JPH048665Y2 - - Google Patents

Description

[Detailed Description of the Invention] (Technical Field) The present invention relates to a filter used as a power source for electronic devices.

(Background Art) Conventionally, switching type power supplies have often been used as power supplies for electronic devices. As is well known, a switching power supply is a method in which a commercial power supply is converted to DC, which is used as a power source to create a high-frequency pulse power supply, and then the desired voltage is rectified and smoothed using a high-frequency transformer to obtain the desired DC power. It is. At that time, power loss can be minimized by using a method of varying the pulse width and frequency of high-frequency pulses as a method of stabilizing the output voltage, so generally speaking, switching power supplies are It is smaller and more efficient than the regulator system.

Here, the noise on the output side of the switching power supply is
Due to the rising and falling parts of the high frequency pulse,
It consists of spike-pulse noise with a wide frequency spectrum, high-frequency ripples that remain after rectifying and smoothing high-frequency pulses, and low-frequency ripples that remain when the commercial power supply is converted to DC. Among these noises, high frequency ripples and low frequency ripples are removed by a power filter connected to the secondary side of the high frequency transformer of the switching power supply.

FIG. 1 shows a circuit diagram of a conventional power supply filter.
This power supply filter is composed of large capacitance capacitors C ₁ and C ₂ and a smoothing choke coil L, and its feature is that the power loss is only due to the DC resistance component of the smoothing choke coil L, and the power loss is small.

However, the aluminum electrolytic capacitors used as large capacitance capacitors C ₁ and C ₂ have high impedance for high frequencies, so they are less effective against high frequency ripples, and they are used to remove transmitted low frequency ripples. However, there are problems in that the capacitance must be quite large, and that the smoothed York coil L is quite large and expensive even if it is used for high frequencies.

FIG. 2 is another circuit diagram of a conventional power supply filter. This circuit is a so-called series regulator system, which converts the commercial power supply into a voltage close to the desired value using a transformer, rectifies and smoothes it, and then uses a series-inserted voltage stabilizing element (transistor).
The output is passed through a transistor. base potential
Since V _B is DC fixed by the Zener diode ZD, an emitter voltage, ie, an output voltage, approximately equal to the base potential V _B can be obtained, regardless of the collector potential V _C. Further, the collector-emitter voltage V _CE of the transistor is V _R +V _BE , and this V _CE is larger than the collector-emitter saturation voltage V _CEO . The unavoidable loss due to transistors is I _O・V _CEO , and I _O・V CEO in the circuit shown in Figure 2.
V _CE = I _O (V _R + V _BE ) is the unnecessary power loss I _O (V _R + V _BE
-Includes V _CEO . In addition, the collector potential V _C is V _C +Δ _H V _C
It is expressed as +Δ _L V _C. However, Δ _H V _C indicates high frequency ripple, and Δ _L V _C indicates low frequency ripple.

As mentioned above, since the base potential V _B is fixed, the emitter potential V _E is V _E ~V _B , and therefore the high frequency ripple Δ _H V _C and the low frequency ripple Δ _L V _C
is blocked. However, the transistor Tr
has a problem in that, where I is the collector current, a power loss of I(V _C -V _E ) occurs, and when the current fluctuation of the collector potential V _C is large, the power loss becomes extremely large. Therefore, such a circuit is not suitable as a power filter for a switching power supply from the viewpoint of efficiency.

(Purpose of the invention) The present invention was made by focusing on these conventional problems, and aims to provide a power supply filter that can efficiently remove high-frequency ripples and low-frequency ripples, and describes its characteristics. In order to make the input terminal voltage of the transistor the average value of the pulsating current voltage to be stabilized, a coil is connected in series to the collector of the transistor, and the voltage control signal of the transistor is stabilized near the peak value of the pulsating current voltage to be stabilized. In order to achieve this, an element consisting of a resistor, a coil, or a diode is connected between one end of the coil and the base of the transistor, and a capacitor is connected to the base of the transistor. .

Hereinafter, the present invention will be described in detail based on embodiments with reference to the drawings.

(Structure and operation of the invention) FIG. 3 is a reference diagram showing a circuit (active ripple filter) for removing high frequency ripples and low frequency ripples in a power supply filter, for explaining the invention. Tr is a transistor that constitutes a voltage stabilizing element, and is used as an emitter follower as shown in the figure. For example, a signal (containing a ripple component) obtained by rectifying and smoothing a signal appearing on the secondary side of a high frequency transformer T of a switching power supply is supplied to the collector. The emitter is also connected to a load (not shown). An element Z constituted by any one of a resistor, a coil, or a diode is connected between the collector and base of the transistor Tr. Also transistor
A capacitor _C6 is connected to the base of the Tr.
Therefore, the previously mentioned resistor R ₁ and the Zener diode
Unlike fixing the base potential DC-wise using a ZD, the base voltage (voltage control signal) can be stabilized only with respect to the AC component (ripple component) of the signal supplied to the collector.
Note that capacitors _C5 and _C7 are smoothing capacitors.

