Bleeder ResistorBleeder Resistors are used as a safety feature to discharge capacitors to safe voltage levels after power is removed. A bleed resistor may be either connected permanently for cost effectiveness and high reliability or switched across a capacitor for rapid discharge without stagnant dissipation. This is used to help improve voltage regulation and is generally used in unregulated direct current (DC) power supplies. The bleeder resistor should have a resistance value high enough so that it does not interfere with the operation of the power supply, but low enough so it will discharge the capacitor in a short time after the power supply has been shut down. There is always a tradeoff between the time to reach a safe discharge and the inert power loss during normal operation. They are connected across the filter capacitors to drain their stored charge and avoid injuring or shocking the user.
Power supplies are a major application for current sensing resistors. Space-saving surface-mount designs are especially popular in small supplies, miniature DC-to-DC converters, small battery charging circuits, switching power supplies, and uninteruptible power systems. Click here to continue.
Just in case if you were looking to cross Caddock's power resistors; Here is our list:
- TO-263 Housing (D-Pak)
- Resistance from 0.01 Ohm to 51K Ohms
- Power Rating to 35 Watts
- Resistance Tolerances to ±1%
- TCR to ±50ppm/K
- Load Stability to 1%
- Solder Reflow Secure at 260°C / 20s
- Isolated Back Plate
A resistor's Temperature Coefficient of Resistance (TCR) tells how much its value changes as its temperature changes. It is usually expressed in ppm/°C (parts per million per degree Centigrade) units. What does that really mean?
Let's use an example: Riedon's 50 ohm 100 Series precision resistor has a (standard) TCR of 20ppm/°C. That means its resistance will not change more than 0.000020 ohms (20.1,000,000) per ohm per degree Centigrade temperature change (within the rated temperature range of -55 to +145°C, measured from
25°C room temperature.)
Assume our resistor is in a product that heats up from room temperature to 50°C. To find our 50W resistor's (maximum) change caused by that 25°C rise, multiply 0.000020 times 50 (the resistor value) times 25 (the temperature change.) The resistor's value would change no more than 0.025 ohms. (0.000020 X 50 X 25 = 0.025W.)
The actual change may be much smaller, depending on the specific characteristics of that resistor. If you must guarantee a smaller resistance change in your application, Riedon can provide a nonstandard TCR as low as 1 ppm/°C.
The subject of power supplies is potentially very broad and the application of resistors in power supplies is quite diverse. Here we will focus on power supply units (PSUs) designed for use in electronic appliances that nominally require fixed DC outputs ranging from just a few volts up to a few kV. Whether such end-equipment is destined for consumer, commercial or industrial markets, the PSU designer will need to pay heed to stringent safety, environment and other regulations in addition to meeting the basic electrical performance requirements. As well as considering the role of resistors in regulating a power supply’s output voltage (or current), we will examine how resistors protect a supply from potential fault conditions, such as output overload, output short- or open-circuit and input surge currents, which can result in a fire or present a shock hazard to users. Power supplies are often defined by their input source, AC or DC, and whether they use linear or switched mode regulation to achieve the desired DC output. AC-DC supplies are typically line powered but a DC in, DC out supply could just be a linear circuit that regulates the output from a battery or other DC source to produce a lower DC level. The term DC-DC converter is usually reserved for supplies that use switched-mode techniques, which can support both step-down (buck) and step-up (boost) conversion for lower and higher voltages respectively. While most power supply manufacturers offer a range of standard units to satisfy various endequipment requirements, some applications demand a custom solution. As a manufacturer and supplier of high performance resistors, Riedon has the experience to help designers choose the right component.
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The HTE series are high-voltage thick film resistors with tolerances of ±1% to ±10%
Riedon’s HTE series uses thick film technology in a non-inductive cylindrical construction for through-hole mounting. They provide resistance values from 1 kΩ to 100 MΩ, while also achieving non-inductive performance and a TCR rating of ±100 ppm. HTE resistors are available from 0.7 W to 15 W power ratings with tolerances between ±1% and ±10%. Their high-voltage design allows for a maximum of 48 kV working voltage rating.
Many transducers use strain gage sensors to convert pressure or force to an electrical output. In these designs, gages are connected as a Wheatstone bridge resulting in an accurate and rugged transducer that can operate in extreme environments.
To achieve accuracy, the bridge is adjusted for manufacturing tolerances and temperature effects. "Compensation" resistors are added to correct for bridge unbalance, and to adjust output sensitivity. Other compensation resistors correct for the errors that result when the transducer is used over a wide changing temperature range.
Wire wound resistors are ideal for compensating strain gage transducers: They offer the necessary accuracy, and perform reliably at high temperatures. They are designed so that resistance value does not change, or changes in a controlled manner, over different temperature.
Riedon has supplied compensation resistors to many customers and recognizes that transducers are highly specialized products normally requiring design-specific compensation resistors. We welcome the opportunity to serve your unique requirements