Alarm circuit of a typical electromagnetic stove

Alarm circuit of a typical electromagnetic stove

Shown is the alarm circuit of a typical induction cooker. If the induction cooker is starting, stopping, turning on, or in a protection state
, the buzzer must sound in order to remind the user.
    This circuit uses a voltage comparator LM324 . It is actually an operational amplifier . This operational amplifier
changes according to the input signal level of pin ◎ and pin @, and the signal output by pin ⑧ will also change.
    The 12 V voltage is added to one end of the buzzer through the lead, and the other end of the buzzer is connected to the @ pin of the operational amplifier LM324 (D). Since
one end of the buzzer is 12 V. If the other end is lower than 12 V, a current will be generated in the buzzer, which will make the buzzer sound.
If the operational amplifier LM324 (D) outputs a pulse signal, the buzzer will also sound and tone. Something changes, and that's
how the buzzer is driven.
    When the buzzer sounds and when it doesn't sound is mainly controlled by the control circuit. For example, when the microprocessor circuit detects overheating
, overvoltage, etc. or changes working status, it will generate a control signal, and the control signal is sent to the Q16 reverse control
transistor . If the control signal sent to Q16 is High level, the transistor Q16 will be turned on. After Q16 is turned on, the collector of the transistor will be grounded,
and the base of the transistor Q15 will also be grounded, and the transistor Q15 will be turned off. On the contrary, when the transistor QJ6 is turned off, the transistor Q15 will be turned on.
After the transistor Q15 is turned on, the ⑨ pin of the operational amplifier LM324 (C) becomes a low voltage: if the transistor Q15 is turned off,
the @ pin of the operational amplifier LM324 (C) is a high voltage. The voltage at pin ⑩ of the operational amplifier LM324 (C) is sent from the power supply through the split-turn circuit, and
this voltage is unchanged. Therefore, the voltage of the control signal is sent to the ⑧ pin of LM324 (C). The level of the @ pin will change
the output of the operational amplifier LM324 (C). The output of the operational amplifier LM324 (C) also controls the transistor Q17. If the output of the operational amplifier LM324 (C)
is high level. The transistor Q17 will be turned on, and the @ pin of the operational amplifier LM324 (D) will become low level. If the transistor Q17
is turned off, the @ pin of the operational amplifier LM324 (D) will become high level. If the level of the @ pin is higher than the @ pin,
the voltage of the @ pin of the operational amplifier LM324 will drop, and the buzzer will sound at the right time. Therefore, whether there is a fault will be detected by detecting the voltage, that is, if
the buzzer does not sound when it is supposed to sound, the voltage of the @ pin of the operational amplifier and the transistor Q17 should be detected. Operational amplifiers C and D are integrated
in LM324. When the buzzer stops alarming, the LM324 should be tested, focusing on the output end. If the output of pin ⑧ and pin @ is abnormal
, you can first check whether the power supply of LM324 is normal. Because the power supply is abnormal, the operational amplifier cannot work properly. If the
voltage is normal but the output is wrong, it means that the operational amplifier LM324 is damaged and needs to be replaced.