An oscillator for a pwm controller

Abstract

The invention discloses an oscillator of a PWM (pulse-width modulation) controller, which comprises three branch circuits connected in parallel with an input voltage source and an operational amplifier, wherein a first branch circuit is provided with a resistor R1 and a resistor R2; a second branch circuit is provided with a resistor R3, a triode N1 and a resistor R4; a third branch circuit is provided with a resistor R5; the resistor R5 is respectively connected with a capacitor C1 and a resistor R6 which are connected in parallel and the anode of a diode D2; and the reverse input end of the operational amplifier is connected between the resistor R6 and a capacitor C2, the non-reverse input end is connected with the collector electrode of the triode N1 and connected with a resistor R7 which is connected in series with the anode of a diode D3, the output end is connected with cathodes of the diode D2 and the diode D3, and the first signal output end and the second signal output end are connected between the resistor R7 and the diode D3. The provided oscillator of a PWM controller has favorable frequency consistency, low rate of change with temperature and wide external synchronization clock frequency range; and synchronization can be realized above and below the natural vibration frequency of the oscillator.

Description

technical field [0001] The invention belongs to the technical field of pulse width modulation control, and relates to an oscillator of a PWM controller. Background technique [0002] The stability of the oscillator directly determines the stability of the frequency of the DC / DC converter. The stability of the switching frequency is an important indicator of the DC / DC converter. The stability of the switching frequency can affect the stability and efficiency of the DC / DC converter. , electromagnetic radiation, reliability and so on. [0003] Currently, the oscillator circuits of PWM (Pulse Width Modulation) controllers used in DC / DC converters are as follows figure 1 As shown, (such as UC1843, UCC1802, etc.) the change rate of the high and low temperature oscillator frequency (-55°C ~ +125°C) is about 20% ~ 30%. [0004] In many noise-sensitive applications, the DC / DC converter usually locks the frequency to the external system clock through the external synchronization fun...

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Problems solved by technology

[0004] In many noise-sensitive applications, the DC / DC converter usually locks the frequency to the external system clock through the external synchronization function. Currently, PWM controllers (such as UC1843, UCC1802, etc.) have external synchronization function circuits such as figure 2 As shown, in order to lock reliably, the oscillator's natural frequency should be about 10% lower than the clock frequency, which limits the application of DC / DC converters

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