Control high power electromagnetic valve 24V. Is there anything wrong with the use of thyristor?

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Control high power electromagnetic valve 24V. Is there anything wrong with the use of thyristor? [Copy link]

 

1. Now the collector of Q5 is measured to be 0 2. The base terminal is 2.7V and PMW is 3V

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24V uses AC

maychang

Changban Jiujiu published on 2020-3-6 15:47 24V uses AC

What is the relationship between your AC24V and the GND in the picture? Where is the S terminal connected to? Is it connected to the "high-power electromagnetic valve"? Where is the other end of the "high-power electromagnetic valve" connected to?

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maychang posted on 2020-3-6 16:10 What is the relationship between your AC24V and the GND in the figure? Where is the S terminal connected to? Is it connected to the "high-power electromagnetic valve"? &ld ...

AC24V is the PCB input power supply. GND in the figure is the common ground after AC is converted to DC24V, which is not isolated. S is the output terminal. RL is P: valve output

maychang

Changban Jiujiu published on 2020-3-6 16:27 AC24V is the PCB input power supply. GND in the figure is the common ground after AC is converted to DC24V, which is not isolated. S end is the output end. RL is P: valve output

The J3 marking in the first post's electrical schematic is inconsistent with the text description in the 4th post. There is no mention of AC24V to DC24V conversion in the first post's diagram or text description.

Please draw the electrical schematic completely, otherwise I can't help you.

maychang

Changban Jiujiu published on 2020-3-6 16:27 AC24V is the PCB input power supply. GND in the figure is the common ground after AC is converted to DC24V, which is not isolated. S end is the output end. RL is P: valve output

If the first post says "GND in the picture is the common ground after AC is converted to DC24V", this "AC to DC" is industrial frequency rectification, the circuit in the first post is probably problematic.

The bidirectional thyristor gate voltage must be referenced to A1.

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maychang published on 2020-3-6 16:49 If the first post "GND in the figure is the common ground after AC to DC24V", this "AC to DC" is power frequency rectification, the first post circuit...

1. The entire PCB power supply is AC24 input converted into DC24V and all subsequent ones use one GND.

2. Pin 1 of J3 connector is pump switch, pin 2 is AC24, and pin 3 is valve switch

3. PWM signal given by STM32

maychang

常伴久久发表于2020-3-6 18:16 maychang 发表于2020-3-6 16:49 If the first post "GND in the figure is the common ground after AC to DC24V", this "AC to...

It turns out that the rectifier circuit you are using is half-wave rectifier.

Since it is half-wave rectification and R100 is zero ohm, AC24V- and GND are actually one node. In other words, the three marks of AC24V-, ground wire and DC24V- are the same point.

In this way, the bidirectional thyristor in the first post can be triggered by -5V through Q5 and Q8.

maychang

常伴久久发表于2020-3-6 18:16 maychang 发表于2020-3-6 16:49 If the first post "GND in the figure is the common ground after AC to DC24V", this "AC to...

I looked at your power supply layout again.

The AC 24V is half-wave rectified and filtered into DC, and then converted into 5V by U8. The 5V is converted into -5V by U11 and converted into 3.3V by U9.

It's quite troublesome.

maychang

常伴久久发表于2020-3-6 18:16 maychang 发表于2020-3-6 16:49 If the first post "GND in the figure is the common ground after AC to DC24V", this "AC to...

However, with this arrangement of the power supply, Q5 and Q8 cannot be turned off when the STM32 outputs a low level. This is the error in this circuit.

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maychang posted on 2020-3-6 19:16 However, with this arrangement of the power supply, Q5 and Q8 cannot be turned off when the STM32 outputs a low level. This is the error of this circuit.

Now I measured that the collector of Q5 has no voltage and the base terminal is 2.7V. I don't know where the problem is.

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maychang posted on 2020-3-6 19:16 However, with this arrangement of the power supply, Q5 and Q8 cannot be turned off when the STM32 outputs a low level. This is the error of this circuit.

Please give me some advice

maychang

Changban Jiujiu published on 2020-3-6 20:30 Please give me some advice

Let’s first explain why it is impossible to shut down Q5 and Q8.

Assuming that the PWM1 pin of STM32 is 0V and current is allowed to flow out (this is very important and will be discussed later), there are two PN junction voltage drops from PWM1 to -5V, one is D2, the other is Q5 emitter junction, and R27. Therefore, the current in R27 is determined to be (5-2*0.7)/3.3=1.1(mA). 1.1mA current flows into the base of Q5, which can completely make Q5 saturated and turned on.

If the STM32 outputs a high level at PWM1, a larger base current must flow into Q5, and it will still be saturated and turned on.

Therefore, the level change at PWM1 cannot control the on and off of Q5, and cannot control the thyristor.

maychang

Changban Jiujiu published on 2020-3-6 20:30 Please give me some advice

The bidirectional thyristor model you selected is BTA08, which is a thyristor with a maximum continuous current of 8A. Its maximum trigger current requirement is 100mA, but your Q5 and R34 cannot guarantee that the thyristor gate trigger current reaches 100mA when Q5 is saturated, and it is only 20mA at most. In this way, it is very likely that the thyristor cannot be triggered.

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maychang posted on 2020-3-7 08:05 The bidirectional thyristor model you selected is BTA08, which is a thyristor with a maximum continuous current of 8A. Its maximum trigger current requirement is 100mA, and your Q5, R3 ...

Can I add QQ? 630219845

maychang

I don't know why this post was posted on the PCB page. It should have been posted on the simulation page or the power supply page.

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maychang posted on 2020-3-7 11:08 I don't know why this post was posted on the PCB page. It should be posted on the analog page or the power page.

How about replacing Q5 with M0C3062

maychang

Changban Jiujiu published on 2020-3-7 12:38 How about replacing Q5 with M0C3062

This should have been considered from the beginning.

By using optocoupler isolation, you can save the power chip that converts +5V to -5V (this chip cannot supply 100mA of current at all). You can even save the chip that converts 24V to +5V, and directly convert 24V to 3.3V for STM32. STM32 cannot directly drive the optocoupler, so you can add a transistor. The 3.3V voltage is enough to drive the optocoupler.

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maychang posted on 2020-3-7 14:57 This should have been done long ago. This arrangement should have been considered from the beginning of the design. Using optocoupler isolation can save the power chip that converts +5V to -5V (the...

But we need to consider the problem of common ground at the output end

maychang

Changban Jiujiu published on 2020-3-7 14:59 But we need to consider the problem of common ground at the output end

Using optocouplers can easily solve the common ground problem.

In the original circuit, if you are not experienced in drawing circuit boards, it is easy to let the current of the pump and solenoid valve and the STM32 power supply current flow through the same ground line, which is a very bad thing. Now that the optocoupler is introduced, this will not happen. The AC current used by the pump and solenoid valve and the DC current used by the STM32 will not flow through the same ground line.

The original design was pretty stupid.