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Preregulated DC-DC Converter Designed Through a Feedforward Technique

IP.com Disclosure Number: IPCOM000042590D
Original Publication Date: 1984-May-01
Included in the Prior Art Database: 2005-Feb-04
Document File: 2 page(s) / 64K

Publishing Venue

IBM

Related People

Azzis, D: AUTHOR [+3]

Abstract

Fig. 1 shows a classical DC-DC converter; output voltage Vout is regulated through a feedback loop which tells the modulator what duty cycle Ton/T will produce a specified Vout whatever happens at the input Vin or at the output Iout. Now let us write: Vout = Vin Ns Ton (1) Np T This clearly shows that Vin affects Vout. Instead of making a conventional feedback, the present design is based on a more complex modulator that will permanently ensure: Vin Ton = constant (2) T The following implementation does it precisely so that eventually we get rid of Vin variations; there remains only the output load effect which is usually rather small (depends on various drops).

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Preregulated DC-DC Converter Designed Through a Feedforward Technique

Fig. 1 shows a classical DC-DC converter; output voltage Vout is regulated through a feedback loop which tells the modulator what duty cycle Ton/T will produce a specified Vout whatever happens at the input Vin or at the output Iout. Now let us write: Vout = Vin Ns Ton (1) Np T This clearly shows that Vin affects Vout. Instead of making a conventional feedback, the present design is based on a more complex modulator that will permanently ensure: Vin Ton = constant (2) T The following implementation does it precisely so that eventually we get rid of Vin variations; there remains only the output load effect which is usually rather small (depends on various drops). The design proposed here operates for Vin from 10 V to 30 V; it maintains Vout = 5 V Å 1% for a specific load, and Vout = 5 V Å 5% when load variations are also considered from 10% to 100%. This result is obtained without a feedback loop, which is essential for stability. As seen in Fig. 2, a current generator is designed with a standard PNP transistor and is supplied from Vin; auxiliary V+ is half of Vin. V+ = 1/2 Vin In the modulator, 2 comparators (LM 339) define the period with a sawtooth generator between Vhi and Vlo. IoT = C(Vhi-Vlo) where C is a constant. Two other comparators define Ton between V2 and V1 . Io.Ton = C(V2-V1) The output is driven through a flip-flop and a divider that drives alternately the two output switchers. I...