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Supertex inc.

www.supertex.com

Doc.# DSFP-MD0105

C070213

MD0105

Block Diagram

Switch Control

COM

A

B

Typical I-V Characteristics

I

A-B

-V

OFF

-V

TRIP

+130V

I

-130V

I

V

A-B

R

+I

PEAK

-I

PEAK

+V

TRIP

+V

OFF

+1.0mA

+1.0mA

Functional Description

The Supertex MD0105 can be considered as a normally

closed switch controlled by a switch control (please refer to

the block diagram). The switch control monitors the voltage

drop across terminals A and B. If the voltage difference is

greater than ±2.0V, the T/R switch will start to open. Once

in the open state, there is a small amount of current flowing

through the T/R switch, 200µA, to detect if the high voltage

is still present or not.

The T/R switch will not close until the voltage across termi-

nal A and B drops below ±2.0V. A pair of back-to-back di-

odes from the receive side of the switch to ground is needed

to complete the circuit and to allow the initial peak current

(about 60mA) to flow through the switch so it can drop ±2.0V.

If the diodes are not present, then there is no current path

and the voltage drop across terminal A and B will be less

than ±2.0V, so the switch will remain in the closed position.

The MD0105 does not require any power supply. There are

only two active pins; one connects to the transmitter side,

one connects to the receiver side.

On Resistance

When the voltage across terminals A and B are below ±2.0V,

the switch is in the receive mode and the R

Once the voltage across the terminals A and B is greater

than ±2.0V, the switch is in the transmit mode and blocking

the high voltage pulses from passing through to the receiver

and damaging it.