Welding App.qxd 4 9/2/04 2:25 PM Page 1 Resistive Components Resistive Components BI Technologies - SMT BI Technologies - ECD BI Technologies - MCD Company Profile Company Profile Company Profile BI Technologies, SMT Division is a World Class manufacturer of thick film Passive Components. The company was established in 1958 in Glenrothes, Scotland. BI Technologies have earned a great reputation as a high quality, high volume, cost effective and responsive supplier of thick film passive components for telecommunications, computer, automotive, medical and industrial applications. BI Technologies has been an innovator and leader in electronic components for more than 50 years manufacturing products for communication, computer, industrial and automotive applications. BI Technologies, Magnetic Component Division, headquartered in Fullerton, California, with a manufacturing base in Kuantan, Malaysia, is a world leader in miniature surface mount high power inductors. The magnetic material and manufacturing expertise of various inductors, choke coils, transformers and assemblies has expanded the customer and market base into automotive, medical, computer, data communication and industrial in addition to other specialized magnetic assembly applications. Product Range Product Range Product Range • Packaged SIL, DIL and Surface Mount Resistor Networks • Chip Resistor Arrays • Chip Resistor - Capacitor Arrays • Planar Power Resistors • Surge Resistors • Thick Film Substrates • Custom Thick Film products • High Voltage Resistors and Networks • Trimming and Precision Potentiometers • Position Sensors • Chip Resistor Arrays • Resistor Networks • Integrated Passive Networks • Inductors • Transformers • Turns Counting Dials • Hybrid Microelectronics and Custom Integration Products • Transformers both surface mount and through hole • Surface Mount high powered inductors • Toroidal inductors (through hole and surface mount) • High power specialty laminate transformers • Data communication modules, filters, and transformers for ethernet and DSL • Common mode filters and chokes • Planar transformer solutions BI Technologies serves a global customer base with manufacturing locations in the United States, Mexico, Scotland, Japan, China and Malaysia. BI Technologies SMT BI Technologies ECD BI Technologies Pte Ltd TT electronics GmbH Telford Road, Glenrothes Fife KY7 4NX, Scotland, UK 4200 Bonita Place Fullerton, CA 92835, USA Max-Lehner-Strasse 31 85354 Freising, GERMANY Tel: +44 1592 662200 Fax: +44 1592 662299 [email protected] Tel: +714 447 2300 Fax: +714 447 2400 [email protected] 514 Chai Chee Lane, #02-01 Bedok Industrial Estate 469029 SINGAPORE TT electronics SA TT electronics S.r.l. BI Technologies Japan Ltd Sales/Technical Support Centre 17 Rue du Kefir, Senia 418 94567 Orly, FRANCE Via Arese 12 20159 Milan, ITALY Tel: +33 1 45 12 3880 Fax: +33 1 45 12 3879 Tel: +39 2 688 8951 Fax: +39 2 689 6995 Kakumaru Building 4/F 1-10 Toyo 7 Chome Koto-ku Tokyo 135, JAPAN Flat 1104, 11/F, Block 1 News Building, No. 2 Shennan Middle Road, Futian District, Shenzhen, CHINA 518027 Tel: +81 3 3615 1811 Fax: +81 3 3647 2443 Tel: +86 755 8209 0230 / 8209 0295 Fax: +86 755 8209 0267 Tel: +65 445 5166 Fax: +65 445 1983 Welding Power Supplies Tel: +49 8161 4908-0 Fax: +49 8161 4908-99 Power Resistor Application Note BPR, BPC, MHP & BSR Series Resistors www.bitechnologies.com · www.ttelectronics.com · www.bitechnologies.co.jp Applications • Capacitor discharge • Snubbing • Inrush limiting Authorised Representative • MOSFET gate drive BI Technologies General Note: BI Technologies reserves the right to make changes in product specification without notice or liability. All information is subject to BI Technologies’ own data and is considered accurate at time of going to print. © BI Technolgies 2004 A subsidiary of TT electronics plc Issue A 08/04 A subsidiary of TT electronics plc BI Technologies Welding App.qxd 2 9/2/04 2:34 PM Page 3 BI Technologies Resistive Components 1. Capacitor Discharge Resistor The MIG arc welding power source shown has a secondary tapped transformer. It consists of a transformer, rectifier and output capacitor. The transformer should have separate primary and secondary windings so that the output is isolated from the power-line ground. The transformer primary to secondary turn ratio determines the amount by which the output voltage is stepped down. The rectifier is a full wave bridge of silicon diodes that converts the AC output voltage to DC and an output filter smoothes the secondary voltage to give a more consistent weld. Using a switch that selects taps on the transformer mechanically controls the secondary output voltage. Increasing the number of secondary turns increases the secondary voltage. This control method has the advantage of being a robust and reliable design. The disadvantages are that the output voltage cannot be controlled remotely and input voltage fluctuations will affect the output. The output filter capacitor is sized on