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UPDAT Universal Battery Charge Controller ED We have made some changes to our Universal Battery Charge Controller published in December 2019 (siliconchip.au/Article/12159) so that it can be built using parts that are actually available. The changes are modest, and the total cost for parts has been reduced. By John Clarke nce upon a time, we at S C O lived in the land of plenty where electronic components were plentiilicon hip ful and readily available, blissfully unaware of future events that would alter our lives. But all that changed when the COVID-19 pandemic suddenly disrupted many markets and manufacturers. This affected the production of semiconductor devices and ICs and dramatically increased the demand for electronics. This has impacted the supply of motor vehicles, mobile phones and many white goods such as washing machines and refrigerators, amongst other items, all of which now depend on semiconductors. The resulting lack of semiconductor supply is also impacting our readers Fig.1: construction is much the same as before, except you can skip soldering the SMD IC (IC2) and a few associated capacitors. Instead, install the TO-92 transistor (Q4), two resistors and zener diode ZD3. These components are all in the upper right-hand corner. The rest of the PCB is identical to the original. siliconchip.com.au Australia's electronics magazine and us. We put considerable effort into maintaining parts supply for our projects via our Online Shop. But once they are sold, we may not be able to replenish the supply straight away, especially if someone buys up all our stock at once. Turning to the Universal Battery Charge Controller, we used one Si8751 isolated Mosfet driver IC in the circuit. While it was available when the article was first published, this is no longer the case, and we don’t expect these to be available for at least another year, if not longer. So we have come up with a new circuit that performs the function of the Si8751 in another way. Fortunately, the changes are straightforward. Our discrete Mosfet driver comprises small-signal NPN transistor Q4, a few resistors and zener diode ZD3. The N-channel Mosfet is replaced with a P-channel type. These changes are highlighted in a cyan box in the updated circuit diagram, Fig.2. The revised PCB, shown in Fig.1, is essentially identical to the original, except for the Mosfet and gate driver component changes. Also see the panel below outlining the changes in the parts required to build this project. These changes do not affect the operation of the Charge Controller as far as the user is concerned. Original design The original circuit using the Si8751 June 2022  81 Fig.2: the only changes in this circuit from the original on page 27 of the December 2019 issue are in the box at upper right. All the components there have been replaced; the N-channel Mosfet is now a P-channel type. This simplifies the driving scheme greatly; it is now an NPN transistor with a few resistors and a zener diode to limit the drive voltage and current to safe levels. (IC2) would drive the N-channel Mosfet gate (Q1) positive whenever the RB3 output of microcontroller IC1 was high, switching Q1 on. This allowed current to flow from the charger to the battery. When the RB3 output went low, Q1’s gate voltage dropped to its source voltage, so the Mosfet was off, and no current flowed to the battery. The Mosfet switch on-time with this arrangement was 5ms and the switch-off time was typically 15μs. 82 Silicon Chip Fast switching was not required in this application, as we’re only switching the Mosfet on and off once every two seconds. The main reason for using this specialised driver (IC2) was that, with Q1 being an N-channel type and its source connected to the battery, it needed a gate voltage of around 20V to switch on. This is not present anywhere in the circuit; it was generated by stacking the isolated power output of IC2 Australia's electronics magazine on top of the battery voltage. Revised Mosfet driver With the revised Mosfet driver circuit, the RB3 output signal from IC1 still controls the Mosfet on and off periods. The Mosfet is now a P-channel type, so the higher voltage is unnecessary. It is switched on by pulling its gate voltage below the charger output voltage, which connects to its source terminal. siliconchip.com.au Switching from an N-channel type to a P-channel type