How do I switch the power supply?

cgha

How do I switch the power supply? [Copy link]

 

I am now driving a solenoid valve, which requires a 24V starting voltage. However, this voltage cannot be on for too long. It needs to be switched to 6V to maintain the voltage immediately after starting. Otherwise, the solenoid valve will easily overheat and be damaged. I am currently using the microcontroller pin driver to switch, but sometimes I don't notice it during simulation and it is still easy to cause 24V to be powered on for a long time. Is there a circuit that can automatically switch to 6V to maintain the voltage after a short period of 24V power-on?

huo_hu

I think the current should be controlled, and a capacitor should be used to provide a large current.

huo_hu

PWM adjustment is also OK, provided there are no mechanical components

cgha

I am currently operating it through a relay. After 24V is turned on, it switches to 6V through a timer. Now I want to know if there is any hardware that can achieve this function. I think this is safer.

qwqwqw2088

The hardware definitely exists, it just depends on how it is implemented.

PWM control, adding MCU control is also a solution

qwqwqw2088

In addition,

We need to figure out what order of magnitude this time is.

If you want to add a hardware control, you can consider choosing a suitable time relay.

maychang

[I am now driving a solenoid valve, which requires a 24V starting voltage, but this voltage cannot last too long. It needs to be switched to 6V immediately after starting to maintain it.]

[The time cannot be too long] How long is it?

cgha

24V needs 100ms, and then immediately switch to 6V. I am currently implementing this through MCU software control of the relay, but I am afraid that there will be problems with the software, such as the relay running away, so I would like to ask if it can be implemented in hardware to be safer. I originally wanted to add a monostable circuit, but I read online that the trigger time of the monostable needs to be shorter than the delay time, which does not apply to my situation. My situation is to avoid the solenoid valve from overheating and burning due to the input trigger time being too long. I also checked and found that a differential circuit should be added before the monostable circuit. Is this too complicated?

maychang

cgha posted on 2023-6-5 11:24 24V needs 100ms, and then immediately switch to 6V. I am now using MCU software to control the relay to achieve this, but I am afraid that the software will have problems, such as running away, so...

The simplest way to implement a 100ms delay in hardware is to use a monostable chip.

A differential circuit is nothing more than a resistor and a capacitor, and is not complicated.

aple0807

This shows that your software structure is not well designed. If you do a good job of function encapsulation, this problem will not exist at all.

chunyang

The appropriate solution needs to consider power consumption. If the requirement for low power consumption is high, a monostable circuit can be used with a MOS tube switch to switch between 24V/6V. The cost of this solution is relatively high. If you don't care about power consumption, you can directly use 24V for power supply, the MOS tube controls the switch, and then connect a resistor in series. The resistance value is to reduce the voltage to 6V. At the same time, connect an electrolytic capacitor of sufficient capacity in parallel to the resistor, and use the charging of the electrolytic capacitor to provide sufficient driving current. The larger the capacitance, the greater the driving current that can be provided. This solution is simple and low in cost, but it is necessary to examine the characteristics of the solenoid valve, and it may not necessarily work. In addition, if the power is turned on again after a short power outage, the capacitor cannot provide a large starting current if the stored electricity is not fully discharged.

In fact, full MCU control is possible, and there is no need to use a 6V power supply. It can be driven based on PWM. This solution is the best solution as long as the solenoid valve supports this working mode, and both cost and reliability are optimal. The malfunction problem can be solved by adopting appropriate logic design, and the reliability of the dual power switching method can also be solved through reasonable design.

led2015

Commonly used chips such as TPS22965 or TPS22966 provide a low resistance channel in normally open mode. Once a start signal is received, it automatically switches to normally closed mode and provides a high blocking channel.

xutong

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