Abstract: A trimmable current source for use with low voltage circuitry includes a plurality of trimming networks. A voltage-divider circuit is connected to the trimming networks. Each of the trimming networks includes a resistor in an isolated epitaxial region series connected to a zener diode. A programming signal, having a voltage level which would normally damage the low voltage circuitry can be applied to the junction of the resistor and zener diode, and to the isolated epitaxial region containing the resistor of the trimming network to be programmed without damage to the low voltage circuitry.