With the above configuration, this circuit can follow DC input fluctuations and make the value of (V _C − V _E ) close to the collector saturation voltage (~0.4V) of the transistor Tr. High frequency ripple Δ _H V _C and low frequency ripple Δ _L V _C , which are alternating current components, can be safely blocked while minimizing power loss between the collector and emitter. Generally, a switching power supply performs the output voltage stabilizing function on the primary side of a high frequency transformer, so even if the filter of the present invention is used, the output voltage stability will not be impaired.

Here, the output voltage of the transistor Tr is the voltage of the element Z
For example, if a resistor is used as the resistor, the collector potential V _C will be increased by an amount corresponding to the sum of the base potential drop V _R due to this resistor and the base-emitter potential drop V _BE .
becomes lower. Transistors generally have a base
The emitter-emitter voltage V _BE (generally about 0.7V) is larger than the collector saturation voltage V _CE (generally 0.4V), and if the output current is I ₀ , the total collector loss P _C is P _C = I _O (V _BE + V _R ) Therefore, the collector loss V _CE ·I _O becomes much larger than the ideal one. According to actual measurements, using 2SC2334 as the transistor Tr, the output current I _O =
When it is 1A, V _BE = 0.7V, V _R = 0.6V,
The collector loss P _C =1.3W, while the V _CE of transistor 2SC2334 is 0.4V, and the collector loss should be able to be reduced to 0.4W.

FIG. 4 is a circuit diagram of an embodiment of a power filter according to the present invention, taking into consideration the above-mentioned points. The circuit shown in the figure differs from the basic circuit shown in Fig. 3 by inserting a smoothing York coil L in series in the collector, and connecting one end of the element Z connected to the base of the transistor Tr to a high-frequency transformer via a diode _D2 . It is characterized by being connected to the secondary winding of the T. With this configuration, the collector voltage V _C of the transistor Tr is set to the average value of the input pulsating current voltage by the choke input circuit, while the base voltage is set to the average value of the input pulsating current voltage by the capacitor input type rectifier circuit. It is considered to be the peak value. Therefore, the base potential V _B is set higher by an amount corresponding to the sum of the base resistance drop _VR and (V _BE −V _C ),
As a result, unnecessary power loss I ₀ (V _R +V _BE −V _C ) is removed.

FIG. 5 is a circuit diagram of another embodiment of the power filter according to the present invention. It will be readily understood that this circuit can be considered similarly to the circuit shown in FIG.

The present invention has been described above based on examples. The voltage stabilizing element is not limited to a transistor (bipolar transistor), but may be a field effect transistor, a three-terminal regulator, or a Darlington-connected transistor.

(Effects of the Invention) As described above, according to the present invention, it is possible to provide a power filter that can efficiently remove high frequency ripples and low frequency ripples. If the present invention is applied to a switching power supply or the like, it is possible to provide a compact, high-efficiency, low-noise power supply suitable for audio equipment, precision measuring instruments, etc.

[Brief explanation of the drawing]

Figure 1 shows an example of the configuration of a conventional power filter;
The figure shows another configuration example of a conventional power filter, FIG. 3 is a reference diagram showing a circuit of a component having a ripple removal function in the circuit configuration of a power filter for explaining the present invention, and FIG. 4 5 is a circuit diagram of one embodiment of the power filter according to the present invention, and FIG. 5 is a circuit diagram of another embodiment of the power filter according to the present invention. Tr...transistor, _R1 ...resistance, _C1 to _C7 ...
... Capacitor, L ... Smoothed York coil, D ₁ ,
D ₂ ... diode, ZD ... Zener diode, T ... high frequency transformer, Z ... element.

Claims (1)

[Claim for Utility Model Registration] A coil is connected in series to the collector of the transistor in order to set the input terminal voltage of the transistor to the average value of the regulated pulsating current voltage, and the voltage control signal of the transistor is set to the average value of the regulated pulsating current voltage. In order to stabilize the voltage near the peak value, an element consisting of a resistor, coil, or diode is connected between one end of the coil and the base of the transistor, and a capacitor is connected to the base of the transistor. A power filter characterized by: