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Moteur de recherche de fiches techniques de composants électroniques |
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Moteur de recherche de fiches techniques de composants électroniques |
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LB20164R7M Fiches technique(PDF) 4 Page - Linear Technology |
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LB20164R7M Fiches technique(HTML) 4 Page - Linear Technology |
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4 / 12 page  4 LT1931/LT1931A 1931fa BLOCK DIAGRA Figure 2 OPERATIO The LT1931 uses a constant frequency, current mode control scheme to provide excellent line and load regula- tion. Operation can be best understood by referring to the Block Diagram in Figure 2. At the start of each oscillator cycle, the SR latch is set, turning on the power switch Q3. A voltage proportional to the switch current is added to a stabilizing ramp and the resulting sum is fed into the positive terminal of the PWM comparator A2. When this voltage exceeds the level at the negative input of A2, the SR latch is reset, turning off the power switch. The level at the negative input of A2 is set by the error amplifier (gm) and is simply an amplified version of the difference between the feedback voltage and the reference voltage of –1.255V. In this manner, the error amplifier sets the correct peak current level to keep the output in regulation. If the error amplifier’s output increases, more current is taken from the output; if it decreases, less current is taken. One function not shown in Figure 2 is the current limit. The switch current is constantly monitored and not allowed to exceed the nominal value of 1.2A. If the switch current reaches 1.2A, the SR latch is reset regardless of the state of comparator A2. This current limit protects the power switch as well as various external components connected to the LT1931. The Block Diagram for the LT1931A is identical except that the oscillator is 2.2MHz and resistors R3 to R6 are one-half the LT1931 values. – + LATCH RQ S 0.01 Ω SW DRIVER COMPARATOR 2 SHUTDOWN SHDN 4 1 – + Σ RAMP GENERATOR RC CC 1.2MHz OSCILLATOR GND 1931 BD R6 80k R4 150k R3 30k Q2 x10 Q1 Q3 R5 80k VIN VIN 5 NFB CPL (OPTIONAL) R2 (EXTERNAL) R1 (EXTERNAL) VOUT NFB 3 A2 A1 gm |
Numéro de pièce similaire - LB20164R7M |
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Description similaire - LB20164R7M |
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