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12V Step-Down Dc Converter Using ADP2300 ADP2301

By Circuit Projects → 24 Nov 2014
Using ADP2300 ADP2301 step-down dc dc regulators with integrated power MOSFET, can be designed a very simple DC DC voltage converter. Output voltage delivered by these circuits can be adjusted from 0.8 volts, up to 0.85xVin , with ±2% accuracy. The maximum output current that can be provided by ADP2300 ADP2301 regulators is up to 1.2 A load current.
12V Step-Down Dc Converter Circuit Diagram
12V Step-Down Dc-Converter-Circuit Diagram
12V Step-Down Dc-Converter-ADP2301
There are two frequency options: the ADP2300 runs at 700 kHz, and the ADP2301 runs at 1.4 MHz. These options allow users to make decisions based on the trade-off between efficiency and total solution size. Current-mode control provides fast and stable line and load transient performance.  Bellow you an see two design examples, which require few common electronic components.First circuit will provide a 2.5V output at a maximum current of 1.2A from an input voltage of 12 volts. Second circuit will provide a 5V output at a maximum current of 1.2A from an input voltage of 12 volts.

Voltage Limiter for Guitar Amplifiers

By Circuit Projects → 31 Oct 2014
Guitar amplifiers using output devices such as the TDA7293 (100 W) or LM3886 (68 W) are surprisingly of ten damaged as a result of excessive supply voltage in the quiescent state. The transformers are of ten used so close to their specification that this problem can even be caused by a high mains input voltage. In most countries the domestic AC outlet voltage is permitted to rise as high 10 % above the nominal (published) value. Since replacing the transformer is not an attractive proposition, the author developed a relatively simple electronic solution to the overvoltage problem: a voltage limiter for the symmetric supply to the amplifier.
The circuit is based on the classical voltage regulator arrangement of a Zener diode connected to the base of a pass transistor. However, in this version we replace the conventional bipolar transistor with a power MOSFET.The circuit is symmetrical with respect to the negative and positive supplies, and so we shall only describe the positive half.
Voltage Limiter for Guitar Amplifiers Circuit Diagram
Voltage-Limiter-for-Guitar-Amplifiers-Circuit diagram
The input voltage (at most 50 V) supplies the chain of Zener diodes D1, D2 and D3 via resistor R3. The resistor limits the current through the Zener diodes to about 5 mA. The series connection of Zener diodes has the advantage that their dissipation is divided among them, as well as giving more options for the total voltage drop by judicious selection of individual components. The sum of the diode voltages (39 V with the values given) must be greater than the desired limiting out-put voltage by the gate-source voltage of the MOSFET. C1 smooths the voltage across the Zener diode chain. The circuit therefore not only limits the voltage, but also reduces the ripple (hum component) on the supply. The gate of the HEXFET is driven via R1. In con-junction with C4, this prevents the FET from oscillating.
Without any load the output voltage is rather higher than expected. With a small load, such as that presented by the output stage in its quiescent state, it falls to the desired value. The circuit then does not provide regulation of the output voltage, but rather a stabilisation function.The operation of the negative half of the circuit is identical to that of the positive half apart from the polarity of the voltages, and hence a P-channel MOSFE T must be used there.
It is worth noting that there is a relatively large degree of variation (up to a few volts) in the gate-source voltage of the HE XFETs used. This can be compensated for by selecting the Zener diodes in the chain and the cur-rent through them, but for most applications the exact voltage at which limiting begins to occur will not be critical.
The HEXFETs must be provided with adequate cooling. If possible, they can be attached to the heatsink already present in the amplifier; other wise, a separate heatsink will be required. A thermal rating of 2.5 K/W will be suitable.
Author :Alfred Rosenkränze - Copyright: Elektor

Ground-free DVM Module Supply from 5 V

By Circuit Projects →
The majority of hand-held digital volt meters use an LCD screen and are powered from a nine volt battery. Inside is most probably an ICL7106 chip (or something compatible). This takes care of measuring the input and driving the LCD. This IC is very popular and can be found in other laboratory and homebrew equipment where it offers a simple solution for both measuring current/voltage and driving the display. So far so good, there is how-ever one feature of this device which needs careful consideration. The power supply to the chip (both the positive and negative connection) must not have any direct connection to either of the two measuring input terminals. It requires floating supplies. This is not a problem for battery powered equipment but needs more thought when the ICL7106 is fitted into mains powered equipment.
Ground-free DVM Module Supply from 5 V Circuit Diagram :
Ground-free DVM Module Supply from 5 V-Circuit Daigram
The simplest, most expensive solution is to use two independent power supplies in the equipment. A battery could also be used as an isolated supply but in a mains powered device it would seem a bit out of place and inconvenient.
In this case the term ‘floating supplies’ means that it is possible to have two separate DC levels. This level of isolation can be achieved with capacitors to separate the two DC supplies. Back in 2003 we published a circuit in the July/August edition of Elektor (circuit number 75) which used a NE555 IC. Unfortunately this design required a supply voltage upwards of 10 V. If the DVM module is fitted to equipment which only uses a 5 V supply (as is often the case) the circuit will not be of much use.The author has solved the problem by modifying the original circuit, using a hex Schmitt trigger inverter type 74HC14N instead of the NE555. One of the inverters generates a square wave of about 75 KHz. The remaining five inverters are wired in parallel to pro-vide more output drive current for the voltage multiplier stage.
DC isolation is provided by capacitors C2 and C3. A classic voltage multiplier configuration is made up of capacitors and diodes. The circuit generates an output of around 8.5 V at a load current of 1 mA. This is sufficient to power the DVM chip. The 5 V supply for the circuit must be stabilised.
The values of the input voltage divider resistors R2 and R3 are independent of the chip’s power supply and must be selected according to the desired measurement range.
Author : Heinz Kutzer  - Copyright : Elektor

Condenser Mic Audio Amplifier

By Circuit Projects →

The compact, low-cost condenser mic audio amplifier described here provides good-quality audio of 0.5 watts at 4.5 volts. It can be used as part of intercoms, walkie-talkies, low-power transmitters, and packet radio receivers. Transistors T1 and T2 form the mic preamplifier. Resistor R1 provides the necessary bias for the condenser mic while preset VR1 functions as gain control for varying its gain. In order to increase the audio power, the low-level audio output from the preamplifier stage is coupled via coupling capacitor C7 to the audio power amplifier built around BEL1895 IC.
Circuit diagram:

Condenser Mic Audio Amplifier circuit schematic

BEL1895 is a monolithic audio power amplifier IC designed specifically for sensitive AM radio applications that delivers 1 watt into 4 ohms at 6V power supply voltage. It exhibits low distortion and noise and operates over 3V-9V supply voltage, which makes it ideal for battery operation. A turn-on pop reduction circuit prevents thud when the power supply is switched on. Coupling capacitor C7 determines low-frequency response of the amplifier. Capacitor C9 acts as the ripple-rejection filter.

Capacitor C13 couples the output available at pin 1 to the loudspeaker. R15-C13 combination acts as the damping circuit for output oscillations. Capacitor C12 provides the boot strapping function. This circuit is suitable for low-power HAM radio transmitters to supply the necessary audio power for modulation. With simple modifications it can also be used in intercom circuits.
Author: D. Prabakaran - Copyright: Electronics For You Mag