 |
|
| If you can't view the Datasheet, Please click here to try to view without PDF Reader . |
|
|
|
| If you can't view the Datasheet, Please click here to try to view without PDF Reader . |
|
|
| Datasheet File OCR Text: |
| LR8 LR8 High Input Voltage Adjustable 3-Terminal Linear Regulator Features 12V to 450V input voltage range Adjustable 1.20V to 440V output regulation 5% output voltage tolerance Output current limiting 10A typical ADJ current Internal junction temperature limiting General Description The Supertex LR8 is a high voltage, low output current, adjustable linear regulator. It has a wide operating input voltage range of 12V to 450V. The output voltage can be adjusted from 1.20V to 440V provided that the input voltage is at least 10V greater than the output voltage. The output voltage can be adjusted by means of two external resistors R1 and R2 as shown in the typical application circuits. The LR8 regulates the voltage difference between VOUT and ADJ pins to a nominal value of 1.20V. The 1.20V is amplified by the external resistor ratio R1 and R2. An internal constant bias current of typically 10A is connected to the ADJ pin. This increases VOUT by a constant voltage of 10A times R2. The LR8 has current limiting and temperature limiting. The output current limit is typically 15mA and the minimum temperature limit is 125C. An output short circuit current will therefore be limited to 15mA. When the junction temperature reaches its temperature limit, the output current and/or output voltage will decrease to keep the junction temperature from exceeding its temperature limit. For SMPS start-up circuit applications, the LR8 turns off when an external voltage greater than the output voltage of the LR8 is applied to VOUT of the LR8. To maintain stability, a bypass capacitor of 1.0F or larger and a minimum DC output current of 500A are required. The device is available in TO-92, TO-243AA (SOT-89), and TO-252 (D-PAK) packages. Applications Off-line SMPS startup circuits Adjustable high voltage constant current source Industrial Controls Motor controls Battery chargers Power supplies LR8 Block Diagram and Typical Application * VOUT R1 C2 RLOAD R2 VIN VIN VOUT ADJ LR8 C1 *Required for conditions where VIN is less than VOUT. 12/03/01 Supertex Inc. does not recommend the use of its products in life support applications and will not knowingly sell its products for use in such applications unless it receives an adequate "products liability indemnification insurance agreement." Supertex does not assume responsibility for use of devices described and limits its liability to the replacement of devices determined to be defective due to workmanship. No responsibility is assumed for possible omissions or inaccuracies. Circuitry and specifications are subject to change without notice. For the latest product specifications, refer to the Supertex website: http://www.supertex.com. For complete liability information on all Supertex products, refer to the most current databook or to the Legal/Disclaimer page on the Supertex website. 1 LR8 Ordering Information Package Options TO-92 LR8N3 * Product marking for TO-243AA: TO-252 LR8K4 LR8 where = 2-week alpha date code TO-243AA* LR8N8 Same as SOT-89. Product supplied on 2000 piece carrier tape reels. Absolute Maximum Ratings VIN Input Voltage Output Voltage Range Operating Ambient Temperature Range Operating Junction Temperature Range Storage Temperature Range *Voltages referenced to ADJ. Pin Configurations 2 (TAB) 1 2 3 -0.5V to +480V* -0.5V to +470V -40C to +85C -40C to +125C -65C to +150C TAB 1 3 123 TO-243AA (SOT-89) VIN TO-92 TO-243AA TO-252 1 1 1 TO-92 VOUT 2 2, TAB 2 (TAB) TO-252 (D-PAK) ADJ 3 3 3 Electrical Characteristics Test conditions unless otherwise specified: -40C < TA < 85C. Symbol VIN - VOUT VOUT VOUT VOUT VOUT VOUT IOUT IOUT IOUT IADJ C2 Parameter Input to Output Voltage Difference Overall Output Voltage Regulation Overall Output Voltage Regulation Line Regulation Load Regulation Temperature Regulation Output Current Limit Output Current Limit Minimum Output Current Adjust Output Current Minimum Output Load Capacitance 5 1 50 125 60 0.3 10 -1 10 Min 12 1.14 375 1.20 400 0.003 1.4 Typ Max 450 1.26 425 0.01 3.0 +1 20 0.5 0.5 15 Units V V V %/V % % mA mA mA A F dB C 120Hz, VOUT = 5V 12V DVOUT/DVIN Ripple Rejection Ratio TLIMIT Junction Temperature Limit 2 LR8 Thermal Characteristics Package TO-92 TO-243AA TO-252 Power Dissipation @ TA=25C 0.74W 1.6W 2.5W JC C/W 125 