This can be achieved in two ways:
1. Implement using a control circuit composed of four relays.
Circuit diagram explanation: This circuit consists of four DC relays. Relays J1, J2, and J3 control three voltage regulators respectively (i.e., their normally open contacts act as power switches for the three power supplies and the three voltage regulators). Relays K1, K2, and K3 are two-contact pushbuttons, serving as start buttons for the three voltage regulators. See the diagram below:
Relay J0, along with R1 and C1, forms a jog control circuit. It is controlled by three buttons, K1 to K3, which are jog buttons and their pressing time should be greater than one second. Pressing button K1 activates branch J0. Since C1 needs to maintain its initial 0V voltage, the voltage in J0 is momentarily increased to 24V, causing J0 to immediately engage. Its normally closed contact opens, de-energizing branches J1 to J3. Subsequently, the internal resistance of J0 charges C1, increasing its voltage from 0. This causes the voltage in J0 to drop from 24V. After a 0.5-second delay, when the voltage in J0 falls below its minimum engagement voltage, J0 disengages, and its normally closed contact closes (reapplying 24V to the upper end of J1 to J3). Since K1 is still pressed (closed), relay J1 is energized and latches (even if the first voltage regulator operates). After a 1-second delay, button K1 is released, de-energizing branch J0. C1 will then discharge through parallel resistor R1 until the voltage across C1 is 0. In other words, the release of button K1 has no effect on branch J0.
If button K2 is pressed again , J0 will be immediately energized and engaged. Since the normally closed contact of J0 opens before the engagement time of J2, the power supply to J1~J3 is disconnected first. 0.5 seconds later, J0 disconnects, and the upper terminals of the three relays are connected to the 24V power supply. Since K2 is still pressed at this time, relay J2 is energized and engaged, thus locking itself. That is, this process first de-energizes the first voltage regulator, and then energizes the second voltage regulator to operate.
This circuit allows only one button to be pressed at a time. Upon pressing, the power supply to three relays is disconnected . After 0.5 seconds, the relay corresponding to the pressed button is energized, closes, and latches, ensuring that only the voltage regulator corresponding to the pressed button operates. The other two circuits remain de-energized.
2. A control circuit is constructed using a microcontroller and three relays, among other components.
Circuit Description: The microcontroller used is 89C2051. P1.0 to P1.2 are connected to three relays (J0, J1, J2), whose contacts serve as power switches for the three voltage regulators. K1, K2, and K3 are the start buttons for the three voltage regulators. See the diagram below:
Programming logic: Similar to the hardware circuit operation, that is: when any start button (such as K1) is pressed , P1.0~P1.2 will immediately output 0 (so that J0~J2 will be de-energized and disconnected), then there will be a 0.5-second delay (i.e., call the 0.5-second delay subroutine), the subroutine will return, and then the output port (such as P1.0) corresponding to the button (K1) will output 1 (high potential), so that the corresponding relay (J0) will be energized and closed, that is, the voltage regulator U1 in the right figure will be energized and work.
Compared to the first type of circuit, the second type is simpler and easier to implement, making it suitable for a wide range of electrical operators.
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