Darlington Pair to Drive DC motor Circuit

A normal variable resistor cannot directly control the speed of a motor since motors draw large amounts of current which would burn out the potentiometer. Instead, the small amount of current that the potentiometer can pass can be amplified into order to run the motor. This amplification can be achieved using Darlington Pair of transistors.

Darlington Pair to Drive DC motor Circuit

Pin-out BFY61 & TIP31C Transistor

The circuit above shows a linear potentiometer connected Between Vs and 0V Such That the voltage at its wiper terminal will of always be somewhere at or Between these two voltages. The small amount of current flowing out of the potentiometer's wiper is amplified by two transistors, connected together in a configuration known as a 'Darlington pair'. The current from the potentiometer is amplified by the first transistor, and then again by the second transistor, greatly Increasing the amount of current That cans be controlled by the potentiometer.

There are, however, a couple of disadvantages of this simple circuit. Firstly, about 0.7V is lost in EACH of the transistor, so the maximum voltage cans That ever be applied to the motor is Vs - 1.4V. Secondly, the transistors are not absolutely linear so the change in motor speed for a given rotation of the potentiometer will from some more subtle in the middle of its range. Because a motor is an inductive load, it will from Produce a 'back-emf' Could the which damage to the second transistor. The 1N4148 signal diode prevents this damage by shorting out the back-emf.

The power supply for this circuit should preferably be un-smoothed (i.e. directly from the power supply rectifier). This helps prevent the motor 'sticking' at low speeds. With the TIP31C transistor given, the maximum power supply voltage may be 60V and the maximum motor current consumption may be 3A.

Source: www.eleinmec.com

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Rangkaian 8038 frequency | Signal Generator

frequency | Signal Generator circuit is a circuit that produces a variety of different waveforms at a desired frequency. It can generate Sine waves, Square waves, Triangular and Sawtooth waveforms as well as other types of output waveforms. There are many "off-the-shelf" waveform generator IC's available and all can be incorporated into a circuit to produce the different periodic waveforms.

Skema Rangkaian 8038 frequency | Signal Generator

IC 8038 Pinout

One such device is the 8038 a precision waveform generator IC capable of producing sine, square and triangular output waveforms, with a minimum number of external components or adjustments. Its operating frequency range can be selected over eight decades of frequency, from 0.001Hz to 300kHz, by the correct choice of the external R-C components.

The frequency of oscillation is highly stable over a wide range of temperature and supply voltage changes and frequencies as high as 1MHz is possible. Each of the three basic waveform outputs, sine, triangle and square are simultaneously available from independent output terminals. The frequency range of the 8038 is voltage controllable but not a linear function. The triangle symmetry and hence the sine wave distortion are adjustable.

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Bistable Multivibrator Using IC 555 Circuit

555 Bistable Multivibrator circuit acts as a basic flip-flop. The Output will stable in two states: output high and output low. The switching of the output waveform is achieved by controlling the Trigger and Reset inputs which are held "HIGH" by the two pull-up resistors, R1 and R2. By taking the Trigger input (pin 2) "LOW", switch in Set position, changes the output state into the "HIGH" state and by taking the Reset input (pin 4) "LOW", switch in Reset position, changes the output into the "LOW" state. This 555 timer circuit will remain in either state indefinitely and is therefore bistable. Then the Bistable 555 timer is stable in both states, "HIGH" and "LOW".

Skema Rangkaian 555 Bistable Multivibrator

Note:

• Trigger (555 pin 2) makes the output high, Trigger is 'active low', it functions when <>
• Reset (555 pin 4) makes the output low. Reset is 'active low', it resets when <>
• The power-on reset, power-on trigger and edge-triggering circuits can all be used as described above for the

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IC 555 Monostable Circuit

Monostable circuit produces one pulse of a set length in response to a trigger input Such as a push button. The output of the circuit stays in the low state Until there is a trigger input, Hence the name "monostable" meaning "one stable state".

This type of circuit is ideal for use in a "push to operate" system for a model displayed at EXHIBITIONS. A visitor cans push a button to start a model's mechanism, moving, and the mechanism will from automatically switches off after a set time.

The circuit diagram of the 555 monostable circuit is given as follows.

Monostable Using IC 555 Circuit

IC 555 Pinout

Note:

• resistor value R and the capacitor value C are unspecified. The values of these components determine the length of time that the monostable output is in the high state, and they may be calculated using the equation below
• T = 1.1RC or R = T/1.1C
  

In the monostable mode, the timer 555 acts as a "one-shot" pulse generator. The pulse Begins Pls the 555 timer receives a signal at the trigger input That falls below a third of the voltage supply. The width of the output pulse is determined by the time constant of an RC network, the which consists of a capacitor (C) and a resistor (R). The output pulse ends Pls the charge on the C equals 2 / 3 of the supply voltage. The output pulse width cans be lengthened or shortened to the need of the specific application by adjusting the values of R and C

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High Voltage Meter or Probe Design

Common voltmeters, digital or analog, usually range to some hundred volts maximum. Higher voltages not only cannot be indicated, but will also destroy the instrument. However, the range of any voltmeter can easily be extended using extra series resistance, as shown in the figure. Calculating the necessary resistance implies knowledge of the input impedance of the voltmeter.

Circuit and formula for constructing high voltage probes. For example, let's assume we want to extend the range of a standard digital voltmeter (input impedance 10MOhm) to 100kV. The maximum DC voltage the meter can take is 1000V. This means we need an external 1GOhm high voltage resistor in series with the meter. The total voltage ios given by the value indicatedby the meter, times 100. If we wanted to read the voltage in kV directly, we would need a resistor 1000 times as large as the input impedance of the voltmeter, i.e. 10GOhm.

Such home-brew high voltage probes are good for DC only. For AC voltages, capacitive input impedance of the meter and capacity of the probe must be matched, which is difficult to achieve because of parasitic capacitance of the resistor chain. A few pF (the capacitance of a 1cm radius metallic sphere) make a big difference, especially at higher frequencies.

Source: kronjaeger.com

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Rangkaian Transistor Tester

The circuit shown below is a simple circuit transistor tester. In some digital and analog avometer now mostly been contained this feature, but it can not hurt us a little more creative. This circuit can also be used to detect whether a transistor is NPN / PNP.

Skema Rangkaian Transistor Tester

Circuit operation is as follows. The 555 timer is set up as a multi-vibrator 12hz. The output on pin 3 drives the 4027 flip-flop. This flip-flop divides the input frequency by two and delivers complementary voltage outputs to pin 15 and 14. The outputs are connected to LED1 and LED2 through the current limiting resistor R3. The LED's are Arranged so Pls That the polarity across the circuit is one way only one LED will from light and Pls the polarity reverses the other LED light earnest, therefore Pls no transistor is connected to the tester the LED's will from alternately flash. Also The 4027 outputs are connected to resistors R4 and R5 with the junction of these two resistors connected to the base of the transistor being tested. With a good transistor connected to the tester, the transistor will of turn on and Produce a short across the LED pair. If a good NPN transistor is connected then LED1 will from flash by Itself and if a good PNP transistor is connected then LED2 will from flash by Itself. If the transistor is open both LED's will from flash and if the transistor is shorted then neither LED will from flash.

IC NE555 Pinout

IC 4027 Pinout

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