In the power amplifier, emt1237 special protection integrated circuit emt1237 is mostly used. Pay attention to some problems when using it, otherwise it may lose its protection due to improper use, and may seriously damage the integrated block (mainly the power supply voltage is not suitable). Each foot's function and application notes 1. Pin1 pin is the DC current overload detection of the output of the power amplifier. This pin is connected to the E pole of the power amplifier power tube through the amplifier circuit. When overcurrent occurs for some reason, it will occur when the E pole is connected in series with a resistance of 0.22 Euro Larger voltage, when the voltage exceeding the set value is detected, the relay will be opened. [ 3. When pin3 connection is different, emt1237 works in different ways. That is, latch mode or self-reset mode. When the IC detects overload or overcurrent, the relay is disconnected. If the detection level returns to normal, the relay will automatically pull in, which is called self-reset mode. In order to pull in again, it is a latch method. When pin3 is grounded through a capacitor of 0.22, it is a latch mode; direct grounding is a self-reset mode. Most of them are latched. 4. AC power failure detection When the AC switch is turned off, the power loss of the amplifier is a transient process, and the midpoint potential cannot be immediately zero, which is manifested as a shock sound, and even damages the speaker. Connect pin4 to the primary of the transformer through R6. When the power is turned off, the IC immediately disconnects the relay. Thus playing a protective role. The value of R6 can be checked It is the power-on delay. The delay time is determined by the values ​​of C3 and R7 on pin7.
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2. Pin 2 is the midpoint voltage protection.
5. Start mute
6. Pin8 is the power supply, and the power supply voltage of emt1237 cannot exceed 8V, typically 3.40V, so R8 must take an appropriate value, please refer to the table for details.
7. Pin6 relay drive. The maximum drive current of this pin is 80MA, and the value of R12 should be determined according to this current value and the power supply voltage used.