Bi-directional Current Regulator

The current regulator is a basic element of circuit design. It is used for a bias current, an output load, a linear voltage ramp generator, etc.
Among the variations, an FET based regulator is well known (J1 and R3 below). The C1 capacitor voltage ramps linear when charged with regulated current. It can be used to generate saw tooth wave.

This regulates the current in one direction only. The constant-current diode has the similar structure internally.
To produce a triangle waveform, discharge the capacitor with the same manner. To make current regulator bi-directional,

#1. Use bridge diodes.

The art of electronics : Paul Horowitz, Cambridge University Press, pp. 290


#2. Parallelize with diodes


* No extra diodes(D1 & D2) are necessary if the constant-current diodes used.

#3. Serialize J-FETs (1)


This makes use of the gate-drain current of the junction FET.

#4. Serialize MOS-FETs.

I found a better one.

A fully implantable stimulator for use in small laboratory animals : Rodney E. Millard and Robert K. Shepherd

While one FET is regulating the current, the other is biased to pass through the current.


#5. Serialize J-FETs (2)

I modified #3 with the hint of #4. While one FET is working, the other passes the current from the source to drain.


The regulated current depends on the characteristics of individual FET (e.g. Idss, gm..). Try some FETs and adjust Rs(R1 & R2) value.

This example drives LEDs with a triangular wave. The electric sandglass gradually changes the color of LEDs with the direction turned by tilt-switches.

R1 : Variable Register 100Kohm-A
D1/2, D3/4, ..D11/12 : Dual-color LEDs (Anode-common).

22 Mar. 2011
Osamu Tamura @ Recursion Co., Ltd.