15 6.25 JA C/W 170 78 50 Mounted on FR4 board, 25mm x 25mm x 1.57mm. Significant PD increase possible on ceramic substrate. Functional Block Diagram VIN Pass Element LR8 VOUT Overtemp & Overcurrent 1.2V 10A ADJ 3 LR8 Typical Application Circuits * VOUT=5.0V R1 6.04K 1% R2 18.2K 1% VOUT = 1.20V 1+ R2 + IADJ R2 R1 VIN=15V to 450V V IN V ADJ OUT LR8 C1 C2 1.0F RLOAD 16.5K Figure 1: High Input Voltage, 5.0V Output Linear Regulator * Required for conditions where VIN is less than VOUT. VIN=15V to 450V VAuxiliary + Vout1 + Vcc FB LR8 V IN VOUT ADJ Vout2 PWM IC Figure 2: SMPS Start-Up Circuit 1F LR8 + VIN = 15V to 450V VIN VOUT ADJ IOUT = R 1.20V R Load Figure 3: High Voltage Adjustable Constant Current Source 4 LR8 Typical Performance Curves Temperature Variation 1.30 VIN VOUT=1.2V VOUT (V) 1.25 LR8 ADJ 12V 2.4K 1.0F 1.20 1.15 1.10 1.05 1.00 -50 -25 0 25 50 75 100 125 T(junction) (C) Adjustment Current 12 11 VIN VOUT=1.2V IADJ (A) LR8 12V, 200V, 400V ADJ 2.4K I ADJ 10 VIN = 400V 9 VIN = 12V 1.0F 8 VIN = 200V 7 6 -50 -25 0 25 50 75 100 125 T(junction) (C) Load Regulation 5.2 VIN VOUT=5.0V IOUT 5.1 LR8 ADJ 25V 18.2K 1% 6.04K 1% 1.0F RLOAD VOUT (V) 5.0 4.9 4.8 0 2 4 6 8 10 IOUT (mA) 5 LR8 Typical Performance Curves VOUT vs. VIN 6 VIN VOUT=5.0V 5 LR8 ADJ 0V to 50V 18.2K 1% 6.04K 1% 1.0F 1K VOUT (V) 4 3 2 1 0 0 10 20 30 40 50 VIN (V) Ripple Rejection -65 VIN VOUT =5.0V IOUT Ripple Rejection Ratio (dB) -64 LR8 20VP-P @ 60Hz 65V ADJ 6.04K 1% 1.0F RLOAD 18.2K 1% -63 -62 -61 -60 0 2 4 6 8 10 IOUT (mA) 6 LR8 Typical Performance Curves Load Transient Response VIN LR8 ADJ 25V 18.2K 1% VOUT=5.0V 6.04K 1% Closed SW 1.0F 10K 523 SW Open Vout Load Transient Response Line Transient Response 400V VIN 0V VIN LR8 ADJ VOUT 6.04K 1% 400V Vin 1.0F 18.2K 1% 10K 5.0V 0V Vout 0V Line Transient Response 400V 400V Vin Vin 0V 5.0V Vout 0V 0V 5.0V Vout 0V Line Power Up Transient Line Power Down Transient 12/03/01rev.2 (c)2001 Supertex Inc. All rights reserved. Unauthorized use or reproduction prohibited. 7 1235 Bordeaux Drive, Sunnyvale, CA 94089 TEL: (408) 744-0100 * FAX: (408) 222-4895 www.supertex.com LR8 LR8 Application Note AN-H40 High Voltage Linear Regulators and Constant Current Sources Using LR8 by Scott Lynch, Senior Applications Engineer Introduction The LR8 is a high voltage 3-terminal adjustable linear regulator. Intended for operation directly off rectified AC mains, the LR8 operates at input voltages up to 450 volts, making it compatible with line voltages up to 240 VAC. It's output voltage adjustability assures that it can be used in most any application. The LR8 is ideally suited for low power off-line DC power supplies and SMPS start-up circuits. Available in a leaded TO-92 package and a surface mount SOT-89 and D-PAK package, it is ideal for applications where space is at a premium. Relevant specifications are shown in the table below. Operation Except for it's higher voltage rating, the LR8 operates like any other 3-terminal adjustable linear regulator. A simple resistive divider sets the output voltage while a capacitor at the output improves transient response and ensures regulator stability. When applicable, an input capacitor is required to provide energy storage for rectified AC. Keeping in mind that the LR8 requires at least a 10V difference between input and output for proper operation, the minimum value for CIN is: CIN > I LOAD t VIN ( pk ) - VOUT - 10V LR8 Specifications Input Voltage Range Output Voltage Range Output Voltage Accuracy Power Dissipation (VOUT +10V) to 450V 1.2V to (VIN - 10V) 5% TO-92: 0.74W TO-243AA (SOT-89): 1.6W TO-252 (D-PAK): 2.5W 0.5 to 10mA 3% 0.01%/V 60dB typ @120Hz where ILOAD = Load current t = Time between peaks of input waveform VIN(pk) = Peak input voltage VOUT = Output voltage Output Current Load Regulation Line Regulation Supply Rejection Note that the LR8 requires a minimum of 0.5mA load current for proper operation. The current through the resistive divider may be included as part of the minimum load. LR8 Block Diagram and Typical Application Needed for protection should V OUT exceed V IN Supply VIN Pass Element LR8 R VOUT = 1.2 v1 + 2 + 10A * R2 R1 VOUT Load R1 CIN Overtemp & Overcurrent 1.2V 10A ADJ COUT 1F R2 8 LR8 Constant Current Operation The LR8 may be configured to provide a constant current output. The current is independent of both supply voltage and load impedance. Constant current operation finds application in driving LEDs and trickle-charging NiCad batteries, as shown below. The