Here are three regulated wall adapters delivering respectively, 6V, 9V and 12V. These projects are to be mounted in plastic cases. When mounted in metal cases, a connection from the case to the earth must be added. Also, is a switch is desired, you can add a SPST switch if you are using a plastic case and a DPST switch if you are using a metal case.
Although the LM78XX regulators have thermal overload protection built in, a fuse was added at the output for two reasons:
- Thermal protection doesn't allow a very precise shutdown. In case of short circuit, the tranformer might be damaged;
- Thermal protection actuates at 125ºC. Such temperature would not be desired, because it can damage the PCB and the case. Also, an heatsink at 125ºC would turn the situation worse.
View attachment Adapt800mA_6V.pdf
List of components (6V 800mA adapter):
C1 10mF electrolytic capacitor (25V);
C2 100nF polyester capacitor (65V);
D1-4 1N5391 rectifier diode;
D5/7 1N4001 rectifier diode;
D6 Red LED (GaAsP/GaP);
F1 100mA slow fuse;
F2 800mA fast fuse;
IC LM7806 voltage regulator (6,8°C/W heatsink);
R1 680Ω carbon resistor (1/2W, 5% tol.);
R2 270Ω carbon resistor (1/4W, 5% tol.);
T Transformer 230V~ 9V~ 16VA.
View attachment Adapt800mA_9V.pdf
List of components (9V 800mA adapter):
C1 6,8mF electrolytic capacitor (35V);
C2 100nF polyester capacitor (65V);
D1-4 1N5391 rectifier diode;
D5/7 1N4001 rectifier diode;
D6 Red LED (GaAsP/GaP);
F1 125mA slow fuse;
F2 800mA fast fuse;
IC LM7809 voltage regulator (5,6°C/W heatsink);
R1 1KΩ carbon resistor (1/2W, 5% tol.);
R2 470Ω carbon resistor (1/2W, 5% tol.);
T Transformer 230V~ 12V~ 20VA.
View attachment Adapt800mA_12V.pdf
List of components (12V 800mA adapter):
C1 4,7mF electrolytic capacitor (35V);
C2 100nF polyester capacitor (65V);
D1-4 1N5391 rectifier diode;
D5/7 1N4001 rectifier diode;
D6 Red LED (GaAsP/GaP);
F1 160mA slow fuse;
F2 800mA fast fuse;
IC LM7812 voltage regulator (4,7°C/W heatsink);
R1 1,5Ω carbon resistor (1W, 5% tol.);
R2 680Ω carbon resistor (1/2W, 5% tol.);
T Transformer 230V~ 15V~ 25VA.
Although the LM78XX regulators have thermal overload protection built in, a fuse was added at the output for two reasons:
- Thermal protection doesn't allow a very precise shutdown. In case of short circuit, the tranformer might be damaged;
- Thermal protection actuates at 125ºC. Such temperature would not be desired, because it can damage the PCB and the case. Also, an heatsink at 125ºC would turn the situation worse.
View attachment Adapt800mA_6V.pdf
List of components (6V 800mA adapter):
C1 10mF electrolytic capacitor (25V);
C2 100nF polyester capacitor (65V);
D1-4 1N5391 rectifier diode;
D5/7 1N4001 rectifier diode;
D6 Red LED (GaAsP/GaP);
F1 100mA slow fuse;
F2 800mA fast fuse;
IC LM7806 voltage regulator (6,8°C/W heatsink);
R1 680Ω carbon resistor (1/2W, 5% tol.);
R2 270Ω carbon resistor (1/4W, 5% tol.);
T Transformer 230V~ 9V~ 16VA.
View attachment Adapt800mA_9V.pdf
List of components (9V 800mA adapter):
C1 6,8mF electrolytic capacitor (35V);
C2 100nF polyester capacitor (65V);
D1-4 1N5391 rectifier diode;
D5/7 1N4001 rectifier diode;
D6 Red LED (GaAsP/GaP);
F1 125mA slow fuse;
F2 800mA fast fuse;
IC LM7809 voltage regulator (5,6°C/W heatsink);
R1 1KΩ carbon resistor (1/2W, 5% tol.);
R2 470Ω carbon resistor (1/2W, 5% tol.);
T Transformer 230V~ 12V~ 20VA.
View attachment Adapt800mA_12V.pdf
List of components (12V 800mA adapter):
C1 4,7mF electrolytic capacitor (35V);
C2 100nF polyester capacitor (65V);
D1-4 1N5391 rectifier diode;
D5/7 1N4001 rectifier diode;
D6 Red LED (GaAsP/GaP);
F1 160mA slow fuse;
F2 800mA fast fuse;
IC LM7812 voltage regulator (4,7°C/W heatsink);
R1 1,5Ω carbon resistor (1W, 5% tol.);
R2 680Ω carbon resistor (1/2W, 5% tol.);
T Transformer 230V~ 15V~ 25VA.
