TDA7850 Car Power Amplifier Circuit

Here’s a design circuit for very simple class AB power amplifier designed in MOSFET technology which use just few external components. Tda7850 power amplifier can be used in car radio audio systems. This is the figure of the circuit;

MOSFET output power stage, Hi-Fi class distortion, Low output noise, ST-BY function, Mute function, auto mute at minim supply voltage detection, Output short circuit to ground, to Vs protection, Overrating chip temperature with soft thermal limiter, Output DC offset detection. The TDA7850's inputs are ground-compatible and can stand very high input signals (±8Vpk) without any performance degradation. Standby and Muting facilities are both CMOS compatible. In true CMOS ports or microprocessors are absent the ST-BY pin can be connected direct to Vs but it’s necessary to connect a 470kΩ resistance between these two pins (Vs and ST-BY). The power supply for TDA7850 power amplifier must be 14.4 volts. The TDA7850 IC must be mounted on a corresponding heat sink for high temperature dissipation.

TDA2005 Audio Amplifier Circuit

Here’s a circuit for car radio audio amplifier circuit is specially designed to work on devices like: car radios, cd-players and similar devices. The car radio audio amplifier circuit is based on the TDA2005 audio IC which can provide a maximum output power of 20 watts into a 4 ohms load, connected in bridge mode configuration. This is the figure of the circuit;

The TDA2005 audio amplifier IC can work in even in bridge mode or stereo mode configuration.  The TDA2005 audio IC is a class B audio amplifier designed in a Multiwatt 11 package and can be ordered in two types TDA2005M used for bridge mode application or TDA2005S used in stereo applications. If the TDA2005 is used in stereo mode it can deliver a 10 + 10 watts output power in a 2 ohms load. The advantage of using the TDA2005 audio amplifier in bridge mode configuration is that the total harmonic distortion (THD) is 1% and the THD for  the stereo configuration  mode is 10 %. The Tda2005 audio amplifier IC supports a wide range of input voltage from 8 volts up to 18 volts. The TDA2005 main features are:  short circuit protection, overrating chip temperature, low external components required , bridge or stereo booster amplifiers with or without boostrapand with programmable gain and bandwidth , no electrical isolation between the package and the heat sink .

Switchstart Ballast Circuit for Fluorescent Tube Lamp

Simplicity, low cost and improved efficiency when compared with the alternative options are the reasons why the switch start circuit has been widely adopted. Moreover, the 230V mains voltage is sufficiently higher than tube running voltage to let the use of the simple series impedance ballast in almost every case. Where the mains voltage is not high enough, for example in most 120V supplied circuits, a quick start circuit incorporating voltage step-up is used to control the lamp. This is the figure of the circuit;

The lamp doesn’t light on first when the voltage is applied to the circuit, so the full mains voltage shows up across the starter via the choke and lamp cathodes. The starter is made of bi metallic contacts sealed within a small discharge bulb with an inert gas filling. The gas could be argon or neon. A glow discharge within the starter is caused by the mains voltage. This will heats up the bi metallic contacts, causing them to approach each other. When the bi metallic stay close, this will let preheat current to run through the choke and both cathodes.

The bi metallic contacts cool down and open since the glow discharge within the starter has now ceased. The voltage across the lamp increases rapidly and hit the lamp because the inductance of the choke tries to preserve current flow. The starter’s contacts close again and the cycle repeats if it doesn’t happen. Current and voltage are controlled by the choke to the correct levels since the lamp has started at the first time. The lamp running current is enough to maintain the cathodes (heaters) hot and sending out electrons without the need for separate heater supplies, which would otherwise be wasteful of energy. The circuit remains open because there is not enough voltage to cause a glow discharge in the starter since the lamp’s running voltage is much less than the mains voltage. Leading current from the mains is drawn by power factor correction (PFC) to counterbalance for the lagging current drawn by the lamp circuit. [Circuit diagram source: NXP Application Note]

Pink (Flicker) Noise Generator Circuit

Here’s a design circuit for a flicker noise generator, an implementation of flicker noise analog modeling presented in NBS technical note #604, “Efficient Numerical and Analog Modeling of Flicker Noise Processes” by J.A. Barnes and Stephen Jarvis, Jr. With the component values shown the schematic diagram, the circuit will give a 1/f noise slope from below 1Hz to over 4KHz. A TLC2272 op-amp is used for this circuit, but any low noise op-amps will work. This is the figure of the circuit;

The op-amp must be a low noise type because the noise generation come from a high value resistor generating about 50nV noise. Use an op-amp with noise voltage less than 15 nV/root-Hz and noise current less than 0.1 pA/root-Hz, an easy-to-find feature in many low-noise modern op-amp devices. To simplify the construction, the capacitor values is slightly different from the calculated values described in the paper, and a bias circuit is provided to allow the use of polarized electrolytic capacitor. Because the electrolytic capacitor has poor tolerance, it should be chosen carefully for best performance. Compared to circuit utilizing deode zener, reverse-biased transistor, or other noisy devices, this circuit give more predictable and repeatable output level.  If we tap the output of the first op-amp through a 100uF capacitor (like as seen in the second op-amp), a precise 5uV/root-Hz white noise will be there as an excellent signal source for audio noise measurement calibration. At the second op-amp, this white noise is filtered to give a flicker noise (pink noise) frequency spectrum, since the pink noise is a subset of white noise in the frequency domain. [Circuit diagram source: techlib.com]