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Digital Pulse Generator with a Programmable Delay

IP.com Disclosure Number: IPCOM000130724D
Original Publication Date: 2005-Dec-10
Included in the Prior Art Database: 2005-Dec-10

Publishing Venue

Siemens

Related People

Juergen Carstens: CONTACT

Abstract

In power converter systems pulse generators are needed, for example, to trigger voltage or current sensing circuitry. In this case the pulse generators are triggered by an event, and certain delay applies to the generated pulse referred to the source trigger signal. Example is the peak voltage detection/sensing in PFC controllers (peak detector) and valley-detection in quasi-resonant controllers (Valley detector) which take a zero-crossing signal as a trigger signal. Using the current solutions by analog means it is difficult or even impossible to achieve an accurate peak-value or valley-value detection as discussed in the following text. The problem of peak detection in PFC application is that in PFC controllers line voltage peak value detection is necessary for purpose of brown-out protection or realization of follower-boost concept. As the state-of-the-art solution RCD networks are used which scale down the line voltage or the rectified line voltage and hold this voltage over several line periods for voltage sensing. One typical of these kinds of circuits is shown in Figure 1 and its typical waveforms are shown in Figure 2.

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Digital Pulse Generator with a Programmable Delay

Idea: Dr. Jing Hu, SG-Singapore; Dr. Leo Lorenz, SG-Singapore

In power converter systems pulse generators are needed, for example, to trigger voltage or current sensing circuitry. In this case the pulse generators are triggered by an event, and certain delay applies to the generated pulse referred to the source trigger signal. Example is the peak voltage detection/sensing in PFC controllers (peak detector) and valley-detection in quasi-resonant controllers (Valley detector) which take a zero-crossing signal as a trigger signal. Using the current solutions by analog means it is difficult or even impossible to achieve an accurate peak-value or valley-value detection as discussed in the following text.

The problem of peak detection in PFC application is that in PFC controllers line voltage peak value detection is necessary for purpose of brown-out protection or realization of follower-boost concept. As the state-of-the-art solution RCD networks are used which scale down the line voltage or the rectified line voltage and hold this voltage over several line periods for voltage sensing. One typical of these kinds of circuits is shown in Figure 1 and its typical waveforms are shown in Figure 2.

In this circuit the line voltage is rectified by the diode-bridge consisting of D1 to D4. The voltage at the bus terminals vbus has a half-sinus form during the normal operation of the PFC stage. Through the scale-down and hold circuit made of diode D5, capacitor C1 and two resistors R1 and R2 a smoothed voltage is obtained. By the voltage divider consisting of R1 and R2 the voltage across the resistor R2 is sensed for purpose of realization of brown-out protection or follower-boost concept in PFC controllers. This voltage has a waveform which is shown as vR2a or vR2b, depending on the time constant of the RC-network. Normally, a high time constant is preferred for a smooth waveform which easies the voltage sensing. But a high time constant results in a low response speed of the circuit upon the change of the input line voltage so that the measured waveform does not follow the changing input line voltage fast enough, just as vR2a shown in Figure 2. On the contrary, if the time constant is too low, the ripple of the sensed voltage is high (vR2b) which makes a accurate sensing of the voltage almost impossible neither, since the averaged value of the voltage vR2 is used for the voltage sensing through this approach, but not the voltage vR2 at its maximum which would be a time-based solution.

Additionally, this circuit suffers from both high costs and high losses. In this circuit a high voltage capacitor is used which results in high costs. Furthermore, due to the needed response time of this circuit the resistance of the voltage divider can not be selected to be very high. This results in high losses in the circuit. These losses present in all operation modes and this makes it difficult to meet the...