The ringing ASIC requires a DC voltage of a certain polarity to operate normally, and the ringing voltage is an AC voltage of 25 Hz. Therefore, the AC power must first be converted to DC power to supply an oscillator that can generate two different frequencies. The 25Hz AC ringing voltage sent from the line is blocked by the capacitor, and the 48V DC voltage is separated from the ringing circuit, and only the AC ringing voltage is allowed to pass. Then, after rectification and filtering, it becomes a relatively smooth DC voltage. The DC voltage is applied to the oscillating circuit, the oscillator oscillates, and the power output stage outputs alternating two different frequency audio voltages to drive the moving coil speaker or the piezoelectric speaker to emit a pleasant sound.
I. Ringing ASIC
Ringing ASICs can be divided into two categories: one is the need for external rectifier circuits and voltage regulators (26 ~ 28V), the circuit principle, performance indicators and package leads are basically the same, the difference is only the use of 2 feet Such as CSC8204, LS8204, LH48204, TA31001P, KA2410, KA241 1, TA31002P, HY9106, etc.; the other type has internal rectifier circuit and Zener diode, and some also have thyristor protection circuit, such integrated circuit has LSl240/A , LHl240, TCMl512A and MC34017.
Second, the actual circuit analysis
1. Ringing circuit composed of CS8204
The ringing circuit composed of CS8204 is shown in Figure 1. This circuit can be used directly in a telephone or as an extended ringing. The AC ringing voltage sent by the line is applied to the a and b terminals, and is stepped down by the DC blocking capacitor C1 and the current limiting resistor R1, and then sent to V1 to V4 for rectification, and filtered by C2 to become a smoother DC voltage for use by the LS8204. . VZl is a Zener diode for protection. It can limit the DC voltage delivered to CS8204 to below 27V, thus ensuring the safety of CS8204. After the rectification, the smoother DC voltage exceeds the starting voltage (ie, the starting voltage), and the oscillator begins to oscillate. The 5t2Hz and 640Hz output signals alternate under the frequency switching control of 10Hz, output from the 8th pin of CS8204, via C4, SWl, R5 or R6 is sent to the transformer T1 to drive the speaker B1 to make a sound. Since the output impedance of the CS8204 is about 1kÎ©, and the impedance of the speaker is only 8Î©, the output transformer T1 should have a ratio of 1300:8 for impedance matching.
C4 has a resistance of 1Î¼F and has a high enough impedance at the oscillating operating frequency to avoid affecting the power supply when the load impedance changes. When the load impedance is large enough, the capacity of the C4 can also be increased. SW1 is used to convert the output volume, and R5 and R6 are current limiting resistors.
2. Ringing circuit composed of LHl240
The ringing circuit composed of LH1240 is shown in Figure 2. LH1240A single-chip electronic ringing circuit has the characteristics of low current consumption, internal self-contained rectifier circuit and Zener diode circuit. The tone and switching frequency can be adjusted by external components, and the hysteresis of voltage and current is unified. Working principle: The 25 Hz, 90V AC ringing voltage sent from the line is applied to the 8th and 1st feet of the LH1240A via C1 and R1, and then becomes a DC voltage of a certain amplitude through the internal rectifier circuit and the Zener diode circuit. The use of an oscillating circuit and a power amplifier inside the integrated circuit is provided. LHl240A's 2 pin is the grounding pin, 7 pin is the internal rectifier filter pin, C2 is the power supply filter capacitor: 3 pin is the control pin to control the scanning rate, changing the C3's capacitance can change the ringing output frequency switching speed, 4 feet is Output frequency control pin, change the resistance value of R2 to change the frequency of the output ringtone, that is, change the ring tone; 5 pin is the ringer output pin, the output impedance is greater than 1kÎ©, R4 is the current limiting resistor, and the ringtone increases when short circuited. The LH1240 circuit can directly drive the piezo-ceramic buzzer. If the integrated circuit is used to drive the moving coil speaker, a transformer is required. The two tone frequencies f1 and f2 are repeatedly and repeatedly generated by the internal oscillator, and are amplified by the power amplifier to drive the speaker.
Output frequency: F1 = 2.7 Ã— 104 / R2 (kÎ©): â€‹â€‹F2 = O.725F1. Scanning frequency: FS=750/C3nF). The technical requirements for using the electronic ringing circuit telephone are: the ringing power sensitivity is not more than 100mVA (operating current is about 11mA); the ringing volume is â‰¥70dB(A); the telephone with the volume adjustment function, the low-end ringing volume is â‰¥55dB ( A).
Third, for audio physiotherapy
1. Use the cs8204 ringing circuit to make an audio physiotherapy instrument (as shown in Figure 3).
CS82041 pin (VCC) is connected to the positive power supply, 2 pin (TR) is the trigger terminal, 3 pin (CL) low frequency oscillator external capacitor r4 pin (RL) low frequency oscillator external resistor, change the external resistor or capacitor, you can change the low frequency oscillation frequency. 5 pin (VSS) is grounded. 6-pin (RH) high-frequency oscillator external resistor, 7-pin (CH) high-frequency oscillator external capacitor, change the external resistor or capacitor, can change the high-frequency oscillation frequency.
fL low frequency: fL = 1 gate. 234W1 (kÎ©), when the low frequency oscillator output is high, the high frequency frequency fH1 = 1 / 1.515W2. When the low frequency oscillator output is low, fH2 = 1.25 fH1 low frequency oscillator determines the switching rate of the high frequency. R7 is a current limiting resistor, W1 is a low frequency frequency adjustment, W2 high frequency frequency adjustment, and W3 audio output intensity adjustment. Reverse the ringing output transformer (8:1300), R5, R6 is the transformer primary current limiting resistor, such as secondary voltage, current is too large, with R6 current limit.
2. Use the LHl240 ringing circuit to make an audio physiotherapy instrument (as shown in Figure 4).
The 48V AC voltage sent by transformer transformer is rectified by D1 to obtain the voltage of 25Hz and 21.2V, which is added to the 8th and 1st pins of LHl240A, and then becomes a certain amplitude through the internal rectifier circuit and Zener diode circuit. The DC voltage is supplied to the oscillating circuit and power amplifier inside the integrated circuit. LH1240A's 1 and 8 feet are AC input terminals, 2 feet are grounding pins, and 3 feet are switching speed control pins. By changing the C3's capacitance, the switching speed of the ringing output frequency can be changed. Pin 4 is the output frequency control pin. Changing the resistance of R2 can change the frequency of the output ringtone. Pin 5 is the audio output. Pin 7 is the internal rectifier filter pin and C2 is the power supply filter capacitor. R4 is the primary current limiting resistor of the transformer, R5 is the secondary current limiting resistor, W1 is the audio frequency adjustment, and W2 is the audio output intensity adjustment.
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