## 2 Investigation of Temperature Dependence of Current and Luminous Flux
### Study of Temperature Dependence of Current and Luminous Flux of LED Spotlight SDO 06-20  
Investigation of temperature dependence current and luminous flux of SDO 06-20 LED spotlight with power 20 W, scheme the control of which is built on high-voltage linear direct current LED driver. In the scheme, the compensating element (field-effect transistor) was connected gradually with LEDs. The driver contains built-in function of temperature compensation. The current was stabilized through LEDs. The general view of LED matrix of the spotlight with electronic components was presented in Figure 19. The spotlight contains fourteen SMD 2835 LEDs with direct voltage 18 V, nominal current 50 mA and power 1 W [15]. Stabilization of the current was provided by two connected in parallel high-voltage stabilizers ICNE2521 DE [19] (Figure 20). Figure 19: General view of the LED matrix of SDO 06-20 spotlight. Figure 18: High-frequency current pulsation through LEDs of Premier-10 lamp. The functional diagram of ICNE2521 DE chip is shown in Figure 21.  
As can be seen from Figures 20 and 21, the current of the spotlight LEDs was stabilized by the circuit--on ICNE2521 DE microcircuit field-effect transistors were connected gradually. SMD-capacitor \(C1\) has small capacity and was used as high-frequency filter, therefore the voltage at the output of VDS diode bridge has the form of rectified sinusoid with 100 Hz pulsation frequency. Resistors \(R1\), \(R2\) determine the amount of current through the spotlight LEDs. The oscillogram of voltage on all spotlight LEDs gradually connected, which also has pulsating shape is represented in Figure 22, and current form through LEDs is shown in Figure 23.  
Figure 21: Functional diagram of ICNE2521 DE. Figure 20: Principle electric scheme of SDO 06-20 spotlight. Figure 22: Voltage oscillogram of SDO 06-20 spotlight LEDs. Current, like the spotlight luminous flux, has pulsating form with 100 Hz pulsation frequency. Dependencies of the relative current values \(I_{imp}\)/\(I_{imp25}\) of SDO 06-20 spotlight on the environment temperature \(T_{c}\) at supply voltage 198 V, 220 V and 242 V were shown in Figure 24.  
As can be seen from Figure 24, dependencies of the spotlight input current on the temperature increases with the increase of the supply voltage, and at 242 V, the current has the largest drop at the temperature higher than +40 \({}^{\circ}\)C.  
Dependencies of the relative luminous flux values \(F\)/\(F_{25}\) of SDO 06-20 spotlight on the environment temperature \(T_{c}\) at supply voltage 198 V, 220 V and 242 V are represented in Figure 25.  
Figure 19:0 Oscillogram of the current through SDO 06-20 spotlight LEDs. Figure 19:1 Dependencies of the relative current values \(I_{imp}\)/\(I_{imp25}\) of SDO 06-20 spotlight on the environment temperature \(T_{c}\) at 198 V, 220 V and 242 V supply voltage. Figure 19:2 Dependencies of the relative luminous flux values \(F\)/\(F_{25}\) of SDO 06-20 spotlight on \(T_{c}\) temperature at198 V, 220 V and 242 V supply voltage. The change in the spotlight luminous flux with temperature is quite significant (Figure 25) and increases with increasing supply voltage. Thus, at 198 V voltage, the drop of the luminous flux within +15... +60 \({}^{\circ}\)C temperature range is 10%, and at 242 V voltage it increases up to 20%. Besides that, as was mentioned above, the spotlight has significant low-frequency current pulsations, and therefore the luminous flux, which could be avoided by means of low-frequency filter capacitor in the spotlight circuit after VDS diode bridge (Figure 20). Investigation of the Temperature Dependence of Current and Luminous Flux of LED Spotlight Feron LL6020 LED  
Let us consider the temperature dependence of current and luminous flux of TM Feron LL6020 LED spotlight with 20 W capacity, the driver of which is built according to the scheme of high-voltage direct current stabilizer based on BP2335 microcircuit.