Tuesday, April 30, 2013
Equalising HEXFETs
When experimenting with audio output stages featuring multiple HEXFETs it quickly becomes apparent that the total power is not divided equally among the individual transistors. The reason for this lies in the wide part-to-part variations in gate-source voltage, which in the case of the IRFP240 (or IRFP9240) can be from 2 V to 4 V. Source resistors in the region of 0.22 Ω as commonly seen in amplifier circuits (see example circuit extract) help to counteract this, but usually not to a sufficient extent. One possible solution to this problem is to ‘select’ the transistors used so that their gate-source voltages match as closely as possible.
For building prototypes or very short production runs this is feasible, but requires additional manual effort in testing the components, and, of course, more transistors must be ordered than will finally be used. The circuit idea shown here allows differences in gate-source voltage between pairs of transistors to be compensated for by the addition of trimmer potentiometers: the idea has been tested in simulation using Simetrix. The second circuit extract shows the required changes.
For building prototypes or very short production runs this is feasible, but requires additional manual effort in testing the components, and, of course, more transistors must be ordered than will finally be used. The circuit idea shown here allows differences in gate-source voltage between pairs of transistors to be compensated for by the addition of trimmer potentiometers: the idea has been tested in simulation using Simetrix. The second circuit extract shows the required changes.
Thursday, April 11, 2013
IR Remote Control Circuit using Op amp 741
IR circuit is called Infrared Circuit. Remote controls are
very much popular now-a-days. It is specially called cordless circuit.
This circuit is very simple and low cost cordless remote control circuit
which is based on infrared rays.
very much popular now-a-days. It is specially called cordless circuit.
This circuit is very simple and low cost cordless remote control circuit
which is based on infrared rays.
Figure 1 shows the transmitter circuit. The transmitter produces infrared rays and that can be easily transmitted up to 4 meters with a special convex lens and a twin LED arrangements.
Figure 2 shows the receiver circuit. Op amp IC1-741 generates high frequency squire wave which provides the gate pulses for SCR1. IC1’s output current flows through SRC1 and it is conducting current and enables the LED to emits infrared rays. The output frequency of Op amp IC1 depends on the variable resistor VR1, which in turns varies the output radiations of the LED.
When IR rays
fall on the photo-transistor T1 of the receiver, then base of the
photo-transistor’s base produces charge carriers at a rate depending on
the rate of arrival of incident radiations at
the pn junction of the transistor. Then the resulting emitter voltage
is amplified by Op amp IC-2 . The amplified signal is rectified by D2.
Finally the amplified signal is to drive the relay.
fall on the photo-transistor T1 of the receiver, then base of the
photo-transistor’s base produces charge carriers at a rate depending on
the rate of arrival of incident radiations at
the pn junction of the transistor. Then the resulting emitter voltage
is amplified by Op amp IC-2 . The amplified signal is rectified by D2.
Finally the amplified signal is to drive the relay.
Parts List:
Tuesday, April 9, 2013
Simple Security Monitor
A remote listening circuit. The area to be monitored is connected via a cable and allows remote audio listening.
Starting from the right hand side, the power supply. I have used 12V as a standard power supply voltage, or a 12V car battery may be used. The circuit is in two halves, a remote microphone preamp, and an audio amplifier based around the National Semiconductor LM386 audio amplifier.
Security Monitor Circuit Diagram :
The remote preamp uses an ECM microphone to monitor sound. A direct coupled 2 stage amplifier built around Q1 and Q2 amplify the weak microphone signal. Preset resistor R2 acts as a gain control, and C1 provides some high frequency roll off to the overall audio response. Q1 is run at a low collector current for a high signal to noise ratio, whilst Q2 collector is biased to around half the supply voltage for maximum dynamic range. The power supply for this preamp is fed via R10 and R6 from the 12V supply. C4 ensures that the preamp power supply is decoupled and no ac voltages are present on the power lines. The amplified audio output from Q2 collector is fed onto the supply lines via C6 a 220u capacitor. The output impedance of Q2 is low, hence the relatively high value of C6. C6 also has a second purpose of letting the output audio signals pass, whilst blocking the dc voltage of the power supply.
At the opposite end, C7 a 10u capacitor, brings home the amplified audio to the listening location. The signal is first further amplifier by a x10 voltage gain amplified using the TL071. C8, a 22p capacitor again rolls off some high frequency response above 100kHz. This is necessary as long wires may pick up a little radio interference. After amplification by the op-amp, the audio is finally passed to the LM386 audio amplifier. R14 acts as volume control. R13 and C12 prevent possible instability in the LM386 and are recommended by the manufacturer. Audio output is around 1 watt into an 8 ohm loudspeaker, distortion about 0.2%. If preferred headphones could be used, although Id recommend a series resistor of the same value impedance as the headphones.
Notes:
You can use this in your garden and listen for any unusual sounds, or maybe just wildlife noises. If you have a car parked in a remote location, the microphone will also pick up any sounds od activity in this area. The cable may be visible or hidden, screened cable is not necessary and you can use bellwire or speaker cable if desired.
Source : http://www.ecircuitslab.com/2012/09/simple-security-monitor.html
Sunday, April 7, 2013
Power Switch Diagram
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Friday, April 5, 2013
LM377 Power amplifier schematic
Various
needs of the amplifiers are all different. Different places and use
also requires a different power amplifier as well. For this time i gave
a circuit schematic power amplifier based on LM377 ic that has
similarities with the LM378 and LM1877. Power is smoothly small ouput
is 2 X 2.5 Watt and the impedance 4 ohms. Use of this amplifier
suitable for portable radio tuner that can be taken every where.
Resistor
R1___________________2K
R2___________________2K
R3___________________1M
R4___________________1M
Capacitor
C1___________________4.7uF 50V
C2___________________4.7uF 50V
C3___________________100n
C4___________________100n
C5___________________470uF 50V
C6___________________470uF 50V
IC
IC1__________________LM377 , LM378 , LM1877
Wednesday, April 3, 2013
Switchmaking Proper Connection
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Monday, April 1, 2013
Blade Plug Trailer
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