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High light LED switching power supply PDF Print E-mail

highly integrated MAX5035 PWM switching converters, high-brightness LED power supply schematic, output current up to 1A. Another similar device MAX5033's output current can reach 500mA. The inductor-based buck regulator can accurately control the flow through the LED (or a few series LED, the total voltage is 12V) current. MAX5035's switching frequency of 125kHz, input voltage range up to 76V (higher voltage need to use the input capacitor and diode). This circuit can be a wide input voltage range to control and maintain constant LED current. Table 2 summarizes the design specifications of the circuit. 

 

1 Suppose a white LED: VF = 4V, ILED = 350mA, VIN = 12V.
Using the circuit in Figure 1 the role of a voltage regulator control terminal LED current

Control voltage and three current-sense resistor in parallel together to the IC's voltage feedback (FB) pin. IC's internal control loop to keep the FB pin voltage is about 1.22V, so, since the control voltage and current detection voltage must be maintained at 1.22V (set by the resistors R1 and R5), a higher control voltage will result in more small current.

In addition to the following equation applies to this exception, the other can also be used to design the output current and control voltage:

In many cases, the use of low frequency (50Hz to 200Hz) PWM mode is very easy to adjust the LED current by controlling the pulse width modulation brightness (Figure 4). Although the LED brightness remains the same during each pulse, the naked eye can detect short-term brightness changes, but this adjustment method has the advantage of spectrum remains unchanged, when the spectrum will be used as adjustable rate flowing through the LED current with changes.

The use of 100Hz, 0V to about 3.9V square wave waveform control, LED current pulse shown in Figure 4. In general, the low-frequency PWM dimming circuit is more efficient than linear LED dimming circuit (Figure 2) is higher.

 High switching frequency (125kHz) allows you to select a small reactor components (L1 and C2).
• Wide input voltage range can achieve high conversion efficiency.
• Output voltage up to 12V, can drive three series of high-brightness green LED.
• No mechanical radiator.
• voltage range extended to 76V, suitable for driving vehicles of high brightness LED.
• can be used to 24V signal lights and architectural lighting.
• by varying the current sense resistor R2, R3 and R4, and the output current of up to 1A.
• Built-in switching power MOSFET, simplify the design.
• through the control input pin, the use of analog voltage amplitude (linear dimming) to adjust the LED brightness.

• by controlling the input, the use of low-frequency PWM signal to adjust brightness.
 
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