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Drive SCR thyristor with 555 - del00015

This circuit gives a burst of pulses to fire 2 SCRs, when pin 4 is taken to 12V the SCR is turned on, to use this circuit you need 12V short pulses phase shifted with respect to AC sine wave on bridge, like this you can control the bridge from near 0% to near 100% ON.



In this 555 circuit, the chip drives a SCR Bridge or Thyristor Bridge. The Phase control can control the power derived by the bank. This is like a Large dimmer. The control is at reset pin from a external pulse circuit. That way battery banks can be charged, electroplating can be done, current and voltage can be controlled with opamps, thyristors are very rugged compared to transistors and MOSFETS in that order.



The Schematic Source file del00015.zip, Use the Eagle PCB and Schematic Design EDA Software.



Thyristor Drive Circuits and Mosfet Circuits are very important in Power Electronics. They form the Output Stage Devices. Earlier Thyristors, SCR, Triacs, SCR Bridges were used in Motor Drives, Power Supplies and Large Battery Chargers. Some old Siemens Application Notes have High Frequency Inverters using SCRs!.

LM3445 - TRIAC dimmable offline LED driver

Later the Mosfet was developed and started taking over the Main Position of the Output Power Device. NPN Transistors were the first favorite for such needs, SCRs were Robust and managed High Voltage and Current without much fuss. The Mosfets are very useful as they can be switched at higher frequency with less Power Loss or Heat.

They can get damaged easily if the designs are not done carefully. Now we have IGBT - Insulated Gate Bipolar Transistor which combines the High Impedance of a MOSFET and the Toughness / Resilience of a Bipolar Transistor.

Reset Voltage

Its an Inhibit, When pin 4 Reset is > 1V, device is Active. When Pin 4 is < 0.4V Output goes Low. When Reset is released, Output remains Low till 555 is Triggered. When you build a 555 Toaster Timer, you could use reset to pop the toast before its fully done.

Washer Timer

The Rotary switch selects R1 to R5 this makes Timing user programmed. Timer is triggered after the water reaches a level and turns on Motor.  The Motor shuts down after the resistor programmed time. Suppose you need a rinsing cycle then think of a Sequential timer.

 

Images above are from the Original Signetics 555 Datasheet

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