SRS Labs SR560 manual Power Regulators, Rear Panel Interfaces, Circuit Description

CIRCUIT DESCRIPTION

regulator that provides twice the current of the LM317 negative battery regulator.

Charging is controlled by changing the set voltage of the regulators based on battery charge status. Flip-flop U703 determines whether the charge regulators will be set to

15.5volts for a quick charge or 13.8 volts for a trickle or "maintain" charge by grounding the bottom of P701 and P702. C712 and R704 insure that the charger always powers up in the "quick" charge mode. P701 and P702 are provided to adjust the open circuit trickle charge voltage to 13.8 volts. D701 and D703 are blocking diodes for the charging circuits while not charging, and D707 and D708 are clamps to guard against battery polarity reversal.

Comparators U708 and U709 are LP365 micropower comparators that monitor the battery voltage. A resistive divider chain sets the four trip points for each comparator. D709 provides a stable 2.5 volt reference against which levels are compared. For each battery, three level indications are provided, and are decoded by multiplexer U704. The "trip" level is 14.5 volts. The trip outputs control the state of U703 and switch the battery charge voltage settings. The "low" level is 11.3 volts and activates the front panel low battery indicator. R730 provides some level hysteresis for the low battery indication to prevent oscillation around the trip point. The "dead" level is

10.7volts and is used to disconnect the load from the batteries before they are damaged by an excessively deep discharge. Q701 and Q703 are power MOSFET switches used to disconnect battery power from the amplifier. Dead level hysteresis is provided by R724. R731 and D711 provide un-interrupted battery power to the system RAM so that stored instrument settings are retained when the power is switched off.

POWER REGULATORS

The +5 V and +10 V supplies are produced with three-terminal regulators U801 and U802, respectively. The -10 V supply is constructed of op-amp U803 and Q801, a N-channel MOSFET as the pass element. The +10 V supply serves as the reference for the -10 V supply through divider R807 and R806.

The power output banana jacks on the rear panel (J801 and J803) are connected to the pre-regulated voltages after the power switch and before the regulators. This output can provide up to 200 mA of power for use as an external bias source, etc. Under some conditions, these jacks may be used to supply the unit with external DC power.

U506D and U506B generate the TTL level input to the processor to indicate when the unit is operating on the AC line.

Capacitors C801 through C821 are logic supply bypass capacitors distributed throughout the printed circuit board.

REAR PANEL INTERFACES

Two optically isolated rear panel interfaces are provided on the SR560. The blanking input accepts a TTL-level signal and grounds the amplifier signal path after the front end for as long as the input is held high. The response time of the blanking input is typically "on" 5 µs after the rising edge and "off" 10 µs after the falling edge. The RS-232 interface allows calibration and control of the instrument at 9600 baud. Data in and out on the connector are tied together, echoing data back to the sender. Hardware handshaking lines CTS, DSR, and CD are tied to DTR. Refer to Appendix A-1for information on remote programming of the SR560.

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