A resistor-type relay isn't a standard, commonly used term in relay technology. It's more likely referring to a relay circuit that includes a resistor for a specific purpose, rather than a distinct type of relay itself. The resistor typically plays a role in suppressing voltage spikes.
Here's a breakdown of how resistors are incorporated in relay circuits and what they accomplish:
The Role of Resistors in Relay Circuits
Resistors are strategically placed in relay circuits to perform various functions, including:
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Voltage Spike Suppression (Flyback Diode/Resistor Combination): When a relay coil is de-energized, the collapsing magnetic field induces a large voltage spike. This spike can damage sensitive electronic components in the control circuit. While a flyback diode is most commonly used to shunt this voltage, a resistor can be added in series with the diode to reduce the stored energy more quickly. The resistor provides a path for the current to dissipate, reducing the magnitude and duration of the voltage spike. This offers a compromise between spike suppression and quicker relay deactivation.
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Current Limiting: Resistors can limit the current flowing through the relay coil, particularly when using a relay with a low coil voltage. This prevents the coil from overheating or burning out.
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Voltage Division: Resistors can create a voltage divider network to provide a specific voltage to the relay coil. This is useful when the available voltage source is higher than the relay's required coil voltage.
Example Circuit: Flyback Diode with Resistor
Here's a simplified example:
- Relay Coil: The inductor that activates the relay.
- Flyback Diode: Placed in parallel with the coil, with the cathode (+) connected to the positive side of the power supply and the anode (-) connected to the negative side. This provides a path for the current when the relay is switched off.
- Resistor: Placed in series with the flyback diode, further limiting voltage spikes.
The combination of a diode and resistor is more typical than solely a resistor used for spike suppression. The diode provides the primary path, and the resistor dampens the response.
Why a Resistor Alone Isn't Ideal for Spike Suppression
While a resistor could theoretically be used alone, it's not very efficient. To effectively suppress the voltage spike, the resistor would need to be relatively small, which would limit the current through the relay coil when energized. If the resistor is large enough to allow sufficient current to flow through the relay coil, it would not be very effective for suppression.
Conclusion
A "resistor type relay" is generally understood to be a relay circuit utilizing a resistor, usually in conjunction with a flyback diode, to protect other circuit components from voltage spikes generated when the relay coil is de-energized. The resistor alone is rarely, if ever, sufficient for spike suppression but is a useful addition to a standard flyback diode.