the basis of the permissible output ripple 3. Inrush Current Limiting Resistor +V out L1 C1 1 D1 C3 D3 C6 2 Output R1 Bleeder Resistor C5 3 230 VAC S1 C7 4 5 C2 D2 C4 D4 Work Clamp C5 - Large Ootput Capacitance T1 MIG arc welding power source - Transformer tapped voltage. To estimate the ripple, consider that the capacitor supplies the maximum output current I continuously, and is charged up to the output voltage every 1/100 s for a fullwave rectifier (50Hz line frequency). The charge Q drawn by the load is I/100s and equals C∆V, where ∆V is the peak to peak output ripple voltage. Thus, C = I/100∆V. The calculations result in large values of C typically a few 100,000 µF and the designs are implemented using large aluminium electrolytic capacitors. A bleeder resistor is connected across the output capacitor to discharge it when the supply is turned off and to remove the hazard of an unexpected voltage. The bleeder resistor should be rated to dissipate the necessary power in steady operation. Bleeder resistors used for this application have typical power ratings of 10 to 30 Watts. BI Technologies BPC, BPR, MHP and BHP power resistors can be used for this application. 2. Snubber Resistor The welding power source shown in the schematic opposite maintains a constant output voltage using an SCR control circuit. An SCR is a rectifier that remains in a nonconductive state, even when forward voltage is applied from anode to cathode, until a positive trigger pulse is applied to the gate and the SCR “fires”. When the SCR “fires” it conducts current with a very low effective resistance, it remains conducting after the trigger pulse has been removed until the forward anode voltage is removed or reversed. The two SCR’s in this design are connected in anti-parallel at the input to the transformer primary allowing power to be controlled during each half cycle of the AC input. The control circuit determines the firing time of the SCR trigger pulses and maintains a constant output voltage for changes in the line voltage and load current. Earlier firing times result in a greater fraction of half-cycle power being delivered to the load and a higher average DC output voltage. Sudden changes in line voltage or load current result in a correction in the timing of the next SCR trigger pulse that can be no further away that one half cycle (10ms for C1 SCR Snubber C3 R1 +V out L1 D1 Gate SCR 1 C5 C4 230 VAC S1 SCR 2 Gate Output R2 Bleeder Resistor C6 C2 T1 D2 Work Clamp C4 - Large Output Capacitance Primary side SCR phase angle control 50Hz input). A large filter capacitance across the rectifier output allows only a small change to occur during any 10ms interval, avoiding the risk of transient dropout and loss of regulation due to sudden changes in load or line. The advantages with this type of power source when compared to the transformer tapped power source are that it requires fewer moving parts. It can be remotely controlled and voltage fluctuations at the input do not affect the weld output. Disadvantages are that it has poor efficiency, low power factor and a low speed of control. One further drawback with SCR converters is that a high rate-of-rise in anode-to-cathode voltage, or dV/dt, occurs when an SCR ceases conduction, or when another SCR in the circuit is gated into conduction. A high peak voltage is produced when an inductive circuit connected to the SCR is interrupted, for example the transformer leakage inductance. If the dV/dt is too large, the device will begin to conduct without a gate signal and will result in erratic circuit operation and potential device damage. A resistor capacitor snubber circuit connected across the SCR device can be employed to limit the SCR dV/dt and ensure reliable circuit operation. BI Technologies BPR, BPC and MHP non-inductive resistors are suitable for this application. Inrush current surges are caused by capacitor charging current and/or transformer magnetising current. The amplitude of the inrush depends where on the input voltage waveform the circuit is switched in. The inrush lasts for a short duration however can be many times greater than the steady state operating current. Large inrush currents can result in nuisance tripping of supply breakers, blown fuses or even permanent damage to the input circuit components. Solutions for limiting inrush transients range from the use of positive temperature co-efficient resistors to “soft-start” techniques that gradually ramp up the power source input current. Few of these solutions meet all of the important criteria of reliability and low cost. Our example circuit shows a thyristor rectifier welding power source that utilises a SCR Snubber R2 C2 Relay SCR 1 +V RL1 out L1 Gate C5 R1 230 VAC S1 Inrush Limiting Resistor Output R4 Bleeder Resistor C4 C6 Gate SCR 2 T1 R3 Work Clamp C4 - Large Output Capacitance C3 SCR Snubber Secondary side phase angle control SCR low value resistor in series with the transformer primary to limit the initial inrush current surge. After a short delay the relay contacts close short circuiting the resistor. The relay contacts must be rated for the full mains voltage and steady state input current. BI Technologies BPC, BPR, MHP and BHP power resistors can be used for this application. 