Circuits & Schematics

The circuit below will trickle charge a four cell pack of AA or AAA NiMH batteries. The circuit draws current from the +5 v available a USB connection and pumps about 70 mA of current into the battery. This should be enough current to fully charge ...

I designed and built this thing many years ago. I published the hobby circuit in the now defunct “Radio Elecronics” magazine back in 1992. The electronic circuit injects a precise 1 Amp of current into any unknown resistor, up to about ...

Some industrial applications require you to feed a low-power dc/dc converter from a three-phase source and possibly to deal with line-to-line voltages of 200 or 400 V rms. Further, the neutral terminal of the ac source may be unavailable for ...

An inverter provides power backup for mains-based appliances in the event of a power failure. Most of the inverters available in the market have complicated circuit designs and are not very economical. Some of them produce a square-wave output, ...

Recently (5/21/25), I published a Design Idea (DI) describing a bidirectional current mirror using just two transistors and a diode, “A two-way mirror current mirror that is” ( Ref. 1 ). That circuit works well in some applications, ...

In the first part ( Ref. 1 ) of this Design Idea (DI), we saw how to use the TDA7052A (or similar) power amp to build a minimalist siren-type power oscillator, and also, having looked at that device’s distortion characteristics under various ...

When audio power amplifiers oscillate, the result is often smoke, perhaps with a well-cooked PCB and a side order of fried tweeter. This two-part Design Idea (DI) shows some interesting ways of (mis-)using a common power amp to produce deliberate ...

The voltage booster is a 'true' charge pump. When the output of the 555 is low, C4 charges from the supply via D1. When the output goes high, the positive end of C4 is forced high (to +24 V in a perfect world), and the charge is transferred ...

Introduction These ultra-simple projects are intended to provide two simple functions without the need for transformers or 'esoteric' parts. The first is a simple charge-pump voltage booster, that will raise your supply voltage by a factor ...

Designing an analog circuit can be a frustrating experience, as noted by Nick Cornford in his Design Idea (DI), “DIY RTD for a DMM” ( Ref. 1 ). With a fortnight’s struggle, I completed the design of 4 mA to 20 mA, two-wire ...