Electronic Keys & Locks

Level Shifter Schematic Circuit Diagram

Connecting a Conrad DCF Receiver Module to a PLC: The Need for Level Shifting

To interface the open-collector output of the Conrad DCF receiver module (order number 121177) – operating at a low voltage range of 1.5–15 V and featuring an NPN open-collector output – with a PLC demanding a positive-switching 24-V signal at approximately 150 mA, a crucial step involves implementing level shifter. This can be accomplished through a straightforward method: employing a miniature relay that establishes a connection between the positive supply voltage for the module and the DCF module output, as illustrated in Figure 1.

Requirements for Level Shifting: Ensuring Compatibility

In this scenario, it is imperative to ensure that the current load on the DCF output does not surpass 1 mA. This solution mandates a 15-V miniature relay with a coil voltage that is compatible, eliminating the necessity for the DCF output to sink more than 1 mA. Remarkably, there are no specific demands on the PLC side, as practically any relay with suitable specifications can handle the task of switching 24 VDC at 150 mA. Besides the conventional electromechanical approach, there is an alternative electronic solution available.

Level Shifter Schematic Circuit Diagram

Creating a Level Shifter without Electrical Isolation: Using Resistors and Transistors

If you’re willing to forgo electrical isolation between two devices. All you require are two resistors and a transistor, as demonstrated in Figure 2. This setup offers a solution without the need for isolation. You have the flexibility to choose any type of Darlington transistor without an integrated resistor or opt for a p-channel MOSFET. Compatible options include BC516 or BD680, but not TIP142. The circuit grounds of both devices are interconnected. Notably, this compact level shifter isn’t limited to a singular application. It showcases how an open-collector output can seamlessly connect to a system with a different supply voltage.

Understanding the Role of Transistors in Electrical Regulation

Transistors, essential components in modern electronics, are miniature semiconductors that not only regulate and control current or voltage flow but also amplify and generate these electrical signals, functioning as switches or gates. Typically, transistors consist of three layers or terminals made of semiconductor material, each capable of carrying a current.

Characteristics of BD680 Transistor

  • Type: PNP
  • Collector-Emitter Voltage, max: -80 V
  • Collector-Base Voltage, max: -80 V
  • Emitter-Base Voltage, max: -5 V
  • Collector Current − Continuous, max: -4 A
  • Collector Dissipation: 40 W
  • DC Current Gain (hfe): 750
  • Operating and Storage Junction Temperature Range: -65 to +150 °C
  • Package: TO-126
  • Electrically Similar to the Popular MJE702 transistor

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