[www.keralites.net] Computerised Static Circuit Breaker

 

There are many circuits available to minimise interferences in electronic circuits. But these circuits may not do much on a device that is operating through a PC. The radio frequency interference (RFI)generated from switching on and off the device will generate disturbance on the screen of the computer monitor. Fig. 1: Computerised static circuit breaker Here is a different approach to minimise the interferences for a device operating through a PC. It is basically a circuit breaker consisting of an inter facing circuitry, computer's parallel-port connector and software program written in 'C.' This gadget can control any electrical equipment with less RFI, thus produce no disturbance on the monitor's screen or nearby equipment. Another attraction of this circuit is that it can be operated either by computer or manually using a switch. The circuit employs two 2P4M SCRs (SCR1 and SCR2) and an MOC3021 optoisolator (see Fig. 1). The SCRs are connected such that a complete AC cycle can pass through the load. However, you may use only one SCR if one half of the cycle is required. Fig. 2: Gate triggering of SCRs When switch S1 is closed, SCR1 fires at the start of the positive half cycle, and it then switches off when the current goes down to zero. At this stage, SCR2 becomes forward biased and at the same time receives a sufficient gate current, which results in the firing of SCR2. Thus during the positive half cycle, SCR1 conducts, and during the negative half cycle, SCR2 conducts. To break the circuit manually, i.e., to stop the flow of current through the load, open switch S1. Since the gate current through switch S1 is small, opening of the gate circuit results in minimising RFI. Here during the positive half cycle, SCR1 will conduct due to triggering pulse at its gate ig1. During the negative half cycle, SCR2 will conduct due to gate pulse ig2. Note that during turn off, ig1 is not applied to SCR1 and thus it will not conduct and the circuit is broken. Fig. 3: Program output of computerised circuit breaker The sequence of gate triggering of SCR1 and SCR2 is shown in Fig. 2. As the gate pulse is applied during zero crossing of load current, it eliminates the occurrence of noise. With the 'C' program (cktbkr.c), you can turn on the load by pressing key '1' and break the circuit (turn off the load) by pressing key '2' on the keyboard. The program output is shown in Fig. 3. Simulation of the circuit using Circuitmaker2000 software will also give satisfactory result. Fig. 3: Pin configuration of 2P4M Precaution. Since you switch the 230V AC load using the PC's parallel port, care must be taken in choosing opto-isolator MOC3021 (with inbuilt light activated silicon bilateral switch). MCT2E will not give satisfactory result. After assembling the circuit, ensure isolation between the power circuit and parallel port before applying supply to it. Note that this circuit will run only on Windows 98 platform. For WinXP/Win2000, you'll need to install a 'UserPort' program in your system. Do not connect the load before applying the supply to the circuit as dV/dt rating of the SCRs may damage the load.

---

www.keralites.net

__._,_.___

Reply to sender | Reply to group | Reply via web post | Start a New Topic

Messages in this topic (1)

Recent Activity:

• New Members 33

Visit Your Group

KERALITES - A moderated eGroup exclusively for Keralites...
To subscribe send a mail to Keralites-subscribe@yahoogroups.com.
Send your posts to Keralites@yahoogroups.com.
Send your suggestions to Keralites-owner@yahoogroups.com.

To unsubscribe send a mail to Keralites-unsubscribe@yahoogroups.com.

Homepage: www.keralites.net

Switch to: Text-Only, Daily Digest • Unsubscribe • Terms of Use

.

__,_._,___