Equivalent series resistance or ESR of Capacitor.

Practical capacitors and inductors as used in electric circuits are not ideal components with only capacitance or inductance. However, they can be treated, to a very good degree of approximation, as being ideal capacitors and inductors in series with a resistance; this resistance is defined as the equivalent series resistance (ESR). If not otherwise specified, the ESR is always an AC resistance measured at specified frequencies, 100 kHz for switched-mode power supply components, 120 Hz for linear power-supply components, and at the self-resonant frequency for general-application components. Audio components may report “Q factor”, incorporating ESR among other things, at 1000 Hz.

In a non-electrolytic capacitor and electrolytic capacitors with solid electrolyte the metallic resistance of the leads and electrodes and losses in the dielectric cause the ESR. Typically quoted values of ESR for ceramic capacitors are between 0.01 and 0.1 ohms. ESR of non-electrolytic capacitors tends to be fairly stable over time; for most purposes real non-electrolytic capacitors can be treated as ideal components.

Aluminium and tantalum electrolytic capacitors with non solid electrolyte have much higher ESR values, up to several ohms; electrolytics of higher capacitance have lower ESR. ESR decreases with frequency up to the capacitor’s self-resonant frequency. A very serious problem, particularly with aluminium electrolytics, is that ESR increases over time with use; ESR can increase enough to cause circuit malfunction and even component damage, although measured capacitance may remain within tolerance. While this happens with normal aging, high temperatures and large ripple current exacerbate the problem. In a circuit with significant ripple current, an increase in ESR will increase heat dissipation, thus accelerating aging.

Electrolytic capacitors rated for high-temperature operation and of higher quality than basic consumer-grade parts are less susceptible to become prematurely unusable due to ESR increase. A cheap electrolytic capacitor may be rated for a life of less than 1000 hours at 85°C (a year is 8760 hours). Higher-grade parts are typically rated at a few thousand hours at maximum rated temperature, as can be seen from manufacturers’ datasheets. If ESR is critical, specification of a part with higher temperature rating, “low ESR” or larger capacitance than is otherwise required may be advantageous. There is no standard for “low ESR” capacitor rating.

Polymer capacitors usually have lower ESR than wet-electrolytic of same value, and stable under varying temperature. Therefore, polymer capacitors can handle higher ripple current. From about 2007 it became common for better-quality computer motherboards to use only polymer capacitors where wet electrolytics had been used previously.

The ESR of capacitors larger than about 1 μF is easily measured in-circuit with an ESR meter.

The following table shows rough guide of typical values of ESR for a range of difference capacitance and voltage rating.


15 Watt Class D Amplifier using TPA3122

class-D amplifier or switching amplifier is an electronic amplifier in which the amplifying devices (transistors, usually MOSFETs) operate as electronic switches, and not as linear gain devices as in other amplifiers. They are rapidly switching back and forth between the supply rails, being fed by a modulator using pulse width, pulse density, or related techniques to encode the audio input into a pulse train. The audio escapes through a simple low-pass filter into the loudspeaker. The high-frequency pulses, which can be as high as 6 MHz, are blocked. Since the pairs of output transistors are never conducting at the same time, there is no other path for current flow apart from the low-pass filter/loudspeaker. For this reason, efficiency can exceed 90%.

Basic operation

Class-D amplifiers work by generating a train of square pulses of fixed amplitude but varying width and separation, or varying number per unit time, representing the amplitude variations of the analog audio input signal. It is also possible to synchronize the modulator clock with an incoming digital audio signal, thus removing the necessity to convert it to analog, The output of the modulator is then used to gate the output transistors on and off alternately. Great care is taken to ensure that the pair of transistors are never allowed to conduct together. This would cause a short circuit between the supply rails through the transistors. Since the transistors are either fully “on” or fully “off”, they spend very little time in the linear region, and dissipate very little power. This is the main reason for their high efficiency. A simple low-pass filter consisting of an inductor and a capacitor are used to provide a path for the low-frequencies of the audio signal, leaving the high-frequency pulses behind. In cost sensitive applications the output filter is sometimes omitted. The circuit then relies on the inductance of the loudspeaker to keep the HF component from heating up the voice coil.

The structure of a class-D power stage is somewhat comparable to that of a synchronously rectified buck converter (a type of non-isolated switched-mode power supply (SMPS)), but works backwards. Whereas buck converters usually function as voltage regulators, delivering a constant DC voltage into a variable load and can only source current (one-quadrant operation), a class-D amplifier delivers a constantly changing voltage into a fixed load, where current and voltage can independently change sign (four-quadrant operation). A switching amplifier must not be confused with linear amplifiers that use an SMPS as their source of DC power. A switching amplifier may use any type of power supply (e.g., a car battery or an internal SMPS), but the defining characteristic is that the amplification process itself operates by switching. Unlike a SMPS, the amplifier has a much more critical job to do, to keep unwanted artifacts out of the output. Feedback is almost always used, for the same reasons as in traditional analog amplifiers, to reduce noise and distortion.

Theoretical power efficiency of class-D amplifiers is 100%. That is to say, all of the power supplied to it is delivered to the load, none is turned to heat. This is because an ideal switch in its on state would conduct all the current but have no voltage loss across it, hence no heat would be dissipated. And when it is off, it would have the full supply voltage across it but no leak current flowing through it, and again no heat would be dissipated. Real-world power MOSFETs are not ideal switches, but practical efficiencies well over 90% are common. By contrast, linear AB-class amplifiers are always operated with both current flowing through and voltage standing across the power devices. An ideal class-B amplifier has a theoretical maximum efficiency of 78%. Class A amplifiers (purely linear, with the devices always “on”) have a theoretical maximum efficiency of 50% and some versions have efficiencies below 20%.


