JPS586332B2 - Shichiyouhatsushin Cairo - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention uses a negative resistance element, such as a constant voltage element, such as a Zener diode, to reduce the difference between the discharge start voltage and discharge stop voltage of a discharge tube, thereby reducing the oscillation period. This invention relates to a relaxation oscillation circuit that can reduce the oscillator.

゛ Conventionally, as shown in Figure 1, a relaxation oscillation circuit using a negative resistance element has been constructed by connecting a series circuit in which a resistor R and a capacitor C are connected in series to a DC battery E, and connecting the capacitor C with a negative resistance element. Discharge tube NL such as neon tube as a resistance element
It is known that these are connected in parallel.

In such a circuit, assuming that the discharge voltage of the discharge tube NL is VB and the discharge stop voltage is Vs, the terminal voltage Vc of the capacitor C is the waveform of the discharge start voltage vB and the discharge stop voltage, as shown in Figure 2. Since it changes between Vs and Vs, the oscillation period is determined by the following equation.

By the way, the discharge starting voltage VB and the discharge stopping voltage Vs in the discharge tube NL are usually unique and fixed. For example, if the discharge starting voltage vB is constant, the discharge stopping voltage Vs is also fixed constant, and it can be set arbitrarily. That is difficult.

This also applies to other negative resistance elements.

Therefore, in this type of circuit, if the oscillation period is to be arbitrarily set, this must be done by selecting the value of the resistor R or capacitor C.

However, as shown in Fig. 2, which is equivalently shown by connecting a DC power source E and an AC power source in series, an AC voltage is superimposed on a DC voltage and applied to a series circuit of a resistor R and a capacitor C (this This often happens when the configuration of a power supply circuit that rectifies and smoothes alternating current to convert it to direct current is simplified.

) It is necessary to prevent the negative resistance element from operating due to the alternating current component, that is, to prevent the discharge tube from starting discharge in response to the voltage of the alternating current component.

Therefore, in such a circuit, the terminal voltage ■c of the capacitor C must satisfy the condition (where Em is the maximum value of the AC voltage), that is, when the resistor R and the capacitor C are in series circuit, The constant must be set to a certain value or higher.

Therefore, in such a circuit, there is a problem that the oscillation period cannot be made smaller than the oscillation period determined by the above-mentioned time constant.

This invention was made in view of these problems, and even when an AC voltage is superimposed on a DC voltage, the oscillation period is set so that the circuit does not respond to the AC component. This invention provides a relaxation oscillation circuit that can be set even smaller than the time constant determined by this.

Examples of the present invention will be described below.

Note that parts common to the circuits shown in FIGS. 1 and 3 described above will be described with the same reference numerals.

First, to explain the embodiment shown in FIG. 4, a series circuit in which a resistor R and a capacitor C are connected in series is connected to a DC power source E, and a discharge tube NL and a constant voltage element are connected to the capacitor C of the series circuit. A series circuit in which a Zener diode DZ is connected in series is connected in parallel.

With such a configuration, the terminal voltage Vo of capacitor C
When the discharge tube NL starts discharging, Vc=VB
(4), and when the discharge is stopped, if the Zener voltage of the Zener diode Dz is Vz, then Vc=Vs+VZ
(5), and the voltage waveform changes between voltage vB and voltage vs+VZD, as shown in FIG.

Therefore, the oscillation period .tau.2 in this case is as follows. Compared with the conventional device 1 shown in FIG. 1, this embodiment has a smaller oscillation period if CR is constant.

In other words, even if the value of CR is set to a certain value so that the circuit does not respond to alternating current, the CR
The oscillation period can be made smaller than the oscillation period determined by .

More specifically, if the Zener diode DZ is connected in series to the discharge tube NL, which is a negative resistance element, as shown in the schematic diagram of FIG. 4, as is clear from the waveform diagram shown in FIG. When the first oscillation is performed by discharging the charge in the capacitor C through the discharge tube NL and the Zener diode DZ, for the second and subsequent oscillations, the capacitor C must be charged by VB-(VZ+Vs). As long as it is charged, it will be fine.

Therefore, in a CR circuit with the same time constant, the charging voltage is (V
B-Vs) to (VB-Vs-Vz).

The reason is that the discharge stop voltage of the capacitor C becomes lower in the second and subsequent oscillations.

In other words, when the discharge of capacitor C stops, discharge tube N
Although the voltage of L1 has decreased to Vs, the relationship between the two is as shown in equation (5).

In other words, the discharge of the capacitor C stops at a voltage higher than Vs by the Zener voltage Vz of the Zener diode DZ.

Therefore, the voltage that must be charged again for the next oscillation is (vB-vs-vz), which is lower than in the case without the Zener diode DZ.

However, the discharge starting voltage vB is not affected by the presence or absence of the Zener diode DZ because no current flows through the Zener diode Dz, so VZ=O.

In addition, by connecting the constant voltage element DZ in series with the negative resistor NL, that is, by using the Zener diode DZ as a discharge tube NL, the input impedance seen from the radio wave side can be lowered, so it can respond with high sensitivity to weak signals. It will also be possible to do so.

Next, the embodiment shown in FIG. 6 will be explained.

In this embodiment, a resistor r is connected in parallel to the constant voltage element, that is, the Zener diode DZ in the embodiment shown in FIG.

This is because the Zener diode Dz usually has a stray capacitance of about several hundred picofarads, which is why the Zener voltage V
Pulsation occurs in s, making it impossible to maintain a constant voltage, causing a drop in the discharge stop voltage of the discharge tube NL, increasing the oscillation period, and causing the problem that the input impedance cannot be reduced. Therefore, a resistor r is provided to eliminate the adverse effects of such stray capacitance.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram showing a conventional relaxation oscillation circuit, Fig. 2 is a waveform diagram of the capacitor terminal voltage of the same circuit, Fig. 3 is an equivalent circuit diagram when an AC voltage is superimposed on the DC radio wave voltage of the same circuit,
FIG. 4 is a circuit diagram showing one embodiment of the invention, FIG. 5 is a waveform diagram of the capacitor terminal voltage of the same embodiment, and FIG. 6 is a circuit diagram showing another embodiment of the invention. E...DC power supply, R...resistance, C capacitor, NL
...Negative resistance element, DZ... Constant voltage element, r...
resistance.

Claims (1)

[Claims] 1. Relaxation oscillation comprising a series circuit of a resistor and a capacitor connected to a DC power supply, and a series circuit of a negative resistance element and a constant voltage Zener diode connected in parallel to the capacitor of this series circuit. circuit. 2. A series circuit of a DC power supply, a resistor and a capacitor connected to this power supply, a series circuit of a negative resistance element and a constant voltage Zener diode connected in parallel to the capacitor of this series circuit, and a series circuit of a constant voltage Zener diode. a relaxation oscillator circuit comprising a resistor connected to 11;