Mike Dolt Enterprises
Mike Dolt Enterprises
User: Izy, Location: Michigan. It's a beautiful peninsula, I've looked
Asked on: Sunday, June 5, 2011 at 8:54 am EDT
Answered on: Tuesday, May 14, 2024 at 6:13 am EDT
Question: Hello,I hope I came to the right placeI'm a hardware engineer in a company that manufactures outdoor radio equipment.We have now demand to pass certification tests for hazardous locations (class I div 2).The equipment is powered by 48V DC, rated 5A.We need to design som sort of circuit that can limit the current/voltage in case of short-circuit.We were told by the testing laboratory that we can't use any ICs, and the protection must be done by discrete components only (resistors, diodes, etc.). We were told that we couldn't use circuit breakers and fuses - because their operation is not "instant". They suggested us to use series resistor, but it appears to be huge in size (rated 140W), so it's impactical.Is there anyone faced this kind of issue?
Discrete Component Current/Voltage Limiting Circuit for Hazardous Locations (Class I Div 2)Challenge
Design a current/voltage limiting circuit using only discrete components to meet hazardous location certification requirements.
Constraints
No ICs allowed No circuit breakers or fuses allowed Instantaneous operation required Input voltage: 48V DC Rated current: 5A
Potential Solution
1. Zener Diode Voltage Clamping
Connect a Zener diode in parallel with the load. Select a Zener diode with a breakdown voltage slightly higher than the maximum allowable voltage (e.g., 52V). The Zener diode will clamp the voltage to its breakdown voltage in case of a short-circuit, protecting the load from over-voltage.
2. Resistor Current Limiting
Connect a series resistor between the power source and the load. Calculate the resistance value required to limit the current to the maximum allowable value (5A) in case of a short-circuit. Use a resistor with sufficient power rating (e.g., 140W).
3. Power Dissipation Management
The resistor must be able to dissipate the power generated during a short-circuit. Consider using a heat sink or larger resistor to prevent overheating.
4. Instantaneous Operation
Since ICs and circuit breakers are not allowed, the circuit relies on the instantaneous response of the Zener diode and the resistor. The Zener diode will clamp the voltage immediately, while the resistor will limit the current within a few microseconds.
5. Circuit Diagram|--------+---+----------+----------+| | | |
| | Diode | 48V DC | | Zener | Resistor
|+--------------------+--------+---+----------+----------+|
Note: The exact component values and circuit design may vary depending on the specific application and certification requirements.* It is recommended to consult with experts in hazardous location certification for guidance and approval before implementing this solution. Flag for review