Loublet Schematic

A PWM circuit primarily based on timer NE555 is that the heart of this circuit. NE555 is wired as an astable multivibrator whose duty cycle will be adjusted by varying the POT R1. The output of IC1 is coupled to the base of transistor Q1 that drives the motor according to the PWM signal available at its base. Higher the duty cycle the typical voltage across motor will be high which ends in higher motor speed and vice versa. modification of DC motor direction is attained using the DPDT switch S1 that on application simply toggles the polarity applied to the motor.

By using IC NE555, which causes wave clear the sector output allows the voltage nearly 6V after the signify on the output from a pulse plus C2 acts charge through D1 to ground and if the pulse harmful capacitor C2 desire discharge. through diode D1 and capacitor C3 to chage so as to negative voltage is about-6V, but being aloof to the run to of absent-5V zener diode ZD1 current output will happen approximately 12mA. To test the circuit or else circuits with the purpose of may well need various circuits, but we take refusal fire-5V power supply-5V, but if the battery 9V circuit can allow us to avail yourself of the volt-5V being desired. 

Description:
This circuit will generate a smaller DC output voltage from a larger DC input voltage.It is quick and simple to make and by changing the value of the zener diode, the circuit can be universally adapted to provide other output voltages.The circuit and all diagrams represent a DC convertor with 12V battery input and 9Volt DC output.

The output voltage is equal to the zener diode voltage less 0.7 volts, or :-

Vo = Vz - 0.7 where V z is the value of the zener diode.

With the 10V zener diode as shown in the diagram the output voltage is about 9.3 Volts DC. The supply voltage used must always be at least a few volts higher than the zener voltage. In this example I have used a 12 Volt DC battery to provide the regulated 9 Volt DC output.


The above graph shows how the output is affected by input voltage variations. This was produced with a load current of 100mA and using a 10 volt rated zener diode. Note that the circuit falls sharply out of regulation when the input voltage falls to 11.5 volt, hence the requirement for an adequate supply voltage.

Temperature stability is very good as the above graph shows. The output voltage changes by 8.5mV for every 10 degree rise in temperature. This is less than 1 mV / degree.

Power Dissipation
With a DC-DC convertor, the most important consideration is power dissipation in the output device. Power dissipation is the product of the transistors emitter current and collector-emitter voltage. With this circuit the maximum power dissipation of the BD139 or maximum collector current cannot be exceeded, otherwise the transistor will be destroyed.
Example:
With a 12 Volt supply and a 9 Volt, 100 mA load the dissipation is as follows. Using a 10 volt zener the output voltage will be about 9.3 volts DC therefore:

VCE * IC = (12 - 9.3) * 100 mA = 2.7 Watts

This is well within the maximum limits of power dissipation and collector current, which for the BD139 are 8 watts and 1 amp respectively. If higher load currents are required then the following circuit may be used.

Output dissipation is calculated in the same way, the BD131 has a maximum power dissipation of 15 watts and collector current of 3 amps. The output voltage is approximately 1.4 volts less than the zener diode voltage and supply voltage must be higher than the input voltage by at least 3 volts.

When using a digital measuring instrument with another electronic circuit it is often necessary or desirable to completely separate the supply for the meter from that for the rest of the electronics.
The ` problem can be solved by using two separate supplies, but it can also be done using a single supply and a DC—DC converter. The type of converter described here is quite compact and can deliver a current of about 50 mA. p The circuit consists of an astable multivibrator (IC1), which switches the voltage supply for a transformer (Tr!) on and off via a transistor (T1).  The transformer secondary voltage is ha|f—wave rectified and smoothed. The output voltage is then limited by zener diode D5. I The transformer used should have a ratio between the windings of 1:1. The firing transformer used for thyristors is ideal for the iob, but a  small audio transformer (frorn a pocket radio) is also suitable. The frequency and pulse width of the circuit can be adapted to the type of transformer used by means of P1 and P2. Firing transformers give the best results at frequencies of about 100 kHz, while audio trans- formers usually work best between 0.5 and 40 kHz. The transformer must, of course, be connected witl· correct polarity. The frequency is found as follows:
F 0.7x (P1 +P2+ R1 + R2) xC1
tchargg =   X    X 
tdigchargg : 0.7 X     X C1.