Simple Crowbar Circuit

In electronic devices, a crowbar circuit is a safety feature that guards against high voltage spikes and surges damaging circuits.

It functions similarly to a fuse, but instead of just burning itself out, it quickly cuts off electricity and stops more harm by causing a short circuit.

Usually, it makes use of a thyristor SCR or TRIAC as the connecting element and a triggering element, such as a transistor or zener diode.

The voltage is continuously monitored by the triggering device.

The triggering element turns on the shorting element when the voltage rises over a certain safe limit.

Circuit Working:

Parts List:

Electronic equipment is protected by the crowbar circuit.

It makes sure the input voltage stays within safe bounds by continually monitoring it.

The circuit acts decisively if a surge or spike raises the voltage over this point.

A direct short circuit is produced, much like when a crowbar is dropped over electrical lines.

The current is forcefully diverted away from the fragile circuit and towards the intervention itself.

Another safety feature, the fuse is triggered by the current surge.

By blowing the overloaded fuse sacrifices itself, cutting off the power supply from the circuit and halting more high voltage damage.

The zener diode is the brains behind this action.

It continuously measures the incoming voltage in order to serve as a voltage reference.

The SCR Silicon Controlled Rectifier is a unique switch that is activated when the voltage exceeds the specified safe limit of the zener.

The SCR, which had been inactive activates and produces the necessary short circuit.

The power supplies connection to the circuit is essentially severed when this current surge hits the fuse.

The crowbar circuit essentially serves as a self sacrificing barrier to guard the circuit against the risks associated with high voltage.

The safeguarding circuit is unaffected even if the circuit itself has to be reset or even fixed after activation.

Formulas:

The crowbar circuit diagram above may be analyzed using a few different formula.

The resistor values required for the circuit are found using these formula.

The current flowing through resistor R1 is computed using the below formula.

The current that passes through the zener diode D1 is restricted by this resistor.

Ohms law may be used to determine the current I flowing through resistor R1:

I = (V_in – V_zener) / R1

where,

• I is the current (in amps) flowing via resistor R1.
• In volts Vin represents the input voltage.
• The zener diode voltage, expressed in volts, is Vzener.
• The resistor R1s resistance is denoted by R1 in ohms.

To get resistor R1s power dissipation, using the below formula.

The following equation can be applied:

P = I² * R1

where,

• P is resistor R1s power dissipation (in watts).
• I is the current (measured in amps) flowing through resistor R1 according to the first formula.
• The resistor R1s resistance, expressed in ohms is R1.

Note:

The behavior of the circuit can also be influenced by the values of C1 and C2.

Transients and noise are filtered out in part by these capacitors.

To get the required performance, you might have to experiment with different capacitor values.

The circuit is protected against overcurrent by the fuse.

Select a fuse rated marginally higher than the circuits maximum anticipated current.

Recall that in order to obtain the most precise values for your circuit, it is critical to review the datasheets for the particular components you are utilizing.

How to Build:

To build a Simple Crowbar Circuit follow the below mentioned steps:

• Assemble all the components as mentioned in the above diagram
• Connect gate of SCR between 9.1V zener diode and resistor R1.
• Connect anode of SCR to positive supply .
• Connect cathode of SCR to ground.
• Connect a capacitor C2 to ground from gate pin of SCR.
• Connect capacitor C1 from positive supply to ground.
• Connect a fuse at positive supply of input DC voltage.
• Connect a diode D2 at positive supply of output DC voltage.

Safety Measures:

• When dealing with crowbar circuits, you may reduce dangers by adhering to certain safety precautions.
• Always remember that when working on electronics projects, safety comes first.

Conclusion:

A simple crowbar circuit is an electrical watchdog.

When it senses too much heat, it watches the voltage and initiates a violent short circuit.

By blowing the fuse, electricity is cut off and the circuit is safeguarded.

Be cautious, though creating them calls for an understanding of electronics and adherence to safety regulations.

References:

Crowbar (circuit)