Adjustable Voltage Step-up (Zero.7-5.5V to 2.7-5.5V)

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I adopted the Max757 PDF specification when deciding on elements. I additionally select elements that had been in inventory and at as low costs as attainable. Keep in thoughts that there is perhaps higher selections! See picture for the circuit scheme. I made some small modifications from the usual structure. I discovered that pin1(SHDN) must be related to pin6(OUT) with the intention to work (it want >1.5V i believe). If it’s floating the circuit might be very unstable. If it’s grounded the booster is turned off.

Full specification of Max757 could be present in pdf:

Should deal with 1.2A (worst-case) and low DC-resistance (<Zero.03Ω) for good effectivity. I discovered one with four.6A/Zero.031Ω.

Should have low ESR (Equivalent sequence resistance) for good efficiency. Could not discover any data about that. I select one movie capacitor (C3=Zero.1µF) and two aluminium electrolytic (C1=150µF resp. C2=100µF). I additionally added one (C4=1µF) movie capacitor in parallel with C2 to filter excessive frequencies.

Rectifier Diode:
A switching Schottky diode is advisable for optimum efficiency. I select 1N5817.

Does not matter I suppose. The present might be very low. The output voltage is about by the equation:
VOUT = (VREF) [(R1 + P1) / R1], the place VREF = 1.25V. Simplified to P1 = (R1) [(VOUT / VREF) – 1]
R1 and P1 ought to usually be 10kΩ to 200kΩ. I select R1 to 47kΩ. I would like 2.7V to five.5V. Then based mostly on R1, P1 must be between 55kΩ and 160kΩ. To obtain that I select two resistors (P1R1 & P1R2), 47kΩ resp. 10kΩ (57kΩ can be equally good however I didn´t have that), in serie with a 100kΩ trim potentiometer. That means a spread of 57-157kΩ and an output voltage vary of two.77-5.43V.

If you want low-battery detector (LBI-pin), you then would want two extra resistors.
The threshold voltage is about by R3 and R4 utilizing the next equation:
R3 = [(VIN / VREF) – 1] (R4)
the place VIN is the specified threshold of the low-battery detector, R3 and R4 are the enter divider resistors at LBI, and VREF is the interior 1.25V reference. R3 and R4 ought to usually be 10kΩ to 200kΩ. I skipped that half. See Max757 PDF.

I additionally put a pink LED in serie with a 470Ω resistor (R2) to point OK/ON-state.

I like to recommend a socket for the IC. If it’s destroyed it could possibly simply get replaced.

Circuit board (Prototype board):
I used a pre-fabricated prototype board from an outdated undertaking. That was not included in complete value however it´s simply three€ for 100x160mm.

These could be discovered at Item quantity in brackets. I used different prototype board, resistors, potentiometer and terminal blocks however comparable is listed right here.

  • IC (DC-DC step-up): MAX757CPA+ – IC, DC/DC UP CONVERTER, DIP8, 757 [1290852]
  • Socket (DIP8): TE CONNECTIVITY / AMP – 1-390261-2 – SOCKET IC, DIL, Zero.three”, 8WAY [1101345]
  • C1 (150µF): PANASONIC – EEUFR1H151, RADIAL, 50V, 150UF [1800679]
  • C2 (100µF): PANASONIC – EEUFC1H101, RADIAL, 50V, 100UF [1848464]
  • C3 (Zero.1µF): EPCOS – B32529C104J, FILM, Zero.1UF, 63V, RADIAL [2112914]
  • C4 (1µF): EPCOS – B32529C105J, FILM, 1UF, 63V, BOXED [1692372]
  • D1 (1N5817): VISHAY FORMERLY I.R. – VS-1N5817, SCHOTTKY, 1A, 20V [1463212]
  • D2 (LED): MULTICOMP – 703-Zero100, 5MM, RED, 400MCD, 643NM [2112111]
  • L1 (22µH): PANASONIC – ELC16B220L, 22UH, four.6A, 0R031 [1749170]
  • P1R1 (10kΩ): MULTICOMP – MF25 10Ok, 10Ok, Zero.25W, 1% [9341110]
  • R1&P1R2 (47kΩ): MULTICOMP – MF25 47Ok, 47Ok, Zero.25W, 1% [9341960]
  • R2 (470Ω): MULTICOMP – MF25 470R, 470R, Zero.25W, 1% [9341943]
  • P1(100kΩ): TE CONNECTIVITY / CITEC – CB10LH104M, SIDE, 100Ok [1227527]
  • Terminal block: IMO PRECISION CONTROLS – 20.101M/2, PCB, 2WAY, 22-12AWG [9632670]
  • Prototype board: ROTH ELEKTRONIK – RE523-HP – PCB, FR2, STRIPES, 2.54MM [1172112]

Tools wanted:

  • Soldering iron
  • Pliers
  • Sharp object (knife)
  • Small noticed

Next step: Pre-Test

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