The main aim of a DC Overvoltage Protector circuit is to protect circuits or electronic devices from harm caused on by high voltage levels in a DC power source.
In many applications where steady and regulated voltage levels are required these circuits are important.
Circuit Working:
Parts List:
A commonly closed 12V relay is connected to a silicon controlled rectifier SCR which is placed along with the 12V supply lines.
The SCRs gate circuit is used to monitor the applied voltage.
Current can flow to the load as long as the applied voltage is below a certain threshold because SCR1 stays inactive and the relays contacts stay closed.
The SCR1s gate receives enough current when the source voltage above 12V which causes it to conduct and turn on the relay and by preventing the current flow to the load.
By serving as a buffer against overvoltage situations this device protects the load from possible damage.
R1 is adjusted to figure out SCR1s trigger point.
When SCR1 is triggered the relays contacts opens stopping further current flow to the load.
Formulas:
The DC over voltage protection circuit design requires the following calculations and formulas:
The Voltage Divider Calculation:
The reference voltage for activating the SCR using the preset should be calculated with a voltage divider formula.
Assuming that a fixed resistor Rf and a preset resistor Vp are used together to build a voltage divider:
Vref = Vin × Rp / Rp + Rf
where,
- The reference voltage that one wish to use to activate the SCR is Vref.
- The input voltage is represented by Vin 12V in the circuit diagram.
- The preset resistance is represented by Rp.
- The fixed resistor Rf is wired in series with the preset.
Calculate the preset SCR gate resistor:
To ensure that the SCR gate receives sufficient current to activate one must choose a resistor Rg between the gate and setting.
The gate current Ig which usually ranges between 10 and 50 mA can be clearly found in the SCR datasheet.
Ig = Vgate−Vref / Rg
where,
- For exact values refer to the datasheet.
- The SCRs gate voltage Vgate is normally between one and two volts.
- Vref stands for the reference voltage set by the voltage divider.
- Rg stands for the gate resistor.
The formulas should be adjusted as follows to get Rg:
Rg = Vgate−Vref / Ig
Calculating Coil Current for Relays:
There must be sufficient current for the relay coil to turn on.
Check that the SCR can provide the required current to the relay coils.
The following is the current passing through Irelays relay coil:
Irelay = Vsupply / Rcoil
where,
- The voltage supply to the relay is indicated by Vsupply 12V.
- The relay coils resistance is represented by the letter Rcoil.
Power Dissipation in the SCR:
Confirm the SCRs capacity to release electricity.
The following is an estimate of the SCRs power loss PSCR:
PSCR = VT × Iload
where,
- According to the SCR datasheet the voltage drop across the conducting SCR is VT and it normally ranges from 1-2V.
- The current that passes through the load and relay is called Iload.
One can generate an accurate design using these calculations, however be sure to confirm with actual component values and datasheets.
Feel free to adjust the settings to match the needs and component ratings.
How to Build:
To build a Simple DC Over Voltage Protector Circuit following steps are required for connections and assembling:
- Connect the positive terminal of the 12V power supply to one side of the load.
- Connect the other side of the load to one of the terminals on the normally closed NC contacts of the relay.
- Connect the common terminal of the relay to the positive terminal of the 12V power supply.
- Connect the SCR1 anode to the point where the load and the relay contacts are connected.
- Connect the SCR1 cathode to the negative terminal of the 12V power supply.
- Connect a preset R1 between the SCR1 gate and the point where the load and relay contacts are connected.
- Connect the SCR1 gate to the point where the load and relay contacts are connected.
Notes:
- To adjust the trigger point to the correct level of overvoltage protection modify the preset R1.
- Ensure that the parts used can manage the voltage and current needs of that specific application.
- To prevent the circuit from being harmed confirm the polarity of the parts and connections.
- To ensure safety and protect the circuit think about implementing a proper enclosure.
- Seek professional help or speak with an expert if you lack experience or are unsure about electronics.
Conclusion:
Finally a circuit known as a DC Overvoltage Protector is an essential part of electronic systems that offers a strong protection against possible harm from high DC voltage levels.
The DC overvoltage protector is an essential safety precaution in situations where maintaining steady and regulated voltage levels is important because of the proper component value selection which ensures an optimal reaction to certain voltage thresholds.
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