4. Gate Drive Resistors The example opposite shows the circuit topology for an inverter welding power source. The input power is rectified to DC using a power factor correction boost converter. A full bridge MOSFET power stage converts the voltage back to AC at high frequency typically 50KHz to 100KHz. The transformer steps down the voltage, which is then rectified and smoothed at the output stage. The advantages of this type of power source are that it has high power conversion efficiency. And due to the high frequency operation of the MOSFET bridge the size of the components can be greatly reduced specifically the transformer and output filter stage. This is because the component size is inversely proportional to the operating frequency. The inverter power source maintains a constant output voltage regardless of changes in input voltage and output current. It has a very quick response time to changes in line and load and produces excellent arc characteristics delivering a true multi-process capability. MOSFET switching losses are due to delays in the switching transients since during these short time intervals a finite voltage and current coexist in the device. Therefore switching speed is the most important criteria required to minimise switching losses. Consequently faster switching Full Bridge Power Stage Input Boost PFC Input Rectifier L1 D5 R2 D1 D3 R snub Q2 Gate Drive 230 VAC Q1 R snub Q4 C snub R1 S1 R4 Gate Drive C snub C1 Gate Drive R snub D2 R snub R5 R3 D4 Q3 Gate Drive Q5 C snub Gate Drive C snub +V out L2 D6 R Snub C3 C snub R6 C2 C4 Work Clamp D7 Output Stage High frequency multi-process inverter welder speeds correspond to an increase in dI/dt of the drain/collector current. Fast dI/dt coupled with stray circuit inductance can cause considerable problems such as increased radiated EMI, large voltage spikes and circuit oscillations. Adding a small resistance at the MOSFET gate can be used to trade efficiency for lower dI/dt and its associated benefits. Resistors used for this application require high repetitive surge capabilities since they are expected to rapidly charge then discharge a MOSFET’s input gate capacitance at a high frequency. BI Technologies BSR resistor is suitable for this application. 3 Welding App.qxd 2 9/2/04 2:25 PM Page 3 BI Technologies Resistive Components 1. Capacitor Discharge Resistor The MIG arc welding power source shown has a secondary tapped transformer. It consists of a transformer, rectifier and output capacitor. The transformer should have separate primary and secondary windings so that the output is isolated from the power-line ground. The transformer primary to secondary turn ratio determines the amount by which the output voltage is stepped down. The rectifier is a full wave bridge of silicon diodes that converts the AC output voltage to DC and an output filter smoothes the secondary voltage to give a more consistent weld. Using a switch that selects taps on the transformer mechanically controls the secondary output voltage. Increasing the number of secondary turns increases the secondary voltage. This control method has the advantage of being a robust and reliable design. The disadvantages are that the output voltage cannot be controlled remotely and input voltage fluctuations will affect the output. The output filter capacitor is sized on the basis of the permissible output ripple 3. Inrush Current Limiting Resistor +V out L1 C1 1 D1 C3 D3 C6 2 Output R1 Bleeder Resistor C5 3 230 VAC S1 C7 4 5 C2 D2 C4 D4 Work Clamp C5 - Large Ootput Capacitance T1 MIG arc welding power source - Transformer tapped voltage. To estimate the ripple, consider that the capacitor supplies the maximum output current I continuously, and is charged up to the output voltage every 1/100 s for a fullwave rectifier (50Hz line frequency). The charge Q drawn by the load is I/100s and equals C∆V, where ∆V is the peak to peak output ripple voltage. Thus, C = I/100∆V. The calculations result in large values of C typically a few 100,000 µF and the designs are implemented using large aluminium electrolytic capacitors. A bleeder resistor is connected across the output capacitor to discharge it when the supply is turned off and to remove the hazard of an unexpected voltage. The bleeder resistor should be rated to dissipate the necessary power in steady operation. Bleeder resistors used for this application have typical power ratings of 10 to 30 Watts. BI Technologies BPC, BPR, MHP and BHP power resistors can be used for this application. 