Sensor circuit analysis, about flame detector

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Sensor circuit analysis, about flame detector [Copy link]

This circuit contains two functions, one is to generate high voltage by self-excitation, and the second is to generate a negative voltage, VCC is 24v. Now I can't figure out these two circuits.

maychang

This doesn't look like a correct circuit. Even the DC path is incorrect, and the circuit doesn't seem to be able to generate any self-excitation.

maychang

"VCC is 24v" There is no VCC label in the first picture. The text description should always be consistent with the electrical schematic, right?

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I have another question. What does it mean that the base of DB237 is grounded through a resistor? Is this how transistors are used?

maychang

Simulation 123456 Published on 2019-1-13 11:36 I have another question. What does it mean that the base of DB237 is grounded through a resistor? Is this used in transistors?

"What does it mean that the base of DB237 is grounded through a resistor? Is this used in transistors?" Yes, it is used in this way.

模拟123456

maychang posted on 2019-1-13 11:34 "VCC is 24v" There is no VCC label in the first post. The text description should always be consistent with the electrical schematic, right?

The mobile phone photo in the first post is not clear, and VC1 is not shown. VC1 is vcc. This picture is the original picture. What does it mean that the DC circuit is different? The base of the BD237 is grounded through a resistor. Can it still be turned on? Is it related to the generation of -VC1?

maychang

Simulation 123456 Posted on 2019-1-13 12:08 The photo taken by the mobile phone in the first post is not clear, and VC1 is not shown. VC1 is vcc. This picture is the original picture. What does the different DC path mean? The BD237...

The electrical schematic diagram in the first post has VC1 and -Vc1, but no VCC. The DC path is incorrect, which means that the resistance of Q2 emitter to GND is very large, and it is connected to VC1 through a 100k resistor.

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maychang posted on 2019-1-13 12:22 The first post There is VC1 and -Vc1 in the electrical schematic, but no VCC. The DC path is incorrect, which means that the resistance of Q2 emitter to GND is very large, and...

The DC path passes through the coil of the voltage regulator.

maychang

Simulation 123456 Published on 2019-1-13 14:11 The DC path passes through the coil of the voltage regulator

No matter how you look at it, this circuit cannot produce self-excited oscillation. After power-on, 24V (assuming VC1 is the VCC mentioned in the text) is applied to the collector of Q2 through the primary side of the transformer, but there is no path from the emitter of Q2 to GND: Q4 cannot be turned on because there is no base bias; Q5 also cannot be turned on because there is no base bias. The cathode of diode D9 is connected to 24V through a 100k resistor and cannot be turned on. There is no path to the emitter of Q2, so there is no current in the primary side of the transformer.

maychang

Simulation 123456 posted on 2019-1-13 14:11 The DC path passes through the coil of the voltage generator

Again: it doesn't look like a correct circuit. This circuit doesn't seem to be able to produce any self-excitation.