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How HTR’s Capacitor Discharge Resistors Protect Against Electrical Hazards


Monday, April 3, 2023

There’s a useful component called Capacitor discharge resistors or Bleeder resistors connected in parallel with the output of a high voltage power supply circuit to discharge the residual electric charge stored in the filter capacitors of the power supply.

To illustrate, let’s consider a switch mode power supply that uses a bridge rectifier to convert AC mains power into DC at either 320V (when the mains voltage is 220/240V) or 160V (when the mains voltage is 110/120V). This voltage is then reduced by the chopper, and one or more filter capacitors are used to smooth out the pulsating output voltage from the rectifier. These capacitors are designed to store enough energy at a high voltage to power the load during the zero crossings of the AC input. Additionally, they’re often chosen to be large enough to supply the load during power breakdowns lasting for a second or so.

However, the problem is that this stored charge can be quite dangerous, especially in high-powered devices like lasers, X-ray machines, radio transmitters, and old-style CRT screens. The stored charge in the capacitors can remain for a significant period of time even after the device has been turned off, posing a risk to anyone who believes the device is safe to handle.

To mitigate this hazard, it’s essential to discharge the capacitors after the power has been turned off. Typically, a large or high-resistance value resistor is connected across the terminals of the capacitor to accomplish this. It’s important to be aware of this issue and take appropriate precautions to avoid serious injury or even death.

It’s important to note that while the device is on, a small current flows through the Capacitor Discharge/Bleeder resistor, which results in a small amount of power wastage. To reduce this wastage, designers need to select an optimal resistance value that balances the speed at which the capacitor can be discharged and the power wastage during normal operation.

HTR offers a range of innovative electronic components, including their HSRC and HSR Series Resistors. These components are designed to discharge the residual electric charge stored in filter capacitors of high voltage power supply circuits, making devices safe for servicing and maintenance after they’ve been switched off.

Contact our engineers today to learn more how you can achieve reliable and efficient solutions to protect your high voltage power supply circuits about with HTR’s HSR and HSRC resistor series. Don’t wait, reach out to IBS now and take the first step towards safer and more reliable electronic designs!

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