Relay Drivers

Many electromechanical switches require a high DC current, on the order of tens to hundreds of milliamps, to remain actuated. Additionally, each device has a specified “pull-in” voltage which must be exceeded in order to overcome the mechanical and electrical hysteresis in the system.

Impellimax fault-tolerant designs can withstand continuous hard short-circuits applied to their outputs, returning to normal operation once the short circuit is removed.

Drivers with high current capabilities are available, routinely sourcing or sinking 3 amperes per output. Internal clamping diodes absorb the inductive kickback without damage.

Impellimax fault-sensing drivers can provide a TTL level signal as built-in-test to identify short circuited loads, absent or open loads, and/or power supply droop beyond safe levels to maintain pull-in.

Some relays operate in a bistable mode, such that they only require a short pulse of high current (typically called a “Set” coil) in order to switch, and then they will remain in that position until a similar current pulse is applied to a different coil (typically called a “Reset” coil) to return to the original switch position. These latching designs use a special Impellimax driver which provides the properly sequenced and timed pulses to make latching relays operate under simple TTL control.

Appnote SD107 is currently undergoing revisions. Please contact the factory for your Relay Driver needs.

Output Buffered 1 of 8 Decoder, with kick protect diodes, for driving Relays and other High Current Loads

• Logic inputs A, B and C are direct connection to a ACT family 1 of 8 decoder. All outputs stay “off” except for the one selected by the three-bit input word. The selected output goes positive, sourcing current into any ground-connected load. Each output of the decoder drives a high-current PNP transistor which allows for high output currents to 100 mA typically, to be driven. Internal snubbing diodes on each output make driving inductive loads very safe and simple.
• The internal +5V protection diode is a very low-drop schottky. Access to the +5V after the protection diode allows the designer to avoid using the diode if so desired. It also allows the protected positive line to be bypassed by an external capacitor, if needed.

• Three channel latching relay driver. Accepts static logic levels as commands, but outputs individual Set and Reset timed outputs to drive latching relay coils. This unit is also available in a hybrid, in configurations of up to 16 channels.