means we have to swap the drain (D) and source (S) terminal connections. That is so that the parasitic internal diode is still facing in the right direction to block current flow to the battery when the channel is not conducting. Now, when the RB3 output is low, transistor Q4 is off and the gate of Mosfet Q1 is held at its source voltage via the 47kW resistor. The Mosfet is therefore off. When the RB3 output goes high, transistor Q4 is switched on via base current through the 10kW resistor. The transistor conducts, and the gate of Q1 is pulled toward the ground via a 4.7kW resistor. The 47kW resistor between the source and gate forms a voltage divider with the 4.7kW pull-down resistor, but since its value is ten times higher than the 4.7kW resistor, the gate is pulled near to ground. Zener diode ZD3 is included to limit the gate to source voltage to 13V to prevent damage to the Mosfet, as it has a gate-source voltage limit of -16V. The switch-on time for the Mosfet is much faster than before, less than 27μs, and the switch-off time is under 270μs (it’s higher because the pull-up resistor value is ten times high than the pull-down resistor). So the switch-on is much faster than with the Si8751, but the switch-off period is a bit longer. Still, as mentioned earlier, the switching time does not need to be particularly fast for our circuit. Part of the reason we have been able to simplify the driving arrangement is that we can now supply high-­current P-channel Mosfets at a reasonable price (see the revised parts list). Traditionally, they have been harder to get and more expensive than equivalent N-channel types. Construction There is very little difference in construction between the original and revised PCBs. Refer to Fig.1 and simply fit the new components in the upper right-hand corner as shown. The Mosfet mounting is identical. As a bonus, this change eliminates the only SMD component in the design, the Si8751 (IC2). Testing, setting up and using the charger are identical to the original and are described in the original article (siliconchip.au/Article/12159). SC siliconchip.com.au Parts List – Updated Battery Charge Controller 1 double-sided PCB, code 14107192, 111 x 81mm 1 diecast aluminium box, 119 x 94 x 34mm [Jaycar HB5067] 1 2A DPDT 5V coil telecom relay (RLY1) [Altronics S4128B] 1 PCB-mount SPDT momentary pubutton switch (S1) [Jaycar SP0380, Altronics S1498] 1 pushbutton switch cap for S1 [Jaycar SP0596, Altronics S1482] 1 SPST micro tactile switch with 0.7mm actuator (S2) [Jaycar SP0600, Altronics S1122] 1 PCB-mount 3.5mm stereo switched socket (CON1) [Jaycar PS0133, Altronics P0092] 2 PCB-mount M205 fuse clips (F1) 1 10A M205 fuse (F1) 2 NTC thermistors (10kW at 25°C) (TH1 and external thermistor) 1 2-way header with 2.54mm spacing (JP1) 2 3-way headers with 2.54mm spacing (JP2, JP3) 3 jumper plugs/shorting blocks (JP1-JP3) 1 18-pin DIL IC socket (for IC1) 1 3.5mm stereo jack plug 1 TO-220 silicone insulating washer and mounting bush (for Q1) 4 6.3mm-long M3 tapped spacers 3 M4 x 10mm machine screws 3 M4 star washers 3 M4 hex nuts 2 M3 x 10mm machine screws 8 M3 x 5mm machine screws 2 M3 hex nuts 4 insulated crimp eyelets (wire size 4mm, eyelet for M4 screw) 2 cable glands for 4-8mm diameter cable 1 2m length of 15A figure-8 automotive cable 1 1m length of twin-core shielded cable (for thermistor) 1 20mm length of 6mm diameter heatshrink tubing 2 large insulated battery terminal alligator clips (red and black) 6 PC stakes (optional) 4 small adhesive rubber feet Semiconductors 1 PIC16F88-I/P micro programmed with 1410719A.HEX (IC1) 1 LM317T 1.5A adjustable positive regulator (REG1) 1 IPP80P03P4L-07 P-channel Mosfet (Q1) [Silicon Chip SC6043] 2 BC337 NPN transistors (Q2, Q3) 1 BC547 or BC337 NPN transistor (Q4) 3 green 3mm LEDs (LED1, LED5, LED6) 2 orange 3mm LEDs (LED2, LED4) 1 red 3mm LED (LED3) 2 18V 1W zener diodes (ZD1, ZD2) 1 13V 1W zener diode (ZD3) 3 1N4004 1A diodes (D1-D3) Capacitors 1 220µF 50V PC electrolytic 1 100µF 16V PC electrolytic 3 100nF MKT polyester 5 10nF MKT polyester Resistors (all 1/4W, 1% metal film unless otherwise stated) 1 51kW 1 47kW W 4 10kW W 1 4.7kW W 1 3.3kW 1 2kW 7 1kW 1 330W 1 120W 1 100W 1W, 5% 1 56W 4 10kW multi-turn top adjust trimpots, 3296W style (VR1-VR4) (code 103) 1 100W multi-turn top adjust trimpot, 3296W style (VR5) (code 101) Items in bold have been changed or added Australia's electronics magazine June 2022  83