TPA3122 is from Texas Instruments. According to the TPA3122 datasheet, it is a 15-W (per channel) efficient, Class-D audio power amplifier for driving stereo single ended speakers or mono bridge tied load. The TPA3122D2 can drive stereo speakers as low as 4Ω. The efficiency of the TPA3122D2 eliminates the need for an external heat sink when playing music. The gain of the amplifier is controlled by two gain select pins. The gain selections are 20, 26, 32, and 36 dB.


  • 10-W/ch into an 4-Ω Load From a 17-V Supply
  • 15-W/ch into an 8-Ω Load From a 28-V Supply
  • Operates from 10 V to 30 V
  • Efficient Class-D Operation
  • Four Selectable, Fixed Gain Settings
  • Internal Oscillator (No External Components Required)
  • Single Ended Analog Inputs
  • Thermal and Short-Circuit Protection with Auto Recovery Feature
  • 20-pin DIP Package

DIP Package Pinout

Terminal Functions

Simplified Application Circuit

Simplified Application Circuit

Complete Circuit

PCB Design

Bottom Side

Top Side

Gain Jumper Settings

Table 1

GAIN1(J2) GAIN0(J1) Amplifier Gain(dB)
ON ON 20

OFF denotes jumper is REMOVED; ON denotes jumper INSTALLED.

Applying Power to the Circuit

  •  Verify correct voltage and input polarity for the external power supplies. Turn ON. The EVM starts operation.
  • Adjust the input signal.
  • Adjust the control inputs to the desired settings as described in the Control Inputs section.
  • Adjust the amplifier gain by installing or removing the gain jumpers, J1 and J2 to yield the gain values described in Table 1.

30V Volt Meter with PIC16F676

This is a simple 30V volt meter using PIC16F676 micro controller with 10-bit ADC (analog to digital converter) and three 7 segment LED displays. You can use this circuit to measure up to 30V DC. The possible applications are on bench power supply or as a digital panel meter in various systems. PIC16F676 is the heart and brain of this circuit. The internal adc of the mcu with a resistor network voltage divider is used to measure the input voltage. Then 3 digits of comm anode 7 segment display is used to display final converted voltage. As you can see in the schematic the displays are multiplexed with each other. It means we switch on one display and put the corresponding digit on this while other two displays are off this cycle goes for each of the displays.


You can find more about driving multiplexed 7 segment led display from a pic mcu in application note from microchip AN557 Four Channel Digital Voltmeter with Display and Keyboard. In my circuit the refresh rate is about 50hz.

Voltage Divider Front End
As you can seen in the schematic the 47k resistor and 10 k trim pot is connected ias a voltage divider configuration. We all know very well that by default pic micro controller ADC reference voltage is set to vcc(+5v in this case). So what we have to do is make such voltage divider that can divide out maximum range 30 volts to 5 volts. So we need is Vin/6 ==> 30/6 =5v voltage divider. And to keep as less as possible attenuation on the under test voltage we have to keep the voltage divider resistor value in few thousand ohms because it takes very little current from the target but as much to drive adc of pic.

10bit adc resolution we get 1023 maximum count
with 5 v reference we get 5/1023 = 0.0048878 V/Count
means if the adc count is 188 then input voltage is 188 * 0.0048878 == 0.918 volts

Now with the voltage divider the maximum voltage is 30v so the calculations will be 30/1023=0.02932 volts/count
if now we get 188 then 188*0.02932=5.5 Volts

You can also increase or decrease the range by changing resistor network and the calculations a little bit.

The capacitor 0.1uf makes the adc input a bit stable because 10bit adc is really sensitive. The 5.1v zener will provide over votage protection to the internal adc because it wont allow voltage more than 5.1v.

Accuracy and calibration
Overall accuracy of this circuit is great but it totally depends on the values of 47K resistor and 10k trim pot. As fine as you can go by adjustment of the trim pot your accuracy goes fine.

Calibration of this circuit is done by adjustment of the 10k trimpot around value of 7.5k or so. All you have to do is take any standard power like 5v or 12v and apply that to the input of the resistor network and adjust the trimpot until you get correct value on the display.

Software Sorce code and Firmware
The sotware is written in c and complied using hi-tech compiler.











Download Firmware: PIC16Voltmeter


This circuit saves both time and electricity for students. It helps to prevent them from dozing  off while studying, by sounding a beep at a fixed time interval, say, 30 minutes. If the student is awake during the beep, he can reset the circuit to beep in the next 30 minutes. If the timer is not reset during this time, it means the student is in deep sleep or not in the room, and the circuit switches off the light and fan in the room, thus preventing the wastage of electricity. The circuit is built around Schmitt-trigger NAND gate IC CD4093 (IC1), timer IC CD4020 (IC2), transistors BC547, relay RL1 and buzzer.
The Schmitt-trigger NAND gate (IC1) is configured as an astable multivibrator to generate clock for the timer (IC2). The time period can be calculated as T=1.38XRXC. If R=R1+VR1=15 kilo-ohms and C=C2=10 F, you’ll get ‘T’ as 0.21 second. Timer IC CD4020 (IC2) is a 14-stage ripple counter. Read More