A bleeder resistor in a rectifier circuit is a resistor connected in parallel with the output of the rectifier. Its purpose is to discharge the filter capacitor when the rectifier is turned off or when the input power is disconnected.
In a rectifier circuit, the output is typically smoothed using a capacitor connected in parallel with the load. This capacitor helps to reduce the ripple voltage and provide a more steady DC voltage. However, when the rectifier is turned off or the input power is disconnected, the capacitor retains some charge, which can be potentially dangerous if someone comes in contact with the circuit.
To address this issue, a bleeder resistor is connected across the capacitor terminals. When the rectifier is turned off, the bleeder resistor provides a discharge path for the stored charge in the capacitor, allowing it to discharge safely over time. This helps to prevent the accumulation of dangerous voltages across the capacitor.
The value of the bleeder resistor is typically chosen to ensure a gradual discharge of the capacitor while maintaining a reasonable power dissipation in the resistor. It is usually calculated based on the desired discharge time constant and the capacitance of the filter capacitor.
In a rectifier circuit, the output is typically smoothed using a capacitor connected in parallel with the load. This capacitor helps to reduce the ripple voltage and provide a more steady DC voltage. However, when the rectifier is turned off or the input power is disconnected, the capacitor retains some charge, which can be potentially dangerous if someone comes in contact with the circuit.
To address this issue, a bleeder resistor is connected across the capacitor terminals. When the rectifier is turned off, the bleeder resistor provides a discharge path for the stored charge in the capacitor, allowing it to discharge safely over time. This helps to prevent the accumulation of dangerous voltages across the capacitor.
The value of the bleeder resistor is typically chosen to ensure a gradual discharge of the capacitor while maintaining a reasonable power dissipation in the resistor. It is usually calculated based on the desired discharge time constant and the capacitance of the filter capacitor.
Purpose of the bleeder resistor
In a rectifier circuit, a bleeder resistor can serve several important purposes. Here are a few common applications of bleeder resistors in rectifier circuits.- Discharge of Filter Capacitors: Rectifier circuits often use filter capacitors to smooth the output voltage. These capacitors store electrical energy, and when the power is switched off, they can retain a charge. A bleeder resistor is connected across the filter capacitors to discharge them gradually when the power is turned off or during maintenance. This ensures that the capacitors are safely discharged, preventing potential hazards.
- Voltage Regulation: In some rectifier circuits, especially those with a voltage regulator, a bleeder resistor is used in conjunction with a zener diode. The bleeder resistor is connected in series with the zener diode and placed across the output of the voltage regulator. This arrangement helps to maintain a minimum load current, which stabilizes the output voltage and improves the regulation of the circuit.
- Start-Up Behavior: In certain rectifier circuits, a bleeder resistor is employed to control the start-up behavior. When the power is initially applied, the bleeder resistor discharges any residual charge in the system, allowing the rectifier circuit to start up from a known state. This can help avoid any unexpected voltage levels or transients during the power-on sequence.
- Safety and Maintenance: If the bleeder resistor is not connected across the filter output, the capacitor will retain its charge for quite some time even when the power supply is switched off and this high voltage can be dangerous to the operational staff. Thus the hazard of electrical shock is reduced.