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HV9901DB1 Universal Relay Driver Introduction The HV9901 is a universal relay driver employing PWM switching techniques utilizing the relay coils inductance to provide efficient operation over a wide supply voltage range. Relay drive is constant-current. Pull-in current, pull-in time, and hold current are all programmable via 2 resistors and a capacitor. An adjustable regulator provides 1mA for external circuitry. The HV9901DB1 demo board contains all the circuitry necessary to demonstrate the operation of the HV9901. Included on-board are a full-wave input rectifier, fuse, the HV9901, and a 10A relay. Provisions for connecting an external relay are available. The circuit may be modified to accomodate the drive requirements of other relays. WARNING!!! Do not connect earth-grounded instruments when connected to the AC line. Doing so will short the AC line, resulting in damage to the demo board and/or the instrument. Use an isolation transformer on the AC line, use high voltage differential probes, or use a floating instrument to make measurements when connected to the AC line. Specifications Relay Drive Current Pull-in Time Contact Form Input Voltage 10400VDC, 24277VAC 72mA pull-in, 24mA hold 20ms Contact Rating Enable Auxillary Regulator (VCC) 10A@125VAC, 6A@277VAC <1.5V off, >3.5V on 5.0V@1mA SPDT (1FormC) Switching Frequency 21kHz Board Layout and Connections Input Voltage Common D2 F1 ~ ~ D1 + Enable Polarity Selector IC1 R3 R1 C4 R7 C5 C2 R2 R4 C3 Relay Contacts Normally Closed C1 K1 D3 Q1 R5 Normally Open Relay Selector R6 WARNING!!! No galvanic isolation. Dangerous voltages are present when connected to the AC line. Input Voltage External Relay Sync Enable VCC Ground Supply voltage. May be a DC source in the range of 10400VDC, or an AC source in the range of 24277VACrms. A full-wave bridge rectifier on board rectifies the AC. Also included is a 250mA 2AG fuse. Relay Contacts For connecting an external load. The PCB traces are rated at 10A for a 20C rise. Relay Selector In the Int position, the on-board relay is operated. In the Ext position, a relay connected to the External Relay terminals is operated. External Relay For connection of an off-board relay. Sync Synchronizes multiple HV9901s to the same frequency or to a master clock. Frequency will be the highest independent frequency. Connect to the Sync pins of other HV9901s or to a master clock. Enable Logic-level enable for relay operation. See Enable Polarity Selector for polarity. VCC Supplies 5V at 1mA for external circuitry. Ground Circuit common. Since galvanic isolation is not provided, ground will be at the AC line potential! Enable Polarity Selector Sets Enable polarity. In the 0 position, Enable is active low. In the 1 position, Enable is active high. F1 250mA HV9901DB1 Schematic D1 DF06 VIN C C1 100nF VIN NC NO K1 NAIS JS1-5V INT RELAY EXT D2 S1J VDD VREF H/D D3 ES1J GND C2 4.7F R1 R2 C3 100nF C4 1.0F R3 Int Reg VREF SYNC 226k PWM GT CS RT 1.21M R6 SYNC Q1 VN2450 11 R5 8.25k 5.0V @ 1mA VCC VCC C5 1.0F VCC FB Aux Reg POL ENI ENO 374k 124k R4 270k R7 EN 1 POL 0 Modifications Connect the coil of the external relay to the External Relay terminals and move the Relay Selector shunt to the Ext position. Pull-in Current, Pull-in Time, and Hold Current For use with other relays, these parameters may be changed via resistors R1 and R2 and capacitor C4. Refer to the HV9901 data sheet for details. Monitoring Relay Current For the on-board relay, coil current may be monitored by replacing the Relay Selector shunt with either a wire loop (for current probe use) or with a low value sense resistor (for voltage probe use). Remember that galvanic isolation is not provided! See warnings on the first page. External Relay Switching Frequency To change the PWM switching frequency, change R6 according to the following equation: f PWM = 3.23kHz + This equation is valid for frequencies 25kHz and above. Be advised that frequencies below 20kHz may cause the relay coil to emit audible noise. And avoid higher frequencies that approach the coils resonant frequency. VCC As provided, the HV9901DB1 supplies 5V for external circuitry. Other volltages in the range 2.0V to 5.5V may be obtained by changing R3. Current rating remains at 1mA. 21.8GHz R6 Note that changing VCC also changes the Enable logic levels. R VCC = 1.25V1 + 3 R4 V EN ( lo ) < 0.3VCC V EN ( hi ) > 0.7VCC |
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