regulator, to the ground side in parallel with the current of the load 10.

When the current flowing through the load 10 increases at the peak of the ripple of the output voltage of the switching regulator, the increase in the ripple voltage is detected by the operational amplifier 12 via the capacitor C4, and the detected voltage is applied to the base of the transistor 15 through the operational amplifiers 13 and 14. As a result, the shunt current increases, and as a result, the increase in load current is suppressed. That is, AC negative feedback is applied to the shunt regulator circuit 11 regarding the ripple component of the load current. As a result, the ripple component of the regulator output supplied to the load 10 is significantly reduced.

The shunt current is a DC component slightly larger than the amplitude of the AC current component (ripple) (a steady current is determined by the resistor R4) and A
Since it does not need to flow a large current corresponding to the DC current of the load as a shunt current as in a general shunt regulator, the heat loss in the resistors R7 and R8 and the transistor 15 is very small. Regulator output 5V, shunt current steady DC value 500
In mA, the power loss is about 2.5W. Therefore, the shunt regulator circuit 11 responds only to a current fluctuation due to a ripple of about ± 500 mA at maximum, and has no control capability for a DC fluctuation of the regulator output due to a fluctuation of the load 10. However, there is no problem with respect to DC fluctuation because the detection voltage is fed back from the end of the load 10 to the oscillator 5 on the primary side to stabilize the DC fluctuation.

[Effect of device]

As described above, according to the present invention, since the shunt regulator that responds only to the AC fluctuation of the output voltage is added to the secondary circuit of the switching regulator, the shunt regulator consumes only a small steady shunt current and the AC voltage of the voltage supplied to the load. Fluctuations can be reduced, and therefore current loss and heat generation of the shunt regulator can be suppressed and output ripple can be reduced.

[Brief description of drawings]

FIG. 1 is a circuit diagram of a switching regulator showing an embodiment of the present invention. The symbols used in the drawings are: 3 ... Transformer 4 ... Switching transistor 5 ... Pulse width modulation oscillator 10 ... Load 11 ... Shunt regulator circuit 15 ... Output transistor.

Claims (1)

[Scope of utility model registration request] 1. A switching regulator circuit having a switching circuit and its control circuit on the primary side of the transformer, the rectified output of the transformer secondary side being fed back to the control circuit to stabilize the output, and the secondary transformer. Side high-pass filter for extracting the AC component of the rectified output voltage, and a current for reducing the AC component in parallel with the load current from the rectified output point of the transformer secondary side based on the error voltage corresponding to the AC component. Switching regulators each including a shunt regulator circuit having a current control element.