2. Snubber Resistor The welding power source shown in the schematic opposite maintains a constant output voltage using an SCR control circuit. An SCR is a rectifier that remains in a nonconductive state, even when forward voltage is applied from anode to cathode, until a positive trigger pulse is applied to the gate and the SCR “fires”. When the SCR “fires” it conducts current with a very low effective resistance, it remains conducting after the trigger pulse has been removed until the forward anode voltage is removed or reversed. The two SCR’s in this design are connected in anti-parallel at the input to the transformer primary allowing power to be controlled during each half cycle of the AC input. The control circuit determines the firing time of the SCR trigger pulses and maintains a constant output voltage for changes in the line voltage and load current. Earlier firing times result in a greater fraction of half-cycle power being delivered to the load and a higher average DC output voltage. Sudden changes in line voltage or load current result in a correction in the timing of the next SCR trigger pulse that can be no further away that one half cycle (10ms for C1 SCR Snubber C3 R1 +V out L1 D1 Gate SCR 1 C5 C4 230 VAC S1 SCR 2 Gate Output R2 Bleeder Resistor C6 C2 T1 D2 Work Clamp C4 - Large Output Capacitance Primary side SCR phase angle control 50Hz input). A large filter capacitance across the rectifier output allows only a small change to occur during any 10ms interval, avoiding the risk of transient dropout and loss of regulation due to sudden changes in load or line. The advantages with this type of power source when compared to the transformer tapped power source are that it requires fewer moving parts. It can be remotely controlled and voltage fluctuations at the input do not affect the weld output. Disadvantages are that it has poor efficiency, low power factor and a low speed of control. One further drawback with SCR converters is that a high rate-of-rise in anode-to-cathode voltage, or dV/dt, occurs when an SCR ceases conduction, or when another SCR in the circuit is gated into conduction. A high peak voltage is produced when an inductive circuit connected to the SCR is interrupted, for example the transformer leakage inductance. If the dV/dt is too large, the device will begin to conduct without a gate signal and will result in erratic circuit operation and potential device damage. A resistor capacitor snubber circuit connected across the SCR device can be employed to limit the SCR dV/dt and ensure reliable circuit operation. BI Technologies BPR, BPC and MHP non-inductive resistors are suitable for this application. Inrush current surges are caused by capacitor charging current and/or transformer magnetising current. The amplitude of the inrush depends where on the input voltage waveform the circuit is switched in. The inrush lasts for a short duration however can be many times greater than the steady state operating current. Large inrush currents can result in nuisance tripping of supply breakers, blown fuses or even permanent damage to the input circuit components. Solutions for limiting inrush transients range from the use of positive temperature co-efficient resistors to “soft-start” techniques that gradually ramp up the power source input current. Few of these solutions meet all of the important criteria of reliability and low cost. Our example circuit shows a thyristor rectifier welding power source that utilises a SCR Snubber R2 C2 Relay SCR 1 +V RL1 out L1 Gate C5 R1 230 VAC S1 Inrush Limiting Resistor Output R4 Bleeder Resistor C4 C6 Gate SCR 2 T1 R3 Work Clamp C4 - Large Output Capacitance C3 SCR Snubber Secondary side phase angle control SCR low value resistor in series with the transformer primary to limit the initial inrush current surge. After a short delay the relay contacts close short circuiting the resistor. The relay contacts must be rated for the full mains voltage and steady state input current. BI Technologies BPC, BPR, MHP and BHP power resistors can be used for this application. 4. Gate Drive Resistors The example opposite shows the circuit topology for an inverter welding power source. The input power is rectified to DC using a power factor correction boost converter. A full bridge MOSFET power stage converts the voltage back to AC at high frequency typically 50KHz to 100KHz. The transformer steps down the voltage, which is then rectified and smoothed at the output stage. The advantages of this type of power source are that it has high power conversion efficiency. And due to the high frequency operation of the MOSFET bridge the size of the components can be greatly reduced specifically the transformer and output filter stage. This is because the component size is inversely proportional to the operating frequency. The inverter power source maintains a constant output voltage regardless of changes in input voltage and output current. It has a very quick response time to changes in line and load and produces excellent arc characteristics delivering a true multi-process capability. MOSFET switching losses are due to delays in the switching transients since during these short time intervals a finite voltage and current coexist