Single Chip Stereo FM Transmitter Circuit

ROHM (www.rohm.com) is originally a resistor producer company, but finally expand their business and produce monolithic IC, and this one used in our circuit is the example. The internal structure of this FM transmitter integrated circuit consist of stereo modulator that creates a stereo composite signal, an FM modulator that modulate a carrier frequency with the composite signal, and an RF amplifier that provide enough power to be transmitted through antenna. This is the figure of the FM transmitter circuit;

The core of this stereo FM transmitter is BA1404 integrated circuit chip. from ROHM. This FM transmitter is ideal for wireless microphone, or for audio interface and distribution for home or car appliance. For example, you can now play your portable mp3/mp4 player on your old car radio sound system that doesn’t have line-input plug. This stereo FM transmitter chip is designed for 75-108 FM band, and you can adjust the operation by trimming the LC network connected to pin 10 of this IC chip. To ease the adjustment, you can use a 22-33p variable capacitor for the 15p capacitor connected to pin 10.  Finally, this stereo FM transmitter works with only 1.5-3V power supply, ideal for battery operation.  More than 3.5V supply voltage could burn this FM transmitter circuit. [Circuit diagram source: ROHM Application Notes]

Buffering TMP01 Temperature Sensor Circuit

This is a circuit for a buffer circuit for TMP01 Temperature Sensor. The output of this sensor is a low impedance dc output voltage with a 5 mV/K temperature coefficient. This sensor can be used in multiple control and measurement applications. The buffered VPTAT voltage output can drive 500 µA into 50 pF (maximum). This is the figure of the circuit;

 

To minimize loading that could create dissipation-induced temperature sensing errors and to ensure accuracy, an external amplifier is used in this circuit. The circuit can drive over 10 mA. It still stable under capacitive loads of up to 0.1 µF. [Circuit diagram source: analog.com]

Analog PID Controller

This circuit is shows us about a form of PID controller. The input signal is buffered and amplified by a non-inverting amplifier and the gain of this stage defines the proportional gain P of the controller. The amplified error signal passes in parallel through an integrator (top) a unity-gain amplifier (middle) and a differentiator (bottom) all of which have inverting behaviour. The final op-amp sum and invert the outputs and passed to the output. The potentiometers labeled D and I control the proportions in which derivative and integral fractions contribute to the output signal which is proportional to the power W to be supplied to the heater. This is the figure of the circuit;

It is most likely to be troublesome by causing an offset between the set-point and oven temperatures. Under some circumstances the integrator may drift and eventually saturate which would prevent it from working properly. To reduce the impact of op-amp offset and bias, the first thing to try would be a resistor, equal in value to R2, between the positive input of the integrating op-amp and ground to eliminate the common-mode bias current. Selecting an op-amp with a good input-offset performance would be the next step.

TL084 Audio Compressor (AGC) Circuit

Compressor or AGC (automatic gain control) is used to manipulate the average amplitude of audio signal, to produce relatively constant volume of signal from high dynamic signal source. The 2N3819 JFET (which is used as a voltage controlled resistor) is the key component. Control voltage which is derived by full-wave rectification followed by a peak detector is provided by the output of the circuit. The full wave rectifier is called a precision absolute value circuit can be found in Tobey, Graeme and Huelsman’s : “Operational Amplifier” (1971)- page 249. Several matched resistor is required by the circuit for correct operation and alternative versions of this sub-circuit, which require fewer matched resistors and overall fewer components, could be advantageously substituted. This is the figure of the design circuit;

The product of R4 and the 4.7 uF capacitor is determine the attack time. It’s becomes reverse biased when the input signal drops D1 and the decay time constant is determined by R5. (Since the original publication date I have discovered that the term ‘release’ is used rather than ‘decay’ in the case of compressors.) Both time constants are something of a compromise, the decay must be fast enough to allow low amplitude signals shortly following high amplitude ones to be given sufficient gain and the attack must be fast if the start of high amplitude signals are not to be overloaded until the gain reduces. After long periods of silence or low amplitude inputs, the problem occurs. The next high amplitude signal will get the ‘full gain treatment’ and so will initially overload the circuit and some distortion will be result. Reduce R4 to zero resulting in minimal attack time (determined by the maximum output current of IC3) is the best that could be done under these circumstance. The circuit is by no means ‘hi-fi’ but will be useful for AGC in tape-recording, radio and signal processing where a signal’s large dynamic range needs to be reduced. The original circuit uses 741 IC for the op-amps and OA81 for the diodes (D1,D2,D3).

