Panel switch wiring

Showing posts with label circuits. Show all posts

Friday, September 19, 2014

Simple and hold circuit using op amp Circuits Wiring diagram

As the name indicates , a sample and hold schema is a schema which samples an input signal and holds onto its last sampled value until the input is sampled again. Sample and hold diagram are commonly used in analogue to digital converts, communication diagram, PWM diagram etc. The schema shown below is of a sample and hold schema based on uA 741 opamp , n-channel E MOSFET BS170 and few passive components.

Description

As the name indicates , a sample and hold schema is a schema which samples an input signal and holds onto its last sampled value until the input is sampled again. Sample and hold diagram are commonly used in analogue to digital converts, communication diagram, PWM diagram etc. The schema shown below is of a sample and hold schema based on uA 741 opamp , n-channel E MOSFET BS170 and few passive components.

In the schema MOSFET BS170 (Q1) works as a switch while opamp uA741 is wired as a voltage follower. The signal to be sampled (Vin) is applied to the drain of MOSFET while the sample and hold control voltage (Vs) is applied to the source of the MOSFET. The source pin of the MOSFET is connected to the non inverting input of the opamp through the resistor R3. C1 which is a polyester capacitor serves as the charge storing device. Resistor R2 serves as the load resistor while preset R1 is used for adjusting the offset voltage.

During the positive half cycle of the Vs, the MOSFET is ON which acts like a closed switch and the capacitor C1 is charged by the Vin and the same voltage (Vin) appears at the output of the opamp. When Vs is zero MOSFET is switched off and the only discharge path for C1 is through the inverting input of the opamp. Since the input impedance of the opamp is too high the voltage Vin is retained and it appears at the output of the opamp.

The time periods of the Vs during which the voltage across the capacitor (Vc) is equal to Vin are called sample periods (Ts) and the time periods of Vs during which the voltage across the capacitor C1 (Vc) is held constant are called hold periods (Th). Taking a close look at the input and output wave forms of the schema will make it easier to understand the working of the schema.

Circuit diagram

Sample and Hold schema using uA741 opamp

Input and output waveforms.

Input and output waveforms - Sample and hold schema

Notes

The schema can be assembled on a vero board.
Use +15V/-15V DC dual supply for powering the opamp.
Capacitor C1 must have minimum leakage current possible and thats why a polyester capacitor is used here.
Mount the IC uA741 on a holder.
The type number of the MOSFET Q1 is not very significant here and so substitution is possible if BS170 is not available.
BS170 is a 60V, 500mA n-channel enhancement mode MOSFET available in TO-92 package.
Preset resistor R1 can be used for offset adjustments.

Sunday, September 7, 2014

Simple 1KHz Sine wave Generator Circuits Wiring diagram

This simple schema generates a good 1KHz sine wave adopting the inverted Wain bridge configuration (C1-R3 & C2-R4). It features a variable output, low distortion and low output impedance in order to obtain good overload capability. A small filament bulb ensures a stable long term output amplitude waveform.

1KHz Sine wave Generator Circuits Diagram

Notes:

The bulb must be a low current type (12V 40-50mA or 6V 50mA) in order to obtain good long term stability and low distortion.
Distortion @ 1V RMS output is 0.15% using a 12V 40mA bulb, raising to 0.5% with a 12V 100mA one.
Using a bulb differing from specifications may require a change of R6 value to 220 or 150 Ohms to ensure proper diagram oscillation.
Set R5 to read 1V RMS on an Audio Millivoltmeter connected to the output with R7 rotated fully clockwise, or to view a sinewave of 2.828V Peak-to-Peak amplitude on the oscilloscope.
With C1, C2 = 100nF the frequency generated is 100Hz and with C1, C2 = 1nF frequency is 10KHz but R5 requires adjustment.
High gain transistors are preferred for better performance.

Parts:

R1____________5K61/4W Resistor

R2____________1K81/4W Resistor

R3,R4________15K1/4W Resistors

R5__________500R1/2W Trimmer Cermet

R6__________330R1/4W Resistor

R7__________470RLinear Potentiometer

C1,C2________10nF63V Polyester Capacitors

C3__________100µF25V Electrolytic Capacitor

C4__________470nF63V Polyester Capacitor

Q1,Q2_______BC23825V 100mA NPN Transistors

LP1___________12V40mA Filament Lamp Bulb (See Notes)

J1__________Phono chassis Socket

SW1__________SPSTSlider Switch

B1_____________9VPP3

Clip for 9V PP3 Battery

Monday, August 25, 2014

Mini and simple power amplifier circuits

What is the meaning of the picture above? The above picture is a miniature audio amplifier and very simple. Here I will give an audio amplifier schematic is very simple which only requires a few components only, can be seen under this scheme.

See from above scheme may occur to you, certainly cheap enough to make this amplifier and quite easy to make. The above simple audio amplifier circuit using an IC as the main amplifier and accompanied by other components. IC used is S1513, which requires a supply voltage ranging from 1.5 volts to 6 volts. And only 0.1 W output power with 4 ohm impedance. For a list components can be seen below.

Part list

C1 = 100nF
C2 = 100uF

C3 = 3n3F

C4 = 1uF
C5 = 1uF
U1 = S1513

Saturday, August 16, 2014

Simple Relay Step Up Circuits

Have you ever needed to power a 12-volt relay in a schema but only had 6 or 9 volts available? This simple schema will solve that problem. It allows 12-volt relays to be operated from 6 or 9 volts, or 24-volt relays from 12 volts. While most normal relays require the manufacturer-specified coil voltage to reliably pull the contacts together, once the contacts are together you only need about half that rated voltage to hold them in. This schema works by using that principle to provide a short burst of twice the supply voltage to move the contacts and then applies the available 6 or 9 volts to the relay to lock the contacts in place.

With reference to Figure A., when the main supply is applied to the schema the 220-µF capacitor, C1, charges quickly to +6 volts through resistor R3. The schema is now awaiting voltage on the control input. When a control voltage (can be as little as 3 volts) is applied to the control input, transistor T1 switches on. The other transistor, a BC558, is also switched on. This allows connection of the relay coil to the main supply rail while T1 shorts the positive terminal of the 220-µF capacitor to ground. Now the negative terminal of the capacitor is at a potential of –6 volts. This is applied to the other side of the relay coil. The relay coil potential is then briefly 12 volts — enough to actuate the contact(s).

However, the coil voltage drops to the supply voltage fairly quickly. The period is determined by the R-C time constant of the relay coil resistance and the 220-µF capacitor. While this schema is simple and works well in many situations, it has a few weaknesses in its current form. The relay may remain energized for as long as one second after the control input has fallen. Also, if the control input goes high before the capacitor has fully recharged, it may not have enough energy to control the relay reliably. Also, the voltage drop across the diode limits the voltage to about 10.8 volts.

The more complex version of the schema shown in Figure B fixes these problems by using an extra transistor and diode. In this arrangement, the BC558 is now isolated from the recharge current of the capacitor. The new transistor provides fast charging for the capacitor. Charging is completed within the mechanical response time of the relay. When using these diagram it should be noted that the contact pressure of the relay contacts may be al little lower than with the nominal coil voltage. It is therefore advisable to keep contact currents well below the maximum specified value.