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9V battery eliminator circuit for car, sometimes you need a 9 volt battery to power some circuit, the problem is that sometimes we don’t have them on hand, or if it is a scheme that requires a little more current, the battery will discharge quickly. Then we could use rechargeable batteries, but the issue is that they are expensive. So, it is better to use a voltage converter circuit as shown here.
The IC used is the 78L08 voltage regulator, which has a low quiescent (quiescent) current and provides enough current to replace a 9-volt battery. The voltage regulator IC 7809 even exists, but the 7808 is easier to find, for voltage to be close to 9 ‘volts’ we use the diode 1n4148 in the ground terminal of the IC, so we will have 8.7 volts that replaces a 9-volt battery quietly. The circuit input has an LC filter and an RC filter. These filters eliminate disturbances coming from the power supply network.
Nowadays, it is easy to find the 78l09 and in this case, the diode D2 (1n4148) can be removed, and a jumper added on the spot.
It was added the suggestion of printed circuit board and reduced size, can be installed in the same place where it would go 9V battery or even the board can be installed in the box where the cells of the 9V battery would be. Simply make the connections using an input connector and connecting a 9V battery clip to the output.
The 78lxx family IC normally supports up to 100mA of current, see the datasheet for more details.
If you prefer you can also use other voltage regulators like LM78L33 (3.3V), LM78l05 (5V), LM78L62 (6.2V), LM78L82 (8.2V), LM7812 (12V), LM7815 (15V). The maximum input voltage is 30V, depending on the manufacturer, check the datasheet of the voltage regulator IC.
Depending on the voltage regulator used you can use it to power various battery or battery-powered electronics, 3V (2 batteries), 5V (3 batteries), 6V (4 batteries), 8V (5 batteries), 9V (9V battery or 6 batteries). Just pay attention to the maximum current of 0.1A.
To power the circuit we will use any DC source up to 30V and 500mA or more, diode D1 serves to protect against reverse polarity.
Circuit diagram 9V battery eliminator circuit for car
Printed Circuit boar for Circuit diagram 9V battery eliminator circuit for car
BOM to assemble the 9V battery eliminator circuit
| Part | Valor | Description | Quantity |
| Capacitors | |||
| C1, C2, C3 | 100n (104) | Capacitor ceramic | 3 |
| C4 | 100uF/16 | Capacitor electrolytic | 1 |
| Miscellaneous | |||
| CN1 | IN | DC Input | 1 |
| CN2 | OUT | Regulated output | 1 |
| Semiconductors | |||
| D1 | 1N4004 | Diode | 1 |
| D2 | 1N4148 | Diode (optional) | 1 |
| IC1 | 78l09 | 78l09 voltage regulator | 1 |
| LED1 | led 3 mm | Led 3 mm red | 1 |
| Resistors and inductors 1/4W | |||
| R1 | 820 ohms | Gray, red, brown, gold | 1 |
| R2 | 10 ohms | Brown, black, gold, gold | 1 |
| L1, L2 | 10uH | Brown, black, gold, silver | 2 |
| Semiconductors | |||
| Solder, Wires, PCB, Box, power supply | |||
Download the files, PCB in PDF, PNG and Gerber. Includes panel with 6 boards per panel.
