Application Note PROFET™+ UNREGULATED PWM FOR LAMP What the designer should know Application Note Rev 1.0, 2013-02-04 Body Power App. Note 1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 2 2.1 2.2 2.3 Lamp Current . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Theory of the lamp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Constant Power Control by PWM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Unregulated PWM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 Power Losses Calculation in the PROFET+ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 4 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 Application Note Smart Hi-Side Switches 2 3 3 3 4 Rev 1.0, 2013-02-04 App. Note Introduction 1 Introduction As the lamp’s impedance is function to the effective power supply, the current flowing into the filament is not only dependant to the supply voltage but also depends on the duty cycle. Some applications in the automotive industry request duty cycle which is independant to the supply voltage. Famous examples are cornering lights, dome lights or brake lights dimming. This application notes describes a simple way to estimate the load current in the lamp and therefore estimate the average power losses flowing into PROFET+ high side switches. 2 Lamp Current 2.1 Theory of the lamp The current flowing into the filament can be estimated by Equation (1). V LAMP P LAMPREF ----------------- × ------------------------V REF V REF I LAMP = (1) The Table 1 sums up the parameters for common lamps used in the automotive application. Table 1 Electrical Wattage Lamp Lamp (W) Accuracy (%) VREF (V) Max DC current (A)1) PWM current (A)2) Maximum current (A)3) 5 10 13.5 0.5 0.7 0.9 7 10 12.8 0.7 1 1.3 10 10 13.5 1 1.3 1.8 15 10 13.5 1.4 2 2.7 21 6 12 2.3 3.1 4.3 27 6 12.8 2.7 3.7 5.0 55 6 13.2 5.2 7.1 9.7 65 6 13.2 6.1 8.4 11.5 1) At 18V 2) At 18V with light emission regulation (with duty cycle regulated according Equation (2)) 3) At 18V with 2% PWM 2.2 Constant Power Control by PWM Most application requires PWM to maintain a constant lighting power. The classical used formula is Equation (2) 2 V PWM d = ------------------2 V LAMP (2) Typically values are VPWM = 13.2V in Europe and VPWM = 12.8V in North America. To keep a constant lighting power means to keep a constant electrical power at the filament, thus keep the temperature filament constant. By the usage of Equation (2), the filament resistance is no more depending on to the root of the supply voltage but remains constant. Figure 1 compares both current assuming a H4 55W lamp and 13V voltage regulation. A difference of 1A can be observed at 18V between DC and power regulated mode. Application Note Smart Hi-Side Switches 3 Rev 1.0, 2013-02-04 App. Note Lamp Current 7,0 6,0 Load Current DC Load Current PWM 5,0 LOAD CURRENT (A) 4,0 3,0 2,0 1,0 0,0 6 8 10 12 14 16 18 SUPPLY VOLTAGE (V) LAMP_CURRENT_DC_PWM.vsd Figure 1 Load Current in DC and Power Regulation. H4 55W with 13V Regulation 2.3 Unregulated PWM The unregulated PWM should be understood as a duty cycle law which is not subject to the supply voltage, but follows another physical dimension, eg time (ramp-up and down of dome lights), steering wheel angle, etc... In those application, the PWM can be 5 to 95% duty cycle at 18V. To find the effective load current requires to suppose that this given duty cycle is coming from a power regulated law. Using Equation (2), the artificial voltage regulation is found by Equation (3). V PWM = d × V LAMP (3) For example, to perform a 5% PWM at 18V is equivalent to have regulated the lamp at 4V. It results in a much higher current at 18V than in DC. Figure 2 and Figure 3 show the load current at three different PWM duty cycle (5%, 50% and 100% or DC) and three voltage, for a H4 55W. 12,0 5% duty cycle 11,0 50% duty cycle 10,0 Courant lampe DC LOAD CURRENT (A) 9,0 8,0 7,0 6,0 5,0 4,0 3,0 2,0 6 8 10 12 14 16 18 SUPPLY VOLTAGE (V) LAMP_CURRENT_NON_REGULATED .vsd Figure 2 Load Current Function of Supply Voltage at Different Duty Cycle. H4 55W as Example Application Note Smart Hi-Side Switches 4 Rev 1.0, 2013-02-04 App. Note Power Losses Calculation in the PROFET+ 11,0 10,0 16V Battery 13,5V Battery LOAD CURRENT (A) 9,0 8V battery 8,0 7,0 6,0 5,0 4,0 3,0 2,0 0 20 40 60 DUTY CYCLE (%) 80 100 LAMP_CURRENT_NON_REGULATED 2.vsd Figure 3 Load Current function of Duty Cycle at Different Battery Voltage. H4 55W as Example 3 Power Losses Calculation in the PROFET+ The PROFET+ control the switching slopes and guarantees a fixed switch ON time. The switching speed is then battery depdendant and the switching time rather independant. Figure 4 and Figure 5 show the power losses at three different PWM duty cycle (5%, 50% and 100% or DC) and three voltages, for a H4 55W, using BTS5010-1EKB. The PWM frequency is fixed to 150 Hz. 0,70 5% duty cycle 50% duty cycle duty cycle 100% POWER LOSSES (W) 0,60 95% duty cycle 0,50 0,40 0,30 0,20 6 8 10 12 14 SUPPLY VOLTAGE (V) Figure 4 16 18 POWER_LOSSES _NON_REGULATED.vsd Power Losses Function of Supply Voltage. H4 55W / BTS5010-1EKB as Example Application Note Smart Hi-Side Switches 5 Rev 1.0, 2013-02-04 App. Note Conclusion 0,80 POWER LOSSES (W) 0,70 0,60 0,50 16V Battery 13,5V Battery 0,40 8V battery 0,30 0,20 0 20 40 60 DUTY CYCLE (%) 80 100 POWER_LOSES _NON_REGULATED 2.vsd Figure 5 Power Losses Function of Duty Cycle. H4 55W / BTS5010-1EKB as Example 4 Conclusion Performing non regulated PWM is possible using PROFET+ devices. The same device than for regulated power or DC usage is capable to drive unregulated PWM. Neverthteless, the power losses in the device increases due to the unregulated power in the lamp and the design should check the power losses in its specific application. Application Note Smart Hi-Side Switches 6 Rev 1.0, 2013-02-04 Edition 2013-02-04 Published by Infineon Technologies AG 81726 Munich, Germany © 2013 Infineon Technologies AG All Rights Reserved. Legal Disclaimer The information given in this document shall in no event be regarded as a guarantee of conditions or characteristics. With respect to any examples or hints given herein, any typical values stated herein and/or any information regarding the application of the device, Infineon Technologies hereby disclaims any and all warranties and liabilities of any kind, including without limitation, warranties of non-infringement of intellectual property rights of any third party. Information For further information on technology, delivery terms and conditions and prices, please contact the nearest Infineon Technologies Office (www.infineon.com). Warnings Due to technical requirements, components may contain dangerous substances. For information on the types in question, please contact the nearest Infineon Technologies Office. Infineon Technologies components may be used in life-support devices or systems only with the express written approval of Infineon Technologies, if a failure of such components can reasonably be expected to cause the failure of that life-support device or system or to affect the safety or effectiveness of that device or system. Life support devices or systems are intended to be implanted in the human body or to support and/or maintain and sustain and/or protect human life. If they fail, it is reasonable to assume that the health of the user or other persons may be endangered.