Online simulation of the dtl nand circuit

This is a NAND gate implemented using diode-transistor logic. Click the inputs on the left to toggle their state. When all inputs are high, the output is low; otherwise the output is high. When all inputs are high (3.6 V), the only path to ground through the 4.7 kΩ resistor is through the base of the transistor. So base current flows. The transistor wants its collector-emitter current to be 100 times the base current. In trying to raise the current to that level, it pulls the collector voltage down to ground level. When any of the inputs is low (at ground), the easiest path to ground through the 4.7 kΩ resistor is through the low input(s). This puts the bottom of the 4.7 kΩ resistor within one diode drop of ground. At this voltage, only very little base current can flow to the right through both the diode and the base of the transistor. With no base current, the transistor is off, keeping the output high.

This page is a utility for simulating dtl nand online with specified initial values.