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Os motores de busca de Datasheet de Componentes eletrônicos |
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Os motores de busca de Datasheet de Componentes eletrônicos |
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LC101N Folha de dados(PDF) 8 Page - Sanken electric |
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LC101N Folha de dados(HTML) 8 Page - Sanken electric |
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8 / 15 page  LC101N LC101N-DSE Rev.1.0 SANKEN ELECTRIC CO.,LTD 8 Nov.19, 2015 http://www.sanken-ele.co.jp/en/ © SANKEN ELECTRIC CO.,LTD. 2015 11. Operational Description 11.1 Basic operation The current control of the LC101N is quite simple. The both end voltage of the setup resistor R1 which is connected between the FB terminal and the LO pin. So that it becomes constant, the emitter-collector voltage of the internal PNP-transistor is linear-controlled by the error amplifier. Figure 11-1 shows the basic circuit of LC101N. ICONST LO FB IN 4 1 8 5 LED U1 R1 ILED1 LO FB IN 4 1 8 5 LED U2 R2 ILED2 LED1 LED2 VF1 VF2 VF1×n VF2×n Figure 11-1 LC101N basic circuit LED current, ILED is calculated by Equation (3). (3) From Equation (3), the setup resistor, R1 is calculated by Equation (4). (4) The reference voltage, VFB for the constant current control is 200 mV. The both end voltage of R1 is controlled to become equal to VFB. The loss of R1, PR1 is calculated by Equation (5). (5) Table 11-1 shows the calculation result of relationship of ILED, R1, and PR1. Table 11-1 The loss of R1, PR1 ILED (mA) R1 (Ω) PR1 (mW) 50 4 10 100 2 20 150 1.33 30 In addition, the loss of the IC, PD is calculated by Equation (6). (6) where, VIN is the voltage between the IN pin and the LO pin, and VLED is the voltage between the LED pin and LO pin. 11.2 Power Supply The power supply should be use the constant-current source. If the constant-voltage source is used, the voltage difference between input and output that does not require for LED becomes the loss of the IC. Though it will operate with the constant-voltage source, if the input-output voltage difference becomes larger than necessary, and all of surplus will be loss in this IC The ability of power supply, PIN is required to satisfy following equation. (7) where, N is number of LED in series, VF is forward voltage of LED, and ICONST is the constant current of power supply. For example, LED current is set to 50 mA in Figure 11-1. The constant current of power supply, ICONST, is set fewer than the total current value of LED-strings A and B (100mA), because the drooping characteristic of constant-current source is considered. In this case, ICONST is set 95 mA. If VF = 3V and n = 7, PIN becomes as follows: 11.3 Current Balance Operation If All LEDs have same VF, and the same current flows to LED-string A and B, the power loss of IC becomes minimum because the circuit is controlled by the constant-current source, ICONST and the internal transistor is a saturated condition. However, the complete equilibrium state is impossible by characteristic variations of VF. If each VF2 of LED string B is smaller than VF1 of LED string A by 0.1 V. |
Nº de peça semelhante - LC101N |
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Descrição semelhante - LC101N |
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