LM1575, LM2575-N, LM2575HV
SNVS106E –MAY 1999–REVISED APRIL 2013
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Pin numbers are for the TO-220 package.
Figure 37. 1.2V to 55V Adjustable 1A Power Supply with Low Output Ripple
Definition of Terms
BUCK REGULATORA switching regulator topology in which a higher voltage is converted to a lower voltage.
Also known as a step-down switching regulator.
BUCK-BOOST REGULATORA switching regulator topology in which a positive voltage is converted to a
negative voltage without a transformer.
DUTY CYCLE (D)Ratio of the output switch's on-time to the oscillator period.
(17)
CATCH DIODE OR CURRENT STEERING DIODEThe diode which provides a return path for the load current
when the LM2575 switch is OFF.
EFFICIENCY (η)The proportion of input power actually delivered to the load.
(18)
CAPACITOR EQUIVALENT SERIES RESISTANCE (ESR)The purely resistive component of a real capacitor's
impedance (see Figure 38). It causes power loss resulting in capacitor heating, which directly affects the
capacitor's operating lifetime. When used as a switching regulator output filter, higher ESR values result in
higher output ripple voltages.
Figure 38. Simple Model of a Real Capacitor
Most standard aluminum electrolytic capacitors in the 100 μF–1000 μF range have 0.5Ω to
0.1Ω ESR. Higher-grade capacitors (“low-ESR”, “high-frequency”, or “low-inductance”') in the
100 μF–1000 μF range generally have ESR of less than 0.15Ω.
EQUIVALENT SERIES INDUCTANCE (ESL)The pure inductance component of a capacitor (see Figure 38).
The amount of inductance is determined to a large extent on the capacitor's construction. In a buck
regulator, this unwanted inductance causes voltage spikes to appear on the output.
OUTPUT RIPPLE VOLTAGEThe AC component of the switching regulator's output voltage. It is usually
dominated by the output capacitor's ESR multiplied by the inductor's ripple current (ΔIIND). The peak-to-
peak value of this sawtooth ripple current can be determined by reading INDUCTOR RIPPLE CURRENT.
24
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