in the device. Therefore switching speed is the most important criteria required to minimise switching losses. Consequently faster switching Full Bridge Power Stage Input Boost PFC Input Rectifier L1 D5 R2 D1 D3 R snub Q2 Gate Drive 230 VAC Q1 R snub Q4 C snub R1 S1 R4 Gate Drive C snub C1 Gate Drive R snub D2 R snub R5 R3 D4 Q3 Gate Drive Q5 C snub Gate Drive C snub +V out L2 D6 R Snub C3 C snub R6 C2 C4 Work Clamp D7 Output Stage High frequency multi-process inverter welder speeds correspond to an increase in dI/dt of the drain/collector current. Fast dI/dt coupled with stray circuit inductance can cause considerable problems such as increased radiated EMI, large voltage spikes and circuit oscillations. Adding a small resistance at the MOSFET gate can be used to trade efficiency for lower dI/dt and its associated benefits. Resistors used for this application require high repetitive surge capabilities since they are expected to rapidly charge then discharge a MOSFET’s input gate capacitance at a high frequency. BI Technologies BSR resistor is suitable for this application. 3 Welding App.qxd 4 9/2/04 2:34 PM Page 1 Resistive Components Resistive Components BI Technologies - SMT BI Technologies - ECD BI Technologies - MCD Company Profile Company Profile Company Profile BI Technologies, SMT Division is a World Class manufacturer of thick film Passive Components. The company was established in 1958 in Glenrothes, Scotland. BI Technologies have earned a great reputation as a high quality, high volume, cost effective and responsive supplier of thick film passive components for telecommunications, computer, automotive, medical and industrial applications. BI Technologies has been an innovator and leader in electronic components for more than 50 years manufacturing products for communication, computer, industrial and automotive applications. BI Technologies, Magnetic Component Division, headquartered in Fullerton, California, with a manufacturing base in Kuantan, Malaysia, is a world leader in miniature surface mount high power inductors. The magnetic material and manufacturing expertise of various inductors, choke coils, transformers and assemblies has expanded the customer and market base into automotive, medical, computer, data communication and industrial in addition to other specialized magnetic assembly applications. Product Range Product Range Product Range • Packaged SIL, DIL and Surface Mount Resistor Networks • Chip Resistor Arrays • Chip Resistor - Capacitor Arrays • Planar Power Resistors • Surge Resistors • Thick Film Substrates • Custom Thick Film products • High Voltage Resistors and Networks • Trimming and Precision Potentiometers • Position Sensors • Chip Resistor Arrays • Resistor Networks • Integrated Passive Networks • Inductors • Transformers • Turns Counting Dials • Hybrid Microelectronics and Custom Integration Products • Transformers both surface mount and through hole • Surface Mount high powered inductors • Toroidal inductors (through hole and surface mount) • High power specialty laminate transformers • Data communication modules, filters, and transformers for ethernet and DSL • Common mode filters and chokes • Planar transformer solutions BI Technologies serves a global customer base with manufacturing locations in the United States, Mexico, Scotland, Japan, China and Malaysia. BI Technologies SMT BI Technologies ECD BI Technologies Pte Ltd TT electronics GmbH Telford Road, Glenrothes Fife KY7 4NX, Scotland, UK 4200 Bonita Place Fullerton, CA 92835, USA Max-Lehner-Strasse 31 85354 Freising, GERMANY Tel: +44 1592 662200 Fax: +44 1592 662299 [email protected] Tel: +714 447 2300 Fax: +714 447 2400 [email protected] 514 Chai Chee Lane, #02-01 Bedok Industrial Estate 469029 SINGAPORE TT electronics SA TT electronics S.r.l. BI Technologies Japan Ltd Sales/Technical Support Centre 17 Rue du Kefir, Senia 418 94567 Orly, FRANCE Via Arese 12 20159 Milan, ITALY Tel: +33 1 45 12 3880 Fax: +33 1 45 12 3879 Tel: +39 2 688 8951 Fax: +39 2 689 6995 Kakumaru Building 4/F 1-10 Toyo 7 Chome Koto-ku Tokyo 135, JAPAN Flat 1104, 11/F, Block 1 News Building, No. 2 Shennan Middle Road, Futian District, Shenzhen, CHINA 518027 Tel: +81 3 3615 1811 Fax: +81 3 3647 2443 Tel: +86 755 8209 0230 / 8209 0295 Fax: +86 755 8209 0267 Tel: +65 445 5166 Fax: +65 445 1983 Welding Power Supplies Tel: +49 8161 4908-0 Fax: +49 8161 4908-99 Power Resistor Application Note BPR, BPC, MHP & BSR Series Resistors www.bitechnologies.com · www.ttelectronics.com · www.bitechnologies.co.jp Applications • Capacitor discharge • Snubbing • Inrush limiting Authorised Representative • MOSFET gate drive BI Technologies General Note: BI Technologies reserves the right to make changes in product specification without notice or liability. All information is subject to BI Technologies’ own data and is considered accurate at time of going to print. © BI Technolgies 2004 A subsidiary of TT electronics plc Issue A 08/04 A subsidiary of TT electronics plc BI Technologies