Jameco 2215988 Руководство - Страница 5
Просмотреть онлайн или скачать pdf Руководство для Водяной насос Jameco 2215988. Jameco 2215988 11 страниц. Automatic turn off water pump on desired level + water level indicator/sensor
Печатать страницуStep 5 - High speed switching diode
1N4148 is a high speed switching diode. The switching diodes are designed such that their reverse recovery time is very small compared
to ordinary diodes. The typical switching time is 4 nsec. It comes in hermetically sealed leaded glass package.
Diode 1N4148 in this circuit is used to short circuit current which is inducted when relay coil is de-energized from power supply. When
circuit disconnects relay coil current of opposite direction is created so we must be sure that other components do not get damaged
because of it. When relay is connected to source diode will not conduct because of the orientation of the anode and cathode, diode will
act like open switch, diode will conduct when positive voltage is applied at the anode of the diode.
To place diode on the board you need to bend diode terminals for 90° like resistors, distance between leads must be 10.1mm. Place
diode on its place near relay pin headers referring to top silk and step image.
Step 6 - Transistors
A transistor is a semiconductor device used to amplify and switch electronic signals and electrical power. It is composed of
semiconductor material with at least three terminals for connection to an external circuit. A voltage or current applied to one pair of the
transistor's terminals changes the current through another pair of terminals. Because the controlled (output) power can be higher than
the controlling (input) power, a transistor can amplify a signal. Today, some transistors are packaged individually, but many more are
found embedded in integrated circuits.
This circuit is using two 2N3904 general purpose transistors which are used as switches. Transistor Q1 is used for grounding positive
input of latch circuit. When input of latch is grounded we have negative output and in that case another transistor which is used for
controlling relay module will turn off and thus will turn off relay. Transistors are controlled by feeding signal to their middle terminal which
is called base.
2N3904 transistors are NPN so that means that they are connected between load and the ground.
NPN
- No current flowing from B to E = No flow from C to E
- Current flowing from B to E = Current allowed to flow from C to E