The following schematic is similar to the peak detector, the difference is the output will not immediately follow the input peaking. The averaging effect will be seen at the output because the output follow the input peak slowly.
Negative and positive cycle difference of 0.5 dB (worst case) can be achieved by using 1% resistor for R1,R2,R3,R4. Use 5% resistor, then the difference will be about 2dB. The R5-C2 affects the averaging time constant, if needed change it to other values.
Not only useful for clearing condensation from a window, the defogger or defroster is also useful for melting snow, ice, and frost that has collected on the window surface. The following circuit schematic diagrams presents the 1994 Ford Explorer defogger. The system has interior fuse panel, power distribution system, timing circuit, rear window defrost grid, heated rear window switch, left power/heated mirror, interior fuse panel, and the right power/heated mirror.
The following circuit schematic diagram is used to convert a low-voltage PWM signal into an amplified and buffered linear output. It is designed for fan speed control. This converter uses PWM outputs to control fan speed as a function of temperature.
A PMOS FET (Q2) and a pair of BJTs (Q1) are used as a linear amplifier. The base of PNP in Q1 acts as the non-inverting input to the amplifier and the emitter of the NPN is the inverting input. The PNP is biased as an emitter follower and the NPN is used as the initial gain an as an emitter follower. The two input voltages approximately track each other because the NPN and PNP operate at roughly the same temperature and current density. The amplifier output is the VGS of Q2 that is amplified at Q2′s drain because of the drop across R2. The output offset of the amplifier primarily is about 100mV because the drop across R3 forces the VGS threshold of Q2. This circuit allows a 3.3V input to provide linear control of a 12V fan.
The cutoff frequency must be selected to reduce the PWM ripple at the output, 1 / [6.28 * R * C], at least two decades below the PWM. Due to high impedance of the circuit led to the use of a resistor value as high as 100k. [source : maxim-ic.com]