Oscillators Circuit Diagrams

Compact RS232 Isolator Schematic Circuit Diagram

Creating an Electrically Isolated RS232 Connection with MAX252

Compact RS232 isolator: An RS232 serial port is commonly utilized by repair technicians for diagnostics and service updates. Additionally, it can serve as a means to control a device when connected to a computer managing a home automation system or a custom integrated audio/video (A/V) system like the CAV-M1000ES Multi-room A/V Distribution System. The MAX252 from Maxim presents a specialized IC designed for establishing an electrically isolated RS232 connection. Such connections prove crucial when interconnecting various pieces of equipment, whether isolated from the mains or not that exhibit different earth potentials.

This chip comes in two variants: A (costlier) and B (more economical). It’s worth noting that the term “inexpensive” is relative, as the B type still carries a price tag of over $30. The B-type offers a maximum isolation voltage of 500 V for one minute, while the A-type can handle up to 1250 V. Furthermore, the A-type can maintain a constant voltage across its terminals of 130 V. Both types support a maximum transmission speed of 9600 baud.

Compact RS232 isoltaer

Creating an Electrically Isolated RS232 Connection with MAX252

The chip’s internal transformer supplies the voltage for the right-hand side of the diagram. On the left-hand side, the input and output levels are TTL-compatible. The inputs exhibit a hysteresis of approximately 0.5 V and incorporate pull-up current sources of 0.4 pA to effectively suppress noise signals. The inputs and outputs on the right-hand side adhere to RS232 compatibility standards. Outputs T1 and T20 provide a 7.5 V voltage to a 3 kΩ load. When operating with a 5 V supply voltage, the IC consumes a current of 90 mA.

Pin 11 of the MAX252 functions as an active-low output-enable input, while pin 3 serves as an active-high shut-down input. A high level at pin 3 prompts the deactivation of the 130 kHz oscillator in the integrated supply, leading T1out and T2out to transition into a high-impedance state. Additionally, the 4 μA pull-up inputs are deactivated, and power acceptance is reduced to 50 μW. For achieving RS232-compatible levels on the left-hand side, the MAX233, as depicted in the diagram, can be employed. This IC also handles the necessary inversion of various signals.

 

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