Universal BatteryUP
DATED
Charge Controller
We have made some changes to our Universal Battery Charge Controller
published in December 2020 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
O
nce upon a time, we lived
in the land of plenty where
electronic components were
plentiful 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 chains for motor vehicles, mobile
phones and many white goods such
as washing machines and refrigerators, among other items, all of which
now depend on semiconductors for
their operation.
The resulting lack of semiconductor supply also impacted our readers
and us. We regularly heard from readers that a particular part for a project
was hard to find and we know how
frustrating that can be. Now, more
than ever remember to check that all
parts are available before spending
money on a circuit.
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.
38
Turning to the Universal Battery
Charge Controller, we used one
Si8751 isolated MOSFET driver IC
in the circuit, which was unavailable
from early 2020 until recently. While
back in stock, it is now considerably
more expensive than it was when we
specified it.
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 version of the PCB,
shown in Fig.1, is essentially identical to the original one, except for
the MOSFET and gate driver component changes. Also see the Parts
List panel below, which outlines the
changes in the devices 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
In the original circuit, the Si8751
(IC2) was used to 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.
Practical Electronics | August | 2023
Universal Battery Charge Controller
Fig.2: the only changes in this circuit from the original on page 19 of the December 2020 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.
The MOSFET switch on-time with
this arrangement was 5ms and the
switch-off time was typically 15μs.
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 the specialised driver (IC2) in the earlier
design 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 on
top of the battery voltage.
Practical Electronics | August | 2023
Revised MOSFET driver
Moving on to the updated MOSFET
driver circuit, the RB3 output signal
from IC1 still controls the MOSFET
on and off periods. However, 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.
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 towards the ground via a
4.7kW resistor.
The 47kW resistor between the
source and gate forms a voltage divider with the 4.7kW pulldown resistor, but since its value is
39
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 / 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
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 higher 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 Practical
Electronics article from December 2020.
Reproduced by arrangement with
SILICON CHIP magazine 2023.
www.siliconchip.com.au
40
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/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) [Farnell,
2443406]
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)
Items in bold have been
changed or added
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)
W
4 10kW
W
1 4.7kW
W
1 51kW
1 47kW
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 (VR1VR4) (code 103)
1 100W multi-turn top adjust trimpot, 3296W style (VR5)
(code 101)
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Practical Electronics | August | 2023
