Stackpole is featuring our high voltage axial leaded resistors. For applications requiring high voltage capability, there are certain factors to consider and some parameters which are less important. This pitch pack will summarize the critical elements of high voltage resistors and describe each high voltage resistor and its strengths and weaknesses relative to those elements.
High voltage applications present some issues that aren’t seen in normal operating conditions for many electronic devices. For example, high voltage resistors typically are manufactured in high resistance values.
This is a necessity since a low resistance value coupled with a high voltage would require extremely high power levels. One of the easiest methods of increasing the voltage handling of a resistive element is to make that element longer and narrower. Obviously narrow resistance elements will not perform well under high power loads. Design engineers must adhere to both the voltage rating. This implies that any resistor can be safely run at full rated voltage only if that voltage does not impose a power level on the resistor that exceeds the power rating.
Stackpole offers the MG / MGM series with outstanding high voltage performance that is many times higher than comparable size film resistors at relatively low cost. In addition, we also offer the ASR / SPR pulse withstanding resistors for those applications requiring relatively low working voltage but high pulse voltage requirements. These two series will be discussed in the following two sections along with a final section on the challenges and solutions to higher voltages in wirewounds.
MG / MGM – High Voltage Metal Glaze Resistors
The MG/MGM series have a metal glaze resistive element which is essentially the same technology as is used in thick film SMD resistor elements. Hence, it offers a good blend of electrical performance with tolerances down to 1% and TCR’s as low as 100 ppm at very competitive costs and is inherently resistant to moisture corrosion. Pricing for this series ranges from $0.078 each to around $0.41 each in full reel quantities depending on size, tolerance, and resistance value. Typical pricing for competitive products from Vishay, Ohmite, and EBG ranges from $1.00 each to up to $5.00 each, so the MG / MGM series offers us an excellent opportunity to greatly reduce costs to our customers that have those competitive products designed in. Maximum working voltages for these series range from 1600 volts for the MG ¼ up to 4000 volts for the MGM3. Resistance values currently range from 100K to 200M, however the mini sizes of the MGM are available in much lower resistance values.
Contact Stackpole for more details on extended resistance value ranges.
ASR / SPR – Anti Surge and Discharge Path Metal Film Resistors
The strength of the ASR and SPR series of resistors is their ability to withstand high voltage surges. The ASR series is available in sizes ranging from mini ¼ watt up to 1 watt. The SPR series discharge path resistors is available in mini ½ watt and 1 watt sizes and is UL1676 recognized. For short time overloads, which require a more robust part than simply a high voltage device, the ASR and SPR series offer outstanding voltage handling ranging from 1KV for the low resistance values in the mini ¼ watt size to 10 KV for the larger sizes. In addition, the SPR is specifically designed to take the discharge from a high voltage capacitor of up to 10KV for many repetitions without significant changes in resistance. It offers better electrical stability and long term reliability than carbon composition resistors and is a good choice as an alternative when the energy and power handling requirements allow its use. The ASR and SPR series are available in resistance values from 100 ohms up to 33M ohms and 5% and 10% tolerances are standard. Pricing for the ASR / SPR series ranges from $0.57 each to $0.14 each in full reel quantities depending on size, tolerance, and resistance value, making them an attractive economical choice for circuits with surge handling requirements.
Wirewounds and High Voltage Handling
Wirewounds, due to their inherent low resistance values, are typically not given a voltage rating. This is because high voltages applied across low resistance values increases the power through the device exponentially. However, larger size wirewounds have room to increase the number of windings necessary to achieve relatively high resistance values. Even if the resistance value allows for higher voltages than usual, care must be taken when using standard wirewound devices. To achieve high resistance values in a wirewound technology requires very thin wire and many more turns than usual. Because of this, the windings of the resistive element are significantly closer to each other which may allow arcing between consecutive windings where there are voids in the coating. However, it is possible to use a lacquer coating under the conformal coat to insulate the windings. It is also possible to use insulated wire for the resistive element, however it is very difficult to use in mass production and would only be considered under extreme circumstances where the lacquer process had previously failed.
Data Sheets can be found at: www.seielect.com
For more information about Stackpole products, contact us at:
Stackpole Electronics, Inc.
2700 Wycliff Road Suite 410,
Raleigh NC 27607
Stackpole Electronics Inc. is a leading global manufacturer of resistors supplying to the worlds largest OEMs, contract manufacturers and distributors. Headquartered in Raleigh, N.C., the privately held company began manufacturing in 1928 as part of Stackpole Carbon Company in St. Mary's, Pennsylvania. Now affiliated with Akahane Electronics, Stackpole has manufacturing facilities in Japan, Taiwan, China and Mexico; warehousing facilities in El Paso, Hong Kong and Japan; and sales offices in Tokyo, Hong Kong and Taiwan.