uPC1237 speaker protection circuit diagram

uPC1237 is powered by a single power supply, and the operating voltage range is 25v~60v. It usually directly uses the positive power supply +Vcc of the power amplifier as the power supply. The voltage of the relay coil is DC 24v, because the limit current of pin ⑥ relay driving end is 80mA. When the relay is powered and closed, the voltage of pin ⑥ is about 0v. If the average voltage of Vcc is > 24v, the voltage reducing current limiting resistor R12 must be connected in series. In order to prevent the relay and integrated circuit from overcurrent and heat damage, the corresponding relationship between the resistance value, power consumption and Vcc average voltage of R12 is shown in Table 1. Enthusiasts can determine R12 by looking up Table 1 based on the average vcc voltage value of their own amplifier.

The ⑦ pin of uPC1237 is the power-on delay terminal. The power-on mute time is determined by the R7 and c3 parameters. That is, after power-on, when the power amplifier circuit reaches balance and stability, the delay circuit will allow the relay contact to connect the speaker . This can completely eliminate the power-on shock noise, and increasing c3 or R7 can extend the power-on silent time.

Pin ⑧ of uPC1237 is the power terminal, and the maximum limit value is 8v. When Vcc is different, the resistance value of R8 is correspondingly different, which can be determined by looking up Table 1.

Pin ④ of uPC1237 is the AC power outage detection terminal, which is used to shut down the power amplifier to mute it. When the power switch of the power amplifier is turned off, the secondary AC voltage of the transformer disappears immediately, the c2 small-capacity capacitor is quickly discharged through the internal resistance of pin ④, and the voltage of pin ④ drops rapidly. The internal circuit controls the relay action to disconnect the output terminal of the power amplifier from the speaker to prevent During the transition process after a power outage, the zero level of the power amplifier output terminal causes a current impact on the speaker when it loses balance (i.e., shutdown impact noise). The maximum limit voltage of pin ④ is 10v. When the AC voltage of the secondary winding of the power amplifier power transformer being monitored is different, the value of the voltage dividing and current limiting resistor R6 will be different accordingly. If it is too large or too small, the speaker protection circuit will not work properly. The corresponding relationship between Ac AC voltage and R6 resistance is shown in Table 2.

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Pin ② of uPC1237 is the DC offset detection terminal at the output end of the power amplifier. If the DC offset voltage at the output end of the power amplifier is too large, the DC current flowing in the speaker's voice coil will be too large, the dynamic range of the voice coil will become smaller, and the sound will be distorted. At the same time, the voice coil will be overheated. Very fragile. In order to protect the speaker, pin ② monitors the DC level of the output terminal of the power amplifier. Once the positive or negative offset voltage of the output terminal of the power amplifier exceeds the set threshold, the internal circuit of uPC1237 releases the relay and disconnects the speaker from the output terminal of the power amplifier to protect the speaker. Purpose. As shown in the figure, the positive offset threshold of the power amplifier output terminal is 1.24v, and the negative offset threshold is -1.04v.

Pin ① of uPC1237 is the over-current detection terminal. The left and right channel overcurrent detection terminals L-E and R-E are respectively connected to the emitter resistors of the final NPN amplifier tubes of the left and right channel power amplifiers of discrete components. The voltage on the emitter resistors will increase due to the increase in output current. When the average output current exceeds the rated current value of the power amplifier or speaker, the voltage on the emitter resistor reaches the overcurrent threshold voltage set by the speaker protection circuit, T1, T3, or one of them turns on, causing T2 to turn on, and the Vcc voltage Added to pin ① through T2, R9 and R11, as long as the current flowing into pin ① exceeds 110uA, the internal overcurrent protection circuit will release the relay and disconnect the speaker, achieving the purpose of speaker overcurrent protection. In the figure, the voltage of the L-E and R-E overcurrent detection valves is 0.67v. For integrated circuit power amplifiers, the emitter resistor of the final power amplifier tube is rarely connected. You can consider omitting the overcurrent detection function and only need to connect pin ① to ground.

The ③ pin of uPC1237 is the working mode selection terminal of the speaker protection circuit. Directly connecting pin ③ to the ground is the automatic reset working mode, that is, after the protection circuit operates and the relay disconnects the speaker, if the power amplifier circuit returns to normal, the relay can automatically resume connecting the speaker. Grounding the ③ pin with a 0.022uF capacitor is a latch operation mode, that is, once the relay operates to disconnect the speaker, even if the power amplifier circuit returns to normal, the relay will continue to remain disconnected until the power switch is turned off once and then turned on again. No matter which working mode, the function of the speaker protection circuit remains unchanged, and the uPC1237 parameters mentioned in the figure and in this article are all latched working modes.

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