Single Transistor Blocking Monostable Circuit

This is a design circuit of blocking monostable circuit. The normal state of the transistor is off because the 10 k resistor has been removed. The conduction will be started using a positive pulse at node “a” and the transformer will do the rest. The transistor will again be turned off (by a hefty negative pulse to the base) after the brief excursion of conduction, in which the output falls to near ground. This is the figure of the circuit;

The trigger pulses are provided by an RC differentiating circuit in this circuit, which produces narrow pulses, alternately positive and negative. The positive pulses which need only be about 1V high is the only monostable responds. The circuit will produce one low-going pulse of brief duration. The pulses will be a normal string of positive pulses if the circuit is followed by a phase inverter. There is no effort has been made to make the pulses as short as possible. These will be 100-200 us wide.

SCR And Triac Triggering Circuit With A Positive Power Supply Circuit

The control-circuit output current has to be amplified when the gate current required to trigger the device is higher than the control-circuit output current capability. For example, A lot of MCUs feature output pins with a current capability around 30 mA today. With IGT, they can switch Triacs safely up to 15 to 20 mA. Below are two solution if a Triac with a 35 or 50 mA IGT has to be controlled by such an MCU. First, Use several MCU output pins in parallel (the best is to use a separate gate resistor between each output pin and the Triac gate to ensure a good current repartition between each pin).

With the bipolar solution, the only way is use a PNP transistor to keep the current sourced to the gate. To set its drive reference to a stable bias, a PNP transistor has to be used, which is the power supply (Vdd) in this case. This is another drawback of the positive power supply topology. A PNP transistor has to be used instead of an NPN transistor to amplify the control circuit output current. Than an NPN, a PNP transistor has a lower current gain and higher price. [Circuit diagram source: STMicroelectronics Notes]

LM2576 Switching Regulator Circuit

This is a design circuit that can be to produce any output voltage, an external feedback resistors can be added. The sLM2576 is a Switching Regulator that can produce 15, 12, 5, 0r 3.3V output voltage from maximum supply voltage of 60V or 40V. This LM2476 featured with voltage reference, switch and feedback path for use in either the negative boost or the buck saturation voltage of The LM2576 switch is typically 1.4V. A heatsink may be needed to solve the power dissipation, however the thermal dissipation is internally limited. The LM2576 has quiescent current of 50 µA in standby (on/off high). This circuit is a testing circuit for LM2576. This is the figure of the circuit;

The electrolytic capacitors at output and input should be connected with leads as close as possible. The power dissipation must be small because the load is 100R, so the heat sink is not needed. The capacitor’s voltage must higher than the voltages used in the experiment. This circuit uses 40V, 1A Schottky diode or the 40V, 3A 1N5822 for heavier currents.

Basic Uninterruptible Power Supply Circuit

This is a design circuit for basic interruptible Power Supply Circuit consist of regular power supply adapter and battery connection. This basic system is a “hot” battery connection, meaning that there is no switching mechanism in connecting and disconnecting the battery, the battery is always connected! This hot connection is very simple to implement and very robust because there would be no switching delay, the output voltage will be 100% continue if a power down happens, until the battery loose its capacity. This is the figure of the circuit;

When the power line is normal, the current from the main adapter (transformer-rectifier diode bridge-filter capacitor) flow to the load through D3, and the battery is charged via R1 and D1. The diode D2 prevent the current at D3 output to be shorted by the empty battery in the normal power line condition. If the power down happens then the battery will supply the current to the load through D 2. Use a 15V AC output transformer for 12 volt lead acid battery. LED1 will indicate if the power line is normal. LED D1 will turn off if the power line is down.