圧電セラミックトランス用素子の一考察
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概要
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Optimal transducer design of piezoelectiric ceramic transformers used for high voltage DC supply, such as DC sources of electrostatic electrography and horizontal deflection circuits of TV receivers are studied in this paper. A ceramic transducer has to be provided with suitable performance in practical use and high durability for a long time. Operating properties of the piezoelectric ceramic transducer in high power drive level is generally non-linear and detriorates with time. However, a ceramic transducer can be used with excellent durability and stability, when transducer is driven within the limits of the linear input level characteristics. The transducer in this paper is designed assuming an input level at a turning point of the linear relation to the non-linear relation with respect to input level characteristics. Such a relation between input resistance and input current is shown in Fig. 2. Resonant frequencies of ceramic transducers with different length ratios of l_g/l_d are calculated. The dimensionless frequency constant (α_1l_d) under conditions of no loading is shown in Fig. 4. For a loaded condition, expressed as a function of Q_<02> (loaded Q) and S (stray capacitance ratio, C_s/C_<02>), the dimensionless frequency constant at the maximum voltage step-up frequency of λ-type resonator (α_1l_d) is shown in Fig. 5. The length ratio of the λ-type resonator in practical use nearly equals √<S^D_<33>/S^E_<11>>, and α_1l_d nearly equals π. Consequently, the equivalent circuit representation shown in Fig. 8 and the relations in eq. (16) are practical and useful in determining the behavior of the ceramic transformer. The maximum voltage step-up ratio (γ_<Lm>) is calculated numerically from eq. (19) and Table 1 of physical constants of the ceramic transducer material as parameters of S and Q_<02>. Dependence of γ_<Lm> on Q_<02> seems to be divided into four portions as shown in Fig. 9. For the first portion, (a) range responding to high Q_<02>, γ_<Lm> can be expressed as eq. (21) which was derived by R. C. Rosen (1956). For the second portion, (b) range responding to medium Q_<02>, γ_<Lm> can be expressed as eq. (22). In the case of application to the horizontal deflection circuit of TV receivers, the values of Q_<02> usually exist in this (b) range. For other two portions, (c) and (d) ranges responding to low Q_<02> and very low Q_<02>, γ_<Lm> can be expressed as eq. (23), or eq. (24) respectively. Requirements of design factors for increasing the tendency of the voltage step-up ratios depend on the value Q_<02>. Design factors for obtaining the optimal voltage step-up ratio in each range of Q_<02>, are listed in Table 2. Other characteristics of the ceramic transformer depending on Q_<02> and S are studied. The field strength of the generator section, V_<out>/l_g is a important design factor depending on the maximum allowable strength (T_<gm>) of the the generator section as in eq. (32). General considerations for transducer design in the range of medium Q_<02> ((b) range) and an example of a 20 kV DC output transducer are described.
- 社団法人日本音響学会の論文
- 1976-08-01