JPH048664Y2 - - Google Patents

Description

[Detailed Description of the Invention] (Technical Field) The present invention relates to a power 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 source is converted to DC, which is used as a power source to create a high-frequency pulse power source, and then the desired voltage is rectified and smoothed using a high-frequency transformer to obtain the desired DC power source. 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 capacity capacitors C ₁ and C ₂ have a 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).
It is output through a transistor. Base potential V _B
Since is fixed in a direct current manner by the Zener diode ZD, an emitter voltage, that is, an output voltage, which is approximately equal to the base potential V _B can be obtained, regardless of the collector potential V _C. Note that the collector potential V _C is V _C +
It is expressed as Δ _H V _C + 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 the problem that, where I is the collector current, a power loss of I(V _C -V _E ) occurs, and when the DC 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. The present invention relates to a power filter having a series insertion type voltage stabilizing element and an AC voltage component stabilizing means for stabilizing a voltage control signal of the element with respect to an AC voltage component of a signal input to the element.

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

(Structure and operation of the invention) FIG. 3 is a reference diagram for explaining the invention. In the figure, Tr is a transistor that constitutes a voltage stabilizing element, and is used as an emitter follower as shown. For example, a signal (containing ripple components) obtained by rectifying and smoothing a signal appearing on the secondary side of a high frequency transformer of a switching power supply is supplied to the collector. The emitter is also connected to a load (not shown). transistor
An element Z composed of any one of a resistor, a coil, or a diode is connected between the collector and base of the Tr. Also the transistor Tr
A capacitor _C6 is connected to the base of.
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 completely blocked while minimizing power loss between the collector and emitter. Generally, a switching power supply performs the output voltage stabilization function on a part of the high frequency transformer, so even if the filter of this circuit is used, output voltage stabilization will not be impaired.

Next, an experimental example using this circuit and the power filter shown in FIG. 1 will be shown. In Figure 1, C ₁ =C ₂ =
When 2200 μF and L = 240 μH, the output ripple is high frequency ripple Δ _H V _C = 100 mV _PP and low frequency ripple Δ _L V _C = 40 mV _PP , whereas in the circuit of the present invention, C ₅ = C ₆ = 220 μF, C ₇ = 100μF, collector
When the resistance value connected between the bases is 75Ω, high frequency ripple Δ _H V _C = 2mV _PP , low frequency ripple Δ _L
V _C =2 mV _PP , and the ripple removal rate between the collector and emitter of the transistor was 50 dB or more. Note that 2SC2334 was used as the transistor. Therefore, according to this circuit, even if the capacitance of the capacitor is 1/10 that of the conventional capacitor, the ripple removal effect is large, and as a result, the cost of the entire power supply device can be reduced. Also, the actual loss of this circuit is 1.3
×(output current). This is because, as described above, the voltage value between the collector and emitter of the transistor is set to a value close to the collector saturation voltage of the transistor.

FIG. 4 shows an embodiment of the present invention. The feature of the present invention is that a resistor R is connected to the collector of the circuit described above. This is due to the following reason. In other words, in general, when a transistor is saturated, V _BEO >
V _CEO , and in a basic ripple filter circuit
A transistor that can withstand collector loss of I _O (V _R +V _BEO ) must be used. Also, when this transistor operates, the voltage between the collector and emitter is
V _CE cannot become smaller than V _R +V _BE even if the collector-emitter saturation voltage V _CEO is low, and V _CE = V _R +
Since V _BE, the transistor loss is I _O (V _R +
V _BEO ), which is the loss at transistor saturation.
I _AO・V Bigger than _CEO . However, V _R is the voltage drop caused by the resistor R connected to the collector of the transistor, and I _O is the maximum collector current value. The maximum allowable collector loss of a transistor is V _CEO・I _O , so I _O
(V _BEO − V _CEO ) need not be consumed by the transistor. For this reason, in the embodiment shown in FIG. 4, a resistor R is connected in series to the collector, and I _O (V _BEO −V _CEO )
This amount is consumed by this resistance R. Therefore, the collector loss of the transistor shown in FIG. 4 can be made smaller than that of the transistor used in FIG. 3, and as a result, an inexpensive transistor can be used. Specifically, if a general transistor with V _BEO = 0.7 and V _CEO = 0.4 V is used, and the collector current I _O = 1 A, in the conventional example, the transistor consumes V _BEO × I _O = 0.7 × 1 = 0.7 W. Must. On the other hand, according to this embodiment, the resistor R=
If you insert 0.3Ω, this resistance R will result in 0.3Ω×1A=
A voltage drop of 0.3V occurs and V _CE decreases to V _CEO = 0.4V. At this time, V _BE remains at 0.7V. Therefore, the total loss remains unchanged at 0.7W, but the transistor loss becomes 0.4W, allowing the use of smaller transistors. Other features are similar 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 used in a switching power supply or the like, it can provide a compact, high-efficiency, and low-noise power supply suitable for audio equipment, precision measuring instruments, and the like.

[Brief explanation of the drawing]

Figure 1 shows an example of the configuration of a conventional power filter;
3 is a reference diagram for explaining the present invention, and FIG. 4 is a circuit diagram of an embodiment of the power filter according to the present invention. Tr...transistor, _C1 to _C7 ...capacitor,
R, R ₁ ...Resistance, L...Smooth York coil,
ZD...Zener diode, Z...element.

Claims (1)

[Claims for Utility Model Registration] A resistor is connected in series to the collector of a transistor, and an element consisting of one of a resistor, a coil, or a diode is connected between one end of the resistor and the base of the transistor. and a capacitor is connected to the base of the transistor, and the product of the resistance value R and the maximum collector current I _O is set equal to the value obtained by subtracting the collector-emitter voltage V _CE from the base-emitter voltage V _BE of the transistor. A power filter characterized by: