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Capacitor kind cost pumps are a widely known, easy, environment friendly, cost-effective (and subsequently standard!) methodology for inverting and multiplying voltage provide rails. Maybe much less well-known, nevertheless, is that additionally they work simply as effectively for dividing voltage (whereas multiplying present). Determine 1 illustrates a Vout = Vin/2, Iout = Iin*2 instance pump constructed across the venerable xx4053 CMOS triple SPDT swap.
Determine 1 xx4053 primarily based, 100kHz, voltage-halving, current-doubling cost pump.
Right here’s the way it works.
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Wow the engineering world along with your distinctive design: Design Concepts Submission Information
The R1C1 time fixed {couples} the Vin/ppv sq. wave discovered at U1pin14 to U1pin9, creating an Fpump oscillator frequency of (roughly):
Fpump = 1 / (2 * 100k * 68 pF * loge(2)) = 100 kHz
Through the Fpump damaging half-cycle (U1pin4 = 0), the higher (U1pin14) finish of C2 is related to Vin whereas the decrease finish (U1pin15) finish is related to Vout, thus charging C2 to:
Vc2-= Vin – Vout
Then, throughout the next Fpump constructive half-cycle (U1pin4 = Vin), the higher finish of C2 connects to Vin whereas the decrease finish connects to Vout, and:
Vc2 = Vout
This deposits a amount of cost onto C3 of:
Q+ = C2((Vin – Vout) – Vout) = C2(Vin – 2Vout)
Through the subsequent damaging half-cycle, once more:
Vc2 = Vin – Vout
Depositing one other cost onto C3 of:
Q- = C2 ((Vin – Vout) – Vout) = C2(Vin – 2Vout)
Thus, every full cycle of Fpump deposits a internet cost onto C3 of:
Q = Q+ + Q- = 2 * C2(Vin – 2Vout)
Which, if Iout = 0, forces Q = 0 and subsequently:
Vin – 2Vout = 0
Vout = Vin / 2
Nevertheless, for the (way more fascinating) case of Iout > 0:
Q = Iout / 100 kHz
2 * C2(Vin – 2Vout) = Iout / 100 kHz
Vin – 2Vout = Iout / 100 kHz / 2 / C2
Vout = (Vin – (Iout / 100 kHz / 2 / C2)) / 2
In different phrases, Vout droops a bit because the output is loaded. It’s because, for a finite C2 Q can also be finite, but in addition to the truth that the U1a and U1b inside switches have non-zero ON resistances.
The mixed impact on Vout versus Iout quantities to an efficient impedance of 150 Ω for Vin = 5 V and is plotted in Determine 2, together with present multiplication “effectivity”. Word that the latter soars previous unity resulting from the truth that solely half of the dollops of C2 cost (the Q+) are drawn from the Vin rail, whereas the Q- are provided from residual voltage on C2, inflicting zero further drain from the rail.
Determine 2 Present multiplying charge-pump Vout and Iout/In present “effectivity” for Vin = 5 V.
So, what’s it good for?
Determine 3 suggests one helpful utility, producing nominally symmetrical +/-Vin/2 bipolar rails from a single constructive supply with minimal present draw from the supply.
Determine 3 Present doubling cost pump plus voltage inverter makes an environment friendly bipolar rail splitter.
Stephen Woodward’s relationship with EDN’s DI column goes again fairly a great distance. Over 100 submissions have been accepted since his first contribution again in 1974.
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