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Peek 2070L Operating Manual - Quality Traffic Systems

Peek 2070L Operating Manual - Quality Traffic Systems

Section 6 — Theory of

Section 6 — Theory of OperationBut what happens to this circuit when AC power is removed (either by theutility going down, or the main power switch being turned off?) The 2070specification defines how this is handled, and the Quixote 2070L meets andusually exceeds those requirements. In normal operation, the AC-to-High-Voltage DC switcher and the DC-to-DC switcher both feed power to anauxiliary supply that runs their internal circuitry; the circuitry that actuallyperforms the power transformation.When AC power is removed, a large capacitor at the output of the AC-to-High-Voltage DC switcher keeps all of the circuits to the right of it poweredup for a short time. This is what gives the 2070 its ability to ‘bridge’ overshort power interrupts. When such a brown-out occurs, the DC-to-DCswitcher keeps operating, fed by this large capacitor. In this state, the DC-to-DC switcher keeps the auxiliary supply powered up for its own operation foras long as power remains in the circuit.While the DC-to-DC switcher is running, it will maintain the output voltages.By design, it can keep a nominal 30 watts supplied (on all of the outputscombined) for approximately 600 milliseconds. These are typical values fora normally outfitted 2070L controller. If additional components have beenadded to the chassis, this time will be shorter. And since the DC-to-DCswitcher keeps the +5V line up during such an event, this also providespower to the microcontroller so that it can continue to perform its monitoringand signal output functions across a short power outage. The +5V Standbyoutput is sent over the backplane to the motherboard, where it suppliesbackup power to the Real-time Clock. When the 2070L is disconnected fromAC for extended periods, a set of large capacitors provide power to the +5VStandby line for up to several weeks.One last note about the power supply operation concerns the 5V SensorInput, and the 5V Feedback and External 5V Sense parts of the blockdiagram. The Sensor Input is provided to monitor the +5V voltage within anoptionally installed VME chassis. The Feedback component monitors boththis ‘external’ signal and the output of the switcher’s own +5V output to verifythat it is generating the proper output. All of the DC outputs from theswitcher are ganged off of this feedback circuit, so if the +5V output isdetected to be low, the power supply will raise its output into the properrange for the +5V channel and would raise the other three DC outputs. Toensure proper regulation of the three 12V outputs, each of these voltageshas a “post regulator” that governs the actual voltage levels. The three 12Voutputs are also power-conditioned with over-voltage protection beforebeing sent to the PS1 and PS2 connectors.68 • Model 2070L Operating Manual

Detailed Systems Description6.2.7 Async Serial ModuleA 2070-7A Async Serial Module provides two channels of asynchronouscommunications between the 2070L and the external world. The operationof the Async Serial module is illustrated below.Figure 24 – Async Serial Module block diagramThe module takes two channels of RS485 communications from thebackplane (SP1 and 2 if the module is installed in slots A2-A4, SP3 and 4 ifthe module is installed in slot A1) and provides it to two RS232 DE9 ports onits front panel. These ports, C21S and C22S, are optically isolated on bothdata and power lines from the backplane of the 2070L. Both channelsprovide full handshaking capability.The C50 ENABLE line, which comes in from the backplane, tells the modulewhether or not to enable channel 2 (the bottom port.) If the C50 port on thefront of the Display module is enabled, it normally uses SP4 forcommunications. To avoid a communications conflict, if the C50 ENABLE isON, then channel 2 on this card is disabled. The C50 ENABLE signal is onlyused by this card if the card is installed in slot A1. (No conflict occursbetween this module’s channel 2 and the Display module’s C50 port if thecard is installed in any of the other slots, since they all assign channel 2 touse the SP2 serial port.)The TX and RX LEDs on the front face of the Async Serial module aresimple TTL displays of the state of those lines for each of the RS232 ports.Model 2070L Operating Manual • 69

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