trickle charger is for applications that require battery backup (i.e. no cycling), such as emergency lights. Constant Current LED Driver R NiCad Battery Trickle Charger R LR8 15V to 450V 15V to 450V LR8 Start-up Circuit The schematic below depicts a simplified off-line switching power supply using the LR8 for start-up. When VBOOT rises above the LR8's output voltage, the LR8 goes into standby mode, consuming very little current. All current is then supplied from the bootstrap circuit rather than from the high voltage source, increasing overall efficiency. The output voltage of the LR8 should be set high enough above the minimum operating voltage of the PWM controller, yet low enough to ensure the bootstrap circuit takes over after start-up. With 240VAC input, instantaneous power dissipation can reach 3.4W (340VDC * 10mA). This level exceeds the LR8's rating, but exists for only as long as it takes for the supply to bootstrap. Thermal mass will prevent die temperature from rising quickly. If boot time is short, die temperatures will not reach the overtemperature protection trip point. It is advisable to mount the LR8 on 2 oz. copper with an area of at least 2.5 square centimeters. Startup Current for Off-line Switching Power Supply bootstrap winding VBOOT D1 VIN AC Mains CIN LR8 R1 VOUT PWM Controller R2 COUT 9 LR8 Comparison with Discrete Startup Implementations The LR8 provides several advantages when compared with discretely implemented start-up circuits. Zener Implementation VIN VOUT Transistor Implementation VIN VOUT VIN LR8 Implementation LR8 VOUT Disadvantages * Continues to draw current from high voltage source after supply has bootstrapped, resulting in inefficiencies * Bias must be set for minimum input voltage, resulting in high current drain at high input voltages * Poor regulation * No current limit * No overtemperature protection * In the Zener implementation, requires large power resistor and Zener Advantages * LR8 goes into standby mode after supply has bootstrapped, drawing no current from high voltage input * Good regulation * Built-in current limiting * Overtemperature protection Exceeding LR8's Current Limit for Startup Applications The LR8 has a built-in current limit of 10mA minimum. If the current drawn by the PWM controller exceeds this limit, the LR8 may still be used. To do this, the LR8's output capacitor supplies a portion of the current until the power supply can bootstrap itself and the LR8 is no longer needed. The following figure graphically illustrates how this is accomplished. Most PWM controllers have an undervoltage lockout (UVL) circuit or programmable start/stop voltages. When the voltage supplied to the PWM controller reaches the turn-on threshold, the controller begins operating and consuming current. If current exceeds the current limit for the LR8, the voltage at VOUT begins to decay. With a large enough capacitor, the supply will bootstrap before voltage decays to the turnoff threshold. VIN 1 1 Input voltage is applied. The LR8 begins operating (in current limiting mode since COUT appears as a short). VOUT begins to rise as COUT charges. The PWM controller draws a small amount of current. VOUT 4 VHYS VBOOT 2 2 tBOOT 3 The output voltage of the LR8 reaches the PWM controller's turn-on threshold. Controller begins operating, drawing current. Bootstrap voltage begins climbing while VOUT decays since current drawn by the controller exceeds the LR8's current limit. 3 IPWM ILR8 10mA 4 Bootstrap voltage reaches the level of the LR8's output and takes over. LR8 current drops to zero. Power supply reaches steady-state operation. 0mA 10 LR8 The minimum capacitance required for given boot-up time is given by the following equation: COUT > t BOOT I PWM - I LIM VHYS where COUT tBOOT IPWM ILIM VHYS = = = = = Capacitor at LR8 output Time required for supply to bootstrap Current used by PWM controller LR8 current limit (10mA min) PWM controller UVL hysteresis Remember that this equation is valid only when PWM current exceeds the LR8's current limit. 11/30/01rev.1 11 1235 Bordeaux Drive, Sunnyvale, CA 94089 TEL: (408) 744-0100 * FAX: (408) 222-4895 www.supertex.com |
Price & Availability of LR8N8
 |
|
|
|
|
All Rights Reserved © IC-ON-LINE 2003 - 2022 |
| [Add Bookmark] [Contact Us] [Link exchange] [Privacy policy] |
|
Mirror Sites : [www.datasheet.hk]
[www.maxim4u.com] [www.ic-on-line.cn]
[www.ic-on-line.com] [www.ic-on-line.net]
[www.alldatasheet.com.cn]
[www.gdcy.com]
[www.gdcy.net] |